Acid fracturing system and method for three-dimensional crack of stratum rock sample

Abstract

The invention provides an acid fracturing system and method for a three-dimensional fracture of a stratum rock sample. The system comprises fracturing equipment, a liquid injection system and collection equipment, the fracturing equipment comprises a confining pressure kettle body, an inner cavity is formed in the confining pressure kettle body and used for containing a rock sample to be tested, and a water injection opening is formed in the rock sample to be tested; the liquid injection system comprises a first container for bearing acid fracturing fluid and a second container for bearing hydraulic fracturing fluid, and the top of the first container and the top of the second container are connected with a water injection opening in a rock sample to be tested through an acid-resistant pipeline; the acquisition equipment comprises oil pressure equipment and a pressure acquisition box; the oil pressure equipment is used for controlling the confining pressure kettle body to apply triaxial stress to the rock sample to be tested at a preset stress value; the pressure acquisition box is used for monitoring and recording the triaxial stress applied to the rock sample to be measured by the confining pressure kettle body. By means of the fracturing system, the influence degree of the fracture net form on the flow conductivity of the acid etching fracture after stratum rock sample crack initiation can be accurately determined under the complex stress condition.

Description

Technical Field

[0001] The invention relates to the field of petroleum and natural gas engineering, and in particular to an acid fracturing system and method for three-dimensional cracks in formation rock samples. Background Art

[0002] Acid fracturing is an oil and gas production process in the field of petroleum and natural gas engineering. It is widely used in carbonate and sandstone reservoirs by establishing a seepage channel between the oil-bearing area and the wellbore and using acid fracturing fluid to reduce the flow resistance of the seepage channel to form a stable production supply. + Concentrated acid fracturing fluid is pumped into the formation to allow H + It undergoes a dissolution reaction with the calcite and dolomite in the stratum. Since there are insoluble mineral particles and special etching structures in the cracks produced by the dissolved calcite and dolomite, the crack surface will have a self-supporting effect, which can provide a more favorable leakage channel for oil and gas.

[0003] However, the acid fracturing process is greatly affected by the formation conditions. The effect of the acid fracturing fluid will be affected by the mineral composition, Young's modulus and compressive strength of the rock. In addition, under the conditions of high temperature and high closure stress, the acid fracturing fluid reacts too quickly with the rock, which will lead to the problem of a short action distance of the acid fracturing fluid, resulting in high permeability fractures only concentrated near the wellbore, while the transformation effect of the far wellbore is poor. Therefore, the existing technology has improved and perfected the acid fracturing technology from multiple angles, and strengthened the compatibility of the acid fracturing technology with specific formations through acid fracturing numerical simulation and acid fracturing indoor experiments, effectively achieving increased and stable production of oil and gas.

[0004] Since the indoor experiments of acid fracturing technology have high requirements for equipment, the existing technology usually focuses on rock plate dissolution experiments and rock plate flow conduction experiments. By using professional equipment such as API standard flow chambers, fluid rheometers, acid-resistant pipelines and optical topography scanners, the morphology of the rock plate after acid application is scanned and the flow conduction capacity of the rock plate after acid etching is tested. In the process of acid fracturing, the existing technology uses the method of merging two rock plates as a single fracture surface to test the flow conduction capacity, only considering the closing stress perpendicular to the fracture surface, and only focusing on the mass transfer of acid fracturing fluid on a single fracture surface, without considering the comprehensive influence of the three-dimensional fracture network of the real formation on acid fracturing under the action of hydraulic fracturing, ignoring the influence of the complex morphology of artificial fractures in the formation on the flow conduction capacity, and the influence of three-dimensional stress on the flow conduction capacity of three-dimensional fractures.

[0005] There is currently no effective solution for how to accurately determine the influence of the fracture network morphology of formation rock samples after fracture on the conductivity of acid-etched fractures under complex stress conditions. Summary of the invention

[0006] The present specification provides an acid fracturing system and method for three-dimensional fractures in formation rock samples, which can accurately determine the influence of the fracture network morphology of the formation rock sample after fracture initiation on the conductivity of the acid-etched fracture under complex stress conditions, thereby solving the technical problem of inaccurate acid fracturing prediction caused by the inability to consider the integrated simulation of fracture initiation and acidization in the acid fracturing experiment.

