[0001] This invention relates generally to earth well drilling apparatus and its use. Particularly,
it relates to apparatus that is useful for drilling one or more bore holes extending
laterally from a lower region of a well into a mineral bearing formation.
[0002] The present invention is directed primarily to a system for the formation of a bore
hole for use in the recovery or enhancement of recovery of oil from an oil-bearing
formation, or for the recovery of mineral deposits or the like, or for drilling through
an underground formation for some other purpose.
[0003] In one aspect, the invention provides earth well drilling apparatus comprising structure
including whipstock means adapted to be positioned within an earth well adjacent to
a mineral bearing formation, said whipstock means comprising a plurality of connected
guideway assemblies laterally extendable from a retracted position substantially within
the outer well to an extended position forming a curved tube bending guideway, piping
within the well to which said whipstock means is attached, anchor means operatively
connected to the rearward side of said whipstock means and having a retracted position
for sliding through said earth well and an anchoring position for locking in a fixed
position relative to said earth well, and erection means slideable within said earth
well, said erection means being pivotally connected at one end to a forward one of
said guideway assemblies and at the other end to extension means extending to the
earth surface, said pivotal connection being of the type to cause said guideway assemblies
to swing into said curved pathway when said extension means is pulled from the earth
surface with said whipstock means fixed at its rearward end.
[0004] The invention also provides a method of forming earth well drilling apparatus for
placing a radial tube laterally into a mineral bearing formation from an earth well
which extends downwardly from the surface of the formation to the region of radial
tube placement, said method making use of structure comprising whipstock means including
a plurality of connected guide assemblies laterally extendable from a retracted position
substantially within the earth well to an extended position forming a curved tube
bending guideway for a drilling tube to be extended radially into the formation, anchor
means operatively connected to the rearward side of said whipstock means and having
a retracted position sliding within said earth well and an anchoring position for
locking in a fixed position relative to said earth well, and erection means slideable
within said earth well, said erection means being pivotally connected to a forward
one of said guide assemblies and at the other end to extension means extending to
the earth surface, said method comprising moving said whipstock means adjacent to
the mineral bearing formation with said whipstock means and anchor means in a retracted
position, moving said anchor means into said anchoring position and pulling from the
earth surface on said extension means of said erection means to cause said forward
one of said guide assemblies to pivot away from said well to a sufficient extent to
form said curved tube bending guideway.
[0005] In another aspect, the invention provides earth well drilling apparatus comprising
a structure adapted to be positioned within the well adjacent an underground formation,
said apparatus comprising means defining a drilling fluid chamber, means defining
a driving fluid chamber, a drill string with an interior fluid passageway and extending
from said driving fluid chamber through said drilling fluid chamber, drillhead means
of the hydraulic jet type attached to the forward end of said drill string in communication
with said interior passageway, first sliding seal means disposed between said driving
fluid chamber means and said drill string, second sliding seal means disposed between
said drilling fluid chamber means and said drill string, said drill string interior
passageway being substantially sealed from said driving fluid chamber and being in
communication with said drilling fluid chamber, whereby when pressurized fluid is
supplied to the driving fluid chamber means, it drives the drill string forward through
the first and second seals and when pressurized fluid is supplied to the drilling
fluid chamber means it flows from the drilling fluid chamber means through the interior
passageway to apply pressure against the drillhead, thereby causing the drill string
to move forward into the formation and causing the pressurized fluid to be directed
against the formation.
[0006] The invention also provides a method for forming a borehole in an underground formation
using a drilling system comprising a drilling fluid chamber sealed from a driving
fluid chamber, and a drill string with an interior passageway in communication with
a drillhead of the hydraulic jet type at its forward end and sealed from said driving
fluid chamber, said method comprising the steps of:
(a) disposing said drill string with its upstream end in said driving fluid chamber
with said interior passageway sealed therefrom, said drill string extending through
a first sliding seal in said driving fluid chamber and then through a second sliding
seal in said drilling fluid chamber with said drillhead downstream of both seals,
said interior passageway communicating with fluid in said drilling fluid chamber;
(b) directing fluid into said driving fluid chamber upstream of said first seal to
push said drill string downstream; and
(c) simultaneously directing fluid into said drilling fluid chamber through said interior
passageway to apply pressure against said drillhead to move said drillhead into the
formation and to cause pressurized fluid to be applied against the formation.
[0007] In another aspect the invention provides a method of gravel packing the exterior
of a hollow production radial tube having an open distal end and extending from a
well bore into the formation, said radial tube and formation defining an annulus therebetween
which is relatively permeable or free of formation, the interiors of said radial tube
and well bore being in fluid communication, said method comprising flowing a slurry
of particles of a size capable of forming a gravel pack from the well bore through
the radial tube interior and out said open distal end into the annulus and back toward
the well bore to form a jacket of gravel pack particles in said annulus.
[0008] The invention also provides production apparatus suitable for withdrawing oil from
an oil-bearing formation, said apparatus comprising a well casing, a perforated hollow
production radial tube extending from the well casing into the formation, the interior
of said radial tube and well bore being in fluid communication, and a substantially
continuous annular jacket of gravel pack particles disposed between the exterior of
said radial tube and the surrounding formation.
[0009] The invention further provides a method of gravel packing the exterior of the radial
port of a production tube which extends down a well bore and projects outwardly therefrom
into a radial bore in an underground formation, said radial portion defining an array
of ports adjacent its distal end, the ports in said array being large enough to pass
a slurry of gravel pack particles, said method comprising moving a hollow tube liner
through the drilling pipe into its radial portion so that the forward end of the liner
is adjacent to and rearward of said port array, said liner comprising a flexible tube
defining opening of a size capable of passing liquid but of substantially blocking
the passage of gravel pack particles, pumping an aqueous gravel packing slurry through
the liner and out the port array and continuing the flow of slurry so that it moves
rearwardly along said radial portion and forms a jacket of gravel pack between said
drilling pipe radial portion and said formation.
[0010] The invention further provides a method of forming spaced perforations in an electrically
conductive production radial tube extending from a well bore in an underground formation,
said method comprising:
(a) passing an elongate hollow perforating tool through the electrically conductive
production radial tube to be perforated until the forward end of said perforating
tool is adjacent the distal end of said radial tube, said perforating tool comprising
an elongate hollow perforating pipe with port means defining spaced ports with electrically
conductive perimeters connected to an electrical power source through said radial
tube;
(b) passing an electrolyte solution through the lumen of said perforating tool and
out said ports to be directed against adjacent regions of said electrically conductive
radial tube while current is supplied to said port perimeters to form spaced perforations
at said adjacent regions; and
(c) withdrawing said perforating tool.
[0011] The invention further provides a method of gravel packing the exterior of a perforated
production radial tube with multiple openings in the well of the tube and extending
from a wellbore into an underground formation, said radial being open at its distal
end, said method comprising:
(a) placing an elongated hollow tube liner with an open distal end within the perforated
radial tube said liner including openings of a size to permit passage of fluid but
not gravel pack particles; and;
(b) pumping a gravel packing slurry through the liner and out its open front end through
said radial tube open end into the formation to flow back toward the wellbore to form
at least a partial jacket of gravel pack between the radial tube and the formation.
[0012] The invention further provides in a curvature probe: an axially extending flexible
shaft, a plurality of axially spaced guide members mounted on the flexible shaft,
two pairs of axially extending sensing wires positioned in quadrature about the shaft
with the two wires in each pair being positioned on opposite sides of the shaft, said
wires passing freely through axially aligned openings in the guide members and being
free to move relative to each other in an axial direction upon bending of the probe,
and means responsive to the relative axial positions of the two wires in each pair
for providing an output signal corresponding to the curvature to which the probe is
bent.
[0013] The invention further provides a method of determining the curvature of a borehole
with a probe having an axially extending flexible shaft and two pairs of sensing wires
arranged in quadrature about the shaft, said wires being held a predetermined radial
distance from the flexible shaft and being free for axial movement relative to each
other upon bending of the probe, the steps of: inserting the probe into the borehole
so that the probe is bent to a curvature corresponding to the curvature of the borehole,
and monitoring the relative axial positions of the sensing wires on opposite sides
of the flexible shaft to determine the curvature of the borehole.
[0014] By way of example, embodiments of the invention in its various aspects will now be
described with reference to the accompanying drawings in which:
Figure 1 is a schematic view in side elevation illustrating the apparatus disposed
within earth well with the drilling tube extended in a lateral hole.
Figure 2 is a detailed view in side elevation illustrating the whipstock in a collapsed
position within its mounting.
Figure 3 is a detailed view in side elevation illustrating the whipstock assembly
in its extended position.
Figure 4 is a detailed sectional view of the whipstock portion of the device illustrating
the interior bending surfaces and wheels.
Figure 5 is a side elevational view in section illustrating a drill string assembly
in accordance with the invention used for moving a radial into the formation.
Figure 6 is another embodiment of the device of Figure 1 with a modified piston arrangement.
Figure 7 is a further schematic view in section of another embodiment using a heavy
rod or pipe to assist driving into the formation.
Figure 8 is another embodiment of the invention using the piston means of Figure 6
and rod of Figure 7.
Figure 9 is an embodiment of a portion of the device of Figure 5 using a drill collar
to provide additional driving force.
Figure 10 is an embodiment of the invention with an open topped drill string.
Figure 11 is a cross-section of a perforated radial tube partially broken away showing
a perforating tool.
Figure 12 is a cross-sectional view of Figure 11 taken along lines 12-12.
Figures 13 and 14 are cross-sectional views of the rearward and forward portions,
respectively, of a perforating tool disposed in a radial pipe.
Figure 15 is a cross-sectional view of the perforating tool taken along the lines
15-15 of Figure 13.
