FIELD OF THE INVENTION
[0001] This invention relates generally to the field of perforating and treating subterranean
formations to increase the production of oil and gas therefrom. More specifically,
the invention provides an apparatus and a method for perforating and treating multiple
intervals without the necessity of removing equipment from the wellbore between steps
or stages.
BACKGROUND OF THE INVENTION
[0002] When a hydrocarbon-bearing, subterranean reservoir formation does not have enough
permeability or flow capacity for the hydrocarbons to flow to the surface in economic
quantities or at optimum rates, hydraulic fracturing or chemical (usually acid) stimulation
is often used to increase the flow capacity. A wellbore penetrating a subterranean
formation typically consists of a metal pipe (casing) cemented into the original drill
hole. Holes (perforations) are placed to penetrate through the casing and the cement
sheath surrounding the casing to allow hydrocarbon flow into the wellbore and, if
necessary, to allow treatment fluids to flow from the wellbore into the formation.
[0003] Hydraulic fracturing consists of injecting fluids (usually viscous shear thinning,
non-Newtonian gels or emulsions) into a formation at such high pressures and rates
that the reservoir rock fails and forms a plane, typically vertical, fracture (or
fracture network) much like the fracture that extends through a wooden log as a wedge
is driven into it. Granular proppant material, such as sand, ceramic beads, or other
materials, is generally injected with the later portion of the fracturing fluid to
hold the fracture(s) open after the pressure is released. Increased flow capacity
from the reservoir results from the easier flow path left between grains of the proppant
material within the fracture(s). In chemical stimulation treatments, flow capacity
is improved by dissolving materials in the formation or otherwise changing formation
properties.
[0004] Application of hydraulic fracturing as described above is a routine part of petroleum
industry operations as applied to individual target zones of up to about 60 meters
(200 feet) of gross, vertical thickness of subterranean formation. When there are
multiple or layered reservoirs to be hydraulically fractured, or a very thick hydrocarbon-bearing
formation (over about 60 meters), then alternate treatment techniques are required
to obtain treatment of the entire target zone. The methods for improving treatment
coverage are commonly known as "diversion" methods in petroleum industry terminology.
[0005] When multiple hydrocarbon-bearing zones are stimulated by hydraulic fracturing or
chemical stimulation treatments, economic and technical gains are realized by injecting
multiple treatment stages that can be diverted (or separated) by various means, including
mechanical devices such as bridge plugs, packers, downhole valves, sliding sleeves,
and baffle/plug combinations; ball sealers; particulates such as sand, ceramic material,
proppant, salt, waxes, resins, or other compounds; or by alternative fluid systems
such as viscosified fluids, gelled fluids, foams, or other chemically formulated fluids;
or using limited entry methods. These and all other methods and devices for temporarily
blocking the flow of fluids into or out of a given set of perforations will be referred
to herein as "diversion agents."
[0006] In mechanical bridge plug diversion, for example, the deepest interval is first perforated
and fracture stimulated, then the interval is typically isolated by a wireline-set
bridge plug, and the process is repeated in the next interval up. Assuming ten target
perforation intervals, treating 300 meters (1,000 feet) of formation in this manner
would typically require ten jobs over a time interval of ten days to two weeks with
not only multiple fracture treatments, but also multiple perforating and bridge plug
running operations. At the end of the treatment process, a wellbore clean-out operation
would be required to remove the bridge plugs and put the well on production. The major
advantage of using bridge plugs or other mechanical diversion agents is high confidence
that the entire target zone is treated. The major disadvantages are the high cost
of treatment resulting from multiple trips into and out of the wellbore and the risk
of complications resulting from so many operations in the well. For example, a bridge
plug can become stuck in the casing and need to be drilled out at great expense. A
further disadvantage is that the required wellbore clean-out operation may damage
some of the successfully fractured intervals.
[0007] One alternative to using bridge plugs is filling the portion of wellbore associated
with the just fractured interval with fracturing sand, commonly referred to as the
Pine Island technique. The sand column in the wellbore essentially plugs off the already
fractured interval and allows the next interval to be perforated and fractured independently.
The primary advantage is elimination of the problems and risks associated with bridge
plugs. The disadvantages are that the sand plug does not give a perfect hydraulic
seal and it can be difficult to remove from the wellbore at the end of all the fracture
stimulations. Unless the well's fluid production is strong enough to carry the sand
from the wellbore, the well may still need to be cleaned out with a work-over rig
or coiled tubing unit. As before, additional wellbore operations increase costs, mechanical
risks, and risks of damage to the fractured intervals.
[0008] Another method of diversion involves the use of particulate materials, granular solids
that are placed in the treating fluid to aid diversion. As the fluid is pumped, and
the particulates enter the perforations, a temporary block forms in the zone accepting
the fluid if a sufficiently high concentration of particulates is deployed in the
flow stream. The flow restriction then diverts fluid to the other zones. After the
treatment, the particulate is removed by produced formation fluids or by injected
wash fluid, either by fluid transport or by dissolution. Commonly available particulate
diverter materials include benzoic acid, napthalene, rock salt (sodium chloride),
resin materials, waxes, and polymers. Alternatively, sand, proppant, and ceramic materials,
could be used as particulate diverters. Other specialty particulates can be designed
to precipitate and form during the treatment.
[0009] Another method for diverting involves using viscosified fluids, viscous gels, or
foams as diverting agents. This method involves pumping the diverting fluid across
and/or into the perforated interval. These fluid systems are formulated to temporarily
obstruct flow to the perforations due to viscosity or formation relative permeability
decreases; and are also designed so that at the desired time, the fluid system breaks
down, degrades, or dissolves (with or without adding chemicals or other additives
to trigger such breakdown or dissolution) such that flow can be restored to or from
the perforations. These fluid systems can be used for diversion of matrix chemical
stimulation treatments and fracture treatments. Particulate diverters and/or ball
sealers are sometimes incorporated into these fluid systems in efforts to enhance
diversion.
[0010] Another possible process is limited entry diversion in which the entire target zone
of the formation to be treated is perforated with a very small number of perforations,
generally of small diameter, so that the pressure loss across those perforations during
pumping promotes a high, internal wellbore pressure. The internal wellbore pressure
is designed to be high enough to cause all of the perforated intervals to fracture
simultaneously. If the pressure were too low, only the weakest portions of the formation
would fracture. The primary advantage of limited entry diversion is that there are
no inside-the-casing obstructions like bridge plugs or sand to cause problems later.
The disadvantage is that limited entry fracturing often does not work well for thick
intervals because the resulting fracture is frequently too narrow (the proppant cannot
all be pumped away into the narrow fracture and remains in the wellbore), and the
initial, high wellbore pressure may not last. As the sand material is pumped, the
perforation diameters are often quickly eroded to larger sizes that reduce the internal
wellbore pressure. The net result can be that not all of the target zone is stimulated.
An additional concern is the potential for flow capacity into the wellbore to be limited
by the small number of perforations.
[0011] Some of the problems resulting from failure to stimulate the entire target zone or
using mechanical methods that require multiple wellbore operations and wellbore entries
that pose greater risk and cost as described above may be alleviated by using limited,
concentrated perforated intervals diverted by ball sealers. The zone to be treated
could be divided into sub-zones with perforations at approximately the center of each
of those sub-zones, or sub-zones could be selected based on analysis of the formation
to target desired fracture locations. The fracture stages would then be pumped with
diversion by ball sealers at the end of each stage. Specifically, 300 meters (1,000
feet) of gross formation might be divided into ten sub-zones of about 30 meters (about
100 feet) each. At the center of each 30 meter (100 foot) sub-zone, ten perforations
might be shot at a density of three shots per meter (one shot per foot) of casing.
A fracture stage would then be pumped with proppant-laden fluid followed by ten or
more ball sealers, at least one for each open perforation in a single perforation
set or interval. The process would be repeated until all of the perforation sets were
fractured. Such a system is described in more detail in
U.S. Patent No. 5,890,536, issued April 6, 1999.
[0012] Historically, all zones to be treated in a particular job that uses ball sealers
as the diversion agent have been perforated prior to pumping treatment fluids, and
ball sealers have been employed to divert treatment fluids from zones already broken
down or otherwise taking the greatest flow of fluid to other zones taking less, or
no, fluid prior to the release of ball sealers. Treatment and sealing theoretically
proceeded zone by zone depending on relative breakdown pressures or permeabilities,
but problems were frequently encountered with balls prematurely seating on one or
more of the open perforations outside the targeted interval and with two or more zones
being treated simultaneously. Furthermore, this technique presumes that each perforation
interval or sub-zone would break down and fracture at sufficiently different pressure
so that each stage of treatment would enter only one set of perforations.
[0013] The primary advantages of ball sealer diversion are low cost and low risk of mechanical
problems. Costs are low because the process can typically be completed in one continuous
operation, usually during just a few hours of a single day. Only the ball sealers
are left in the wellbore to either flow out with produced hydrocarbons or drop to
the bottom of the well in an area known as the rat (or junk) hole. The primary disadvantage
is the inability to be certain that only one set of perforations will fracture at
a time so that the correct number of ball sealers are dropped at the end of each treatment
stage. In fact, optimal benefit of the process depends on one fracture stage entering
the formation through only one perforation set and all other open perforations remaining
substantially unaffected during that stage of treatment. Further disadvantages are
lack of certainty that all of the perforated intervals will be treated and of the
order in which these intervals are treated while the job is in progress. When the
order of zone treatment is not known or controlled, it is not possible to ensure that
each individual zone is treated or that an individual stimulation treatment stage
has been optimally designed for the targeted zone. In some instances, it may not be
possible to control the treatment such that individual zones are treated with single
treatment stages.
[0014] One example of a device used in the aforementioned instances can be seen in the document
US 2,986,214 which is considered as the closest prior art.
[0015] To overcome some of the disadvantages that may occur during stimulation treatments
when multiple zones are perforated prior to pumping treatment fluids, an alternative
mechanical diversion method has been developed that involves the use of a coiled tubing
stimulation system to sequentially stimulate multiple intervals with separate treatment.
As with conventional ball sealer diversion, all intervals to be treated are perforated
prior to pumping the stimulation treatment. Then coiled tubing is run into the wellbore
with a mechanical "straddle-packer-like" diversion tool attached to the end. This
diversion tool, when properly placed and actuated across the perforations, allows
hydraulic isolation to be achieved above and below the diversion tool. After the diversion
tool is placed and actuated to isolate the deepest set of perforations, stimulation
fluid is pumped down the interior of the coiled tubing and exits flow ports placed
in the diversion tool between the upper and lower sealing elements. Upon completion
of the first stage of treatment, the sealing elements contained on the diversion tool
are deactivated or disengaged, and the coiled tubing is pulled upward to place the
diversion tool across the second deepest set of perforations and the process is continued
until all of the targeted intervals have been stimulated or the process is aborted
due to operational upsets.
[0016] This type of coiled tubing stimulation apparatus and method have been used to hydraulically
fracture multiple zones in wells with depths up to about 8,000 feet. However, various
technical obstacles, including friction pressure losses, damage to sealing elements,
depth control, running speed, and potential erosion of coiled tubing, currently limit
deployment in deeper wells.
[0017] Excess friction pressure is generated when pumping stimulation fluids, particularly
proppant-laden and/or high viscosity fluids, at high rates through longer lengths
of coiled tubing. Depending on the length and diameter of the coiled tubing, the fluid
viscosity, and the maximum allowable surface hardware working pressures, pump rates
could be limited to just a few barrels per minute; which, depending on the characteristics
of a specific subterranean formation, may not allow effective placement of proppant
during hydraulic fracture treatments or effective dissolution of formation materials
during acid stimulation treatments
[0018] Erosion of the coiled tubing could also be a problem as proppant-laden fluid is pumped
down the interior of the coiled tubing at high velocity, including the portion of
the coiled tubing that remains wound on the surface reel. The erosion concerns are
exacerbated as the proppant-laden fluid impinges on the "continuous bend" associated
with the portion of the coiled tubing placed on the surface reel.