[0007] This specification provides an acid fracturing system and method for three-dimensional fractures in formation rock samples, which is implemented as follows:

[0008] An acid fracturing system for three-dimensional fractures in formation rock samples, comprising: a fracturing device, a fluid injection system connected to the fracturing device, and a collection device electrically connected to the fracturing device and the fluid injection system, wherein:

[0009] The fracturing equipment comprises: a confining pressure kettle body, wherein an inner cavity is provided in the confining pressure kettle body, wherein the inner cavity is used to place a rock sample to be tested, and a water injection port is provided on the rock sample to be tested;

[0010] The injection system comprises: a first container carrying acid fracturing fluid and a second container carrying hydraulic fracturing fluid, the tops of the first container and the second container being connected to the water injection port on the rock sample to be tested through an acid-resistant pipeline;

[0011] The collection equipment includes: an oil pressure device and a pressure collection box; the oil pressure device is used to control the confining pressure kettle body to apply triaxial stress to the rock sample to be tested with a preset stress value; the pressure collection box is used to monitor and record the triaxial stress applied by the confining pressure kettle body to the rock sample to be tested.

[0012] In one embodiment, the inner cavity of the confining pressure autoclave body is a cube, wherein the six faces of the inner cavity of the cube are composed of six groups of pads and thermal insulation cotton, each group of pads includes a first pad, a second pad and a third pad, the first pad has a side length of 300 mm, the second pad has a side length of 200 mm, the third pad has a side length of 100 mm, the first pad, the second pad and the third pad are all 5 mm thick, the first pad, the second pad and the third pad are placed in sequence from the outside to the inside to form a face of the inner cavity of the confining pressure autoclave body, and the six groups of pads are combined to form the inner cavity of the cube; the thermal insulation cotton is arranged on the outside of the inner cavity of the cube composed of the six groups of pads.

[0013] In one embodiment, according to the size of different rock samples to be tested, the size of the inner cavity of the cube is adjusted by placing the combination of the pads. When the side length of the rock sample to be tested is 100 mm, the first pad, the second pad and the third pad in the six groups of pads are placed in the confining pressure autoclave from the outside to the inside in sequence to form an inner cavity of the cube with a side length of 100 mm. When the side length of the rock sample to be tested is 200 mm, the first pad and the second pad in the six groups of pads are placed in the confining pressure autoclave from the outside to the inside in sequence to form an inner cavity of the cube with a side length of 200 mm.

[0014] In one embodiment, the bottom of the first container is connected to the top of the second container through an acid-resistant pipeline, the upper end of the first container carries acidified fracturing fluid, and the lower end carries hydraulic fracturing fluid provided by the second container, and a piston top plate is provided inside the first container to separate the fracturing fluids at the upper and lower ends.

[0015] In one embodiment, the liquid injection system further comprises: a circulating water device and a liquid storage tank;

[0016] The bottom of the second container is connected to the circulating water device through an acid-resistant pipeline, and a piston top plate is arranged inside the second container, with hydraulic fracturing fluid carried on the upper end and clean water pumped into the circulating water device carried on the lower end;

[0017] The top of the second container is also connected to the liquid storage tank, which stores hydraulic fracturing fluid. When the hydraulic fracturing fluid in the second container is insufficient, the liquid storage tank is pressurized by the air compressor at the bottom to drive the hydraulic fracturing fluid in the liquid storage tank into the second container.

[0018] In one embodiment, it further includes: a controller;

[0019] A first valve is provided on the acid-resistant pipeline between the first container and the water injection port on the rock sample to be tested, a second valve is provided on the acid-resistant pipeline between the first container and the second container, and a third valve is provided on the acid-resistant pipeline between the second container and the water injection port on the rock sample to be tested;

[0020] The controller is electrically connected to the acquisition device; the first valve, the second valve and the third valve are electrically connected to the controller; the controller is also electrically connected to the circulating water device; the controller performs on-off control of the first valve, the second valve and the third valve according to the fracturing fluid medium set in the acquisition device, and performs injection control on the circulating water device, so as to alternately inject acid fracturing fluid and hydraulic fracturing fluid into the injection port on the rock sample to be tested;

[0021] A flow meter and a fluid pressure gauge are also provided on the acid-resistant pipeline between the second container and the third valve, and the flow meter and the fluid pressure gauge are electrically connected to the controller; the controller collects data from the flow meter and the fluid pressure gauge, and controls the flow rate and fluid pressure of the hydraulic fracturing fluid in the second container according to the flow parameters set by the collection equipment.

