Technical Field
[0001] The present invention relates to the oil industry and can be used to increase the
volume of pumped-out fluid, oil recovery efficiency and oil production rate, to improve
oil quality and rheological (kinetic) properties, as well as to reduce natural salt
(calcium, magnesium, sodium and potassium), hydrated and hydrated hydrocarbonaceous
deposits harmfull to downhole ECPP operations on downhole area elements (DAE), including
the electric centrifugal pumping plant (ECPP), flow column and casing pipe.
Background
[0002] Various methods for stimulation of the downhole area and the productive formation
which use mechanical, thermal, physical, chemical and electromagnetic techniques and
combinations thereof in order to increase hydrocarbon production efficiency are known.
[0003] In the case of mechanical stimulation of formations, permeability is increased due
to the appearance of new channels and fractures connecting the formations with the
bottom hole zone. Mechanical treatment techniques (hydraulic fracturing of the formation,
shot-firing operations) are applied to dense rock formations.
[0004] Thermal stimulation is used to remove paraffin and resins settled on pore channel
walls, and for reinforcing chemical bottom hole zone treatment techniques.
[0005] Physical techniques are based on stimulation using vibration, ultrasound, etc. They
are primarily used to remove residual water and solid fine particles from the bottom
hole zone in order to increase oil rock permeability.
[0006] Mechanical, thermal and physical techniques are known to be, in some cases, rather
effective, although the use of these techniques involves considerable financial expense
and power consumption.
[0007] The use of chemical productive formation stimulation techniques is based on interaction
reactions between injected chemical agents, primarily various acids, and certain rocks
which dissolve to expand pore channels and increase the permeability of formations.
The use of chemical agents is effective in some cases but expensive. It can also be
environmentally hazardous.
[0008] Electromagnetic stimulation techniques enable a significant reduction in power consumption
along with high efficiency. An important advantage of such techniques is that the
stimulation is applied simultaneously with the main production process and does not
hinder it.
[0009] A significant factor affecting production efficiency is protection from unwanted
hard deposits for the equipment and downhole area. The build-up of unwanted hard deposits
in oil and gas wells and production equipment is an acute problem in the oil industry.
Salt, paraffin, and wax deposits, as well as asphaltene deposits, create major problems
for the oil industry worldwide. The formation of deposits often causes falls in production
and increased operating expenses in hydrocarbon production.
[0010] The typical process resulting in the formation of deposits during hydrocarbon production
is the depositing of low-solubility salts from mineralized water in the oil field.
Some oil field water contains a sufficient quantity of sulfated ions with barium,
calcium and/or strontium ions to enable the formation of barium sulfate (BaSO4) and/or
strontium sulfate (SrSO4) in the form of scale. Deposits are generally formed from
such compound classes, which include: calcium carbonate (CaCO3), calcium sulfate (CaSO4),
barium sulfate (BaSO4), barium sulfide (BaS), barium tiosulfate (BaS2O3), strontium
sulfate (SrSO4), sodium carbonate (Na2CO3), sodium sulfate (Na 2SO4), sodium sulfide
(Na2S), potassium carbonate (K2CO3), potassium sulfate (K2 SO4), magnesium sulfate
(MgSO4), magnesium chloride (MgCl2), sodium chloride (NaCl), zinc sulfide (ZnS), zinc
sulfite (ZnSO3), zinc sulfate (ZnSO4), lead sulphite (PbS), lead sulfite (PbSO3),
lead sulfate (PbSO4), etc. as well as combinations of the above listed.
[0011] Chemical treatment methods to remove unwanted deposits such as salts, paraffin, asphaltenes
and hydrates, include acid treatment or treatment using various other chemicals in
order to remove unwanted deposits. The type of chemical treatment process often depends
on the type of precipitate or deposit. Chemicals such as polyelectrolytes, phosphonates,
poly-phosphino carboxylic acids, organophosphonic acids (such as diethylentriamine
penta methyl phosphonic acid) and polymers such as polyacrylate, polyvinyl sulfonate,
sulfonated polyacrylates, phosphomethylated polyamines, etc., are often used to reduce
or prevent the build-up of unwanted hydrocarbonaceous deposits, such as salt crystals,
on the inner surfaces of the production string. Typically, such chemicals are effective
only for specific types of deposits and limited to such use. Despite certain advantages,
chemical treatment is usually expensive, in many cases harmful for the environment
and often rather sensitive and effective only with a specific type of crude oil or
specific types of unwanted deposits. Chemical treatments often require special equipment
for injecting chemicals into the deepest sections of the well bore.
[0012] Methods for electrophysical and electromagnetic stimulation of well production are
currently becoming relevant. This stimulation is based on the following factors. When
minerals such as calcium carbonate, acid salt of carbonic acid, magnesium carbonate
and magnesium bicarbonate, are dissolved in water, positive and negative ions can
be observed. When the maximum volume of the material, which can be dissolved for the
specified temperature and pressure values, is obtained, the solution should be saturated
and in case of modification of the conditions at which saturation concentration of
the substance has increased, the solution becomes supersaturated. If the solution
contains the required seed crystals, the dissolved substances are crystallized out
of the solution and can result in the deposit of sediment in the downhole area.