[0019] Most seal elements (e.g., "cup" seal technology) currently used in the coiled tubing
stimulation operations described above could experience sealing problems or seal failure
in deeper wells as the seals are run past a large number of perforations at the higher
well temperatures associated with deeper wells. Since the seals run in contact with
or at a minimal clearance from the pipe wall, rough interior pipe surfaces and/or
perforation burrs can damage the sealing elements. Seals currently available in straddle-packer-like
diversion tools are also constructed from elastomers which may be unable to withstand
the higher temperatures often associated with deeper wells.
[0020] Running speed of the existing systems with cup seals is generally on the order of
4,57 to 9,14 m/min (15 to 30 feet-per-minute) running downhole to 9,14 to 18,3 m/min
(30 to 60 feet-per-minute) coming uphole. For example, at the lower running speed,
approximately 13 hours would be required to reach a depth of 3660 m (12,000 feet)
before beginning the stimulation. Given safety issues surrounding nighttime operations,
this slow running speed could result in multiple days being required to complete a
stimulation job. If any problems are encountered during the job, tripping in and out
of the hole could be very costly because of the total operation times associated with
the slow running speeds.
[0021] Depth control of the coiled tubing system and straddle-packer-like diversion tool
also becomes more difficult as depth increases, such that placing the tool at the
correct depth to successfully execute the stimulation operation may be difficult.
This problem is compounded by shooting the perforations before running the coiled
tubing system in the hole. The perforating operation uses a different depth measurement
device (usually a casing collar locator system) than is generally used in the coiled
tubing system.
[0022] In addition, the coiled tubing method described above requires that all of the perforations
be placed in the wellbore in a separate perforating operation prior to pumping the
stimulation job. The presence of multiple perforation sets open above the diversion
tool can cause operational difficulties. For example, if the proppant fracture from
the current zone were to grow vertically and/or poor quality cement is present behind
pipe, the fracture could intersect the perforation sets above the diversion tool such
that proppant could "dump" back into the wellbore on top of the diversion tool and
prevent further tool movement. Also, it could be difficult to execute circulation
operations if multiple perforation sets are open above the diversion tool. For example,
if the circulation pressures exceed the breakdown pressures associated with the perforations
open above the diversion tool, the circulation may not be maintained with circulation
fluid unintentionally lost to the formation.
[0023] A similar type of stimulation operation may also be performed using jointed tubing
and a workover rig rather than a coiled tubing system. Using a diversion tool deployed
on jointed tubing may allow for larger diameter tubing to reduce friction pressure
losses and allow for increased pump rates. Also, concerns over erosion and tubing
integrity may be reduced when compared to coiled tubing since heavier wall thickness
jointed tubing pipe may be used and jointed tubing would not be exposed to plastic
deformation when run in the wellbore. However, using this approach would likely increase
the time and cost associated with the operations because of slower pipe running speeds
than those possible with coiled tubing.
[0024] To overcome some of the limitations associated with completion operations that require
multiple trips of hardware into and out of the wellbore to perforate and stimulate
subterranean formations, methods have been proposed for "single-trip" deployment of
a downhole tool string to allow for fracture stimulation of zones in conjunction with
perforating. Specifically, these methods propose operations that may minimize the
number of required wellbore operations and time required to complete these operations,
thereby reducing the stimulation treatment cost. These proposals include 1) having
a sand slurry in the wellbore while perforating with overbalanced pressure, 2) dumping
sand from a bailer simultaneously with firing the perforating charges, and 3) including
sand in a separate explosively released container. These proposals all allow for only
minimal fracture penetration surrounding the wellbore and are not adaptable to the
needs of multi-stage hydraulic fracturing as described herein.
[0025] Accordingly, there is a need for an improved method and apparatus for individually
treating each of multiple intervals of a subterranean formation penetrated by a wellbore
while maintaining the economic benefits of multi-stage treatment. There is also a
need for a method and apparatus that can economically reduce the risks inherent in
the currently available stimulation treatment options for hydrocarbon-bearing formations
with multiple or layered reservoirs or with thickness exceeding about 60 meters (200
feet) while ensuring that optimal treatment placement is performed with a mechanical
diversion agent that positively directs treatment stages to the desired location.
SUMMARY OF THE INVENTION
[0026] This invention provides an apparatus and method for perforating and treating multiple
intervals of one or more subterranean formations intersected by a wellbore.
[0027] The apparatus consists of a deployment means (e.g., coiled tubing, jointed tubing,
electric line, wireline, downhole tractor, etc.) with a bottomhole assembly ("BHA")
comprised of at least a perforating device and a re-settable mechanical sealing mechanism
that may be independently actuated via one or more signaling means (e.g., electronic
signals transmitted via wireline; hydraulic signals transmitted via tubing, annulus,
umbilicals; tension or compression loads; radio transmission; fiber-optic transmission;
on-board BHA computer systems, etc.).
[0028] The method includes the steps of deploying the BHA within the wellbore using a deployment
means where the deployment means may be a tubing-string, cable, or downhole tractor.
The perforating device is positioned adjacent to the interval to be perforated and
is used to perforate the interval. The BHA is positioned within the wellbore using
the deployment means, and the sealing mechanism is actuated so as to establish a hydraulic
seal that positively directs fluid pumped down the wellbore to enter the perforated
interval. The sealing mechanism is released. The process can then be repeated, without
removing the BHA from the wellbore, for at least one additional interval of the one
or more subterranean formations.
[0029] The deployment means can be a tubing string, including a coiled tubing or standard
jointed tubing, a wireline, a slickline, or a cable. Rather than tubing or cable deployment,
the deployment means could also be a tractor system attached to the BHA. The tractor
system may be a self-propelled, computer-controlled, and carry on-board signaling
systems such that it is not necessary to attach cable or tubing to control and actuate
the BHA and/or tractor system. Alternatively, the tractor system could be controlled
and energized by cable or tubing umbilicals such the tractor system and BHA are controlled
and actuated via signals transmitted downhole using the umbilicals. Many different
embodiments to the invention can exist depending on the suspension means and specific
components of the BHA.
[0030] In the first embodiment of the invention, when the deployment means is a tubing string,
once an interval has been perforated the BHA can be moved and the sealing mechanism
actuated to establish a hydraulic seal below the perforated interval. Then treating
fluid can be pumped down the annulus between the tubing string and the wellbore and
into the perforated interval. And a second treating fluid, such as nitrogen, could
also be pumped down the tubing string at the same time that the first treating fluid
is pumped down the annulus between the tubing string and the wellbore.
[0031] In the second embodiment, when the suspension means is a tubing string, once an interval
has been perforated the BHA can be moved and the sealing mechanism actuated to establish
a hydraulic seal above the perforated interval. Then treating fluid can be pumped
down the tubing string and into the perforated interval.
[0032] In the third embodiment, when the deployment means is a tubing string, the BHA can
be moved and the sealing mechanism actuated to establish a hydraulic seal above and
below the perforated interval (where the sealing mechanism consists of two seal elements
spaced sufficient distance apart to straddle the perforated interval). In this third
embodiment, treating fluid can be pumped down the tubing string itself, through a
flow port placed in-between the two seal elements of the sealing mechanism and into
the perforated interval.
[0033] In a fourth embodiment of the invention, when the BHA is deployed in the wellbore
using a wireline, slickline or cable, the BHA would be moved and the sealing mechanism
actuated to establish a hydraulic seal below the perforated interval to be treated,
and the treating fluid would be pumped down the annulus between the wireline, slickline,
or cable, and the wellbore.
[0034] In a fifth embodiment of the invention, an "umbilical" is deployed as an additional
means to actuate a BHA component. In the most general sense, the umbilical could take
the form of a small diameter tubing or multiple tubing to provide hydraulic communication
with BHA components; and/or the umbilical could take the form of a cable or multiple
cables to provide electrical or electro-optical communication with BHA components.
[0035] In a sixth embodiment of the invention, when the deployment means is a tractor system
attached to the BHA, the BHA can be moved and the sealing mechanism actuated to establish
a hydraulic seal below the perforated interval. The treating fluid can be pumped down
the wellbore and into the perforated interval.
[0036] In a seventh embodiment of the invention, abrasive fluid-jet cutting technology is
used for perforating and the BHA is suspended by tubing such that the BHA can be moved
and the sealing mechanism actuated to establish a hydraulic seal below the perforated
interval. The treating fluid would then be pumped down the annulus between the tubing
and wellbore.
[0037] One of the primary advantages of this apparatus and method is that the BHA, including
the sealing mechanism and the perforating device, does not need to be removed from
the wellbore prior to treatment with the treating fluid and between treatment of multiple
formation zones or intervals. Another primary advantage of this apparatus and method
is that each treatment stage is diverted using a mechanical diversion agent such that
precise control of the treatment diversion process is achieved and each zone can be
optimally stimulated. As a result, there are significant costs savings associated
with reduction in the time required to perforate and treat multiple intervals within
a wellbore. In addition, there are production improvements associated with using a
mechanical diversion agent to provide precisely-controlled treatment diversion when
stimulating multiple formation interval within a wellbore. As such, the inventive
method and apparatus provide significant economic advantages over existing methods
and equipment since the inventive method and apparatus allow for perforating and stimulating
multiple zones with a single wellbore entry, and subsequent withdrawal, of a bottomhole
assembly that provides dual functionality as both a mechanical diversion agent and
perforating device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The present invention and its advantages will be better understood by referring to
the following detailed description and the attached drawings in which:
Figure 1 illustrates one possible representative wellbore configuration with peripheral equipment
that could be used to support the bottomhole assembly used in the present invention.
Figure 1 also illustrates representative bottomhole assembly storage wellbores with surface
slips that may be used for storage of spare or contingency bottomhole assemblies.
Figure 2A illustrates the first embodiment of the bottomhole assembly deployed using coiled
tubing in an unperforated wellbore and positioned at the depth location to be perforated
by the first set of selectively-fired perforating charges. Figure 2A further illustrates that the bottomhole assembly consists of a perforating device,
an inflatable, re-settable packer, a re-settable axial slip device, and ancillary
components.
Figure 2B represents the bottomhole assembly, coiled tubing, and wellbore of Figure 2A after the first set of selectively-fired perforating charges are fired resulting
in perforation holes through the production casing and cement sheath and into the
first formation zone such that hydraulic communication is established between the
wellbore and the first formation zone.
Figure 2C represents the bottomhole assembly, coiled tubing, and wellbore of Figure 2B after the bottomhole assembly has been re-positioned and the first formation zone
stimulated with the first stage of the multiple-stage, hydraulic, proppant fracture
treatment where the first stage of the fracture treatment was pumped downhole in the
wellbore annulus existing between the coiled tubing and production casing. In Figure 2C, the sealing mechanism is shown in a de-activated position since, for illustration
purposes only, it is assumed that no other perforations besides those associated with
the first zone are present, and as such, isolation is not necessary for treatment
of the first zone.
Figure 3A represents the bottomhole assembly, coiled tubing, and wellbore of Figure 2C after the bottomhole assembly has been re-positioned and the second set of selectively-fired
perforating charges have been fired resulting in perforation holes through the production
casing and cement sheath and into the second formation zone such that hydraulic communication
is established between the wellbore and the second formation zone.
Figure 3B represents the bottomhole assembly, coiled tubing, and wellbore of Figure 3A after the bottomhole assembly has been re-positioned a sufficient distance below
the deepest perforation of the second perforation set to allow slight movement upward
of the BHA to set the re-settable axial slip device while keeping the location of
the circulation port below the bottom-most perforation of the second perforation set.
Figure 3C represents the bottomhole assembly, coiled tubing and wellbore of Figure 3B after the re-settable mechanical slip device has been actuated to provide resistance
to downward axial movement ensuring that the inflatable, re-settable packer and re-settable
mechanical slip device are located between the first zone and second zone perforations.