[0022] This specification also provides a method for acid fracturing using the above-mentioned acid fracturing system for three-dimensional fractures in formation rock samples, comprising:

[0023] Obtain the rock sample to be tested of preset size and half side length of the rock sample to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore;

[0024] Applying triaxial stress to the rock sample to be tested at a preset stress value;

[0025] Connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameters of the hydraulic fracturing fluid in the second container through the acquisition equipment;

[0026] Injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording a fluid pressure curve during the fracturing process through a collection device, and stopping the injection of the hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first predetermined time length;

[0027] Injecting clean water into the rock sample to be tested after fracturing at a preset flow rate, and recording the fluid pressure curve during the injection of clean water through a collection device, stopping the injection of clean water when the change amplitude of the fluid pressure curve during the injection of clean water is less than a second preset value and reaches a second preset time, determining an average value of a curve segment in which the change amplitude of the fluid pressure curve during the injection of clean water is less than the second preset value and reaches a second preset time as the pressure difference value of the first water injection port, and calculating the conductivity of the rock sample to be tested before acidification according to the determined pressure difference value of the first water injection port;

[0028] Connecting the acid-resistant pipeline between the first container and the rock sample to be tested, injecting acid fracturing fluid into the rock sample to be tested at a preset flow rate, and stopping the injection of the acid fracturing fluid when the injection amount of the acid fracturing fluid reaches the preset injection amount;

[0029] Injecting clean water into the rock sample to be tested after fracturing and acidification at a preset flow rate, and recording the fluid pressure curve during the injection of clean water through a collection device, stopping the injection of clean water when the change amplitude of the fluid pressure curve during the injection of clean water is less than a third preset value and reaches a third preset time, determining an average value of a curve segment in which the change amplitude of the fluid pressure curve during the injection of clean water is less than the third preset value and reaches a third preset time as the pressure difference value of the second water injection port, and calculating the conductivity of the rock sample to be tested after acidification according to the determined pressure difference value of the second water injection port;

[0030] The influence of acid fracturing on the conductivity of the rock sample to be tested is determined according to the conductivity of the rock sample to be tested before acidizing and the conductivity of the rock sample to be tested after acidizing.

[0031] In one embodiment, calculating the conductivity of the rock sample to be tested before acidizing according to the determined pressure difference value of the first water injection port includes:

[0032] Obtaining the flow rate of the injected fluid before acidizing and the viscosity of the injected fluid before acidizing;

[0033] The conductivity of the rock sample before acidizing was calculated according to the following formula:

[0034]

[0035] Among them, KW b is the conductivity of the fractures on the rock sample before acidizing, q b is the flow rate of the injected fluid before acidification, μ b is the viscosity of the injected fluid before acidizing, r e is the half side length of the rock sample to be tested, r w is the radius of the wellbore, Δp wb is the pressure difference value of the first water injection port.

[0036] In one embodiment, calculating the conductivity of the rock sample to be tested after acidizing according to the determined pressure difference value of the second water injection port includes:

[0037] Obtaining the flow rate of the injected fluid after acidizing and the viscosity of the injected fluid after acidizing;

[0038] The conductivity of the rock sample after acidification is calculated according to the following formula:

[0039]

[0040] Among them, KW a is the conductivity of the fractures on the rock sample after acidification, q a is the flow rate of the injected fluid after acidification, μ a is the viscosity of the injected fluid after acidification, r e is the half side length of the rock sample to be tested, rw is the radius of the wellbore, Δp wa is the pressure difference value of the second water injection port.

[0041] An electronic device comprises a processor and a memory for storing instructions executable by the processor, wherein the steps of the above method are implemented when the processor executes the instructions.

[0042] A computer-readable storage medium stores a computer program / instruction, which implements the steps of the above method when executed by a processor.

[0043] The acid fracturing system and method for three-dimensional fractures in formation rock samples provided in the present application obtain rock samples to be tested of preset sizes and half side lengths of the rock samples to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore; apply triaxial stress to the rock samples to be tested at preset stress values; connect the acid-resistant pipeline between the second container and the rock samples to be tested, and set the flow parameters of the hydraulic fracturing fluid in the second container through a collection device; inject hydraulic fracturing fluid into the rock samples to be tested at a preset flow rate, perform fracturing on the rock samples to be tested, and record the fluid pressure curve during the fracturing process through a collection device, and stop the injection of hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first preset time; inject clean water into the rock samples to be tested after fracturing at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a collection device, and stop the injection of clean water when the change amplitude of the fluid pressure curve during the clean water injection process is less than a second preset value and reaches a second preset time, and determine that the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches a second preset time. The average value of the curve segment from the first container to the second predetermined time length is used as the pressure difference value of the first water injection port, and the conductivity of the rock sample to be tested before acidification is calculated according to the determined pressure difference value of the first water injection port; the acid-resistant pipeline between the first container and the rock sample to be tested is connected, and the acid fracturing fluid is injected into the rock sample to be tested, and when the injection amount of the acid fracturing fluid reaches the preset injection amount, the injection of the acid fracturing fluid is stopped; clean water is injected into the rock sample to be tested after fracturing and acidification at a preset flow rate, and the fluid pressure curve during the injection of clean water is recorded by the acquisition equipment, and when the clean water is injected When the change amplitude of the fluid pressure curve during the process is less than the third preset value and reaches the third preset time, the injection of clean water is stopped, and the average value of the curve segment in which the change amplitude of the fluid pressure curve during the injection of clean water is less than the third preset value and reaches the third preset time is determined as the pressure difference value of the second water injection port, and the conductivity of the rock sample to be tested after acidification is calculated according to the determined pressure difference value of the second water injection port; the influence of acid fracturing on the conductivity of the rock sample to be tested is determined according to the conductivity of the rock sample to be tested before acidification and the conductivity of the rock sample to be tested after acidification. The above scheme can accurately determine the influence of the fracture network morphology of the formation rock sample after fracturing on the conductivity of the acid-etched fracture under complex stress conditions, thereby solving the technical problem of inaccurate acid fracturing prediction caused by the inability to consider the integrated simulation of fracturing and acidification in the acid fracturing experiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of this specification, the drawings required for use in the embodiments will be briefly introduced below. The drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0045] Figure 1 It is a structural schematic diagram of an acid fracturing system for three-dimensional fractures of a formation rock sample provided by the present application;

