APPARATUS AND METHOD FOR IN-SITU PERMEABILITY ENHANCEMENT OF RESERVOIR ROCK

Abstract

A method of in-situ rock permeability enhancement involves penetration of a target formation by a well, downhole injection of a fluid, action on the fluid by static pressure and shock waves of a specific pattern transmitted downhole along a fluid waveguide and directed to the target formation from a wave reflector, thereby generating dilatant decompaction of the rock. The action on the fluid by static pressure and by shock waves occurs simultaneously, so that static pressure exceeds the capillary pressure in pores of the most common size in the decompacting rock by no less than 1.3 times. The selected shock wave amplitude is equal to or greater than the compressive or tensile stress necessary for dilatant decompaction of the rock. The proposed technical solution will make it possible to improve the efficiency of the in-situ permeability enhancement and rock decompaction process while reducing energy consumption and operating costs.

Description

BACKGROUND OF THE INVENTION

The present invention relates to mining activity and may be used to recover subsoil resources through conventional or purpose-drilled wells.

An essential factor in the extraction of subsoil resources is rock permeability, which determines the effectiveness of the technology employed. Depending on rock type, the process of permeability enhancement directly affects productivity, energy consumption and equipment wear. Various permeability enhancement methods are currently available.

One documented method of rock permeability enhancement (USSR Certificate of Authorship No. 1030540 IPC3, 1980) is based on focusing directed wave energy on rocks at their depths of occurrence and involves penetration of the target formation by a well, downhole injection of fluid, and in-situ application of pulse-pattern wavefield energy emitted from a downhole transmission source. Rocks are impacted by emitted pulses with periodic waveforms and an asymmetrical distribution of energy relative to zero amplitude. This method makes it possible to achieve more effective fracturing of the target rocks while reducing processing time and the cost of the recovered subsoil resource.

A drawback of this method is that the efficiency of the process is low, since losses of the energy transmitted to the target formation are substantial, resulting in a failure to generate adequate rock permeability.

The in-situ permeability enhancement method (USSR Certificate of Authorship No. 1240112 IPC3 E21 B43/28, 1983) that most closely approximates the subject of this application involves penetration of the target formation by a well, downhole injection of fluid, action on the fluid by static pressure and by shock waves of a specific pattern transmitted downhole along a fluid waveguide and directed to the target formation from a wave reflector, thereby generating dilatant decompaction of the rock.

A deficiency of this method is that while energy intensive, it yields inadequate permeability enhancement owing to the lack of alignment between static pressure in the fluid and pore pressure in the rock coupled with significant losses of wave energy transmitted to the formation.

An essential factor at mineral production is rock permeability facilitating rock fragmentation. Depending on the rock density the process of permeability increase influences significantly productiveness of the mineral production, power intensity and deterioration of the equipment applied at mineral production.

A device for increasing in situ rock permeability is known comprising a wave device consisting of a wave generator, an emitter, a fluid channel and a well reflector. At that the wave reflector is connected with the wave generator and the emitter by means of the fluid channel which is the well filled with the process fluid. The disadvantage of the known device is that it does not provide sufficient rock permeability and also has high energy consumption and short operational life due to high vibration of the wave generator.

Accordingly, there is a need for an improved device and method that increases in-situ rock permeability, improves the efficiency of operation, reduces energy consumption, and increases device operational life. The present invention fulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

The objective of the invention presented here is to create an in-situ permeability enhancement method that increases the effectiveness of said permeability enhancement while reducing energy consumption and operating costs by minimizing losses of wave energy.

This objective is achieved in a manner similar to the documented method of in-situ permeability enhancement described above, which involves penetration of the target formation by a well, downhole injection of fluid, action on the fluid by static pressure and by shock waves of a specific pattern transmitted downhole along a fluid waveguide and directed to the target formation from a wave reflector, thereby generating dilatant decompaction of the rock. However, under this new invention, the action on the fluid by static pressure and by shock waves occurs simultaneously, so that static pressure exceeds the capillary pressure in pores of the most common size in the decompacting rock by no less than 1.3 times, while the selected shock wave amplitude is equal to or greater than the compressive or tensile stress necessary for dilatant decompaction of the rock.