Figure 16 is a side elevational view of a forward portion of a pipe cutting device
disposed in a radial tube.
Figure 17 is a side view of a combination porous plug filter and pipe cutter as disposed
in a radial tube.
Figure 18 is a side view of a radial tube partially broken away illustrating a liner
for the radial tube, partially as disposed in the formation.
Figure 19 is a cross-sectional view taken along the lines 19-19 of Figure 18.
Figure 20 is a side elevation view partially in section of a perforated radial tube
illustrating a liner and a sand dune sensor.
Figure 21 is a cross-sectional view taken along the line 21-21 of Figure 20.
Figure 22 is a side view partially broken away of a radial tube in the formation,
a permeable liner and plug filters at its distal and proximal ends.
Figure 23 is a cross-sectional view of Figure 22 taken along the lines 23-23.
Figure 24 is a schematic diagram of one embodiment of a curvature probe system incorporating
the invention.
Figure 25 is a fragmentary sectional view of the curvature probe in the embodiment
of Figure 24.
Figure 26 is a cross-sectional view taken along lines 26-26 in Figure 25.
A. Mechanically Actuated Whipstock Assembly
[0015] Figure 1 schematically shows an earth well 10 which extends down to the mineral bearing
formation 12. In this instance, the well is shown provided with a casing 14 which
may extend down to an underreamed cavity 16 that is adjacent to the formation 12.
Structure 17 includes piping extending in the well consisting, in this instance, of
outer piping 18 in the form of a pipe string with a lowermost section 18a shown in
Figure 2, within which a drilling tube 20 is normally disposed. As shown in Figure
4, a seal 22 is mounted within the pipe string and forms a seal between the pipe string
and drilling tube 20. The upper end of the drill pipe is above seal 22 when the drilling
tube is retracted. Before the drilling tube is extended, it is within pipe string
18 with its drilling head 24 located below seal 22. Structure 17 also includes housing
26 serving to carry whipstock means 28. Seal 22 is preferably incorporated into the
coupling adjacent the upper end of whipstock means 28. Alternatively, it may be disposed
in some other portion of outer piping 18. Figure 1 also schematically shows a production
rig 30 of the mobile type and a reel carrying truck 32 which may carry a supply of
drilling tube 20, which brings supply drilling tube for use in the well but is not
connected during placement of the drilling tube.
[0016] As shown in Figures 2, 3 and 4, housing 26 carries five bending assemblies 30, 32,
34, 36 and 38 pivotally connected at hinges. Housing 26 contains the whipstock means
in a deerected position, anchor means and means for erecting and deerecting the whipstock
means as described hereinafter. Outer piping 18 includes clearance for the whipstock
means to be erected. As illustrated in Figures 1, 3 and 4 clearance is to the left
and right of the whipstock. By using whipstock sections 30, 32, 34, 36 and 38 of rectangular
shape, housing 26 is in the form of flat rigid side plates 40 interconnected at the
bottom by lift pin 42 and at the top by bolts 44 mounted to the interior piping and
assemblies as described below. Lift pin 42 is pivotally connected to the most forward
whipstock segment 38.
[0017] Referring specifically to Figures 1 and 2, housing 26 is lowered into casing 14 until
it reaches the desired position adjacent to formation 12. All components of this system
are contained within the structure during such passage in a manner that permits the
system to be lowered through a preexisting casing.
[0018] Referring again to Figure 2, anchor means 46 is illustrated in a retracted position
within the casing with the whipstock means deerected. Anchor means 46 is operatively
connected to the rearward side of whipstock means 28. In the illustrated retracted
position, it slides within the earth well. In the anchored position illustrated in
Figure 3, it locks in a fixed position relative to the earth well and causes the whipstock
means 28 to raise from the fixed anchor position and thus, lift pin 42 can be raised
during erection as described below.
[0019] One significant feature of the system is that there is relative movement between
casing 10 and the inner piping 48 which is used to actuate erection and deerection
of the whipstock means 28. Thus, when a part is described as being mounted to the
inner piping, it moves when that part moves. The only part in the system which is
not fixidly mounted is the anchor means which functions as set out below.
[0020] Inner piping 48 is mounted in outer piping 18 and, in combination with other portions
of structure 17 serves to anchor, erect and deerect whipstock means 28. Inner piping
48 is threadedly connected at its forward end or lowermost segment the top segment
30 of whipstock means 28.
[0021] The system also includes deerection means comprising an upper deerection spring 52
and a lower deerection spring 54. Upper deerection spring retainer 56 is mounted to
inner piping 48 and includes a lower shoulder 56a for retaining spring 52. An erection
sliding seam 58 is mounted to the interior of inner piping 48 to maintain a seal with
the drilling tube when the system is erected as described below. A lower spring retaining
ring 60 is mounted to outer piping 18. Similarly, an upper spring retaining ring 62
is mounted to inner piping 48 while a lower spring retaining ring 64 is mounted to
outer piping 18. Springs 52 and 54 provide the same kind of compressive forces for
erection and deerection of the system as described below. They function in a similar
manner and are additive in their compressive forces. If desired, a single spring could
be utilized with the desired amount of force.
[0022] Anchor means 46 is the only portion of the illustrated apparatus that is not fixidly
secured to either outer piping 18 or inner piping 48. Components of anchor means 46
are drag springs 66 slidably carried by inner piping 48 and projects through slot
67 in outer piping 18 to ride against casing 14 while the assembly is being lowered
into position. Drag springs 66 serve to center the overall unit and to provide sufficient
frictional force against casing 14 to permit the anchor to lock into position against
it when outer piping 18 is pulled upwardly as described below.
[0023] Anchor means 46 also includes anchor jaws 68 with a saw tooth-like outer surface
68a for embedding into casing 14 when urged outwardly as set out below. The interior
surface of anchor jaws 68 are sloping walls 68b which slope inwardly in an upward
direction to provide a surface against which a correspondingly sloped ramp may act.
Jaws 68 are slidably mounted to ride on inner piping 48 and are spring mounted so
that they are urged inwardly unless actuated. When the system is lowered to the desired
elevation adjacent the formation in the position illustrated in Figure 2, anchor
jaws 68 are out of registry with vertical slot 67 and so are retained within outer
piping 18 by abutting against the adjacent wall of that structure. Such anchor jaws
are the same elevation as the vertical slots so that when it is desired to anchor
the system, outer piping 18 is rotated relative to inner piping 48 causing the anchor
jaws to move into registry with such slots whereby they are urged outwardly against
the casing.
[0024] A jaw extension ramp 70 is mounted to outer piping 18 including a sloped upper wall
70a of a shape which mates with the inner sloping wall 68b of anchor jaws 68 to cause
the anchor jaws to be urged outwardly when ramp 70 is moved upwardly relative to the
jaws.
[0025] The operation of anchor means 46 is as follows. When the desired elevation adjacent
to the formation is reached, the outer piping 18 is rotated relative to inner piping
48 to permit anchor jaws 68 to move into registry through their corresponding slots.
The slots extend a sufficient distance below jaws 68 to permit upward movement of
outer piping 18 to erect the system as described below. Structure 17 is pulled by
an extension arm 72 which may comprise a pipe which extends all the way to the surface.
Extension arm 72 includes a passage through which the drilling tube projects as described
below. Then extension member 72 is pulled upwardly, both the outer piping 18 and inner
piping 48 are correspondingly pulled because they are connected at lifting pin 42.
With the jaws in the slot, drag spring 66 provides sufficient resistance against upward
movement that anchor jaws 68 begin to be locked into an embedded position in the casing
wall when urged against the wall by jaw extension ramp 70 as the inner piping is pulled
upwardly. Outer piping 18 is not affected because of the slot clearance.
[0026] Once the system is anchored, whipstock means 28 begins to erect because lift pin
42 is being moved upwardly while the top segment 30 of whipstock means 28 is being
retained in a fixed elevational position by anchor means 46. Since guideway assembly
38 is pivotally mounted to lifting pin 42 and because lifting pin 42 is mounted eccentrically
(towards the left hand side as illustrated) segment 38 begins to pivot to the left
until the sloping upper wall 38a contacts the corresponding lower wall 36a of guideway
assembly 36. Such pivoting begins at the bottom rather than the top because the lower
piping segment 18a forms a shroud which maintains upper guideway assembly 30 in a
fixed position during the initial erection. This permits the system to be erected
into the desired configuration. Thereafter, after erection is begun, piping segment
18a clears upper guideway assembly 30 to permit it to be erected as illustrated in
Figure 3.
[0027] Springs 52 and 54 are partially compressed prior to lowering of the system into the
earth well. This serves to maintain whipstock means 28 in a straight line deerected
configuration within side plates 40 for passage through the earth well be keeping
the whipstock in tension. During erection, by pulling of the outer casing upwardly,
upward retaining rings 56 and 62, being mounted to inner piping 48 are in a fixed
elevational position while lower retaining rings 60 and 64, being mounted to outer
piping 18 move upwardly to cause springs 52 and 54 to be further compressed. This
assists in deerecting the system as described below. Such additional compression also
stiffens the system which applies a strain load on the whipstock means to strengthen
the hinges in the erected position.
[0028] Whipstock means 28 may be maintained in an erected position by insertion of a slip
collar at the surface. When deerection is to be accomplished, the slip collar (not
shown) is removed to permit the outer structure to move downwardly.
[0029] Referring to Figure 4, a detailed view of the erected whipstock is illustrated. At
the top of the whipstock is a high pressure seal which provides piston-like forces
to push the piping through the whipstock and into the formation in the manner described
with respect to U.S. patent 4,527,639, incorporated herein by reference. Briefly,
summarized, high pressure fluid is directed against a fluid pressure bearing area
to the rearward side of the drillhead which is of the hydraulic jet type, including
one or more jet type openings. When the drilling tube is forced through the whipstock,
bending forces are applied to cause the tube to conform generally to the curve of
the whipstock so that the tube is caused to turn into the formation. The pressurized
drilling fluid presses against the seal and the portion of the guide pipe upstream
from he seal so that the force is directed against the rearward side of the drill
head causing it to project in a forward direction.