[0046] Figure 2 This is a method flow chart of an embodiment of the acid fracturing method for three-dimensional fractures in formation rock samples provided by the present application;

[0047] Figure 3 It is a schematic diagram of the effect of the acid fracturing system for three-dimensional fractures in formation rock samples provided by the present application on a rock sample to be tested;

[0048] Figure 4 It is a schematic diagram of the curve of fluid pressure change over time before and after acidification provided by the present application;

[0049] Figure 5 It is a schematic diagram of the relationship between the conductivity and the closure stress before and after acidification provided in the present application;

[0050] Figure 6 This is a hardware structure block diagram of an electronic device for an acid fracturing method for three-dimensional fractures in a formation rock sample provided in the present application. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this specification.

[0052] In view of the problem that the existing acid fracturing technology does not take into account the comprehensive influence of the three-dimensional fracture network of the real formation under the action of hydraulic fracturing on the acid fracturing, and ignores the influence of the complex morphology of artificial fractures in the formation on the conductivity and the influence of three-dimensional stress on the conductivity of three-dimensional fractures, in this example, a system and method for acid fracturing three-dimensional fractures of formation rock samples are provided.

[0053] Specifically, Figure 1As shown, in this example, an acid fracturing system for three-dimensional fractures of formation rock samples is provided, and the acid fracturing system may include: a fracturing device, a fluid injection system connected to the fracturing device, and a collection device electrically connected to the fracturing device and the fluid injection system, wherein: the fracturing device includes: a confining pressure kettle body 16, and an inner cavity 19 is provided in the confining pressure kettle body, wherein the inner cavity 19 is used to place a rock sample 21 to be tested, and a water injection port 20 is provided on the rock sample 21 to be tested; the fluid injection system includes: a carrier for acid fracturing fluid 2 The first container 3 and the second container 13 carrying the hydraulic fracturing fluid 8, the tops of the first container 3 and the second container 13 are connected to the water injection port 20 on the rock sample 21 to be tested through the acid-resistant pipeline 1; the collection equipment includes: an oil pressure device 22 and a pressure collection box 24; the oil pressure device 22 is used to control the confining pressure kettle body 16 to apply triaxial stress to the rock sample 21 to be tested with a preset stress value; the pressure collection box 24 is used to monitor and record the triaxial stress applied by the confining pressure kettle body 16 to the rock sample 21 to be tested.

[0054] Furthermore, the inner cavity 19 in the confining and pressure kettle body 16 can be a cube, a rectangular parallelepiped, a sphere, etc. Preferably, it can be a cube. Specifically, taking the inner cavity 19 in the confining and pressure kettle body 16 as a cube as an example, the six faces of the inner cavity 19 of the cube are composed of six groups of pads 18 and thermal insulation cotton 17, each group of pads 18 includes a first pad, a second pad and a third pad, the first pad has a side length of 300 mm, the second pad has a side length of 200 mm, the third pad has a side length of 100 mm, and the first pad, the second pad and the third pad are all 50 mm thick. The first pad, the second pad and the third pad are placed in the confining and pressure kettle body 16 from the outside to the inside to form one face of the inner cavity 19, and the six groups of pads 18 are combined to form the inner cavity 16 of the cube; the thermal insulation cotton 17 is arranged on the outside of the inner cavity 19 of the cube composed of the six groups of pads 18.