Figure 3D represents the bottomhole assembly, coiled tubing and wellbore of Figure 3C after the inflatable, re-settable packer has been actuated to provide a barrier to
flow between the portion of the wellbore directly above the inflatable, re-settable
packer and the portion of the wellbore directly below the inflatable, re-settable
packer.
Figure 3E represents the bottomhole assembly, coiled tubing, and wellbore of Figure 3D after the second formation zone has been stimulated with the second stage of the
multiple stage hydraulic proppant fracture treatment where the second stage of the
fracture treatment was pumped downhole in the wellbore annulus existing between the
coiled tubing and production casing.
Figure 3F represents the bottomhole assembly, coiled tubing, and wellbore of Figure 3E after the inflatable, re-settable packer has been de-activated thereby re-establishing
pressure communication between the portion of the wellbore directly above the inflatable,
re-settable packer and the portion of the wellbore directly below the inflatable,
re-settable packer. The re-settable mechanical slip device is still energized and
continues to prevent movement of the coiled tubing and bottomhole assembly down the
wellbore.
Figure 4A represents a modified bottomhole assembly, similar to the bottomhole assembly described
in Figures 2A through 2C and Figures 3A through 3F, but with the addition of a mechanical-plug, settable with a select-fire charge setting
system, located below the string of perforating guns. Figure 4A also represents the coiled tubing, and wellbore of Figure 3F after an additional, third perforating and fracture stimulation operation has been
performed. In Figure 4A, it is noted that only the second and third fractures and perforation sets are shown.
In Figure 4A, the modified bottomhole assembly is shown suspended by coiled tubing such that the
location of the bridge-plug is located above the last perforated interval and below
the next interval to be perforated.
Figure 4B represents the bottomhole assembly, coiled tubing, and wellbore of Figure 4A after the mechanical-plug has been select-fire-charge-set in the well and after the
bottomhole assembly has been re-positioned and the first set of selectively-fired
perforating charges have been fired and result in perforation holes through the production
casing and cement sheath and into the fourth formation zone such that hydraulic communication
is established between the wellbore and the fourth formation zone.
Figure 5 represents a second embodiment of the invention. In this embodiment, the suspension
means is a tubing string, and once an interval has been perforated, the BHA can be
moved and the sealing mechanism actuated to establish a hydraulic seal above the perforated
interval. Then treating fluid can be pumped down the tubing string and into the perforated
interval.
Figure 6 represents a third embodiment of the invention. The suspension means is a tubing
string, and the BHA can be moved and the sealing mechanism actuated to establish a
hydraulic seal above and below the perforated interval (where the sealing mechanism
consists of two seal elements spaced sufficient distance apart to straddle the perforated
interval). In this third embodiment, treating fluid can be pumped down the tubing
string itself, through a flow port placed in-between the two seal elements of the
sealing mechanism and into the perforated interval.
Figure 7 represents a fourth embodiment of the invention. The BHA is suspended in the wellbore
using a wireline (or slickline or cable). The BHA would be moved and the sealing mechanism
actuated to establish a hydraulic seal below the perforated interval to be treated,
and the treating fluid would be pumped down the annulus between the wireline, slickline,
or cable, and the wellbore.
Figures 8A and 8B represent a fifth embodiment of the invention that utilizes an umbilical tubing,
deployed interior to the tubing used as the deployment means, for actuation of the
re-settable sealing mechanism.
Figure 9 represents a sixth embodiment of the invention that utilizes a tractor system attached
to the BHA such that BHA can be moved and the sealing mechanism actuated to establish
a hydraulic seal below the perforated interval. The treating fluid can be pumped down
the wellbore and into the perforated interval.
Figure 10 represents a seventh embodiment of the invention that utilizes abrasive or erosive
fluid-jet cutting technology for the perforating device. The BHA is suspended in the
wellbore using jointed tubing and consists of a mechanical compression-set, re-settable
packer, an abrasive or erosive fluid jet perforating device, a mechanical casing-collar
locator, and ancillary components. In this embodiment, perforations are created by
pumping an abrasive fluid down the jointed tubing and out of a jetting tool located
on the BHA such that a high-pressure high-speed abrasive or erosive fluid jet is created
and used to penetrate the production casing and surrounding cement sheath to establish
hydraulic communication with the desired formation interval. After setting the re-settable
packer below the zone to be stimulated, the stimulation treatment can then pumped
down the annulus located between the tubing string and the production casing string.
DETAILED DESCRIPTION OF THE INVENTION
[0039] The present invention will be described in connection with its preferred embodiments.
However, to the extent that the following description is specific to a particular
embodiment or a particular use of the invention, this is intended to be illustrative
only, and is not to be construed as limiting the scope of the invention. On the contrary,
the description is intended to cover all alternatives, modifications, and equivalents
that are included within the spirit and scope of the invention, as defined by the
appended claims.
[0040] The present invention provides a new method, new system, and a new apparatus for
perforating and stimulating multiple formation intervals, which allows each single
zone to be treated with an individual treatment stage while eliminating or minimizing
the problems that are associated with existing coiled tubing or jointed tubing stimulation
methods and hence providing significant economic and technical benefit over existing
methods.
[0041] Specifically, the invention involves suspending a bottomhole assembly in the wellbore
to individually and sequentially perforate and treat each of the desired multiple
zones while pumping the multiple stages of the stimulation treatment and to deploy
a mechanical re-settable sealing mechanism to provide controlled diversion of each
individual treatment stage. For the purposes of this application, "wellbore" will
be understood to include below ground sealed components of the well and also all sealed
equipment above ground level, such as the wellhead, spool pieces, blowout preventers,
and lubricator.
[0042] The new apparatus consists of a deployment means (e.g., coiled tubing, jointed tubing,
electric line, wireline, tractor system, etc.) with a bottomhole assembly comprised
of at least a perforating device and a re-settable mechanical sealing mechanism that
may be independently actuated from the surface via one or more signaling means (e.g.,
electronic signals transmitted via wireline; hydraulic signals transmitted via tubing,
annulus, umbilicals; tension or compression loads; radio transmission; fiber-optic
transmission; etc.) and designed for the anticipated wellbore environment and loading
conditions.
[0043] In the most general sense, the term "bottomhole assembly" is used to denote a string
of components consisting of at least a perforating device and a re-settable sealing
mechanism. Additional components including, but not limited to, fishing necks, shear
subs, wash tools, circulation port subs, flow port subs, pressure equalization port
subs, temperature gauges, pressure gauges, wireline connection subs, re-settable mechanical
slips, casing collar locators, centralizer subs and/or connector subs may also be
placed on the bottomhole assembly to facilitate other anticipated auxiliary or ancillary
operations and measurements that may be desirable during the stimulation treatment.
[0044] In the most general sense, the re-settable mechanical sealing mechanism performs
the function of providing a "hydraulic seal", where hydraulic seal is defined as sufficient
flow restriction or blockage such that fluid is forced to be directed to a different
location than the location it would otherwise be directed to if the flow restriction
were not present. Specifically, this broad definition for "hydraulic seal" is meant
to include a "perfect hydraulic seal" such that all flow is directed to a location
different from the location the flow would be directed to if the flow restriction
were not present; and an "imperfect hydraulic seal" such that an appreciable portion
of flow is directed to a location different from the location the flow would be directed
to if the flow restriction were not present. Although it would generally be preferable
to use a re-settable mechanical sealing that provides a perfect hydraulic seal to
achieve optimal stimulation; a sealing mechanism that provides an imperfect hydraulic
seal could be used and an economic treatment achieved even though the stimulation
treatment may not be perfectly diverted.
[0045] In the first embodiment, coiled tubing is used as the deployment means and the new
method involves sequentially perforating and then stimulating the individual zones
from bottom to top of the completion interval, with the stimulation fluid pumped down
the annular space between the production casing and the coiled tubing. As discussed
further below, this embodiment of the new apparatus and method offer substantial improvements
over existing coiled tubing and jointed tubing stimulation technology and are applicable
over a wide range of wellbore architectures and stimulation treatment designs.
[0046] Specifically, the first preferred embodiment of the new method and apparatus involves
the deployment system, signaling means, bottomhole assembly, and operations as described
in detail below, where the various components, their orientation, and operational
steps are chosen, for descriptive purposes only, to correspond to components and operations
that could be used to accommodate hydraulic proppant fracture stimulation of multiple
intervals.
[0047] In the first preferred embodiment for a hydraulic proppant fracture stimulation treatment,
the apparatus would consist of the BHA deployed in the wellbore by coiled tubing.
The BHA would include a perforating device; re-settable mechanical sealing mechanism;
casing-collar-locator; circulation ports; and other ancillary components (as described
in more detail below).
[0048] Furthermore, in this first preferred embodiment, the perforating device would consist
of a select-fire perforating gun system (using shaped-charge perforating charges);
and the re-settable mechanical sealing mechanism would consist of an inflatable, re-settable
packer; a mechanical re-settable slip device to prevent downward axial movement of
the bottomhole assembly when set; and pressure equalization ports located above and
below the inflatable re-settable packer.
[0049] In addition, in this first preferred embodiment, a wireline would be placed interior
to the coiled tubing and used to provide a signaling means for actuation of select-fire
perforation charges and for transmission of electric signals associated with the casing-collar-locator
used for BHA depth measurement.
[0050] Referring now to
Figure 1, an example of the type of surface equipment that could be utilized in the first preferred
embodiment would be a rig up that used a very long lubricator
2 with the coiled tubing injector head
4 suspended high in the air by crane arm
6 attached to crane base
8. The wellbore would typically comprise a length of a surface casing
78 partially or wholly within a cement sheath
80 and a production casing
82 partially or wholly within a cement sheath
84 where the interior wall of the wellbore is composed of the production casing
82. The depth of the wellbore would preferably extend some distance below the lowest
interval to be stimulated to accommodate the length of the bottomhole assembly that
would be attached to the end of the coiled tubing
106. Coiled tubing
106 is inserted into the wellbore using the coiled tubing injection head 4 and lubricator
2. Also installed to the lubricator
2 are blow-out-preventors
10 that could be remotely actuated in the event of operational upsets. The crane base
8, crane arm
6, coiled tubing injection head
4, lubricator
2, blow-out-preventors
10 (and their associated ancillary control and/or actuation components) are standard
equipment components well known to those skilled in the art that will accommodate
methods and procedures for safely installing a coiled tubing bottomhole assembly in
a well under pressure, and subsequently removing the coiled-tubing bottomhole assembly
from a well under pressure.
[0051] With readily-available existing equipment, the height to the top of the coiled tubing
injection head
4 could be approximately 90 feet from ground level with the "goose-neck"
12 (where the coil is bent over to go down vertically into the well) approaching approximately
105 feet above the ground. The crane arm
6 and crane base
8 would support the load of the injector head
4, the coiled tubing
106, and any load requirements anticipated for potential fishing operations (jarring and
pulling).
[0052] In general, the lubricator
2 must be of length greater than the length of the bottomhole assembly to allow the
bottomhole assembly to be safely deployed in a wellbore under pressure. Depending
on the overall length requirements and as determined prudent based on engineering
design calculations for a specific application, to provide for stability of the coiled
tubing injection head
4 and lubricator
2, guy-wires
14 could be attached at various locations on the coiled tubing injection head
4 and lubricator
2. The guy wires
14 would be firmly anchored to the ground to prevent undue motion of the coiled tubing
injection head
4 and lubricator
2 such that the integrity of the surface components to hold pressure would not be compromised.
Depending on the overall length requirements, alternative injection head/lubricator
system suspension systems (coiled tubing rigs or fit-for-purpose completion/workover
rigs) could also be used.