[0030] Whipstock means 28 functions as follows: Above seal 22 is a guide ring 80 which guides
drilling tube 20 through the seal 22 and allows water to enter a bypass system whereby
water can be used to flush the small annulus between the interior guide walls of the
whipstock and the drilling tube. Prior to application of the hydraulic forces, the
drilling tube is placed into the seal. Then, the system is pressurized so that drilling
tube 20 moves past the first two wheels 82 in the system. Then, the drilling tube
causes a bending action toward the backside of the whipstock means and loads the third
wheel 86 in guideway assembly 30.
[0031] The drilling tube now enters guideway assembly 32 and is guided by the first two
wheels 88 causing the drilling tube to be guided along the ramp of that section until
it hits the last ramp 90 just above the last wheel 92 to force the drilling tube to
load onto wheel 94 and start the bending motion of the drilling tube toward the right
hand side of the drawing. Wheels 92 and 94 provide the initial bending of the drilling
tube into about a one foot radius which allows it to move through guideway assemblies
34 and 36 without substantial additional bending moments.
[0032] Wheels 98 in guideway assembly 34 and wheels 100 in guideway assembly 36 act as guide
wheels to position drilling tube 20 relative to guideway assembly 38 which serves
as a straightener. The ramps in guideway assemblies 34 and 36 assist in loading the
drilling tube 20 onto such wheels if the bending is not sufficiently precise. As drilling
tube 20 exits guideway assembly 36, it is guided by the wheels in that segment to
cause the drillhead to contact the ramp at the bottom of guideway assembly 38 which
loads the drillhead onto straightener wheel 102 mounted in carriage 104 which forces
the drillhead to the top of segment 38 and causes it to move into the formation in
a straight line. Carriage 104 is adjustable so that by calibration, the position
of wheel 102 may be set so that the drillhead proceeds horizontally into the formation
or at any desired angle.
[0033] One advantage of whipstock means 28 is that it projects to both sides of the housing
and so less underreaming is required than if it projected only to one side. As illustrated,
the whipstock means assumes an inverted comma shape with the drillhead turning at
a relatively sharp angle just prior to moving into the formation. Underreaming may
be accomplished in a conventional manner.
[0034] Another advantage of the internal mechanism of the whipstock means is that due to
the unique use of rollers and slides, the friction is low, the drillhead can make
the initial turn without damage and the drilling tube is maintained in a relatively
round configuration during the turning. The use of the wheels and ramps permits this
to be accomplished with minimum flattening of the system.
[0035] A significant advantage of the present system is that the whipstock means is erected
by the simple mechanical force of pulling from the surface rather than by the use
of a hydraulic cylinder to cause erection. One advantage of such erection is the precise
knowledge that the whipstock means is fully erected to permit the radial to move horizontally
into the formation. This is known because when the outer structure is pulled upwardly
at the surface a predetermined distance for full erection, the whipstock is erected.
This is to be contrasted with hydraulic cylinders which are not as precise in their
operation due to leaks and the like. Also, since there is a continuous string to the
surface, pipe stretch does not affect the function of erection.
[0036] The system of the present invention is also capable of ready deerection to either
move structure 17 to another portion of the same earth well or to pull it totally
out of the earth well for reuse in another earth well. In essence, deerection is accomplished
by releasing the anchor means from the casing, causing the inner piping to move downwardly
relative to the outer structure and thereby moving lifting pin downwardly to pull
the segments of the whipstock into a straight line as illustrated in Figure 2. Springs
52 and 54 are maintained under sufficient compression so that even during deerection,
the segments of the whipstock means are maintained under tension to prevent spontaneous
erection of the system.
[0037] During deerection, the outer structure is moved downwardly causing lift pin 42 to
move correspondingly downwardly and to move the whipstock means into a straight line
or retracted position. With the whipstock means in a straight line, continued lowering
of the outer structure 26 causes inner piping 48 to be pulled downwardly at lift pin
42 and thereby causing ramp 70 to move downwardly out of engagement with the corresponding
inner walls of 68b of jaws 68. In this manner, jaws 68 collapse against inner piping
48. Then, outer structure 26 is rotated relative to jaws 68 to cause the jaws to move
out of registry with the corresponding slot and to be thereby retained in a retracted
position by adjacent wall segments of the outer structure. With the jaws 68 prevented
from locking against the inner wall of casing 14, the entire unit may be lifted up
out of the earth well.
[0038] Should the above deerection system not work due to sand clogging of the jaw slots
or the like, backup systems may be provided. In one backup system, jaw extension ramp
70 is mounted to inner piping 48 by shear pin 110. If the jaws will not release in
a manner set out above, sufficient pushing force is applied from the surface against
structure 17 to shear the shear pins and cause ramp 70 to fall out of engagement with
jaws 68. For this purpose, support spring 112 is provided below the ramp 70 which
is sealed by upper and lower wiper rings 114 and 116 respectively against sand from
moving into the system. In this manner, when shear pins 110 are sheared, ramp 70 may
fall a sufficient distance to release jaws 68 due to the clearance provided by spring
112.
[0039] As set forth above, during erection of the whipstock, outer piping moves upwardly
relatively to fixed inner piping 48. Therefore, a potential gap may be created between
the uppermost segment of piping 48 and the drilling tube moving through the piping.
It is essential to maintain a hydraulic seal in order to utilize the piston-like
forces described above to push the drilling tube through the inner piping and out
the whipstock by hydraulic forces. Accordingly, sliding seal 58 is mounted to the
outer piping 18 to provide a high pressure hydraulic seal to prevent any gap during
relative movement of the outer piping and inner piping.
[0040] In operation of the present system, a radical is placed in the desired mineral bearing
formation, typically in an oil field. The surrounding formation may be heated as by
injection of steam and oil is caused to flow either back to the same well or towards
another production well. In typical operation, prior to production in this manner,
the drilling tube portion projecting into the formation is severed near the whipstock
by conventional means. In order to deerect the system, the drilling tube is first
removed from the whipstock section by pulling upwardly from the surface. This, of
course, is facilitated by first severing the portion of the drilling pipe projecting
into the formation. Thereafter, deerection is accomplished as set forth above.
[0041] The above system is particularly effective when used in conjunction with a drilling
pipe propelled by hydraulic forces as set forth in above. For that purpose, hydraulic
seals are provided in this system to accomplish the piston-like effect. However, it
should be understood that the system may also be employed to move a radial pipe into
the formation by some other means.
B. Multiple Hydraulic Forces
[0042] In general, the present invention comprises an improvement over the hydraulic piston-effect
method and apparatus of U.S. patent 4,527,639. That application describes a system
in which hydraulic forces are applied against a drillhead to pull a pipe into the
formation. The present system adds to that pulling force a pushing force from the
other end of the drill pipe.
[0043] Referring to the embodiment of Figure 5, the ground level 10 above the underground
mineral bearing formation 212 is illustrated. A drill string 214 is formed of a metal
tube of the solid wall type which may, for example, have an outer diameter (OD) of
approximately 1.25 in. and of a character which may be coiled on a spool and passed
downwardly into the system prior to sealing the system into the form shown in Figure
5. When sufficient length of the drill string is provided to reach the desired ultimate
radial length, the string is severed and lowered down the guide pipe.
[0044] As used herein, the term "drill string" encompasses a single unitary hollow pipe
of the type which may be used for radial hollow tube section 214a or multiple sections
connected together, some of which may not be hollow, such as a sucker rod with threaded
attachments to each end to provide dead weight as described in embodiments set forth
hereinafter. Drill string 214 is typically in the form of a hollow pipe and defines
an interior passageway 214b which extends from drillhead 216 upstream in the system
to multiple ports 214c for reasons described below. Upstream of ports 214c may comprise
a hollow or solid pipe so long as the interior passageway is sealed towards the top
of the drill string.
[0045] In the illustrated embodiment, drill string 214 comprises a pipe connected at its
forward end to drillhead means 216 of the hydraulic jet type including multiple ports
216a through which the drilling fluid exits to bear against and erode the formation
in its path. A removable cap 218 is secured into the other end of drill string 214.
The purpose for the cap is to seal the interior of drill string 214 at the location
of the cap. The cap may be removed periodically to permit the lowering of a wire line
tool through the system to determine the position of the drillhead 216 at any point
in time.
[0046] As illustrated, the system operates within a pre-existing cemented-in well casing
219 in which outer piping 220 is mounted leaving an annular chamber 221 therebetween
suitable for the passage of cuttings from the drillhead as described below. Outer
piping 220 is sealed at its lower end to a guide pipe 222 including interior rollers
224. Guide pipe 222 is in turn connected to whipstock means 226 which includes four
segments 226a, 226b, 226c, 226d and 226e in an inverted comma position. Drill string
214 moves through rollers 224 and whipstock means 226 to turn from a generally vertical
direction to a generally horizontal direction forming radial 214a. Whipstock means
226 is lowered into the formation in a collapsed position and is formed
in situ into a whipstock of the illustrated shape in the manner described above.
[0047] Means 227 defining a driving fluid chamber 228 is provided in the form of cylindrical
inner piping 230 which is sealed from the annular space surrounding the same. A first
sliding seal 232 is mounted to the inner wall of inner piping 230 through which drill
string 214 slides. Inner piping 230 is surrounded by outer piping 220. Outer piping
220 and inner piping 230 at least partially define drilling fluid chamber 234 which
is sealed from driving fluid chamber 228.