[0055] Specifically, a heating device is also provided in the confining pressure kettle body 16. Before the rock sample 21 to be tested is subjected to acid fracturing, the rock sample 21 to be tested is heated to a preset temperature. The thermal insulation cotton 17 is used to prevent the temperature of the rock sample 21 to be tested from dissipating. The triaxial stress applied by the hydraulic equipment 22 to the rock sample 21 to be tested can realize independent loading control of stresses in three directions.

[0056] Furthermore, according to the sizes of the different rock samples 21 to be tested, the size of the inner cavity 19 of the cube is adjusted by placing the combination of the pads 18. Specifically, when the side length of the rock sample 21 to be tested is 100 mm, the first pad, the second pad and the third pad in the six groups of pads 18 are placed in the confining pressure kettle body 16 from the outside to the inside in turn to form the inner cavity 19 of the cube with a side length of 100 mm. When the side length of the rock sample 21 to be tested is 200 mm, the first pad and the second pad in the six groups of pads 18 are placed in the confining pressure kettle body 16 from the outside to the inside in turn to form the inner cavity 19 of the cube with a side length of 200 mm.

[0057] However, it is worth noting that the above-mentioned number of groups of pads, the number of pads in each group, the size and shape of the pads, the combination of the pads, the placement of the pads in the inner cavity and the size of the inner cavity are merely exemplary descriptions. In actual implementation, the appropriate number of groups, quantity, size, shape, combination and placement can be selected according to actual needs, and the present application does not limit this.

[0058] Furthermore, the bottom of the first container 3 is connected to the top of the second container 13 through an acid-resistant pipeline 1, the upper end of the first container 3 carries the acidified fracturing fluid 2, and the lower end carries the hydraulic fracturing fluid 8 provided by the second container 13, and a piston top plate is provided inside the first container 3 to separate the fracturing fluids at the upper and lower ends.

[0059] Furthermore, the injection system also includes: a circulating water device 10; the bottom of the second container 13 is connected to the circulating water device 10 through an acid-resistant pipeline 1, and a piston top plate is arranged inside the second container 13, the upper end of which carries hydraulic fracturing fluid 8, and the lower end of which carries clean water pumped into the circulating water device 10; by pumping clean water into the second container 13 through the circulating water device 10, the piston top plate in the second container 13 can be driven to move up, so that the hydraulic fracturing fluid 8 at the upper end of the second container 13 enters the lower end of the first container 3 and the water injection port 20 of the rock sample 21 to be tested.

[0060] Furthermore, the flow rate change of the hydraulic fracturing fluid 8 in the upper part of the second container 13 can also be monitored by the flow rate change in the circulating water device 10. Specifically, when the clean water in the circulating water device 10 reaches the bottom, all the clean water in the circulating water device 10 enters the lower end of the second container 13, and the remaining amount of hydraulic fracturing fluid in the second container 13 is insufficient. In order to observe the flow rate change in the above-mentioned circulating water device 10, the material of the outer shell of the circulating water device 10 can be acrylic glass.

[0061] Furthermore, the injection system also includes: a liquid storage tank 14; the top of the second container 13 is connected to the liquid storage tank 14, and the liquid storage tank 14 stores hydraulic fracturing fluid 8; when the remaining amount of hydraulic fracturing fluid 8 at the upper end of the second container 13 is insufficient, the hydraulic valve 12 is opened, and the liquid storage tank 14 is pressurized by the air compressor 15 at the bottom, driving the hydraulic fracturing fluid 8 in the liquid storage tank 14 into the second container 13, and at the same time driving the clean water at the lower end of the second container 13 back to the circulating water device 10.

[0062] Specifically, the pre-configured hydraulic fracturing fluid 8 can be stored in the fluid storage tank 14 , and the concentration and viscosity of the hydraulic fracturing fluid 8 can be adjusted according to experimental needs.

[0063] Specifically, the material of the above-mentioned acid-resistant pipeline 1, the first container 3 and the second container 3 can be Harbin alloy material. However, it is worth noting that the above-mentioned material description for each device is only an exemplary description. In actual implementation, the appropriate material can be selected according to actual needs, and this application does not limit this.

[0064] Furthermore, the injection system also includes: a controller 11; a first valve 5 is provided on the acid-resistant pipeline 1 between the first container 3 and the water injection port 20 on the rock sample 21 to be tested, a second valve 4 is provided on the acid-resistant pipeline 1 between the first container 3 and the second container 13, and a third valve 6 is provided on the acid-resistant pipeline 1 between the second container 13 and the water injection port 20 on the rock sample 21 to be tested; the controller 11 is electrically connected to the acquisition equipment; the first valve 5, the second valve 4 and the third valve 6 are electrically connected to the controller 11; the controller 11 is also electrically connected to the circulating water device 10; the controller 11 controls the on-off of the first valve 5, the second valve 4 and the third valve 6 according to the fracturing fluid medium set by the acquisition equipment, and controls the injection of the circulating water device 10, so as to realize the alternating injection of acidified fracturing fluid 2 and hydraulic fracturing fluid 8 into the water injection port 20 on the rock sample 21 to be tested.