[0053] Also shown in
Figure 1 are several different wellhead spool pieces which may be used for flow control and
hydraulic isolation during rig-up operations, stimulation operations, and rig-down
operations. The crown valve
16 provides a device for isolating the portion of the wellbore above the crown valve
16 from the portion of the wellbore below the crown valve
16. The upper master fracture valve
18 and lower master fracture valve
20 also provide valve systems for isolation of wellbore pressures above and below their
respective locations. Depending on site-specific practices and stimulation job design,
it is possible that not all of these isolation-type valves may actually be required
or used.
[0054] The side outlet injection valves
22 shown in
Figure 1 provide a location for injection of stimulation fluids into the wellbore. The piping
from the surface pumps and tanks used for injection of the stimulation fluids would
be attached with appropriate fittings and/or couplings to the side outlet injection
valves
22. The stimulation fluids would then be pumped into the wellbore via this flow path.
With installation of other appropriate flow control equipment, fluid may also be produced
from the wellbore using the side outlet injection valves
22. It is noted that the interior of the coiled tubing
146 can also be used as a flow conduit for fluid injection into the wellbore.
[0055] The bottomhole assembly storage wellbores
24 shown in
Figure 1 provide a location for storage of spare or contingency bottom-hole assemblies
27, or for storage of bottomhole assemblies that have been used during previous operations.
The bottomhole assembly storage wellbores
24 may be drilled to a shallow depth such that a bottomhole assembly that may contain
perforating charges may be safely held in place with surface slips
26 such that the perforating charges are located below ground level until the bottomhole
assembly is ready to be attached to the coiled tubing
106. The bottomhole assembly storage wellbores
24 may be drilled to accommodate placement of either cemented or uncemented casing string,
or may be left uncased altogether. The actual number of bottomhole assembly storage
wellbores
24 required for a particular operation would depend on the overall job requirements.
The bottomhole assembly storage wellbores
24 could be located within the reach of the crane arm
6 to accommodate rapid change-out of bottomhole assemblies during the course of the
stimulation operation without the necessity of physically relocating the crane base
8 to another location.
[0056] Referring now to
Figure 2A, coiled tubing
106 is equipped with a coiled tubing connection
110 which may be connected to a shear-release/fishing neck combination sub
112 that contains both a shear-release mechanism and a fishing neck and allows for the
passage of pressurized fluids and wireline
102. The shear-release/fishing neck combination sub
112 may be connected to a sub containing a circulation port sub
114 that may provide a flow path to wash debris from above the inflatable, re-settable
packer
120 or provide a flow path to inject fluid downhole using the coiled tubing
106. The circulation port sub
114 contains a valve assembly that actuates the circulation port
114 and the upper equalization port
116. The upper equalization port
116 may be connected to a lower equalization port
122 via tubing through the inflatable, re-settable packer
120. Both the circulation port
114 and the upper equalization port
116 would preferably be open in the "running position", thereby allowing pressure communication
between the internal coiled-tubing pressure and the coiled tubing by casing annulus
pressure. Within this document, "running position" refers to the situation where all
components in the bottomhole assembly possess a configuration that permits unhindered
axial movement up and down the wellbore. The lower equalization port
122 located below the inflatable, re-settable packer
120 is always open and flow through the equalization ports is controlled by the upper
equalization port
116. The circulation and equalization ports can be closed simultaneously by placing a
slight compressive load on the BHA. To prevent potential back-flow into the coiled
tubing when the circulation port
114 is open in the running position, a surface pressure can be applied to the coiled
tubing
106 such that the pressure inside the circulation port
114 exceeds the wellbore pressure directly outside the circulation port
114. The re-settable, inflatable packer 120 is hydraulically isolated from the internal
coiled tubing pressure in the running position. The inflatable, re-settable packer
120 can gain pressure communication via internal valving with the internal coiled tubing
pressure by placing a slight compressive load on the BHA. Mechanically actuated, re-settable
axial position locking devices, or "slips,"
124 may be placed below the inflatable, re-settable packer
120 to resist movement down the wellbore. The mechanical slips
124 may be actuated through a "continuous J" mechanism by cycling the axial load between
compression and tension. A wireline connection sub
126 is located above the casing collar locator
128 and select-fire perforating gun system. A gun connection sub
130 connects the casing collar locator
128 to select-fire head
152. The perforating gun system may be designed based on knowledge of the number, location,
and thickness of the hydrocarbon-bearing sands within the target zones. The gun system
will be composed of one gun assembly (e.g.,
134) for each zone to be treated. The first (lowest) gun assembly will consist of a select-fire
head
132 and a gun encasement
134 which will be loaded with perforating charges
136 and a select-fire detonating system.
[0057] Specifically, a preferred embodiment of the new method involves the following steps,
where the stimulation job is chosen, for descriptive purposes, to be a multi-stage,
hydraulic, proppant-fracture stimulation.
- 1. The well is drilled and casing is cemented across the interval to be completed, and
if desired, one or more bottomhole assembly storage wellbores are drilled and completed.
- 2. The target zones within the completion interval are identified (typically by a combination
of open-hole and cased-hole logs).
- 3. The bottomhole assemblies (BHA), and perforating gun assemblies to be deployed on
each BHA anticipated to be used during the stimulation operation, are designed based
on knowledge of the number, location, and thickness of the hydrocarbon-bearing sands
within the target zones.
- 4. A reel of coiled tubing is made-up with a preferred embodiment BHA described above.
The reel of coiled tubing would also be made-up to contain the wireline that is used
to provide a signaling means for actuation of the perforating guns. Preferably, the
desired quantity of appropriately configured spare or contingency BHA's would also
be made-up and stored in the bottomhole assembly storage wellbore(s). The coiled tubing
may be pre-loaded with fluid either before or after attaching the BHA to the coiled
tubing.
- 5. As shown in Figure 1, the coiled tubing 106 with BHA is run into the well via a lubricator 2 and the coiled tubing injection head 4 is suspended by crane arm 6.
- 6. The coiled tubing/BHA is run into the well while correlating the depth of the BHA
with the casing collar locator 128 (Figure 2A).
- 7. The coiled tubing/BHA is run below the bottom-most target zone to ensure that there
is sufficient wellbore depth below the bottom-most perforations to locate the BHA
below the first set of perforations during fracturing operations. As shown in Figure 2A, the inflatable, re-settable packer 120 and re-settable mechanically actuated slips 124 are in the running position.
- 8. As shown in Figure 2B, the coiled tubing/BHA is then raised to a location within the wellbore such that
the first (lowest) set of perforation charges 136 contained on the first gun assembly 134 of the select-fire perforating gun system are located directly across the bottom-most
target zone where precise depth control may be established based on readings from
the casing-collar-locator 128 and coiled tubing odometer systems (not shown). The action of moving the BHA up to
the location of the first perforated interval will cycle the mechanical slip "continuous
J" mechanism (not shown) into the pre-lock position where subsequent downward motion
will force the re-settable mechanical slip 124 into the locked position thereby preventing further downward movement. It is noted
that additional cycling of the coiled tubing axial load from compression to tension
and back will return the re-settable mechanical slips to running position. In this
manner, the mechanical slip continuous J mechanism coupled with the use of compression
and tension loads transmitted via the suspension means (coiled tubing) are used to
provide downhole actuation and de-actuation of the mechanical slips.
- 9. The first set of perforation charges 136 are selectively-fired by remote actuation via wireline 102 communication with the first select-fire head 132 to penetrate the casing 82 and cement sheath 84 and establish hydraulic communication with the formation 86 through the resultant perforations 230-231. It will be understood that any given set of perforations can, if desired, be a set
of one, although generally multiple perforations would provide improved treatment
results. It will also be understood that more than one segment of the gun assembly
may be fired if desired to achieve the target number of perforations whether to remedy
an actual or perceived misfire or simply to increase the number of perforations. It
will also be understood that an interval is not necessarily limited to a single reservoir
sand. Multiple sand intervals could be perforated and treated as a single stage using
other diversion agents suitable for simultaneous deployment with this invention within
a given stage of treatment.
- 10. As shown in Figure 2C, the coiled tubing may be moved to position the circulation port 114 directly below the deepest perforation 231 of this first target zone to minimize potential for proppant fill above the inflatable,
re-settable packer 120 and minimize high velocity proppant flow past the BHA.
- 11. The first stage of the fracture stimulation treatment is initiated by circulating
a small volume of fluid down the coiled tubing 106 through the circulation port 114 (via a positive displacement pump). This is followed by initiating the pumping of
stimulation fluid down the annulus between the coiled tubing 106 and production casing 82 at fracture stimulation rates. The small volume of fluid flowing down the coiled
tubing 106 serves to keep a positive pressure inside the coiled tubing 106 to resist proppant-laden fluid backflow into the coiled tubing 106 and to resist coiled tubing collapse loading during fracturing operations. It is
noted that as an alternative means to resist coiled tubing collapse, an internal valve
mechanism may be used to maintain the circulation port 114 in the closed position and with positive pressure then applied to the coiled tubing
106 using a surface pump. As an illustrative example of the fracture treatment design
for stimulation of a 15-acre size sand lens containing hydrocarbon gas, the first
fracture stage could be comprised of "sub-stages" as follows: (a) 18900 ℓ (5,000 gallons)
of 2% KCl water; (b) 7570 ℓ (2,000 gallons) of cross-linked gel containing 119.8 kg/m3 (1 pound-per-gallon) of proppant; (c) 11400 ℓ (3,000 gallons) of cross-linked gel
containing 239.6 kg/m3 (2 pounds-per-gallon) of proppant; (d) 18900 ℓ (5,000 gallons) of cross-linked gel
containing 359,5 kg/m3 (3 pounds-per-gallon) of proppant; and (e) 11400 ℓ (3,000 gallons) of cross-linked
gel containing 479,3 kg/m3 (4 pound-per-gallon) of proppant such that 132 000 ℓ (35,000 pounds) of proppant
are placed into the first zone.
- 12. As shown in Figure 2C, all sub-stages of the first fracture operation are completed with the creation of
the first proppant fracture 232.
- 13. At the end of the first stage of the stimulation treatment, should proppant in the
wellbore prevent the coiled tubing/BHA from immediate movement; fluid can be circulated
through the circulation port 114 to wash-over and clean-out the proppant to free the coiled tubing/BHA and allow movement.
- 14. As shown in Figure 3A, the coiled tubing/BHA is then pulled uphole to slightly above the second deepest
target zone such that the second set of perforation charges 146 contained on the select-fire perforating gun system 144 are located slightly above the second deepest target zone where again precise depth
control is established based on readings from the casing-collar-locator 128 and coiled tubing odometer systems. The action of moving the BHA upward (to slightly
above the second interval to be perforated) will cycle the re-settable mechanical
slip "continuous J" mechanism into the pre-lock position. Further cycling of compression/tension
loads are performed to place the mechanical slip continuous J mechanism back into
the running position. The coiled tubing/BHA is then moved downward to position the
perforation charges 146 contained on the select-fire perforating gun system 144 directly across from the second deepest target zone where again precise depth control
is established based on readings from the casing-collar-locator 128 and coiled tubing odometer systems.
- 15. The second set of perforation charges 146 are selectively-fired by remote actuation via the second select-fire head 142 to penetrate the casing 82 and cement sheath 84 and establish hydraulic communication with the formation 86 through the resultant perforations 240-241.
- 16. As shown in Figure 3B, the coiled tubing may be moved down the wellbore to position the BHA several feet
below the deepest perforation 241 of the second target zone. Subsequent movement of the BHA up the wellbore to position
the circulation port 114 directly below the deepest perforation 241 of this second target zone will cycle the re-settable mechanical slips 124 into the pre-lock position, where subsequent downward motion will force the re-settable
mechanical slips 124 into the locked position thereby preventing further downward movement.
- 17. As shown in Figure 3C, downward movement engages the re-settable mechanical slips 124 with the casing wall 82 thereby preventing further downward movement of the BHA. A compression load on the
coiled tubing is then applied and this load closes the circulation port 114 and upper equalization port 116, and creates pressure communication between the inflatable, re-settable packer 120 and the internal coiled tubing pressure. The compression load also locks the circulation
port 114 into a position directly below the deepest perforation 241 of this second target zone (to minimize potential for proppant fill above the inflatable,
re-settable packer 120 and minimize high velocity proppant flow past the BHA) and with the re-settable,
inflatable packer 120 positioned between the first and second perforated intervals.