[0048] Means is provided for forming a seal between drilling fluid chamber 234 and drill
string 214 in the form of a second seal 235 mounted to guide pipe 222 through which
drill string 214 passes.
[0049] Means (not shown) is provided for supplying hydraulic fluid to driving fluid chamber
228 and drilling fluid chamber 234. As illustrated, the fluid moves through conduit
236 in which the major portion of the fluid is passed. A portion of the drilling fluid
in conduit 236 may be bled off by valve means 238 into conduit 240 for passage into
stationary driving fluid chamber 228. Conduit 240 passes through a sealed aperture
241, in a domed sealed top 220a mounted to outer piping 220. In an alternative embodiment
illustrated in Figure 6, a separate source of driving fluid may be employed.
[0050] When the system is in operation, the drill string 214 passes through whipstock means
226 and becomes a radial or lateral tube or duct 214a suitable for the injection of
hot fluids such as steam into the formation to heat up the viscous oil for removal.
In the alternative, heat from the hot fluid causes the oil to flow back towards the
casing containing a production pump as well as a radial.
[0051] The general principal of forming a radial in accordance with the present invention
uses (a) a hydraulic pulling force applied by urging fluid against the drillhead means
16 which thereby pulls the radial into the formation from the downstream end of the
drill string in combination with (a) a hydraulic driving or pushing force applied
in driving fluid chamber 228 against the upstream end of the drill string. The former
type of force is generally described in U.S. patent 4,527,639. Briefly, drill string
214 is adapted to move through seals 232 and 235, through whipstock means 226, and
into the formation. An open passageway is provided from conduit 236 through drilling
fluid chamber 234, ports 214c, into the interior fluid passageway 214b and forward
to the rearward side of drillhead means 216.
[0052] The fluid exits through multiple fluid exit ports provided in the drillhead means
for the passage of the drilling fluid into the adjacent formation. High pressure fluid
flowing from drilling fluid chamber 234 applies pressure against the rearward side
of the drillhead to cause drill string 214 to move in a forward direction. The only
portion of the drill string which passes through whipstock 226 comprises a hollow
tube in the form of a radial which is stressed and deformed plastically in a physical
metallurgical sense to bend and turn into the radial, preferably in a horizontal
direction, so as to be moved into the formation. The high pressure liquid issuing
from the drillhead drills out the formation and forms cuttings which are slurrified
and passed backwardly along the outer periphery of drill string 214 as illustrated
by arrows A on Figure 5 for movement outside the outer piping 220 to the surface.
Alternatively, if the drilling fluid pressure is greater than the formation pressure,
the fluid may be directed into the surrounding formation under such force that the
formation fracs or fractures, causing fissures into which the formed slurry can flow,
whereby little, if any, cuttings are moved rearwardly along the radial and so lifting
of such cuttings is not required.
[0053] The system also includes a pushing force by fluid being passed through conduit 240
into driving fluid chamber 228 and applies against cap 218 at the top of the drill
string.
[0054] The location of driving fluid chamber 228 and drilling fluid chamber 234 may be at
the top of the drill string or at some point below that so long as seal 232 is above
whipstock means 226. There is some advantages in placing the cylinders towards the
top of the well (at the well head) in that the force may be carried to the radial
by a heavy or dead weight sucker rod as described below which helps to overcome frictional
forces in the whipstock. Also, a long length of tubular pipe may be eliminated and
replaced with a rod since the portion of drill string 214 above ports 214c need not
be an open passageway.
[0055] One advantage of this system is that it is capable of drilling radial bores with
a non-rotating drill string, and that the bore hole may be cased while drilling.
[0056] The system may be installed as follows: A preexisting well casing placed in the surrounding
formation in the vicinity of the whipstock may be underreamed by a conventional means.
The whipstock may be lowered into the predetermined position by use of a string system
formed of segments with threaded attachments on adjacent segments. It may remain in
place and form the portion of the drill string terminating at cap 218, above ports
214c. Such ports maintain open communication between the interior passageway and the
fluid in drilling fluid chamber 234 during movement of the radial through the whipstock
and to the desired final position in the formation. This string, or a tubing string
separately placed, may remain in place forming a dead weight to provide additional
pushing force against the drill string. Alternatively, the string may be removed so
long as there is sufficient drill string extending upwardly so that a portion extends
through seal 232 from the time of driving the drill string forward through the whipstock
through the ultimate placement of the radial.
[0057] After placement of drill string 214 at a position just prior to movement into the
whipstock to which the hydraulic forces of the system are applied, the system can
be sealed as by putting top 220a on the casing to seal the top of driving fluid cylinder
means 228.
[0058] When the drill string is forced through whipstock means 226, bending forces are applied
to cause it to conform generally to the curve of the whipstock, whereby the drill
string is caused to turn towards a generally horizontal position into the formation.
The details of forming this curvature are described in U.S. Patent 4,527,679.
[0059] A number of systems can be employed for determining the position of the radial in
the formation. For example, a reel with a line attached to the top of the drill string
may be employed so long as there is access to the reel at the surface. Alternatively,
an acoustical assembly may be used with a transmitted signal emitting from the drillhead
which reflects back to give a measured transit time and movement. Another system would
be to measure distance as a function of the displacement of fluid flowing into the
driving fluid chamber. However, if the tubing joints are not completely tight, leakage
may occur which could cause an error.
[0060] Referring to Figure 6, another embodiment of the invention is illustrated with a
different form of driving mechanism but the the remainder of the apparatus the same.
Like parts will be designated with like numbers in the two systems and the description
with respect to such like parts in Figure 5 will apply to the system of Figure 6.
[0061] In the system of Figure 6, a piston body 250 is attached to the upstream side of
drill string 214 of a cylindrical shape and having a cross-sectional area which may
be substantially larger (e.g., 1.1 to 10 times, preferably 2 to 4 times larger) than
the cross-sectional area of the drill string, in the plane perpendicular to the direction
of movement of the piston body. It includes a removable plug 252 mounted at its top
which can be removed to install a wireline device in the drill string in an analogous
manner to that of plug 218. A third high pressure seal 254 is mounted to the exterior
wall of piston body 250 in close sealing engagement with the cylindrical side wall
of inner piping 230. (Alternatively, seal 254 may be mounted to the interior wall
of inner piping 230). Means is provided for bleeding off fluid in the chamber formed
below piston body 250 and above first seal 232. Such means is in the form of ports
256 which direct the fluid to the outside of outer piping 220 without contacting or
restricting the flow of fluid in chamber 234 when piston body 250 is actuated by driving
fluid supplied by conduit 258 to driving fluid chamber 228. Drilling fluid is supplied
by conduit 260 to drilling fluid chamber 234. Thus, in this embodiment, independent
sources of fluid are provided for the two chambers.
[0062] Piston body 250 is sufficiently long so that it maintains a seal with seal 254 when
a corresponding length of drill string is moved by the hydraulic forces through whipstock
226 and out the radial to the desired distance. The use of an enlarged cross-sectional
area for the piston body permits a multiplication of the driving force supplied by
the system. Thus, a doubling of the cross-sectional area leads to a corresponding
doubling of the force which is applied to the top of the drill string when the remainder
of the parameters are maintained constant. The amount of force applied against the
top of piston body 250 is also controlled by the pressure of the fluid supplied by
conduit 258 to driving fluid chamber 234. In this manner, a close control of the system
may be maintained by varying the pressure of such driving fluid in line 258. If desired,
the control may be further augmented by the use of a restraint such as a cable (not
shown) which is operatively associated with the drill string such as by connection
to the drill string near the top of it which controls the maximum rate of movement
of the system. However, the rate of movement can be controlled by a corresponding
variance in the fluid applied in line 258 without the requirement of the cable restraint.
[0063] In another embodiment, not shown, the force multiplication of the embodiment of Figure
6 is accomplished by a system similar to the embodiment of Figure 5. In this instance,
seal 232 has a cross-sectional area substantially larger (e.g., 1.1 to 10 times, preferably
2-104 times larger) than the cross-sectional area of seal 235. The cross-section
of that portion of drill string 214 which passes through seal 232 during drilling
is correspondingly enlarged without enlarging the cross-section which passes through
seal 235.
[0064] Referring to Figure 7, another embodiment of the system of Figure 5 is illustrated
with like parts designated in like numbers. The only difference between the two systems
comprises the use of a solid metal rod portion 214d at the top of drill string 214.
Rod 214d provides a dead weight driving force to the drillhead which is additive to
the hydraulic forces described above. Rod 214d is suitably in the form of a threaded
rod which may be threaded at connection 214e to the remainder of drill string 214.
The dimensional constraints of rod 214d are that it be long enough to maintain a seal
with seal 232 during the application of hydraulic forces and that they extend to
the position no further along the drill string than a point upstream of ports 214c.
As set forth above, below ports 214c an interior passageway is formed which communicates
with the drillhead 216.
[0065] Referring to Figure 8, another embodiment of the invention is illustrated which is
similar to that of Figure 6. Like parts in Figure 8 will be designated with like numbers
of Figure 6. The difference between Figure 6 and Figure 8 is in the area of the drill
string above ports 214c. In the instance of Figure 8, a solid metal rod portion 262
interconnects the bottom of piston body 250 and the area of drill string above ports
214c. Such rod 262 constitutes, in essence, a piston rod in the form of a sucker
rod with screw threaded connections to both the piston body and top of the drill string.
One advantage of this interconnection is that it provides the additional dead weight
to drive the drill head described with respect to Figure 7.
[0066] Referring to Figure 9 an embodiment of the invention is illustrated similar to that
of Figure 6. In this instance, a continuous hollow pipe drill string 214 is illustrated
as in Figure 6. The major difference in the two embodiments is the inclusion of a
weighted drill collar 264 mounted to the drill string at a point below seal 232 and
above ports 214c. The advantage of this location is that the drill collar need not
pass through any seals. The dead weight may be also added at some other point in the
system so long as it does not interfere with any of the seals.