[0065] Specifically, in order to achieve the acidification of the rock sample 21 to be tested, the first valve 5 and the second valve 4 are opened, and the third valve 6 is closed. The controller 11 controls the circulating water device 10 to inject clean water into the lower end of the second container 13, drives the piston top plate inside the second container 13 to move up, so that the hydraulic fracturing fluid 8 at the upper end of the second container enters the lower end of the first container 3, and further drives the piston top plate in the first container 3 to move up, so that the acidified fracturing fluid 2 at the upper end of the first container 3 enters the water injection port 20 on the rock sample 21 to be tested through the acid-resistant pipeline 1, so as to achieve acidification of the rock sample 21 to be tested.

[0066] Specifically, in order to achieve the fracturing effect on the rock sample 21 to be tested, the third valve 6 is opened, the first valve 5 and the second valve 4 are closed, and the controller 11 controls the circulating water device 10 to inject clean water into the lower end of the second container 13, drives the piston top plate inside the second container 13 to move up, and allows the hydraulic fracturing fluid 8 at the upper end of the second container 13 to enter the water injection port 20 on the rock sample 21 to be tested.

[0067] Furthermore, a flow meter 7 and a fluid pressure gauge 9 are also provided on the acid-resistant pipeline 1 between the second container 13 and the third valve 6, and the flow meter 7 and the fluid pressure gauge 9 are electrically connected to the controller 11; the controller 11 collects data from the flow meter 7 and the fluid pressure gauge 9, and controls the flow rate and fluid pressure of the hydraulic fracturing fluid 8 in the second container 13 according to the flow parameters set by the collection equipment.

[0068] Furthermore, the acquisition device also includes: a data acquisition terminal 25 and a data processing terminal 26; the data acquisition terminal 25 collects the data transmitted from the controller 11 and the pressure acquisition box 24; the data processing terminal 26 processes the data transmitted from the controller 11 and the pressure acquisition box 24; in order to ensure the safe operation of the system, a voltmeter 23 is also provided at the port of the data processing terminal, and the voltmeter 23 is used to display the voltage of the entire system. When the voltage of the system exceeds the voltmeter limit, the system stops running.

[0069] This specification also provides a method for acid fracturing based on the acid fracturing system of the three-dimensional fractures of the formation rock sample, specifically, Figure 2 As shown, the acid fracturing method for three-dimensional fractures in a formation rock sample comprises the following steps:

[0070] S101: Obtain a rock sample to be tested of a preset size and a half side length of the rock sample to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore.

[0071] Specifically, rock samples exposed on the ground at the research site are collected to obtain rock samples to be tested, which are then cut, drilled and cemented in a simulated manner to form a cube with a preset side length.

[0072] S102: applying triaxial stress to the rock sample to be tested at a preset stress value.

[0073] Specifically, before fracturing the rock sample to be tested, an acidified fracturing fluid meeting a preset concentration and viscosity is added to a first container, a hydraulic fracturing fluid meeting a preset concentration and viscosity is added to a second container, and the injection equipment is connected to the fracturing equipment through an acid-resistant pipeline.

[0074] Furthermore, the inner cavity in the confining pressure autoclave is adjusted to be consistent with the size of the rock sample to be tested, the rock sample to be tested is placed in the inner cavity and heated to a preset temperature, and triaxial stress is applied to the rock sample to be tested through a collection device.

[0075] S103: connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameters of the hydraulic fracturing fluid in the second container through a collection device.

[0076] Specifically, the third valve is opened, the first valve and the second valve are closed, and the pumping flow rate of the hydraulic fracturing fluid is set through the acquisition equipment so that the hydraulic fracturing fluid enters the water injection port on the rock sample to be tested, so as to achieve fracturing of the rock sample to be tested.

[0077] S104: injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording the fluid pressure curve during the fracturing process through a data acquisition device, and stopping the injection of the hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first predetermined time.

[0078] S105: Inject clean water into the rock sample to be tested after fracturing at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a data acquisition device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than a second preset value and reaches a second preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches the second preset time, and use it as the pressure difference value of the first water injection port. Calculate the conductivity of the rock sample to be tested before acidification according to the determined pressure difference value of the first water injection port.