- 18. A further compression load is set down on the coiled tubing/BHA to test the re-settable
mechanical slips 124 and ensure that additional downward force does not translate into further movement
of the BHA down the wellbore.
- 19. As shown in Figure 3D, the inflatable, re-settable packer 120 is actuated by pressurizing the coiled tubing 106 to effect a hydraulic seal above and below the inflatable, re-settable packer 120. A compression load is maintained on the BHA to maintain pressure communication between
the internal coiled tubing pressure and the inflatable, re-settable packer 120, to keep the circulation port 114 and the upper equalization port 116 closed, and to keep the re-settable mechanical slips 124 in the locked and energized position. The inflatable, re-settable packer 120 is maintained in the actuated state by maintaining pressure in the coiled tubing
106 via a surface pump system (it is noted that alternatively, the inflatable, re-settable
packer could be maintained in an actuated state by locking pressure in to the element
using an internal valve remotely controlled from surface by a signaling means compatible
with other BHA components and other present signaling means).
- 20. The second stage of the fracture stimulation treatment is initiated with fluid pumped
down the annulus between the coiled tubing 106 and production casing 82 at fracture stimulation rates while maintaining compression load on the BHA to keep
the circulation port 114 and upper equalization port 116 closed, and maintaining coiled tubing pressure at a sufficient level to resist coiled
tubing string collapse and to keep the inflatable, re-settable packer 120 inflated and serve as a hydraulic seal between the annular pressure above the packer
before, during and after the fracture operation and the sealed wellbore pressure below
the inflatable, re-settable packer.
- 21. All sub-stages of the fracture operation are pumped leaving a minimal under-flush
of the proppant-laden last sub-stage in the wellbore so as not to over-displace the
fracture treatment. If during the course of this treatment stage, the seal integrity
of the inflatable, re-settable packer 120 is believed to be compromised, the treatment stage could be temporarily suspended
to test the packer seal integrity above the highest (shallowest) existing perforations
(e.g., perforation 240 in Figure 3D) after setting the inflatable, re-settable packer 120 in blank pipe. If the seal integrity test were to be performed, it could be desirable
to perform a circulation/washing operation to ensure any proppant that may be present
in the wellbore is circulated out of the wellbore prior to conducting the test. The
circulation/washing operation could be performed by opening the circulation port 114 and then pumping of circulation fluid down the coiled tubing 106 to circulate the proppant out of the wellbore.
- 22. As shown in Figure 3E, all sub-stages of the second fracture operation are completed with the creation of
a second proppant fracture 242.
- 23. After completing the second stage fracture operation and ceasing injection of stimulation
fluid down the annulus formed between the coiled tubing 106 and production casing 82, a small tension load is applied to the coiled tubing 106 while maintaining internal coiled tubing pressure. The small applied tension first
isolates the inflatable, re-settable packer pressure from the coiled tubing pressure
thereby locking pressure in the inflatable, re-settable packer 120 and thereby maintaining a positive pressure seal and imparting significant resistance
to axial movement of the inflatable, re-settable packer 120. In the same motion, the applied tension may then open the circulation port 114 and equalization port 116 thereby allowing the coiled tubing pressure to bleed off into the annulus formed
by the coiled tubing 106 and production casing 82 while simultaneously allowing the pressure above and below the inflatable, re-settable
packer 120 to equilibrate. The surface system pump providing internal coiled tubing pressure
may be stopped after equilibrating the downhole pressures.
- 24. After the pressures inside the coiled tubing, in the annulus formed by the coiled
tubing 106 and production casing 82 above the inflatable, re-settable packer 120, and in the annulus formed by the BHA and production casing 82 below the inflatable, re-settable packer 120 equilibrate, a compressive load placed on the coiled tubing will close the circulation
port 114 and upper equalization port 116 before releasing the pressure trapped within the inflatable, re-settable packer 120 into the coiled tubing 106. This release of internal pressure from the inflatable, re-settable packer 120 will allow the inflatable, re-settable packer 120 to retract from the production casing wall, as shown in Figure 3F, in the absence of an external differential pressure across the inflatable, re-settable
packer 120 which could otherwise result in forces and movement that could damage the coiled
tubing 106 or BHA.
- 25. Once the inflatable, re-settable packer 120 is unset, as shown in Figure 3F, tension pulled on the coiled tubing/BHA could de-energize the re-settable mechanical
slips 124 thereby allowing the BHA to be free to move and be repositioned up the wellbore.
- 26. If at the end of the second stage of the stimulation treatment, proppant in the wellbore
prevents the coiled tubing/BHA from immediate movement, fluid may be circulated through
the circulation port 114 to wash-over and clean-out the proppant to free the coiled tubing/BHA and allow upward
movement of the BHA after releasing the inflatable, re-settable packer.
- 27. The process as described above is repeated until all planned zones are individually-stimulated
(Figures 3A to 3F represent a BHA designed for a three zone stimulation).
- 28. Upon completion of the stimulation process, the components of the BHA are returned
to running position and the coiled tubing/BHA assembly is removed from the wellbore.
- 29. If all the desired target zones have been stimulated, the well can be immediately
placed on production.
- 30. If it is desirable to stimulate additional zones, a reel of coiled tubing may be
made-up with a slightly modified BHA as shown in Figure 4A. In this assembly, the only alteration to the BHA of the preferred embodiment described
above may be the addition of a select-fire-set mechanical plug 164 or select-fire set bridge-plug 164 located below the lowest select-fire gun assembly as shown in Figure 4A. In general, the select-fire-set mechanical plug 164 can be either a bridge plug or a fracture baffle. A fracture baffle would generally
be preferred if it is desirable to simultaneously produce zones separated by the plug
immediately after the stimulation job.
- 31. The modified BHA, shown in Figure 4A, consists of a select-fire perforating gun system (Figure 4A depicts a gun system comprising perforating guns 174, 184 and 194 with associated charges 176, 186 and 196 and select-fire heads 172, 182 and 192), a casing-collar-locator 128, flow ports 114, 116 and 122, an inflatable, re-settable packer 120, a re-settable mechanical axial slip device 124 and select-fire bridge plug 164 set using select-fire head 162. The modified BHA is run into the well via a lubricator and the coiled tubing injection
head suspended by crane or rig above the wellhead.
- 32. The coiled tubing/BHA is run into the well while correlating the depth with the casing
collar locator.
- 33. As shown in Figure 4A, the coiled tubing/modified BHA is run into the wellbore to position the select-fire
mechanical-plug 164 above the last previously stimulated zone 252.
- 34. As shown in Figure 4B the select-fire firing head 162 is fired to set the select-fire mechanical plug 164 above the last previously stimulated zone 252.
- 35. After the bridge-plug select-fire head 162 is activated to set the select-fire bridge-plug 164, the coiled tubing/modified BHA is then raised to a location within the wellbore such
that the first (lowest) set of perforation charges 176 contained on the select-fire perforating gun system are located directly across the
next, bottom-most target zone to be perforated where precise depth control may be
established based on readings from the casing-collar-locator 128 and coiled tubing odometer systems located on the surface equipment. The action of
moving the BHA up to the location of the first perforated interval will cycle the
re-settable mechanical slips 124 into the locked position and will require cycling the coiled tubing axial load from
compression to tension and back to return the re-settable mechanical slips to running
position.
- 36. As shown in Figure 4B, the first set of perforation charges 176 on the modified BHA are selectively-fired by remote actuation via the second select-fire
head 172 to penetrate the casing 82 and cement sheath 84 with perforations 270, 271 and establish hydraulic communication with the formation 86 through the resultant perforations 270-271.
- 37. If there is insufficient space between the last previously placed perforations 250, 251 and the location of the next set of perforations 270, 271 to be stimulated to enable appropriate placement of the BHA for perforation, isolation
and stimulation of the next set of perforations 270, the select-fire bridge plug 164 may be set below the last previously stimulated perforations 250, 251, and the inflatable, re-settable packer may be employed during the first stimulation
operation to isolate the upper-most perforations 270, 271 from the previously stimulated perforations 250, 251.
- 38. The entire process as described above is then repeated as appropriate until all planned
zones are individually-stimulated (Figure 4A and Figure 4B represent a BHA designed for an additional three zone stimulation operation).
[0058] It will be recognized by those skilled in the art that the preferred suspension method
when proppant-laden fluids are involved would be conventional jointed tubing or coiled
tubing, preferably with one or more circulation ports so that proppant settling in
the wellbore could easily be circulated out of the wellbore. Treatments such as acid
fracturing or matrix acidizing may not require such a capability and could readily
be performed with a deployment system based on cable such as slickline or wireline,
or based on a downhole tractor system.
[0059] It will be recognized by those skilled in the art that depending on the objectives
of a particular job, various pumping systems could be used and could involve the following
arrangements: (a) pumping down the annulus created between the cable or tubing (if
the deployment method uses cable or tubing) and the casing wall; (b) pumping down
the interior of the coiled tubing or jointed tubing if the suspension method involves
the use of coiled tubing or jointed tubing and excess friction and proppant erosion
were not of concern for the well depths considered; or (c) simultaneously pumping
down the annulus created between the tubing (if the deployment method involves tubing)
and the casing wall and the interior of the tubing if excess friction and proppant
erosion were not of concern for the well depths considered.
[0060] Figure 5 illustrates a second embodiment where coiled tubing is used as the deployment means
and excess friction is not of concern and either proppant is not pumped during the
job or use of proppant is not of concern.
Figure 5 shows that coiled tubing
106 is used to suspend the BHA and BHA components. In this embodiment, the individual
zones are treated in sequential order from shallower wellbore locations to deeper
wellbore locations. In this embodiment, as shown in
Figure 5, circulation port
114 is now placed below the inflatable, re-settable packer
120 such that treatment fluid may be pumped down the interior of coiled tubing
106, exit the circulation port
114, and be positively forced to enter the targeted perforations. As an illustration of
the operations,
Figure 5 shows that the inflatable, re-settable packer
120 has been actuated and set below perforations
241 that are associated with a previous zone hydraulic fracture
242. The inflatable, re-settable packer
120 provides hydraulic isolation such that when treatment fluid is subsequently pumped
down the coiled tubing
106, the treating fluid is forced to enter previously placed perforations
230 and
231 and create new hydraulic fractures
232. The operations are then continued and repeated as appropriate for the desired number
of formation zones and intervals.
[0061] Figure 6 illustrates a third embodiment where coiled tubing is used as the deployment means
and excess friction is not of concern and either proppant is not pumped during the
job or use of proppant is not of concern.
Figure 6 shows that coiled tubing
106 is used to suspend the BHA and BHA components. In this embodiment, the individual
zones may be treated in any order. In this embodiment, as shown in
Figure 6, a straddle-packer inflatable sealing mechanism
125 is used as the re-settable sealing mechanism and the circulation port
114 is now placed between the upper inflatable sealing element
121 and the lower inflatable sealing element
123. When the upper inflatable sealing element
121 and the lower inflatable sealing element
123 are actuated, treatment fluid may be pumped down the interior of coiled tubing
106 to exit the circulation port
114, and then be positively forced to enter the targeted perforations. As an illustration
of the operations,
Figure 6 shows that the upper inflatable sealing element
121 and the lower inflatable sealing element
123 have been actuated and set across perforations
241 that are associated with the next zone to be fractured. The inflatable, re-settable
packer
120 provides hydraulic isolation such that when treatment fluid is subsequently pumped
down the coiled tubing
106, the treating fluid is forced to enter previously placed perforations
240 and
241 and create new hydraulic fractures
242. The operations are then continued and repeated as appropriate for the desired number
of formation zones and intervals.