[0067] Drillhead 216 may be of any type which provides a rearward surface against which
the force of the drilling fluid has directed and which provides ports through which
the drilling fluid may exit, preferably in a direction axially aligned with the horizontal
drilling path of the radial hole, together with other ports in other directions, if
desired. Suitable drillheads for use in accordance with the present invention are
described in U.S. Patent 4,527,639.
[0068] The foregoing systems constitute an improvement over the system of U.S. Patent 4,527,639
in the provision of the various forces to move the drill string through the whipstock
and into the formation. The dead weight forces facilitate the system to overcome frictional
forces in the whipstock and the formation. The hydraulic driving forces transmitted
in driving fluid chamber 228 provide further hydraulic forces together with precise
control of the amount of force to be applied depending upon the formation into which
the radial is to move. If the system requires particularly large forces to move the
radial into the formation, the cross-sectional area of the piston of Figure 6 may
be increased to provide such assistance.
[0069] Another advantage resides in the separation of the fluid applying hydraulic forces
in isolated driving fluid chamber 228 and drilling fluid chamber 234 because the required
fluid pressure in the former chamber, being isolated from the large volume drilling
fluid in the latter chamber, provides a precise measure of the resistance to movement
of the drillhead. It has been found that when this pressure exceeds a predetermined
level, the system may have become irreversibly stuck embedded in a resistant area
of the formation if drilling continues. By monitoring the driving fluid pressure,
when this level is exceeded, the drill string may be withdrawn a short distance and
the hole redrilled, resulting in avoidance of the sticking problem.
[0070] Referring to Figure 10, a further embodiment is illustrated with a single fluid
source and an open-topped drill string. The embodiment is similar to that of Figure
6, and so like numbers will be used to designate like parts. Instead of separate conduits
258 and 260 for piston driving fluid and drilling fluid respectively, a single conduit
264 provides fluid for both functions. To do so, piston body 250 includes a hollow
lumen and an open top 250a so that the fluid passes through from the open top through
the lumen of drill string 214 and out ports 216a of drillhead 216. As described regarding
Figure 6, the enlarged seal 254 relative to seal 232 provides a force multiplication
to the system. Other differences of Figure 10 from Figure 6 are that parts 214c and
seal 235 are eliminated because all fluid provided to the system passes through the
open top of piston body 250.
[0071] Overall the system of Figure 10 is a simplication from that of Figure 6 since it
eliminates dual fluid sources and seal 235. Conversely, it does not include the advantage
of the control achieved by separation of the piston driving fluid force from the drilling
fluid source.
C. Gravel Packing
[0072] A particularly effective system for placing radial tube 20 is by use of the assembly
of Figures 1-4. Preferably, the drill string forms a piston sliding in a guide tube.
Pressurized fluid flowing through the piston body applies pressure against the drillhead
causing it to move into the formation at the same time as it is cutting a pathway
for itself. A system of this type is described in U.S. patent 4,527,639. A modification
of this system is described above.
[0073] In the above system, during drilling, radial tube 20 passes through whipstock 28.
Drilling fluid passes through the ports of drillhead 24 creating an annulus 42 between
radial tube 20 and the surrounding formation. A feature of the invention is to provide
an effective means of gravel packing of annulus 42.
[0074] Gravel packing constitutes the placement of particles in an oil permeable porous
mass or jacket (termed "gravel pack") in a zone, such as annulus 42. The gravel pack
passes oil while filtering out most of the particles in the surrounding formation.
Such gravel, typically in a sieve size range of 6 to 40, is placed by passage to the
desired area in a slurry form and compacted in that area. For example, it is well
known to pack underreamed area 16 with gravel pack particles.
[0075] In general, gravel packing is accomplished by flowing the slurry of particles, of
approximate size to form gravel pack, from within the well bore through the lumen
of radial tube 20 and out openings in the distal end of the tube into annulus 42 and
back toward the well bore to form a jacket of gravel pack in the annulus. After termination
of gravel pack flow, water may be flowed through the radial tube at a pressure and
for a time sufficient to remove the particles from the radial tube lumen.
[0076] In one aspect of the invention, illustrated in Figures 11-15, the radial tube is
perforated after placement in the formation. The radial tube is perforated with multiple
openings disposed toward the distal end through which the gravel pack slurry is flowed.
Preferably, additional perforations are also formed at spaced intervals along the
remaining length of radial tube 20.
[0077] Perforation may be accomplished electrolytically by use of a perforating tool 344
which is functional in combination with an electrically conductive radial tube 20.
The tool includes an elongate hollow perforating tube portion 346 terminating at its
forward end in a nose portion 348 including circumferentially spaced electrically
conductive nose port walls 350 defining about 8 to 16 outer diameter ports 350a extending
through hollow nose portion 348. Nose portion 348 is formed of an electrically insulative
material which insulates port walls 350 from each other. In turn, such port walls
are electrically connected to a source of power, suitably through an electrically
conductive connector 352 which in turn is electrically connected to a conductor embedded
in tube portion 346 which then connects to the power source. This same electrical
conductor connects conductive tube port walls 355 defining ports 355a formed on three
fin-like ridges 356 spaced approximately equidistantly, as best illustrated in Figure
15. Ridges 356 serve to center tube portion within the radial tube so that the tube
ports 355a are approximately equidistant from the radial tube 338 to provide gravel
pack ports of approximately uniform size. Tube port walls 355 are electrically conductive
cylinders projecting through the tube portion walls and electrically connected through
flexible metal sheath 358 which extends from connector 352 to the source of power.
Metal sheath 358 is insulted by outer electrically insulted jacket 360 and inner electrically
insulted jacket 362. Tube portion 346 is sufficiently flexible to pass through the
turn of whipstock means 336.
[0078] In operation, an appropriate electrolyte, such as an aqueous solution of potassium
chloride, is passed from the surface through the interior of the tube portion 346
and the hollow nose portion 348, and ports 350a to contact the portions of the electrically
conductive radial tube 338 adjacent such ports. By passing the electrolyte through
the ports and simultaneously applying the electrical current, perforations are formed
in the region adjacent to ports 350a of a size sufficient to pass gravel pack particles.
To accomplish this objective, it is preferable to flow the electrolyte only from within
with hollow perforating tool 346 and out the ports. A suitable rear connector assembly
364 for accomplishing this objective is illustrated in Figure 13. Assembly 364 includes
a hollow metal tube 366 electrically connected by adaptor 368 to metal sheath 358.
At the other end of tube 366 is means providing entry of the electrolyte into the
tube and for passing of current to it. In this instance, such means comprises electrically
conductive spaced bars 370. Another electrically conductive adaptor 372 interconnects
the rearward side of bars 370 and electrical cable 374 which extends to the source
of electrical power. A flexible seal 376 is provided around tube 366 to block the
passage of electrolyte in the annulus between tube 366 and radial tube 338 so that
the fluid is directed through bars 370 to the inside of tool 346. In this manner,
electrolyte passes through ports 350a and 355a in a concentrated stream to provide
a precise area of electrolyte contact during formation of the perforations.
[0079] When perforations are formed only at the distal end of radial tube 20 through ports
350a, the elongate hollow perforating 344 is passed through radial tube 20 until its
forward end is adjacent that end. Then, the electrolyte solution is passed through
the lumen of the perforating tool and out ports 350a to be directed against adjacent
regions of the electrically conductive radial tube while current is supplied to the
port walls 350 to form spaced perforations at the adjacent regions of the radial tube.
Thereafter, the perforating tool is withdrawn.
[0080] If desired, perforations are also formed at spaced intervals along the length of
the radial tube by including the aforementioned port walls 355 and passing the electrolyte
through the ports 355a to perforate the radial tube 20 in a similar manner to the
perforations formed at the distal end.
[0081] Referring to Figure 16, an electrolytic pipe cutting device 380 is illustrated connected
to an electric cable 382 which, in turn, is connected to the source of electrical
power, not shown. Device 382 includes a nose cone 384 suitably formed of an impact
resistant material such as nylon and an electrically conductive metal strip 386 electrically
connected to cable 382. Cutting device 380 also includes ceramic rings 388 on both
sides of metal strip 386 serving as heat sinks to remove heat generated at strip 386
during cutting. Cutting device 380 also includes forward and rearward liquid channeling
sections 390 and 392, respectively, with channels 390a and 392a respectively, serving
to channel the flow of liquid passing ring 386.
[0082] In operation, the cutting device of Figure 15 is pushed to a predetermined area of
radial pipe 20 and an aqueous electrolytic solution, such as of potassium chloride,
is pumped passed the cutting device 380 and out drillhead ports 350a. In the illustrated
embodiment, the cutting device 380 is directed to the drillhead until nose portion
384 abuts the rearward side of the drillhead to position strip 386. Then, the electrolyte
is directed passed strip 386 while a DC power source energizes the strip. An electrical
circuit is completed between strip 386 and the adjacent wall of radial tube 20 and
the radial tube is severed. As will be explained more fully hereinafter, after severing,
pipe cutting device 380 is pulled out of radial tube 20. A suitable permeable filter
device is placed proximal to the opening formed at the severed distal end of radial
tube 20 of a type which blocks flow of formation particles into radial tube 20 while
permitting the flow of oil. This may be accomplished simultaneously by use of a pipe
cutting filter device assembly as shown in Figure 17.
[0083] In order to deerect whipstock means 28 for placing other radial pipes into the formation,
radial tube 20 is severed at its proximal end. Then, the main drill string is pulled
out of the well and the whipstock is repositioned at a desired location. For example,
the whipstock may be left at the same elevation and rotated to a different radial
position. Thereafter, another drill string is passed through the whipstock in the
manner described above to form spokes projecting from the well axis.