[0079] Specifically, before calculating the conductivity of the rock sample to be tested before acidizing according to the determined pressure difference value of the first water injection port, it is also necessary to obtain the flow rate of the injected fluid before acidizing and the viscosity of the injected fluid before acidizing, and then calculate the conductivity of the rock sample to be tested before acidizing according to the following formula based on the obtained flow rate of the injected fluid before acidizing, the viscosity of the injected fluid before acidizing and the pressure difference value of the water injection port before acidizing:

[0080]

[0081] Among them, KW b is the conductivity of the fractures on the rock sample before acidizing, q b is the flow rate of the injected fluid before acidification, μ b is the viscosity of the injected fluid before acidizing, r e is the half side length of the rock sample to be tested, r w is the radius of the wellbore, Δp wb is the pressure difference value of the first water injection port.

[0082] S106: connecting the acid-resistant pipeline between the first container and the rock sample to be tested, injecting acid fracturing fluid into the rock sample to be tested, and stopping the injection of the acid fracturing fluid when the injection amount of the acid fracturing fluid reaches a preset injection amount.

[0083] Specifically, the first valve and the second valve are opened, the third valve is closed, and the pumping flow rate of the hydraulic fracturing fluid is set through the acquisition equipment. The acidified fracturing fluid at the upper end of the first container is pushed by the hydraulic fracturing fluid at the lower end and enters the water injection port on the rock sample to be tested after fracturing, so as to achieve acidification of the rock sample to be tested.

[0084] S107: Inject clean water into the rock sample to be tested after fracturing and acidification at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a data acquisition device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than a third preset value and reaches a third preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the third preset value and reaches the third preset time, and use it as the pressure difference value of the second water injection port. Calculate the conductivity of the rock sample to be tested after acidification according to the determined pressure difference value of the second water injection port.

[0085] Specifically, before calculating the conductivity of the rock sample to be tested after acidizing according to the determined pressure difference value of the second water injection port, it is necessary to obtain the flow rate of the injected fluid after acidizing and the viscosity of the injected fluid after acidizing, and then calculate the conductivity of the rock sample to be tested after acidizing according to the following formula based on the obtained flow rate of the injected fluid after acidizing, the viscosity of the injected fluid after acidizing and the pressure difference value of the second water injection port:

[0086]

[0087] Among them, KW a is the conductivity of the fractures on the rock sample after acidification, q a is the flow rate of the injected fluid after acidification, μ a is the viscosity of the injected fluid after acidification, r e is the half side length of the rock sample to be tested, r w is the radius of the wellbore, Δp wa is the pressure difference value of the second water injection port.

[0088] S108: Determine the influence of acid fracturing on the conductivity of the rock sample to be tested according to the conductivity of the rock sample to be tested before acidizing and the conductivity of the rock sample to be tested after acidizing.

[0089] The acid fracturing system and method for three-dimensional fractures in the above-mentioned formation rock sample are specifically described below in conjunction with a specific embodiment. However, it is worth noting that this specific embodiment is only for better illustrating the present application and does not constitute an improper limitation on the present application.

[0090] In this example, an indoor experimental measurement system and method for acid fracturing of formation rock samples are provided, which can measure and compare the effects of indoor experiments on acid fracturing of formation rock samples in the field of oil and gas engineering. The experimental system and method mainly consist of two parts, namely the experimental system and the calculation method, which can be used to simulate the acid fracturing process of real formations, realize the integrated simulation of fracturing and acidizing of three-dimensional fractures of formation rock samples, and can also be used as an analysis method of acid fracturing, so that the experimental environment and results are closer to the real formation conditions, and provide a theoretical basis and foundation for field experiments in oil and gas engineering.

[0091] There are two main problems with existing acid fracturing indoor experiments: one is that it can only simulate a single fracture surface and cannot achieve the acidification of three-dimensional fractures; the other is that the fractures used in the experiment are not generated by hydraulic fracturing of real rock samples. In this case, a true triaxial stress loading device is used to apply triaxial confining pressure to the cube rock sample, and hydraulic fracturing fluid and acid fracturing fluid are alternately injected into the rock sample through the injection equipment to achieve fracturing and acidification of the rock sample. The experimental system also includes a collection device that can monitor and record the fluid pressure curve in real time, determine the fracturing pressure of the rock sample and the seepage pressure difference of the fracture according to the change value of the fluid pressure curve, input the seepage pressure difference, hydraulic parameters and rock sample parameters into the radial flow conductivity calculation formula, and calculate the conductivity of the rock sample before and after acidification. This method can quantitatively compare the effect of acid fracturing fluid on the three-dimensional fractures of the rock sample.