[0062] Figure 7 illustrates a fourth embodiment where a wireline
102 is used as the deployment means to suspend the BHA and BHA components. In this embodiment,
the individual zones are treated in sequential order from deeper wellbore locations
to shallower wellbore locations. In this embodiment, as shown in
Figure 7, treatment fluid may be pumped down the annulus between the wireline
102 and production casing wall
82 and be positively forced to enter the targeted perforations. In this embodiment,
the inflatable re-settable packer
120 also contains an internal electrical pump system
117, powered by electrical energy transmitted downhole via the wireline, to inflate or
deflate the inflatable, re-settable packer
120 using wellbore fluid.
Figure 7 shows that the inflatable, re-settable packer
120 has been actuated and set below the perforations
241 that are associated with the next zone to be fractured. The inflatable, re-settable
packer
120 provides hydraulic isolation such that when treatment fluid is subsequently pumped
down the annulus between the wireline
102 and production casing
82, the treating fluid is forced to enter perforations
240 and
241 and create new hydraulic fractures
242. The operations are then continued and repeated as appropriate for the desired number
of formation zones and intervals.
[0063] A fifth embodiment involves deployment of additional tubing strings or cables, hereinafter
referred to as "umbilicals", interior and/or exterior to coiled tubing (or jointed
tubing). As shown in
Figure 8A and
Figure 8B, a tubing umbilical
104 is shown deployed in the interior of the coiled tubing
106. In this embodiment, the tubing umbilical
104 is connected to the re-settable sealing mechanism
120 and in this embodiment the re-settable sealing mechanism
120 is now actuated via hydraulic pressure transmitted via the umbilical
104. In general, multiple umbilicals can be deployed either in the interior of the coiled
tubing and/or in the annulus between the coiled tubing and production casing. In general,
the umbilicals can be used to perform several different operations, including but
not limited to, providing (a) hydraulic communication for actuation of individual
BHA components including, but not limited to, the sealing mechanism and/or perforating
device; (b) flow conduits for downhole injection or circulation of additional fluids;
and (c) for data acquisition from downhole measurement devices. It is noted that as
shown in
Figure 8A, the BHA also includes centralizers
201, 203, and
205 that are used to keep the BHA centralized in the wellbore when BHA components are
in the running position.
[0064] The use of an umbilical(s) can provide the ability to hydraulically engage and/or
disengage the re-settable mechanical sealing mechanism independent of the hydraulic
pressure condition within the coiled tubing. This then allows the method to be extended
to use of re-settable mechanical sealing mechanisms requiring independent hydraulic
actuation for operation. Perforating devices that require hydraulic pressure for selective-firing
can be actuated via an umbilical. This may then allow the wireline, if deployed with
the coiled tubing and BHA, to be used for transmission of an additional channel or
channels of electrical signals, as may be desirable for acquisition of data from measurement
gauges located on the bottomhole assembly; or actuation of other BHA components, for
example, an electrical downhole motor-drive that could provide rotation/torque for
BHA components. Alternatively, an umbilical could be used to operate a hydraulic motor
for actuation of various downhole components (e.g., a hydraulic motor to engage or
disengage the re-settable sealing mechanism).
[0065] The use of an umbilical(s) can provide the ability to inject or circulate any fluid
downhole to multiple locations as desired with precise control. For example, to help
mitigate proppant settling on the sealing mechanism during a hydraulic proppant fracture
treatment, umbilical(s) could be deployed and used to provide independent continuous
or intermittent washing and circulation to keep proppant from accumulating on the
sealing mechanism. For example, one umbilical could run to just above the re-settable
mechanical sealing mechanism while another is run just below the re-settable mechanical
sealing mechanism. Then, as desired, fluid (e.g., nitrogen) could be circulated downhole
to either or both locations to wash the proppant from the region surrounding the sealing
mechanism and hence mitigate the potential for the BHA sticking due to proppant accumulation.
In the case of fluid circulation, it is noted that the umbilical size and fluid would
be selected to ensure the desired rate is achieved and is not unduly limited by friction
pressure in the umbilical.
[0066] In addition to umbilicals comprised of tubing strings that provide hydraulic communication
downhole as a signaling means for actuation of BHA components (or possibly as a signal
transmission means for surface recording of downhole gauges), in general, one or more
wireline or fiber-optic cables could be deployed in the wellbore to provide a electrical
or electro-optical communication downhole as a signaling means for actuation of BHA
components (or possibly as a signal transmission means for surface recording of downhole
gauges).
[0067] Figure 9 illustrates a sixth embodiment of the invention where a tractor system, comprised
of upper tractor drive unit
131 and lower tractor drive unit
133, is attached to the BHA and is used to deploy and position the BHA within the wellbore.
In this embodiment, the individual zones are treated in sequential order from deeper
wellbore locations to shallower wellbore locations. In this embodiment, the BHA also
contains an internal electrical pump system
117, powered by electrical energy transmitted downhole via the wireline
102, to inflate or deflate the inflatable, re-settable packer
120 using wellbore fluid. In this embodiment, treatment fluid is pumped down the annulus
between the wireline
102 and production casing wall
82 and is positively forced to enter the targeted perforations.
Figure 9 shows that the inflatable, re-settable packer
120 has been actuated and set below the perforations
241 that are associated with the next zone to be fractured. The inflatable, re-settable
packer
120 provides hydraulic isolation such that when treatment fluid is subsequently pumped
down the annulus between the wireline
102 and production casing
82, the treating fluid is forced to enter perforations
240 and
241 and create new hydraulic fractures
242. The operations are then continued and repeated as appropriate for the desired number
of formation zones and intervals.
[0068] As alternatives to this sixth embodiment, the tractor system could be self-propelled,
controlled by on-board computer systems, and carry on-board signaling systems such
that it would not be necessary to attach cable or tubing for positioning, control,
and/or actuation of the tractor system. Furthermore, the various BHA components could
also be controlled by on-board computer systems, and carry on-board signaling systems
such that it is not necessary to attach cable or tubing for control and/or actuation
of the components. For example, the tractor system and/or BHA components could carry
on-board power sources (e.g., batteries), computer systems, and data transmission/reception
systems such that the tractor and BHA components could either be remotely controlled
from the surface by remote signaling means, or alternatively, the various on-board
computer systems could be pre-programmed at the surface to execute the desired sequence
of operations when the deployed in the wellbore.
[0069] In a seventh embodiment, abrasive (or erosive) fluid jets are used as the means for
perforating the wellbore. Abrasive (or erosive) fluid jetting is a common method used
in the oil industry to cut and perforate downhole tubing strings and other wellbore
and wellhead components. The use of coiled tubing or jointed tubing as the BHA suspension
means provides a flow conduit for deployment of abrasive fluid-jet cutting technology.
To accommodate this, the BHA is configured with a jetting tool. This jetting tool
allows high-pressure high-velocity abrasive (or erosive) fluid systems or slurries
to be pumped downhole through the tubing and through jet nozzles. The abrasive (or
erosive) fluid cuts through the production casing wall, cement sheath, and penetrates
the formation to provide flow path communication to the formation. Arbitrary distributions
of holes and slots can be placed using this jetting tool throughout the completion
interval during the stimulation job. In general, abrasive (or erosive) fluid cutting
and perforating can be readily performed under a wide range of pumping conditions,
using a wide-range of fluid systems (water, gels, oils, and combination liquid/gas
fluid systems) and with a variety of abrasive solid materials (sand, ceramic materials,
etc.), if use of abrasive solid material is required for the wellbore specific perforating
application.
[0070] The jetting tool replaces the conventional select-fire perforating gun system described
in the previous six embodiments, and since this jetting tool can be on the order of
one-foot to four-feet in length, the height requirement for the surface lubricator
system is greatly reduced (by possible up to 60-feet or greater) when compared to
the height required when using conventional select-fire perforating gun assemblies
as the perforating device. Reducing the height requirement for the surface lubricator
system provides several benefits including cost reductions and operational time reductions.
[0071] Figure 10 illustrates in detail a seventh embodiment of the invention where a jetting tool
310 is used as the perforating device and jointed tubing
302 is used to suspend the BHA in the wellbore. In this embodiment, a mechanical compression-set,
re-settable packer
316 is used as the re-settable sealing device; a mechanical casing-collar-locator
318 is used for BHA depth control and positioning; a one-way full-opening flapper-type
check valve sub
304 is used to ensure fluid will not flow up the jointed tubing
302; a combination shear-release fishing-neck sub
306 is used as a safety release device; a circulation/equalization port sub
308 is used to provide a method for fluid circulation and also pressure equalization
above and below the mechanical compression-set, re-settable packer
316 under certain circumstances; and a one-way ball-seat check valve sub
314 is used to ensure that fluid may only flow upward from below the mechanical compression-set,
re-settable packer
316 to the circulation/equalization port sub
308.
[0072] The jetting tool
310 contains jet flow ports
312 that are used to accelerate and direct the abrasive fluid pumped down jointed tubing
302 to jet with direct impingement on the production casing
82. In this configuration, the mechanical casing collar locator
318 is appropriately designed and connected to the mechanical compression-set, re-settable
packer
316 such as to allow for fluid flow upward from below mechanical compression-set, re-settable
packer
316 to the circulation/equalization port sub
308. The cross-sectional flow area associated with the flow conduits contained within
the circulation/equalization port sub
308 are sized to provide a substantially larger cross-sectional flow area than the flow
area associated with the jet flow ports
312 such that the majority of flow within the jointed tubing
302 or BHA preferentially flows through the circulation/equalization port sub
308 rather than the jet flow ports
312 when the circulation/equalization port sub
308 is in the open position. The circulation/equalization port sub 308 is opened and
closed by upward and downward axial movement of jointed pipe 302.
[0073] In this embodiment, jointed tubing
302 is preferably used with the mechanical compression-set, re-settable packer
316 since the mechanical compression-set, re-settable packer
316 can be readily actuated and de-actuated by vertical movement and/or rotation applied
via the jointed tubing
302. Vertical movement and/or rotation is applied via the jointed tubing
302 using a completion rig-assisted snubbing unit with the aid of a power swivel unit
as the surface means for connection, installation, and removal of the jointed tubing
302 in to and out of the wellbore. It is noted that the surface hardware, methods, and
procedures associated with use of a completion rig-assisted snubbing unit with a power
swivel unit are common and well-known to those skilled in the art for connection,
installation, and removal of jointed tubing in/from a wellbore under pressure. Alternatively,
use of a completion rig with the aid of a power swivel unit, and stripping head in
place of the snubbing unit, could accommodate connection, installation, and removal
of the jointed tubing in/from a wellbore under pressure; again this is common and
well-known to those skilled in the art for connection, installation, and removal of
jointed tubing in/from a wellbore under pressure. It is further noted that the surface
rig-up and plumbing configuration will include appropriate manifolds, piping, and
valves to accommodate flow to, from, and between all appropriate surface components/facilities
and the wellbore, including but not limited to, the jointed tubing, annulus between
jointed tubing and production casing, pumps, fluid tanks, and flow-back pits.
[0074] Since the mechanical compression-set, re-settable packer is actuated via jointed
tubing
302 vertical movement and/or rotation, fluid can be pumped down the jointed tubing
302 without the necessity of additional control valves and/or isolation valves that may
otherwise be required if an inflatable packer was used as the re-settable sealing
device. The interior of the jointed tubing
302 is used in this fashion to provide an independent flow conduit between the surface
and the jetting tool
310 such that abrasive fluid can be pumped down the jointed tubing
302 to the jetting tool
310. The jet flow ports
312 located on the jetting tool
310 then create a high velocity abrasive fluid jet that is directed to perforate the
production casing
82 and cement sheath
84 to establish hydraulic communication with the formation
86.