[0084] In order to sever the distal end of radial tube 20, a cutting device 380 is positioned
near the distal end of radial tube 20. The pipe is severed by passing current through
the device while simultaneously flowing an electrolytic solution by it as described
above. One way to precisely position the cutting device is to include a rigid bar
as a portion of the flexible cable of a length such that it cannot make the full turn
through the whipstock. The cutting device is positioned at a predetermined distance
downstream from the rigid pipe so that it is near the distal end of radial tube 20.
After cutting, cutting device 380 may be pulled to the surface through cable 382.
Alternatively, it may be left in place by providing an automatic detachment such as
an electric fuse device at the cable connection so that the cutter remains in place
while the cable is pulled to the surface. This embodiment is more fully described
with respect to Figure 17.
[0085] Figure 17 illustrates an assembly 396 of permeable plug filter portion 398 and pipe
cutting portion 400 disposed in radial tube 20. Plug filter portion 398 is constructed
to be capable of substantially blocking gravel pack particle flow while passing fluids
such as oil. As illustrated, it comprises a bottle brush-like permeable plug including
a spine 402 and wire brushes 404 projecting radially from its axis 402 which is mounted
to the adjacent portion of pipe cutting portion 400. Further filtration means such
as steel wool may be placed between turns of the wire brushes 404 to enhance filtering.
Pipe cutting portion 400, including metal strip 397, may be constructed in the same
manner as pipe cutting device 386 and interconnected to a suitable source of power
through cable 406. Suitable detachment means, not shown, may be provided between cutting
device portion 400 and plug filter means 398 for detachment after severing of pipe
20 adjacent metal strip 397. Such detachment means may comprise an electric fuse or
a detachable threaded connection or the like. After severing near the proximal end
of radial tube 20, cutting device portion 400 may be withdrawn followed by a removal
of the main drill string to permit deerection of the whipstock. Plug filter means
portion 398 serves to maintain the interior of radial tube 20 essentially free of
gravel pack or formation particles to permit the oil to accumulate efficiently in
the radial tube. For this purpose, as illustrated in Figure 23, such plug filter means
may be placed at both the distal and proximal ends of the radial tube in combination
with a liner as described hereinafter. However, in a simplified version of the invention,
plug filter means may be placed at the distal and proximal ends of radial tube 20
without the use of a liner so that the oil flows into the radial tube only through
the plug filter means, and thereafter through the gravel pack into the underreamed
cavity 16 for pumping to the surface in accordance with conventional technology.
[0086] Referring to Figures 18 and 19, a radial tube 20 is illustrated in the formation
of a porous, elongate, hollow tube liner 410 defining lumen 410a coaxially disposed
within the radial tube. Radial tube 20 includes drillhead 24 with ports 24a and circumferentially
spaced ports 412 disposed close to the drillhead. Ports 412 serve to permit the flow
of gravel pack particles through lumen 410a of liner 410 during gravel packing. Radial
tube 20 also includes ports 414 spaced longitudinally along the radial tube. Liner
410 is sufficiently flexible so that it may be passed through the curve of whipstock
means 28 without undue friction. Liner 410 is also sufficiently permeable to liquid
so that a portion of the water content of the slurry passing through lumen of 410a
of liner 410 passes out ports 24a into annulus 42. A suitable form of liner 410 to
accomplish these objectives is conventional BX electrical conduit for electrical cable,
typically formed of a metal spiral wound in a coil with spaces between adjacent coil
segments. If desired to increase fluid porosity, additional ports such as slits 416
may be provided in the liner.
[0087] As set forth above, prior to placing radial tube 20, the formation adjacent the whipstock
is underreamed and the whipstock is erected. Then, slotted liner 410 is placed. In
one mode, a flexible piston may be placed on its nose, formed of a material such as
Velcro, so that it can be pumped down by passing fluid in the annulus between liner
410 and radial tube 20. Alternatively, liner 410 can be pushed down either by radial
tubing and by an internal stiffener rod to provide sufficient rigidity to prevent
collapse of the liner during placement. After placement, the internal stiffener rod
is removed. In either event, liner 410 is placed until the forward end abuts the rearward
side of the drillhead. Then, gravel pack slurry is flowed through the liner and out
ports 412 in a distal direction as shown by arrows A and then in a proximal direction
in annulus 42 as shown by arrows B. During passage through lumen 410a, the gravel
is partially dewatered and increases in gravel concentration. A suitable initial concentration
of gravel in the slurry is about 1-4 pounds per gallon which may be concentrated about
25-50% during dewatering. Suitably, ports 412 near drillhead 24 are approximately
twice the cross-sectional area of radial tube 20. This large area minimizes the pressure
drop through the ports and thus the slurry velocity to avoid entrainment of the gravel
pack in the formation. Otherwise, such entrainment could deleteriously affect the
imprecisely sized intersticies between the gravel grains thereby reducing the life
of the gravel pack. The gravel flowing out ports 412 at such lower velocity than during
drilling flows towards the well bore and forms a dune 417 because the gravel flow
is below the slurrification velocity. The moving sand dune 417 fills up a portion
of the annulus 42 and leaves an open area, referred to as an ullage 418, which is
segment shaped with a relatively flat bottom and curved top. The face of the sand
dune 417 gradually moves to fill up annulus 42 in the range of about 50-90% of the
total cross-section of the annulus. As the dune 417 moves back towards the well bore,
the water which passed through ports 414 reenters the slurry and tends to preclude
sanding off or plugging of the slurry as the sand dune moves toward the well bore.
Figure 18 shows the sand dune 417 in transit prior to reaching the well bore.
[0088] Referring to Figure 20, liner 410 is illustrated again within radial tube 20. Electrical
conductivity sensing means 420 is disposed intermediate forward segment 410a and rearward
segment 410 near the proximal end of radial tube 20. Sensing means 420 serves to detect
the presence of gravel pack by a drop in conductivity which occurs when the gravel
pack contacts it. As illustrated. sensing means 420 includes an electrically insulating
housing 424 which contains axially spaced electrodes 426, 428 and 430. Electrode 428
is oppositely charged to electrodes 426 and 430, one of which is redundant. The electrical
conductivity of the medium disposed between the two oppositely charged electrodes
is monitored. Such medium constitutes the liquid of slurry flowing from annulus 42
through ports in radial tube 20 to contact the electrodes. The drop in conductivity
caused by the sand dune 417 contacting it is sensed and, in response, gravel flow
is discontinued.
[0089] Thereafter, plug filter means are placed at both ends of radial tube 20 and the tube
distal end is severed from the remaining portion of the drilling string, so that the
whipstock may be deerectd and additional radial tubes placed into the formation in
the same manner. After placement of the desired number of radial tubes, a slotted
liner may be placed down the well bore and gravel pack pumped around the liner to
fill the underreamed area 16 and to backfill any remaining void areas in the annulus
which have not been previously filled by the sand dune gravel pack jacket.
[0090] Referring to Figures 22 and 23, a preferred embodiment of the system is illustrated
after completion of gravel packing. Specifically, the radial tube 20 is of the same
type as illustrated in Figure 18 with like parts denoting like numbers and with a
severed proximal end 20. The system includes a liner 410 of the aforementioned type
disposed within the radial tube. Permeable plug filter means 432 and 434 are placed
at the proximal and distal ends, respectively, of the radial tube in the manner described
above. Pipe cutting device 380 may also be used to sever the portion of liner 410
disposed between device 380 pipe and radial tube 20. Additional gravel pack 436 is
placed in a conventional manner using a slotted liner in the well by pumping through
the well and the underreamed portion and continuing pumping until the remainder of
the annulus is filled.
[0091] The radial tube of Figures 22 and 23 is now fully gravel packed and in combination
with the conventional well bore is suitable for production. Oil from the surrounding
formation flows through radial tube perforations 414 and permeable liner 410 into
lumen 410a of the radial tube and from there into a sump at the well bore for pumping
to the surface in accordance with conventional technology. In the preferred embodiment,
multiple radials are placed and disposed in the manner of spokes projecting from an
axis.
D. Curvature Probe
[0092] As illustrated in Figure 24, a curvature probe, useful for locating the drillhead,
has an elongated body 511 of generally circular cross-section. A roll sensor 512 is
mounted in the forward section of the body, a curvature sensor 513 is mounted in the
central section, and electronic circuitry 514 for processing signals from the roll
sensor and the curvature sensor is mounted in the rear section of the body. The roll
sensor is of suitable known design, and it provides an output signal corresponding
to the orientation of the probe about its longitudinal axis. In one presently preferred
embodiment, the roll sensor utilizes a gravitational reference, and the output signal
from this device indicates the orientation of the probe relative to the downward direction,
i.e. toward the center of the earth.
[0093] The length of the probe is substantially longer than the diameter, and the outer
diameter of the probe is slightly less than the diameter of hole to be logged. In
one embodiment, the probe has a diameter of the order 3/4 of an inch, and the central
section in which the curvature sensor is located has a length on the order of 18 inches.
[0094] As illustrated in Figure 25, the curvature sensor has an axially extending flexible
shaft 516 positioned centrally within the probe body. The flexible shaft is freely
bendable about its axis, but it is torsionally rigid, i.e. it does not twist about
its axis when rotated. In one presently preferred embodiment, the shaft comprises
a double-woven cable which is substantially neutral and has no bias which favors or
resists flexing in a particular direction. This type of cable is commonly employed
for control drives.