More particularly, the present invention is directed to an apparatus for in-situ permeability enhancement of reservoir rock. The apparatus includes a wave generator operably connected to a coniform adapter, an emitter housing having a first end attached to the wave generator and surrounding the coniform adapter; and a moveable bearing and fluid tube fluidly connected to a second end of the emitter housing, wherein the emitter housing and fluid tube define a fluid channel. The emitter housing preferably is a hollow conoid body hermetically sealed to a hollow frustum body at their widest points.

The emitter housing preferably includes an emitter section that is configured as decreasing along a longitudinal axis of the fluid channel according to the following formula:

F_H0=(p_Ha_HF_H+p_Ka_KF_K)/(p_H0a_H0)

where:

F_H0—is a zero section of the fluid channel;

p_H0—is process fluid density in the zero section;

a_H0—is wave velocity in the process fluid in the zero section;

F_H—is a current section of the fluid channel;

p_H—is process fluid density in the current section;

a_H—is wave velocity in the process fluid in the current section;

F_K—is an estimated section of the fluid channel according to a length of the fluid channel;

p_K—is process fluid density in the estimated section; and

a_K—is wave velocity in the estimated section.

The apparatus preferably includes a coniform well wave reflector disposed in a wellbore proximate to a mineral stratum in the reservoir rock and associated with the fluid channel. The coniform well wave reflector has a height that is not less than ¼ of a wavelength generated by the emitter. A fluid waveguide cross-section changes towards a bottom of the wellbore according to the following formula:

F_*o=(p_*a_*F_*+p_Ma_MF_M)/p_*oa_*o,

where:

F_*o is the initial fluid waveguide cross-section;

p_*o is the initial process fluid density;

a_*o is the initial wave velocity in the process fluid;

F_* is the current fluid waveguide cross-section;

p_* is the current process fluid density;

a_* is the current wave velocity in the process fluid;

F_M is the cross-section of the rock mass impacted by the wave;

p_M is the density of the rock mass; and

a_M is the wave velocity in the rock mass.

A method for in-situ permeability enhancement of reservoir rock begins with providing a wave generating system having a wave generator operably connected to a coniform adapter, an emitter housing having a first end attached to the wave generator and surrounding the coniform adapter, a moveable bearing and fluid tube fluidly connected to a second end of the emitter housing, and a well wave reflector disposed in a wellbore in fluid communication with the fluid tube. The emitter housing, fluid tube, and wellbore are filled with a process fluid. An energy wave is generating in the process fluid via the wave generator and coniform adaptor. The energy wave is redirected from the wellbore into a mineral stratum in the reservoir rock proximate to the wellbore.

The energy wave is preferably at a wavelength commensurate with a thickness of the mineral stratum, while a processing time is determined based on a specified length of a fracture being created in the mineral stratum, according to the following formula:

L≥λ=T·a≥ΔÍ·n

Where:

L is the thickness of the target formation;

λ is the wavelength;

T is the wave processing time;

a is the wave velocity;

Δ Í is the increase in fracture length per wave passage; and

N is the number of wave passages needed to achieve the specified fracture length.

The energy wave is preferably in alignment with areas of cross-section change so that acoustic impedances of wave guides are in equilibrium, according to the following formula:

F_*op_*oa_*o=p_*a_*F_*+p_Ma_MF_M

where:

F_*o is the initial cross-section of a fluid waveguide;

p_*o is the initial process fluid density;

a_*o is the initial wave velocity in the process fluid;

p_* is the current process fluid density;

a_* is the current wave velocity in the process fluid;

F_* is the current fluid waveguide cross-section;

F_M is the cross-section of the rock mass impacted by the wave;

p_M is the density of the rock mass;

a_M is the wave velocity in the rock mass.

The energy wave preferably simultaneously transfers both static pressure and shock waves such that the static pressure exceeds capillary pressure in pores of the most common size in the reservoir rock by no less than 1.3 times, and the shock wave amplitude is equal to or greater than the compressive or tensile stress necessary for dilatant decompaction of the reservoir rock.

Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is an environmental depiction illustrating use of the system of the present invention;

FIG. 2 is a cross-sectional illustration of the system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a device, i.e., wave generator, and method that improves upon existing devices and methods for increasing in-situ rock permeability in wells and reservoirs. In the following description, a wave generator system is generally referred to by reference numeral 10. The invention is disclosed in the drawings where FIG. 1 represents an environmental layout drawing of the device for increasing in situ rock permeability and FIG. 2 represents the wave generator with emitter.

As shown in FIG. 2, inventive wave generating system 10 for increasing in-situ rock permeability includes a wave generator 12, an emitter 14, a fluid channel 16 and a well reflector 18. According to the invention, the emitter 14 is made in the form of a conoid body 14a and a frustum body 14b hermetically connected together at their respective bases. The desired size and configuration of the emitter 14 is estimated on the basis of the condition of the desired wave conformance, and is connected at its smaller base to the wave generator 12 located generally superior to the emitter 14. The possibility of reciprocal wave displacement exists in the direction of the velocity vector of the wave motion. A wave momentum generator 12a is preferably used as the wave generator 12.

It is expedient when the emitter section 14 is made as decreasing along the fluid channel or its longitudinal axis 15 according to the following formula:

F_H0=(p_Ha_HF_H+p_Ka_KF_K)/(p_H0a_H0)

where: F_H0—is zero section of the emitter;

p_H0—is emitter material density in zero section;

a_H0—is wave velocity in the emitter material in zero section;

p_H—is emitter material density in current section;

a_H—is wave velocity in the emitter material in current section;

F_H—is current section of the emitter;

p_K—is channel fluid density;

a_K—is wave velocity in the fluid channel; and

F_K—is estimated section of the fluid channel according to emitter length.

The well wave reflector section 18 is preferably made as decreasing exponentially along the well axis. The well wave reflector 18 is preferably not less than ¼ of the generated wavelength in height. Implementation of the well reflector 18 according to such parameters provides more complete wave energy reflection into the decompacted stratum surrounding the well.

The emitter 14 preferably contains a coniform adapter 20 located in its center. Usage of the wave momentum generator 12a as the wave generator 12 allows to generate waves of a defined structure and to significantly reduce energy consumption due to the reduction of wave energy losses, as well as, to increase the device operational life as a whole. Due to the fact that the generator 12 is located above and installed with the possibility of reciprocal wave displacement in the direction of the velocity vector of the wave motion, the displacement takes place towards the bottom of a column of water in the fluid channel 16, to which the defined quantity of motion is transferred without energy loss in the wave. Implementation of the emitter 14 in the form of the conoid body 14a and the frustum body 14b hermetically connected together at their bases provides optimal concentration and transfer of the waves along the channel 16 due to which energy loss of the wave is reduced.

The coniform adapter 20 is installed in the central part of the emitter 14 which provides optimal wave transfer from the wave momentum generator 12a to the fluid channel 16 as a result of which the wave energy losses are reduced in the emitter 14 itself. Due to the fact that the section of the well wave reflector 18 is made as decreasing exponentially along the well axis, the wave conformance between the wave generated and the rock is provided as a result of which maximum wave energy transfer into the decompacted stratum is achieved.

The emitter section 14 is preferably made as variable and decreasing along its length according to a definite dependence, thus providing the wave conformance of the channel and more efficient operation of the device 10.

The system 10 for increasing in-situ rock permeability can be mounted using a hoisting mechanism 22, for example, an excavator, an autocrane, etc. The device comprises the wave device consisting of a wave generator 12, an emitter 14 made in the form of conoid body 14a and frustum body 14b hermetically connected together at their bases and estimated on the basis of the condition of the wave conformance. The emitter 14 contains the coniform adapter 20 located in the center of the emitter 14.

The smaller base of the frustum body 14b of the emitter 14 is connected to the wave generator 12 made in the form of the wave momentum generator 12a located above. The wave momentum generator is designed with the possibility of reciprocal wave displacement in the direction of the velocity vector of the wave motion.