[0075] Figure 10 shows the jetting tool
310 has been used to place perforations
320 to penetrate the first formation interval of interest, and that the first formation
interval of interest has been stimulated with hydraulic fractures
322. Figure 10 further shows the jetting tool
310 has been repositioned within the wellbore and used to place perforations
324 in the second formation interval of interest, and that the mechanical compression-set,
re-settable packer
316 has been actuated to provide a hydraulic seal within the wellbore in advance of stimulating
perforations
324 with the second stage of the multi-stage hydraulic proppant fracture treatment.
[0076] It is noted that the jet flow ports
312 may be located within approximately six-inches to one-foot of the mechanical compression-set,
re-settable packer
316 such that after pumping the second proppant fracture stage, should proppant accumulation
on the top of the mechanical compression-set, re-settable packer
316 be of concern, non-abrasive and non-erosive fluid can be pumped down the jointed
tubing
302 and through the jet flow ports
312 and/or the circulation/equalization port sub
308 as necessary to clean proppant from the top of the mechanical compression-set, re-settable
packer
316. Furthermore, the jetting tool
310 may be rotated (when the mechanical compression-set, re-settable packer
316 is not actuated) using the jointed tubing
302 which may be rotated with the surface power swivel unit to further help to clean
proppant accumulation that may occur above the mechanical compression-set, re-settable
packer
316. Since the perforations are created using a fluid jet, perforation burrs will not
be created. Since perforation burrs are not present to potentially provide additional
wear and tear on the elastomers of the mechanical compression-set re-settable packer
316, the longevity of the mechanical compression-set re-settable packer 316 may be
increased when compared to applications where perforation burrs may exist.
[0077] It is further noted that the flow control provided by the one-way ball-seat check
valve sub
314 and the one-way full-opening flapper-type check valve sub
304 only allows for pressure equalization above and below the mechanical compression-set,
re-settable packer
316 when the pressure below the mechanical compression-set, re-settable packer
316 is larger than the pressure above the mechanical compression-set, re-settable packer
316. In circumstances when the pressure above the mechanical compression-set, re-settable
packer
316 may be larger than the pressure below the mechanical compression-set, re-settable
packer
316, the pressure above the mechanical compression-set, re-settable packer
316 can be readily reduced by performing a controlled flow-back of the just stimulated
zone using the annulus between the jointed tubing
302 and the production casing
82; or by circulation of lower density fluid (e.g., nitrogen) down the jointed tubing
302 and up the annulus between the jointed tubing
302 and production casing
82.
[0078] The one-way full-opening flapper-type check valve sub
304 is preferred as this type of design accommodates unrestricted pumping of abrasive
(or erosive) fluid downhole, and furthermore allows for passage of control balls that,
depending on the specific detailed design of individual BHA components, may be dropped
from the surface to control fluid flow and hydraulics of individual BHA components
or provide for safety release of the BHA. Depending on the specific tool design, many
different valving configurations could be deployed to provide the functionality provided
by the flow control valves described in this embodiment.
[0079] As alternatives to this seventh embodiment, a sub containing a nipple could be included
which could provide the capability of suspending and holding other measurement devices
or BHA components. This nipple, for example, could hold a conventional casing-collar-locator
and gamma-ray tool that is deployed via wireline and seated in the nipple to provide
additional diagnostics of BHA position and location of formation intervals of interest.
Additionally, multiple abrasive jetting tools can be deployed as part of the BHA to
control perforation cutting characteristics, such as hole/slot size, cutting rate,
to accommodate various abrasive materials, and/or to provide system redundancy in
the event of premature component failure.
[0080] It will be recognized by those skilled in the art that many different components
can be deployed as part of the bottomhole assembly. The bottomhole assembly may be
configured to contain instrumentation for measurement of reservoir, fluid, and wellbore
properties as deemed desirable for a given application. For example, temperature and
pressure gauges could be deployed to measure downhole fluid temperature and pressure
conditions during the course of the treatment; a densitometer could be used to measure
effective downhole fluid density (which would be particularly useful for determining
the downhole distribution and location of proppant during the course of a hydraulic
proppant fracture treatment); and a radioactive detector system (e.g., gamma-ray or
neutron measurement systems) could be used for locating hydrocarbon bearing zones
or identifying or locating radioactive material within the wellbore or formation.
[0081] Depending on the specific bottomhole assembly components and whether the perforating
device creates perforation holes with burrs that may damage the sealing mechanism,
the bottomhole assembly could be configured with a "perforation burr removal" tool
that would act to scrape and remove perforation burrs from the casing wall.
[0082] Depending on the specific bottomhole assembly components and whether excessive wear
of bottomhole assembly components may occur if the assembly is run in contact with
the casing wall, centralizer subs could be deployed on the bottomhole assembly to
provide positive mechanical positioning of the assembly and prevent or minimize the
potential for damage due to the assembly running in contact with the casing wall.
[0083] Depending on the specific bottomhole assembly components and whether the perforation
charges create severe shock waves and induce undue vibrations when fired, the bottomhole
assembly may be configured with vibration/shock dampening subs that would eliminate
or minimize any adverse effects on system performance due to perforation charge detonation.
[0084] Depending on the deployment system used and the objectives of a particular job, perforating
devices and any other desired BHA components may be positioned either above or below
the re-settable sealing mechanism and in any desired order relative to each other.
The deployment system itself, whether it be wireline, electric line, coiled tubing,
conventional jointed tubing, or downhole tractor may be used to convey signals to
activate the sealing mechanism and/or perforating device. It would also be possible
to suspend such signaling means within conventional jointed tubing or coiled tubing
used to suspend the sealing and perforating devices themselves. Alternatively, the
signaling means, whether it be electric, hydraulic, or other means, could be run in
the hole externally to the suspension means or even housed in or comprised of one
or more separate strings of coiled tubing or conventional jointed tubing.
[0085] With respect to treatments that use high viscosity fluid systems in wells deeper
than about 2440 m (8,000 feet), several major technological and economic benefits
are immediately derived from application of this new invention. Reducing the friction
pressure limitations allows treatment of deeper wells and reduces the requirement
for special fracture fluid formulations. Friction pressure limitations are reduced
or eliminated because the high viscosity fluid can be pumped down the annulus between
the coiled tubing or other suspension means and production casing. Since friction
pressure limitations can be reduced or eliminated from that experienced with pumping
high viscosity fluid systems down the interior of coiled tubing, well depths where
this technique can be applied are substantially increased. For example, assuming 3,81
cm (1-1/2-inch) coiled tubing deployed in a 14 cm (5-1/2-inch) outer diameter 2513
kg/m (17-pound-per-foot) casing, the effective cross-sectional flow area is approximately
equivalent to a 12,7 cm (5-inch) outer diameter casing string. With this effective
cross-sectional flow area, well depths on the order of 6100 m (20,000 feet) or greater
could be treated and higher pump rates (e.g., on the order of 10 to 30-barrels-per-minute
or more) could be achieved for effective proppant transport and hydraulic fracturing
using high viscosity fluids.
[0086] Since the annulus typically may have greater equivalent flow area, conventional fracturing
fluids can be used, as opposed to special low-viscosity fluids (such as Dowell-Schlumberger's
ClearFrac™ fluid) used to reduce friction pressure drop through coiled tubing. The
use of conventional fracturing fluid technology would then allow treatment of formations
with temperatures greater than 250°F, above which currently available higher-cost
specialty fluids may begin to degrade.
[0087] The sealing mechanism used could be an inflatable device, a mechanical compression-set
re-settable packer, a mechanical compression-set straddle-packer design, cup-seal
devices, or any other alternative device that may be deployed via a suspension means
and provides a re-settable hydraulic sealing capability or equivalent function. Both
inflatable and compression set devices exist that provide radial clearance between
seals and casing wall (e.g., on the order of 0.25-inches to 1-inch for inflatable
devices or 0.1 - 0.2 inches for compression-set devices) such that seal wear and tear
would be drastically reduced or eliminated altogether. In a preferred embodiment of
this invention, there would be sufficient clearance between the sealing mechanism
in its deactivated state and the casing wall to allow rapid movement into and out
of the wellbore without significant damage to the sealing mechanism or without pressure
control issues related to surging/swabbing the well due to tool movement. The increased
clearance between the seal surface and the casing wall (when the seal is not actuated)
would also allow the coiled tubing/BHA to be tripped in and out of the hole at much
faster speeds than are possible with currently available coiled tubing systems. In
addition, to minimize potential undesirable seal wear and tear, in a preferred embodiment,
the perforating device would accommodate perforating the casing wall such that a perforation
hole with a relatively smooth edge would be achieved. Alternatively, the mechanical
re-settable sealing mechanism may not need to provide a perfect hydraulic seal and
for ,example, could retain a small gap around the circumference of the device. This
small gap could be sized to provide a sealing mechanism (if desired) whereby proppant
bridges across the small gap and provides a seal (if desired) that can be removed
by fluid circulation. Furthermore depending on the specific application, it is possible
that a stimulation job could proceed in an economically viable fashion even if a perfect
hydraulic seal was not obtained with the mechanical re-settable sealing mechanism.
[0088] Since the perforating device is deployed simultaneously with the re-settable sealing
mechanism, all components can be depth controlled at the same time by the same measurement
standard. This eliminates depth control problems that existing methods experience
when perforation operations and stimulation operations are performed using two different
measurement systems at different times and different wellbore trips. Very precise
depth control can be achieved by use of a casing-collar-locator, which is the preferred
method of depth control.
[0089] The gross height of each of the individual perforated target intervals is not limited.
This is in contrast to the problem that existing coiled tubing systems possess using
a straddle-packer like device that limits application to 15 - 30 feet of perforated
interval height.
[0090] Since permanent bridge plugs are not necessarily used, the incremental cost and wellbore
risk associated with bridge plug drill-out operations is eliminated.
[0091] If coiled tubing is used as the deployment means, it is possible that the coiled
tubing string used for the stimulation job could be hung-off in the wellhead and used
as the production tubing string, which could result in significant cost savings by
eliminating the need for rig mobilization to the well-site for installation of conventional
production tubing string comprised of jointed tubing.
[0092] Controlling the sequence of zones to be treated allows the design of individual treatment
stages to be optimized based on the characteristics of each individual zone. Furthermore,
the potential for sub-optimal stimulation because multiple zones are treated simultaneously
is essentially eliminated by having only one open set of perforations exposed to each
stage of treatment. For example, in the case of hydraulic fracturing, this invention
may minimize the potential for overflush or sub-optimal placement of proppant into
the fracture. Also, if a problem occurs such that the treatment must be terminated,
the up-hole zones to be stimulated have not been compromised, since they have yet
to be perforated. This is in contrast to conventional ball sealer or coiled tubing
stimulation methods, where all perforations must be shot prior to the job. Should
the conventional coiled tubing job fail, it may be extremely difficult to effectively
divert and stimulate over a long completion interval. Additionally, if only one set
of perforations is open above the sealing element, fluid can be circulated without
the possibility of breaking down the other multiple sets of open perforations above
the top sealing element as could occur in the conventional coiled tubing job. This
can minimize or eliminate fluid loss and damage to the formation when the bottomhole
circulation pressure would otherwise exceed the formation pore pressure.
[0093] The entire treatment can be pumped in a single trip, resulting in significant cost
savings over other techniques that require multiple wireline or rig work to trip in
and out of the hole in between treatment stages.
[0094] The invention can be applied to multi-stage treatments in deviated and horizontal
wellbores. Typically, other conventional diversion technology in deviated and horizontal
wellbores is more challenging because of the nature of the fluid transport of the
diverter material over the long intervals typically associated with deviated or horizontal
wellbores.
[0095] Should a screen-out occur during the fracture treatment, the invention provides a
method for sand-laden fluid in the annulus to be immediately circulated out of the
hole such that stimulation operations can be recommenced without having to trip the
coiled tubing/BHA out of the hole. The presence of the coiled tubing system provides
a means to measure bottomhole pressure after perforating or during stimulation operations
based on pressure calculations involving the coiled tubing string under shut-in (or
low-flow-rate) conditions.