[0013] Seed crystals are formed by clustering positive and negative ions of the material.
Due to such distribution of charges, ions which include more than one atom can be
considered as dipoles, and when affected by an electric field, such ions become oriented
towards this field. This process significantly increases the possibility of collisions
between opposite-charged particles as they will move in opposite directions to each
other (particularly, in case of alternating electric field), and also increases the
growth of clusters of opposite-charged ions of the dissolved material.
[0014] Additionally, the electric field reduces the attracting forces which cause attraction
of water molecules to ions with the result that the charged particles aggregate to
form a seed crystal. These seed crystals have a surface charge that attracts a large
number of ions and clusters thereof (which can be obtained in the supersaturated solution),
and the seed crystals grow quickly and trigger the growth of other crystals (i.e.
sedimentation of the dissolved material) if the solution is not supersaturated. If
the pressure is reduced (many substances forming the precipitable material are characterized
by decreasing water solubility with decreasing pressure), the crystals continue growing
until the volume of the dissolved material is reduced again.
[0015] Homogeneous seed crystals grow in a solution in this manner, the crystals can also
be formed on any foreign substance or flat surface with jagged steps. Electrical charges
will be concentrated on such jagged edges, which will attract charged particles to
initiate the process of crystallization. If there are no available homogeneous seed
crystals in this part of the solution, the dissolved material will be crystallized,
in a similar way, on the heterogeneous seed crystals which should similarly be present
on DAE. This results in increase of sediment on their surfaces.
[0016] Homogeneous seed crystals initiate the process of crystallization at a higher pressure
than crystallization on heterogeneous seed crystals on the surface. As a result, all
material susceptible to precipitation from the solution should be deposited in this
way prior to the process of heterogeneous depositing on the surface.
[0017] Asphaltene and paraffin wax deposits made from the oil content of a water-and-oil
mixture are reduced similarly on DAE surfaces. Both asphaltenes and paraffin waxes
can use seed crystals, as it is described above, as a crystal nucleus on which suspended
particles settle (the latter visually resemble granules) up to the solidification
point.
[0018] There is a known method of electromagnetic stimulation of oil field fluid (patent
No.
RU 2208141, IPC E21B43/24 dated July 10, 2003) used for increasing the extraction ratio of oil
or other vaporable fluids from oil springs on the ground or in the sea. According
to this method, an electromagnetic wave radiator is positioned in the well, and a
high-frequency electric field electrode is placed with it or separately. Oil formations
are initially stimulated by super-high frequency electromagnetic waves, then 15 to
30 kHz waves, and, finally, 0.01 to 15 Hz waves, until the formation is partially
heated. The oil formation is then stimulated by a high-frequency electric field which
is brought into phase with the electromagnetic field and the natural electric field,
providing thereby mutual induction of the electromagnetic field and the electric field,
resonance and modification of the physical and mechanical properties of the oil formation.
Water evaporation caused by heating produces additional vapor pressure on the formation.
[0019] However, this method requires considerable power consumption and sophisticated designs
for the equipment installed in the well.
[0020] There is a known method for stimulation of oil formation fluid during oil production
which includes the creation of an oscillating process directly in the treated oil
fluid by carrier electromagnetic waves in the 3*10-5 to 3*1014 Hz frequency range,
which modulate information signals resonant to hydrocarbons of the treated oil fluid
and form standing waves (patent No.
RU2281387 C2, E21B 43/16, dated April 20, 2006). Directional standing waves are formed using a
resonant wave device (generator) submerged in the well, and the control of resonant
standing waves is carried out by an antenna field positioned at the surface which
includes movable resonant modules, waveguides, etc.
[0021] The use of the known method for resonance and wave stimulation of the well oil fluid
enables the reanimation of wells with a low flow rate, flooded areas, low-gravity
oil, etc., by increasing oil recovery efficiency, oil quality and rheological properties,
as well as reducing the water content in the pumped-out fluid.
[0022] However, the known method has a considerable disadvantage in that the two subsystems,
the ground level and the submerged systems, must be closely coordinated, which requires
a complex algorithm for adjustment of the subsystems and, accordingly, provision of
an appropriate and reliable well-to-surface communications channel.
[0023] The method closest to the one in the invention, is a method for stimulation of oil
field downhole area using the electromagnetic protector of the well electric centrifugal
pumping plant; the protector forms an electromagnetic field in the downhole area using
an electromagnetic signal radiator connected to the generator output (patent No.
RU2444612, IPC E21B 37/00 dated March 10, 2012). The radiator winding's outputs are connected
to a variable capacitance diode with its control input connected to the output of
the control unit controlling the generator operation according to the signal from
the wave analyzer. The device has a channel for communication with the surface. The
generator forms short pulses at the frequency determined by the control device in
order to provide free resonant oscillations in the radiator circuit, the wave analyzer
unit estimates the dominant frequency expected value and dispersion of free oscillations
occurred in the emitter circuit and generates a feedback signal to the control device
in order to adjust the frequency using the variable capacitance diode In this case,
wave stimulation of the downhole area is formed by the radiator circuit and based
on settings decided in advance allowing for the particular composition of the deposits
according to empirical laboratory and production data.