[0095] A plurality of guide members or spacers 517 are mounted on shaft 516. Each of the
members comprises a generally annular body having a central opening 518 through which
the flexible shaft extends. In most of the guide members, openings 518 are of slightly
larger diameter than shaft 516 so that the guide members are free to move in the axial
direction on the shaft. Each of the guide members has an outer peripheral surface
519 with a contour corresponding to the cross-sectional contour of the opening in
which the probe is used. The guide members are preferably fabricated of a rigid material
such as nylon, but they can be fabricated of any suitable material.
[0096] Means is provided for maintaining the guide members at an axially spaced relationship
on the flexible shaft. This means includes compression springs 521 which are positioned
coaxially about the shaft and bear against the confronting faces of the guide members.
The guide members and springs are retained on the shaft by hubs 522 which are affixed
to the shaft by suitable means such as set screws (not shown) near the ends of the
shaft. In addition, every sixth one of the guide members is affixed to the shaft
in a similar manner. The hubs and the stationary guide members are positioned to
hold the springs in a partially compressed condition which maintains the spacing of
the guide members and does not significantly impair the ability of the probe to flex
or bend.
[0097] The end portions of the flexible shaft are connected to end pieces 523 by universal
joints 524. The end pieces are generally cylindrical bodies of the same diameter as
guide members 517, and they are axially aligned with the guide members.
[0098] Sensing wires 526 extend longitudinally of the probe in parallel spaced relation
to flexible shaft. The sensing wires are positioned in quadrature about the shaft
and arranged in pairs, with the two wires in each pair being on opposite sides of
the shaft. The sensing wires pass through axially aligned openings 527 in guide members
517 and hubs 522 and are affixed at one end to end pieces 523. The free ends of the
sensing wires are connected to transducers 528 which provide electrical output signals
corresponding to the positions of the free ends. The movement of the free ends, and
hence the sensitivity of the probe, is dependent upon the distance of the wires from
the center line of the probe, increasing as the wires are positioned farther from
the center. The transducers are mounted in bores 529 in end pieces 523, with the transducers
for the two pairs of wires being positioned at opposite ends of the wires. The axes
of the wires and the transducers are offset from each other, and the wires are connected
to the transducers by radially extending connector plates 531. Being affixed to shaft
516, the transducer bodies move relative to the sensing wires, providing greater sensitivity
on a differential basis.
[0099] In the presently preferred embodiment, the position sensing transducers are linear
voltage differential transformers (LVDTs) such as the Schaevitz XS-B series of sub-miniature
LVDTs. These devices produce output signals corresponding to the displacement of magnetic
cores to which the sensing wires are connected. Each transformer has a primary coil
flanked by two secondary coils on a cylindrical form, with the core moving axially
within the coils and providing a path for magnetic flux linking the coils. When the
primary coils is energized with an alternating current, voltages are induced in the
two secondary coils. These coils are connected in series opposition, and the net output
of the transformer is the difference between the voltages induced in the two coils,
which is zero when the core is at the center or null position. When the core is moved
from the null position, the induced voltage in the coil toward which the core is moved
increases, while the induced voltage in the opposite coil decreases. This produces
a differential voltage output that varies linearly as the core moves from one end
of its travel to the other. The two output signals from the transformers associated
with the wires in each pair are summed together to provide a single output signal
for the pair.
[0100] Referring again to Figure 24, an excitation signal for the LVDTs is provided by a
source 533 located at the surface of the earth and connected to the probe by a cable
534. In one presently preferred embodiment, the excitation signal is an AC voltage
on the order of 20 volts RMS and a frequency of 2 kHz. Source 533 also provides operating
power (±10 VDC) for the probe. After processing by circuitry 514, the output signals
from the LVDTs are transmitted to the surface of the earth by cable 534 and converted
to DC signals by a rectifier 536. The DC signals are converted to digital signals
by an analog-to-digital converter 537 and applied to a computer 538 which determines
the curvature of the probe from these signals. The computer also processes information
provided by roll sensor 512 to determine the orientation or direction of the curvature.
[0101] For clarity and ease of illustration, the transducer and roll sensor wiring has been
omitted from Figures 24 and 25. However, the wires for the roll sensor and the transducers
at the forward or distal end of the probe extend in an axial direction through openings
539 in guide members 517 and pass through suitable openings in the end pieces.
[0102] The central section of the probe is enclosed within a flexible casing 541 which comprises
a flexible tubing 542 surrounded by a layer of fabric 543 which has a high tensile
strength, and a layer of crushable material 544. The tubing is fabricated of a flexible
material such as a suitable plastic, and in one presently preferred embodiment, it
comprises a Hytrel tubing having a wall thickness on the order of 0.035 inch. The
fabric layer 543 comprises a fabric woven or braided of fibers having a high tensile
strength, e.g. 250,000 lb/in², and one presently preferred fabric is an aromatic polyamide
fiber manufactured by DuPont under the trademark Kevlar. Outer layer 544 permits
the probe to be crushed or deformed slightly to accommodate small irregularities and
help to keep the probe centered within the hole in which it is used. In one presently
preferred embodiment, the crushable material is a material having a pile of the type
employed in Velcro fasteners. This material provides a crush on the order to 0.030
inch.
[0103] Roll sensor 12 and electronic circuitry 514 are packaged in the manner described
in U.S. 4,524,324. This package includes a flexible body comprising a mass of cushioning
material in which the sensors and electronic components are embedded, with a flexible
outer casing of fabric having a high tensile strength.
[0104] The interior of the probe is sealed and filled with a fluid such as silicone oil
to provide insulation and to maintain a pressure balance inside and outside the probe.
When the probe is driven hydraulically through an oil well casing or another borehole
in the earth, it is subjected to pressures on the order of 3,000-5,000 PSI.
[0105] If desired, the effective diameter of the probe can be increased for use in larger
holes by mounting extension rings (not shown) over the guide members outside probe
casing. A compressive material (not shown) is placed between the rings to prevent
buckling, and a crushable material (not shown) is placed on the outer surfaces of
the rings.
[0106] Operation and use of the curvature probe, and therein the method of the invention,
are as follows. The probe is inserted into the borehole or other opening where curvature
is to be measured and propelled through the hole by suitable means such as pressurized
fluid. As the probe travels through the hole, it flexes or bends in accordance with
the curvature of the hole. As the probe bends, the free ends of the sensing wires
on opposite sides of the probe move in opposite directions by amounts depending upon
the radius of curvature. The positions of the free ends are monitored by the LVDTs,
and the signals produced by the LVDTs are combined and processed to determine the
curvature of the opening.
[0107] The probe has been found to have an accuracy on the order of ±1% in pitch (inclination
or profile) and ±2% in yaw (plan or azimuth). This accuracy compares favorably with
the results obtained with relatively expensive optical instruments and makes the probe
suitable for use in applications requiring a high degree of accuracy.
[0108] It is apparent from the foregoing that a new and improved curvature probe and method
have been provided. While only certain presently preferred embodiments have been described
in detail, as will be apparent to those familiar with the art, certain changes and
modifications can be made without departing from the scope of the invention as defined
by the following claims.
1. Earth well drilling apparatus comprising structure including whipstock means adapted
to be positioned within an earth well adjacent to a mineral bearing formation, said
whipstock means comprising a plurality of connected guideway assemblies laterally
extendible from a retracted position substantially within the outer well to an extended
position forming a curved tube bending guideway, piping within the well to which said
whipstock means is attached, anchor means operatively connected to the rearward side
of said whipstock means and having a retracted position for sliding through said
earth well and an anchoring position for locking in a fixed position relative to said
earth well, and erection means slidable within said earth well, said erection means
being pivotally connected at one end to a forward one of said guideway assemblies
and at the other end to extension means extending to the earth surface, said pivotal
connection being of a type to cause said guideway assemblies to swing into said curved
pathway when said extension means is pulled from the earth surface with said whipstock
means fixed at its rearward end.
2. The apparatus of Claim 1 in which said erection means includes a wall segment defining
slot means, said anchor means including retractable jaw means capable of retention
by said wall segment in a retracted position and of projecting through said slot means
into contact with said earth well wall in said locking position.
3. The apparatus of Claim 1 together with deerection means serving to urge said extended
guide assemblies into their retracted position.
4. The apparatus of Claim 3 in which said deerection means comprises compression spring
means for maintaining sufficient pressure between said extension member and said guide
assemblies at said pivotal connection to keep said guide assemblies in tension, whereby
release of the pulling force on said erection means urges said whipstock means to
move to its retracted position.
5. The apparatus of Claim 1 in which said curved tube bending guideway is in a generally
inverted comma shape with one portion projecting into the formation to one side of
said pivotal connection and the other portion projecting into the formation to the
other side of said pivotal connection.
6. A method of forming earth well drilling apparatus for placing a radial tube laterally
into a mineral bearing formation from an earth well which extends downwardly from
the surface of the formation to the region of radial tube placement, said method making
use of a structure comprising whipstock means including a plurality of connected
guide assemblies laterally extendible from a retracted position substantially within
the earth well to an extended position forming a curved tube bending guideway for
a drilling tube to be extended radially into the formation, anchor means operatively
connected to the rearward side of said whipstock means and having a retracted position
sliding within said earth well and an anchoring position for locking in a fixed position
relative to said earth well, and erection means slideable within said earth well,
said erection means being pivotally connected to a forward one of said guide assemblies
and at the other end to extension means extending to the earth surface, said method
comprising moving said whipstock means adjacent to the mineral bearing formation with
said whipstock means and anchor means in a retracted position, moving said anchor
means into said anchoring position and pulling from the earth surface on said extension
means of said erection means to cause said forward one of said guide assemblies to
pivot away from said well to a sufficient extent to form said curved tube bending
guideway.
7. The method of Claim 6 together with the step of moving a drilling tube through
said guideway to cause it to bend and pass into said formation forming a radial tube.