[0096] The presence of the coiled tubing or conventional jointed tubing system, if used
as the deployment means, provides a means to inject fluid downhole independently from
the fluid injected in the annulus. This may be useful, for example, in additional
applications such as: (a) keeping the BHA sealing mechanism and flow ports clean of
proppant accumulation (that could possibly cause tool sticking) by pumping fluid downhole
at a nominal rate to clean off the sealing mechanism and flow ports; (b) downhole
mixing applications (as discussed further below); (c) spotting of acid downhole during
perforating to aid perforation hole cleanup and communication with the formation;
and (d) independently stimulating two zones isolated from each other by the re-settable
sealing mechanism. As such, if tubing is used as the deployment means, depending on
the specific operations desired and the specific bottomhole assembly components, fluid
could be circulated downhole at all times; or only when the sealing element is energized,
or only when the sealing element is not energized; or while equalization ports are
open or closed. Depending on the specific bottomhole assembly components and the specific
design of downhole flow control valves, as may be used for example as integral components
of equalization ports subs, circulation port subs or flow port subs, downhole flow
control valves may be operated by wireline actuation, hydraulic actuation, flow actuation,
"j-latch" actuated, sliding-sleeve actuated, or by many other means known to those
skilled in the art of operation and actuation of downhole flow control valves.
[0097] The coiled tubing system still allows for controlled flowback of individual treatment
stages to aid clean up and assist fracture closure. Flowback can be performed up the
annulus between the coiled tubing and the production casing, or alternatively, flowback
may even be performed up the coiled tubing string if excessive proppant flowback were
not to be considered a problem.
[0098] The perforating device may be comprised of commercially-available perforating systems.
These gun systems could include what will be referred to herein as a "select-fire"
system such that a single perforation gun assembly is comprised of multiple charges
or sets of perforation charges. Each individual set of one or more perforation charges
can be remotely controlled and fired from the surface using electric, radio, pressure,
fiber-optic or other actuation signals. Each set of perforation charges can be designed
(number of charges, number of shots per foot, hole size, penetration characteristics)
for optimal perforation of the individual zone that is to be treated with an individual
stage. With current select-fire gun technology, commercial gun systems exist that
could allow on the order of 30 to 40 intervals to be perforated sequentially in a
single downhole trip. Guns can be pre-sized and designed to provide for firing of
multiple sets of perforations. Guns can be located at any location on the bottomhole
assembly, including either above or below the mechanical re-settable sealing mechanism.
[0099] Intervals may be grouped for treatment based on reservoir properties, treatment design
considerations, or equipment limitations. After each group of intervals (preferably
5 to approximately 20), at the end of a workday (often defined by lighting conditions),
or if difficulties with sealing one or more zones are encountered, a bridge plug or
other mechanical device would preferably be used to isolate the group of intervals
already treated from the next group to be treated. One or more select-fire set bridge
plugs or fracture baffles could be run in conjunction with the bottomhole assembly
and set as desired during the course of the completion operation to provide positive
mechanical isolation between perforated intervals and eliminate the need for a separate
wireline run to set mechanical isolation devices or diversion agents between groups
of fracture stages.
[0100] In general, the method can be readily employed in production casings of 11,4 cm (4-1/2
inch) diameter to 17,8 cm (7-inch) diameter with existing commercially available perforating
gun systems and mechanical re-settable sealing mechanisms. The inventive method could
be employed in smaller or larger casings with mechanical re-settable sealing mechanisms
appropriately designed for the smaller or larger casings.
[0101] If select-fire perforating guns are used, each individual gun may be on the order
of 61 to 244 cm (2 to 8 feet) in length, and contain on the order of 8 to 20 perforating
charges placed along the gun tube at shot density ranging between 1 and 6 shots per
foot, but preferably 2 to 4 shots per foot. In a preferred embodiment, as many as
15 to 20 individual guns could be stacked one on top of another such that the assembled
gun system total length is preferably kept to less than approximately 24,4 to 30,5
m (80 to 100 feet). This total gun length can be run into the wellbore using a readily-available
surface crane and lubricator system. Longer gun lengths could also be used, but may
require additional or special surface equipment depending on the total number of guns
that would make up the complete perforating device. It is noted that in some unique
applications, gun lengths, number of charges per gun, and shot density could be greater
or less than as specified above as final perforating system design would be impacted
by the specific formation characteristics present in the wellbore to stimulated
[0102] In order to minimize the total length of the gun system and BHA, it may be desirable
to use multiple (two or more) charge carriers uniformly distributed around and strapped,
welded, or otherwise attached to the coiled tubing or connected below the mechanical
re-settable sealing mechanism. For example, if it were desired to stimulate 30 zones,
where each zone is perforated with a 1,22 m (4-ft) gun, a single gun assembly would
result in a total length of approximately 45,7 m (150 feet), which may be impractical
to handle at the surface. Alternatively, two gun assemblies located opposite one another
on the coiled tubing could be deployed, where each assembly could contain 15 guns,
and total length could be approximately 22,9 m (75-feet), which could readily be handled
at the surface with existing lubricator and crane systems.
[0103] An alternative arrangement for the perforating gun or guns would be to locate one
or more guns above the re-settable mechanical sealing mechanism. There could be two
or more separate gun assemblies attached in such a way that the charges were oriented
away from the components on the bottomhole assembly or the coiled tubing. It could
also be a single assembly with charges loaded more densely and firing mechanisms designed
to simultaneously fire only a subset of the charges within a given interval, perhaps
all at a given phase orientation.
[0104] Although the perforating device described in this embodiment used remotely fired
charges or fluid jetting to perforate the casing and cement sheath, alternative perforating
devices including but not limited to chemical dissolution or drilling/milling cutting
devices could be used within the scope of this invention for the purpose of creating
a flow path between the wellbore and the surrounding formation. For the purposes of
this invention, the term "perforating device" will be used broadly to include all
of the above, as well as any actuating device suspended in the wellbore for the purpose
of actuating charges or other perforating means that may be conveyed by the casing
or other means external to the bottomhole assembly or suspension method used to support
the bottomhole assembly.
[0105] The BHA could contain a downhole motor or other mechanism to provide rotation/torque
to accommodate actuation of mechanical sealing mechanisms requiring rotation/torque
for actuation. Such a device, in conjunction with an orienting device (e.g., gyroscope
or compass) could allow oriented perforating such that perforation holes are placed
in a preferred compass direction. Alternatively, if conventional jointed tubing were
to be used, it is possible that rotation and torque could be transmitted downhole
by direct rotation of the jointed tubing using rotation drive equipment that may be
readily available on conventional workover rigs. Downhole instrumentation gauges for
measurement of well conditions (casing collar locator, pressure, temperature, pressure,
and other measurement gauges) for real-time downhole monitoring of stimulation job
parameters, reservoir properties, and/or well performance could also be deployed as
part of the BHA.
[0106] In addition to the re-settable mechanical diversion device, other diversion material/devices
could be pumped downhole during the treatment including but not limited to ball sealers
or particulates such as sand, ceramic material, proppant, salt, waxes, resins, or
other organic or inorganic compounds or by alternative fluid systems such as viscosified
fluids, gelled fluids, foams, or other chemically formulated fluids, or other injectable
diversion agents. The additional diversion material could be used to help minimize
the duration of the stimulation treatment as some time savings could be realized by
reducing the number of times the mechanical diversion device is set, while still achieving
diversion capabilities over the multiple zones. For example in a 914 m (3,000 foot)
interval where individual zones nominally 30,5 m (100 feet) apart are to be treated,
it may be desirable to use the re-settable mechanical diversion device working in
152 m (500 foot) increments uphole, and then divert each of the six stages with a
diverting agent carried in the treating fluid. Alternatively, limited entry techniques
could be used for multiple intervals as a subset of the gross interval desired to
be treated. Either of these variations would decrease the number of mechanical sets
of the mechanical diversion device and possibly extend its effective life.
[0107] If a tubing string is used as the deployment means, the tubing allows for deployment
of downhole mixing devices and ready application of downhole mixing technology. Specifically,
the tubing string can be used to pump chemicals downhole and through the flow ports
in the bottomhole assembly to subsequently mix with the fluid pumped in the tubing
by production casing annulus. For example, during a hydraulic fracturing treatment,
it may be desirable to pump nitrogen or carbon dioxide downhole in the tubing and
have it mix with the treatment fluid downhole, such that nitrogen-assisted or carbon
dioxide-assisted flowback can be accommodated.
[0108] This method and apparatus could be used for treatment of vertical, deviated, or horizontal
wellbores. For example, the invention provides a method to generate multiple vertical
(or somewhat vertical) fractures to intersect horizontal or deviated wellbores. Such
a technique could enable economic completion of multiple wells from a single pad location.
Treatment of a multi-lateral well could also be performed wherein the deepest lateral
is treated first; then a plug is set or sleeve actuated to isolate this lowest lateral;
the next up-hole lateral is then treated; another plug is set or sleeve actuated to
isolate this lateral; and the process repeated to treat the desired number of laterals
within a single wellbore.
[0109] If select-fire perforating guns are used, although desirable from the standpoint
of maximizing the number of intervals that can be treated, the use of short guns (i.e.,
4-ft length or less) could limit well productivity in some instances by inducing increased
pressure drop in the near-wellbore reservoir region when compared to use of longer
guns. Well productivity could similarly be limited if only a short interval (i.e.,
4-ft length or less) is perforated using abrasive jetting. Potential for excessive
proppant flowback may also be increased leading to reduced stimulation effectiveness.
Flowback would preferably be performed at a controlled low-rate to limit potential
proppant flowback. Depending on flowback results, resin-coated proppant or alternative
gun configurations could be used to improve the stimulation effectiveness.
[0110] In addition, if tubing or cable are used as the deployment means to help mitigate
potential undesirable proppant erosion on the tubing or cable from direct impingement
of the proppant-laden fluid when pumped into the side-outlet injection ports, an "isolation
device" can be rigged up on the wellhead. The isolation device may consists of a flange
with a short length of tubing attached that runs down the center of the wellhead to
a few feet below the injection ports. The bottomhole assembly and tubing or cable
are run interior to the isolation device tubing. Thus the tubing of the isolation
device deflects the proppant and isolates the tubing or cable from direct impingement
of proppant. Such an isolation device would consist of an appropriate diameter tubing
such that it would readily allow the largest outer diameter dimension associated with
the tubing or cable and bottomhole assembly to pass through unhindered. The length
of the isolation device would be sized such that in the event of damage, the lower
master fracture valve could still be closed and the wellhead rigged down as necessary
to remove the isolation tool. Depending on the stimulation fluids and the method of
injection, an isolation device would not be needed if erosion concerns were not present.
Although field tests of isolation devices have shown no erosion problems, depending
on the job design, there could be some risk of erosion damage to the isolation tool
tubing assembly resulting in difficulty removing it. If an isolation tool is used,
preferred practices would be to maintain impingement velocity on the isolation tool
substantially below typical erosional limits, preferably below about 54.9 m/sec (180
ft/sec), and more preferably below about 18.3 m/sec (60 ft/sec).
[0111] Another concern with this technique is that premature screen-out may occur if fluid
displacement during pumping is not adequately measured as it may be difficult to initiate
a fracture with proppant-laden fluid across the next zone to be perforated. It may
be preferable to use a KCl fluid or some other non-gelled fluid or fluid system for
the pad rather than a gelled pad fluid to better initiate fracturing of the next zone.
Pumping the job at a higher rate with a non-gelled fluid between stages to achieve
turbulent flush/sweep of the casing will minimize the risk of proppant screen-out.
Also, contingency guns available on the tool string would allow continuing the job
after an appropriate wait time.
[0112] Although the embodiments discussed above are primarily related to the beneficial
effects of the inventive process when applied to hydraulic fracturing processes, this
should not be interpreted to limit the claimed invention which is applicable to any
situation in which perforating and performing other wellbore operations in a single
trip is beneficial.