[0024] However, this method does not provide an adequate level of resonant wave stimulation
of the fluid and the productive formation taking into account the entire range of
downhole area parameters. Accordingly, it is not efficient enough to increase oil
production and is only a specific means of protecting wells and production equipment
against hydrated and hydrocarbonaceous deposits of a certain type.
[0025] The objective of this invention is to reduce fluid viscosity, separate the fluid
into light hydrocarbons and energized water, increase the drainage function of fractures,
capillaries and pores in the productive formation, and to reduce natural hydrated
and hydratocarbonaceous deposits on the downhole area elements, that is the electric
centrifugal pumping plant, flow column, and casing pipe, through resonant stimulation
of fluid hydrocarbons and energized aqueous salt solutions, with low power consumption
and using comparatively simple equipment.
Summary
[0026] The formulated problem is solved by a method for stimulating the downhole area during
hydrocarbon production in which a device with a radiator and a controlled generator
is positioned on the base of the electric submersible element of the electric centrifugal
pumping plant in order to create an electromagnetic wave field in the downhole area,
in which, unlike the prototype, the electromagnetic wave field is radiated at a frequency
that is resonant for the downhole area and determined on the basis of practical experience,
modelled results, or testing, which testing is carried out at specified intervals,
and during intervals between two tests the generator is operated in the resonant frequency
mode, at the resonant frequency being determined during testing, with the radiator
forming standing electromagnetic waves which disperse the wave energy throughout the
whole downhole area.
[0027] The essence of the method according to the invention consists in the creation of
a high-frequency axial electromotive force (emf) of conductivity in the downhole area
due to electric charge carriers in this area, namely, electrons in metal, ions in
solution, charged solid particles and emf polarization of dielectric molecules, which,
in turn, causes a coaxial electromagnetic field in the downhole area; the coaxial
electromagnetic field is dispersed in the form of standing waves, being constantly
stimulated by the electromagnetic oscillation radiator at the resonant frequency which
is determined by available practical experience, modelled results, or testing. For
example, the length of the standing wave equals 2,498 m at a frequency of approximately
120 kHz. The standing waves formed in the electromagnetic field disperse wave energy
through the downhole area which facilitates the formation of homogeneous seed crystals
in the oil well fluid and, consequently, crystals formed in the fluid are transported
by the fluid without being deposited on the DAE surfaces, as homogeneous seed crystals
attract material from the solution ten times more strongly than heterogeneous seed
crystals on the surface and in consequence crystals are formed as suspended solids
in the fluid.
[0028] Additionally, the resonance and wave stimulation results in the excitation and separation
of hydrocarbons in the fluid into lighter fractions, which leads to reduced hydrocarbon
viscosity and consequently, increased hydrocarbon mobility both in the well and in
the productive formation zone around the well. The resonance and wave stimulation
also contributes to the increased drainage function of fractures, capillaries and
pores in the oil field due to the removal of:
- settled and accreted heavy hydrocarbons and asphaltene-resin-paraffin deposits;
- clays, colloid dispersed formations, microparticles of rock, etc., dissolved and/or
washed out of the fluid by energized water;
- absorbed and strongly bound water on the surface of mineral particles.
Detailed Description
[0029] The claimed method is implemented in the following way. Before the well assembly
is lowered, a sealed container with the generator and the radiator is fixed and connected
to the electric submersible motor (ESM) base of the ECPP. The assembly is lowered
into the well. When the ESM is started, the generator is switched on, as the device
is supplied from the stator winding of the ESM, similar to the prototype. If the resonant
excitation frequency is known in advance through available practical experience or
modelled results, the generator is started at this frequency. Otherwise, testing is
carried out. For example, the testing mode is enabled and the generator excites the
radiator to emit very short power pulses at intervals. The shorter the pulse is, the
wider the spectrum is. Thus, resonant damped harmonic oscillations with the frequency
and the damping period depending on the environmental parameters are set up in the
radiator. Once the frequency and the damping period are determined, the generator
is switched to the resonant frequency radiation mode with the power determined according
to the damping period which corresponds to the operating mode. Resonant standing electromagnetic
waves form along the axis in the downhole area both in test mode and in operating
mode.
[0030] It should be noted that in the claimed method fluid is conventionally moved from
the formation reservoir to the production well due to the differential pressure drawdown
in the productive formation caused by reducing the dynamic level of the oil well fluid
in the casing string of the well, which is consistent with well-proven the hydrocarbon
production technology.
[0031] Low power consumption is a not insignificant advantage of the claimed method, the
generator power consumption for radiation is approximately 100 W. The device is concentrated
in the submersed part, and additional surface equipment, a communication channel,
etc., are not needed.
[0032] Thus, the use of the claimed method for resonant wave stimulation of the fluid and
the downhole area allows wells to be revived and significantly extends the life of
oil fields with low flow rate, flooded areas, low-gravity oil etc, due to the increase
in oil recovery efficiency, oil quality and rheological properties. Moreover, the
method provides protection of the downhole area elements from harmful deposits.