A movable bearing 24 is fixed to the lower part of the conoid body 14a of the emitter 14. The upper part of the moveable bearing is made in the form of sphere for providing coincidence of axes at mounting of the device 10 on the well. A tube 26 extends from the moveable bearing 24 into the well. A fluid connection 28 is fixed to the tube 26, which fluid connection 28 is connected with the pumping main 30 for supplying process fluid under pressure into the well. The coniform well wave reflector 18 with the peak oriented toward the device 10 is located at the upper part of the well and connected with the wave generator 12 and the emitter 14 by means of the fluid channel 16 formed by the fluid filling the well.

The system 10 operates the following manner. The system 10 is mounted using a hoisting mechanism 22, for example, an excavator. A well 32 is drilled in the rock mass and a mineral stratum 34 is uncovered. The system 10 is connected to the high pressure pumping main 30 through the fluid connector 28 located in the movable bearing 24. The process fluid is supplied under pressure into the well 32, for example, by means of a high pressure pumping unit, through a check valve in the amount providing filling of the well till overflow.

After filling the well 32 and the emitter 14 with the process fluid, the coniform adapter 20 is constantly in contact with the process fluid and transfers reciprocal wave displacement in the direction of the velocity vector of the wave motion generator 12a. The waves are of a defined frequency which are transferred from the wave momentum generator 12a through the coniform adapter 20 as a result of which the displacement takes place towards the bottom of the column of process fluid due to transferring the quantity of the wave motion to it from the generator 12 through the coniform adapter 20.

A compression-rarefaction wave is reflected along the well axis upon reflection from the inner surface of the frustum body 14b. While passing through the conoid body 14a of the emitter 14, the compression-rarefaction wave is emitted to the fluid channel 16 with subsequent redirection by the well wave reflector 18 to the mineral stratum 34. Thus, the system 10 provides the conditions of the wave conformance in the zones of the section difference according to the equality of the wave (acoustic) impedance of the channels and maximum wave energy transfer into the decompacted stratum.

Operation of the system 10 allows to effect the process of dilatant decompaction of the rocks in situ thus significantly increasing rock permeability. Therefore, the proposed engineering solution allows to improve efficiency of the device operation and to provide sufficient rock permeability at energy consumption reduction and device operational life increase.

At the same time, wavelength is held commensurate with the thickness of the formation, while wave processing time is determined based on the specified length of the fracture being created in the formation, in accordance with the following formula:

L≥λ=T·a≥ΔÍ·n

where L is the thickness of the target formation;

λ is the wave length;

T is the wave processing time;

a is the wave velocity;

Δ Í is the increase in fracture length per wave passage;

N is the number of wave passages needed to achieve the specified fracture length.

In addition, the fluid waveguide cross-section changes towards the bottomhole in the wave emission zone per the following formula:

F_*o=(p_*a_*F_*+p_Ma_MF_M)/p_*oa_*o,

where:

F_*0 is the initial fluid waveguide cross-section;

p_x is the current fluid density;

a_* is the current wave velocity in the fluid;

F_* is the current fluid waveguide cross-section;

p_M is the density of the rock mass;

a_M is the wave velocity in the rock mass;

F_M is the cross-section of the rock mass impacted by the wave;

p_*o is the initial fluid density;

a_*o is the initial wave velocity in the fluid.

It is preferable that a wave be emitted along a fluid waveguide in a way that is in alignment with areas of cross-section change so that the acoustic impedances of wave guides are in equilibrium:

F_*op_*oa_*o=p_*a_*F_*+p_Ma_MF_M,

where: F_*o is the initial cross-section of the fluid waveguide;

p_*o is the initial fluid density;

a_*o is the initial wave velocity in the fluid;

p_* is the current fluid density;

a_* is the current wave velocity in the fluid;

F_* is the current fluid waveguide cross-section;

F_M is the cross-section of the rock mass impacted by the wave;

p_M is the density of the rock mass;

a_M is the wave velocity in the rock mass.

Since the action on the fluid by static pressure and by shock waves occurs simultaneously, losses of wave energy directed at the target formation are minimized, thereby significantly reducing the consumption of energy needed to run the process.