8. The method of Claim 6 in which said curved tube bending guideway is in a generally
inverted comma shape with one portion projecting into the formation to one side of
said pivotal connection and the other portion projecting into the formation to the
other side of said pivotal connection.
9. The method of Claim 6 with the step of collapsing said extended whipstock means
into its retracted position, and retracting said anchor means and removing said whipstock
structure.
10. Earth well drilling apparatus comprising a structure adapted to be positioned
within the well adjacent an underground formation, said apparatus comprising means
defining a drilling fluid chamber, means defining a driving fluid chamber, a drill
string with an interior fluid passageway and extending from said driving fluid chamber
through said drilling fluid chamber, drillhead means of the hydraulic jet type attached
to the forward end of said drill string in communication with said interior passageway,
first sliding seal means disposed between said driving fluid chamber means and said
drill string, second sliding seal means disposed between said drilling fluid chamber
means and said drill string, said drill string interior passageway being substantially
sealed from said driving fluid chamber and being in communication with said drilling
fluid chamber, whereby when pressurized fluid is supplied to the driving fluid chamber
means, it drives the drill string forward through the first and second seals and when
pressurized fluid is supplied to the drilling fluid chamber means it flows from the
drilling fluid chamber means through the interior passageway to apply pressure against
the drillhead, thereby causing the drill string to move forward into the formation
and causing the pressurized fluid to be directed against the formation.
11. The apparatus of Claim 10 in which the driving fluid chamber means includes piping
and the first sealing means is attached to the inner surface of said piping in fluid
sealing engagement with said drill string.
12. The apparatus of Claim 10 in which said drill string includes an upstream piston
body portion with an enlarged cross-section relative to the downstream portion of
said drill string, third sliding seal means between the upstream piston body portion
and the driving chamber means above said second seal, and means for bleeding off fluid
disposed in said inner piping between said third seal and second seal.
13. The apparatus of Claim 10 together with whipstock means disposed downstream of
said first seal, said drill string substantially changing direction on movement through
said whipstock means.
14. The apparatus of Claim 10 in which said drill string includes a solid metal rod
portion to provide a dead weight driving force to the drillhead.
15. A method for forming a bore hole in an underground formation using a drilling
system comprising a drilling fluid chamber sealed from a driving fluid chamber, and
a drill string with an interior passageway in communication with a drillhead of the
hydraulic jet type at its forward end and sealed from said driving fluid chamber,
said method comprising the steps of:
(a) disposing said drill string with its upstream end in said driving fluid chamber
with said interior passageway sealed therefrom, said drill string extending through
a first sliding seal in said driving fluid chamber and then through a second sliding
seal in said drilling fluid chamber with said drillhead downstream of both seals,
said interior passageway communicating with fluid in said drilling fluid chamber,
(b) directing fluid into said driving fluid chamber upstream of said first seal to
push said drill string downstream, and
(c) simultaneously directing fluid into said drilling fluid chamber through said
interior passageway to apply pressure against said drillhead to move said drillhead
into the formation and to cause pressurized fluid to be applied against the formation.
16. The method of Claim 15 in which the apparatus also includes a piston body at the
upper end of said drill string of an enlarged cross-section relative to the drill
string cross-section area and also includes third sliding seal between the piston
body and the driving chamber means above said second seal, and in which step (b) is
performed by directing fluid against the upstream side of said piston body in said
driving fluid chamber.
17. The method of Claim 15 in which downstream of the first seal, the drill string
is passed through a whipstock in which it changes directions.
18. A method of gravel packing the exterior of a hollow production radial tube having
an open distal end and extending from a well bore into the formation, said radial
tube and formation defining an annulus therebetween which is relatively permeable
or free of formation, the interiors of said radial tube and well bore being in fluid
communication, said method comprising flowing a slurry of particles of a size capable
of forming a gravel pack from the well bore through the radial tube interior and out
said open distal end into the annulus and back toward the well bore to form a jacket
of gravel pack particles in said annulus.
19. The method of Claim 18 in which said well bore is generally vertical and said
radial tube extends generally horizontally into the formation.
20. The method of claim 18 together with the step of perforating the forward portion
of the radial tube by forming multiple opening therein with said tube disposed in
the formation prior to the flow of said slurry through the radial tube.
21. Production apparatus suitable for withdrawing oil from an oil-bearing formation,
said apparatus comprising a well casing, a perforated hollow production radial tube
extending from the well casing into the formation, the interior of said radial tube
and well bore being in fluid communication, and a substantially continuous annular
jacket of gravel pack particles disposed between the exterior of said radial tube
and the surrounding formation.
22. The production apparatus of Claim 21 in which said well bore is substantially
vertical and said radial tube is substantially horizontal, together with whipstock
means through which said radial pipe projects.
23. The production apparatus of Claim 21 together with multiple perforations near
the distal end of said radial tube and plug filter means disposed within said radial
tube adjacent said multiple perforations, said plug filter means being capable of
substantially blocking gravel pack flow but of passing fluids.
24. The production apparatus of Claim 21 together with a hollow tube liner disposed
within said radial pipe adjacent to said radial pipe perforations for passing oil
from said radial pipe into said formation while substantially blocking passage of
the gravel packing from the jacket into the radial pipe.
25. The production apparatus of Claim 21 in which said radial tube includes an array
of ports disposed toward its distal end and the forward end of said liner is disposed
adjacent said port array.
26. The system of Claim 21 together with plug filter means disposed at said port array
and capable of substantially gravel pack flow but of passing fluids.
27. A method of gravel packing the exterior of the radial port of a production tube
which extends down a well bore and projects outwardly therefrom into a radial bore
in an underground formation, said radial portion defining an array of ports adjacent
its distal end, the ports in said array being large enough to pass a slurry of gravel
pack particles, said method comprising moving a hollow tube liner through the drilling
pipe into its radial portion so that the forward end of the liner is adjacent to and
rearward of said port array, said liner comprising a flexible tube defining opening
of a size capable of passing liquid but of substantially blocking the passage of gravel
pack particles, pumping an aqueous gravel packing slurry through the liner and out
the port array and continuing the flow of slurry so that it moves rearwardly along
said radial portion and forms a jacket of gravel pack between said drilling pipe radial
portion and said formation.
28. The method of Claim 27 in which said radial portion includes additional ports
extending rearwardly from said port array, and during the pumping of said slurry the
liquid in said slurry passes through the openings of said liner and additional ports
to assist in retaining in slurrified form, gravel packing particles adjacent said
additional ports.
29. The method of Claim 27 together with the step of disposing permeable plug filter
means in said radial tube adjacent said port array after gravel packing to substantially
block gravel particles in the adjacent formation from flowing into the interior of
the liner while permitting the passage of oil from the formation into the radial
tube.
30. A method of forming spaced perforations in an electrically conductive production
radial tube extending from a well bore in an underground formation, said method comprising
(a) passing an elongate hollow perforating tool through the electrically conductive
production radial tube to be perforated until the forward end of said perforating
tool is adjacent the distal end of said radial tube, said perforating tool comprising
an elongate hollow perforating pipe with port means defining spaced ports with electrically
conductive perimeters connected to an electrical power source through said radial
tube,
(b) passing a electrolyte solution through the lumen of said perforating tool and
out said ports to be direct against adjacent regions of said electrically conductive
radial tube while current is supplied to said port perimeters to form spaced perforations
at said adjacent regions, and
(c) withdrawing said perforating tool.
31. The method of Claim 30 in which said radial tube projects generally horizontal
into said formation from a generally vertical well bore through a whipstock, and said
perforating tool is flexible and turns through said whipstock.
32. A method of gravel packing the exterior of a perforated production radial tube
with multiple openings in the well of the tube and extending from a wellbore into
an underground formation, said radial being open at its distal end, said method comprising
(a) placing an elongated hollow tube liner with an open distal end within the perforated
radial tube said liner including openings of a size to permit passage of fluid but
not gravel pack particles, and
(b) pumping a gravel packing slurry through the liner and out its open front end through
said radial tube open end into the formation to flow back toward the wellbore to form
at least a partial jacket of gravel pack between the radial tube and the formation.
33. The method of Claim 32 together with the step of
(c) severing the radial tube towards its proximal end.
34. In a curvature probe: an axially extending flexible shaft, a plurality of axially
spaced guide members mounted on the flexible shaft, two pairs of axially extending
sensing wires positioned in quadrature about the shaft with the two wires in each
pair being positioned on opposite sides of the shaft, said wires passing freely through
axially aligned openings in the guide members and being free to move relative to each
other in an axial direction upon bending of the probe, and means responsive to the
relative axial positions of the two wires in each pair for providing an output signal
corresponding to the curvature to which the probe is bent.
35. The curvature probe of Claim 34 wherein the guide members are axially movable
on the flexible shaft, with means between adjacent ones of the guide members for maintaining
the guide members in a spaced relationship.
36. The curvature probe of Claim 35 wherein the means for maintaining the guide members
in a spaced relationship includes compression springs which are positioned coaxially
of the flexible shaft and bear against the confronting faces of the guide members.
37. The curvature probe of Claim 34 wherein the means responsive to the axial positions
of the wires includes a transducer connected to one end of each of the wires.
38. The curvature probe of Claim 37 wherein the transducers are linear voltage differential
transformers.
39. In a method of determining the curvature of a borehole with a probe having an
axially extending flexible shaft and two pairs of sensing wires arranged in quadrature
about the shaft, said wires being held a predetermined radial distance from the flexible
shaft and being free for axial movement relative to each other upon bending of the
probe, the steps of: inserting the probe into the borehole so that the probe is bent
to a curvature corresponding to the curvature of the borehole, and monitoring the
relative axial positions of the sensing wires on opposite sides of the flexible shaft
to determine the curvature of the borehole.