Since static pressure exceeds capillary pressure in pores of the most common size in the decompacting rock, the static pressure in the fluid comes into alignment with the capillary pressure of the rock, which drives the process of dilatant decompaction and enhances the permeability of the rock.

The dilatant process of rock fragmentation occurs via shear stress along the faces of crystals or blocks of crystals. As a result of this shear strain, the entire rock mass is covered with a uniform network of newly formed fractures, while existing fractures, pores and capillaries grow in size. The volume of the decompacted rock mass increases as a result of elastic compression of the neighboring rock mass.

It has been established experimentally that the process of dilatant decompaction is optimized when static pressure exceeds capillary pressure by at least 1.3 times. Since the selected shock wave amplitude is equal to or greater than compressive or tensile stress, the necessary conditions are created for dilatant rock decompaction. It should be noted that the necessary condition for dilatant decompaction is the presence of unequal loading of that part of the rock mass that is covered by a wave at each moment in time—in particular the presence of tensile stresses caused by this disequillibrium in micro- and macrovolumes of the decompacted rock.

Wave length depends on the thickness of the target bed, while the wave treatment time is based on the pre-determined length of the fracture to be created in the bed, thereby ensuring that wave length is in conformity with the characteristics of the target rock. As a result, losses of wave energy through diffusion beyond the target bed are reduced and the process of permeability enhancement occurs more efficiently. In thin beds, wave length is restricted to a minimum value that is no less than the length of fractures created in the rock mass, since a low amplitude wave will not spread through such fractures.

Since the wave is emitted along a fluid waveguide in such a way that the wave conforms to differences in section thickness and remains in alignment with the wave (acoustic) impedance of the wave channel and the wave channel cross-section changes towards the bottom hole in the wave emission zone according to a specific formula which takes into account fluid density in the channel, wave velocity in the fluid and in the rock mass, and density of the rock, the process of permeability enhancement proceeds more efficiently.

The inventive method is carried out as follows. A well is drilled into the target rock mass, exposing a mineral deposit. A process fluid is injected into the well. Waves are emitted into the well from a surface-mounted system 10 from the generator 12 through the emitter 14 and travel along a fluid waveguide with a variable cross-section. The waves are then directed by a reflector towards the target rock formation or stratum. The waves conform to differences in section thickness and remain in alignment with the wave (acoustic) impedance of the waveguide, creating the conditions for full wave transmission.

The process fluid is simultaneously impacted by static pressure and shock waves, such that the static pressure exceeds by at least 1.3 times the capillary pressure in pores of the most common size within the rock mass, and compensates for the rock pressure forcing fluid from its pores and capillaries towards the wellbore. Shock wave amplitude is selected so it is equal to or greater than the compressive or tensile stress along the plane of the target bed, thereby creating dilatant deformation and decompaction of the rock mass under conditions of non-uniform loading within microvolumes resulting from the difference in rock pressure at the lower and upper surfaces of that portion of the rock mass that is affected by wave activity, along with non-conformities within these microvolumes resulting from differences in capillary pressure due to variations in pore size and the structural-wave non-uniformities within the rock mass.

The optimum wave length is selected to be commensurate with the bed thickness, while wave treatment time is based on the specified length of the fracture. The selection of these features minimizes the loss of wave energy beyond the target bed and increases the efficiency of the permeability enhancement process.

The process of dilatant rock decompaction occurs at stress values that are lower than those associated with traditional compression crushing, thereby reducing energy consumption. For example, at tensile stresses of up to 5 MPa in granite, stresses of 0.5 to 3 MPa applied along a plane perpendicular to the direction of the tensile stress will be sufficient to produce dilatant shear of crystal faces.

The process of rock decompaction and permeability enhancement is controlled from the surface based on rock permeability/fluid absorption during injection of the fluid into the well. Thus, general permeability at the start of the process will range up to 50 mD for low-permeability rock, which under the simultaneous impact of waves and static pressure will gradually increase to 1000 mD or greater, depending on technological requirements. This process may take several minutes to several hours, depending on rock hardness. Therefore, the proposed technical solution will make it possible to improve the efficiency of the in-situ permeability enhancement and rock decompaction process while reducing energy consumption and operating costs.

Although several embodiments have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention.

Claims

1. An apparatus for in-situ permeability enhancement of reservoir rock, comprising:

a wave generator operably connected to a coniform adapter;

an emitter housing having a first end attached to the wave generator and surrounding the coniform adapter; and

a moveable bearing and fluid tube fluidly connected to a second end of the emitter housing, wherein the emitter housing and fluid tube define a fluid channel.

2. The apparatus of claim 1, wherein the emitter housing comprises a hollow conoid body hermetically sealed to a hollow frustum body at their widest points.

3. The apparatus of claim 1, wherein an emitter section is configured as decreasing along a longitudinal axis of the fluid channel according to the following formula:

FH0=(pHaHFH+pKaKFK)/(pH0aH0)

where:

FH0—is a zero section of the fluid channel;

pH0—is process fluid density in the zero section;

aH0—is wave velocity in the process fluid in the zero section;

FH—is a current section of the fluid channel;

pH—is process fluid density in the current section;

aH—is wave velocity in the process fluid in the current section;

FK—is an estimated section of the fluid channel according to a length of the fluid channel;

pK—is process fluid density in the estimated section; and

aK—is wave velocity in the estimated section.

4. The apparatus of claim 1, further comprising a coniform well wave reflector disposed in a wellbore proximate to a mineral stratum in the reservoir rock and associated with the fluid channel.

5. The apparatus of claim 4, wherein the coniform well wave reflector has a height that is not less than ¼ of a wavelength generated by the emitter.

6. The apparatus of claim 4, wherein a fluid waveguide cross-section changes towards a bottom of the wellbore according to the following formula:

F*o=(p*a*F*+pMaMFM)/p*oa*o,

where:

F*o is the initial fluid waveguide cross-section;

p*o is the initial process fluid density;

a*o is the initial wave velocity in the process fluid;

F* is the current fluid waveguide cross-section;

p* is the current process fluid density;

a* is the current wave velocity in the process fluid;

FM is the cross-section of the rock mass impacted by the wave;

pM is the density of the rock mass; and

aM is the wave velocity in the rock mass.

7. A method for in-situ permeability enhancement of reservoir rock, comprising the steps of:

providing a wave generating system having a wave generator operably connected to a coniform adapter, an emitter housing having a first end attached to the wave generator and surrounding the coniform adapter, a moveable bearing and fluid tube fluidly connected to a second end of the emitter housing, and a well wave reflector disposed in a wellbore in fluid communication with the fluid tube;

filling the emitter housing, fluid tube, and wellbore with a process fluid;

generating an energy wave in the process fluid via the wave generator and coniform adaptor; and

redirecting the energy wave from the wellbore into a mineral stratum in the reservoir rock proximate to the wellbore.

8. The method of claim 7, wherein the energy wave is at a wavelength commensurate with a thickness of the mineral stratum, while a processing time is determined based on a specified length of a fracture being created in the mineral stratum, according to the following formula:

L≥λ=T·a≥ΔÍ·n

Where:

L is the thickness of the target formation;

λ is the wavelength;

T is the wave processing time;

a is the wave velocity;

Δ Í is the increase in fracture length per wave passage; and

N is the number of wave passages needed to achieve the specified fracture length.

9. The method of claim 7, wherein the energy wave is in alignment with areas of cross-section change so that acoustic impedances of wave guides are in equilibrium, according to the following formula:

F*op*oa*o=p*a*F*+pMaMFM

where:

F*o is the initial cross-section of a fluid waveguide;

p*o is the initial process fluid density;

a*o is the initial wave velocity in the process fluid;

p* is the current process fluid density;

a* is the current wave velocity in the process fluid;

F* is the current fluid waveguide cross-section;

FM is the cross-section of the rock mass impacted by the wave;

pM is the density of the rock mass;

aM is the wave velocity in the rock mass.

10. The method of claim 7, wherein the energy wave simultaneously transfers both static pressure and shock waves such that: the static pressure exceeds capillary pressure in pores of the most common size in the reservoir rock by no less than 1.3 times; and the shock wave amplitude is equal to or greater than the compressive or tensile stress necessary for dilatant decompaction of the reservoir rock.