[0092] Specifically, the indoor experimental measurement system for acid fracturing of formation rock samples can be divided into injection equipment, fracturing equipment and collection equipment according to the functions of the modules, such as Figure 1 As shown, the system may include an acid-resistant pipeline 1, an acidizing fracturing fluid 2, a #1 intermediate container 3 (corresponding to the first container mentioned above), a second valve 4, a first valve 5, a third valve 6, a flow meter 7, a hydraulic fracturing fluid 8, a fluid pressure gauge 9, a circulating water device 10, an electric signal controller 11 (corresponding to the controller mentioned above), a hydraulic valve 12, a #2 intermediate container 13 (corresponding to the second container mentioned above), a liquid storage tank 14, an air compressor 15, a confining pressure kettle 16, thermal insulation cotton 17, a pad 18, a cube inner cavity 19, a water injection port 20, a rock sample 21, an oil pressure device 22, a voltmeter 23, a pressure collection box 24, a data collection terminal 25, and a data processing terminal 26.

[0093] Among them, the acid-resistant pipeline is made of Hastelloy alloy material, the acid-resistant pipeline includes an infusion pipeline and an adapter, a first valve is arranged on the acid-resistant pipeline between the #1 intermediate container and the water injection port of the rock sample, a second valve is arranged on the acid-resistant pipeline between the #1 intermediate container and the #2 intermediate container, and a third valve is arranged on the acid-resistant pipeline between the #2 intermediate container and the water injection port of the rock sample. The electric signal controller is electrically connected to the first valve, the second valve and the third valve, and the pumping of hydraulic fracturing fluid and acid fracturing fluid is realized through the cooperation of the adapter with the #1 intermediate container, the first valve, the second valve, the third valve and the water injection port.

[0094] Specifically, the #1 intermediate container and the #2 intermediate container are both made of Harbin alloy material. The tops of the #1 intermediate container and the #2 intermediate container are connected to the water injection port of the rock sample through acid-resistant pipelines. The upper part of the #1 intermediate container stores acid fracturing fluid, and the lower part is connected to the #2 intermediate container through the acid-resistant pipeline 1 and the second valve. The upper part of the #2 intermediate container stores hydraulic fracturing fluid, and the lower part is connected to the circulating water device. Piston top plates are provided in the #1 intermediate container and the #2 intermediate container to ensure that the fluids in the upper and lower parts will not be mixed.

[0095] Furthermore, when it is necessary to pump acidified fracturing fluid, the hydraulic fracturing fluid provided by the #2 intermediate container is pumped into the lower part of the #1 intermediate container, driving the acidified fracturing fluid in the upper part of the #1 intermediate container into the acid-resistant pipeline, and the first valve and the second valve are opened and the third valve is closed through the electric signal controller, so that the acidified fracturing fluid is pumped into the water injection port of the rock sample. This process can achieve the acidification of the rock sample. When it is necessary to pump hydraulic fracturing fluid, the fluid supply equipment is mainly completed by the #2 intermediate container. The first valve and the second valve are closed and the third valve is opened through the electric signal controller, so that the hydraulic fracturing fluid in the #2 intermediate container enters the water injection port of the rock sample as the only fracturing fluid medium. The concentration and viscosity of the above-mentioned acidified fracturing fluid 2 and hydraulic fracturing fluid can be adjusted according to the experimental plan.

[0096] Furthermore, in order to facilitate the use and storage of hydraulic fracturing fluid, the top of the #2 intermediate container is connected to the fluid storage tank through an infusion pipeline, and the fluid parameters of the hydraulic fracturing fluid can be configured in the fluid storage tank. After the hydraulic fracturing fluid is configured, the hydraulic valve is opened, and the air compressor at the bottom of the fluid storage tank is used to increase the pressure, drive the top plate in the fluid storage tank to rise, and pump the hydraulic fracturing fluid into the #2 intermediate container.

[0097] Furthermore, the flow rate changes of the hydraulic fracturing fluid in the upper part of the #2 intermediate container can be monitored based on the flow rate changes in the circulating water device. When the hydraulic fracturing fluid in the upper part of the #2 intermediate container is insufficient, the clean water in the circulating water device will also bottom out at the same time. In the process of pumping the hydraulic fracturing fluid in the storage tank into the upper part of the #2 intermediate container, the piston top plate in the #2 intermediate container will be driven to move downward, so that the clean water in the lower part of the #2 intermediate container will return to the circulating water device. The outer shell of the circulating water device is made of acrylic glass, and the flow rate changes of the liquid inside the circulating water device can be observed.

[0098] Furthermore, a flow meter and a fluid pressure gauge are provided at the outlet of the #2 intermediate container, and the flow meter and the fluid pressure gauge are electrically connected to the electric signal controller. Changes in the flow rate and fluid pressure of the #2 intermediate container are collected and recorded through the electric signal controller and the collection device.

[0099] Furthermore, in the acquisition equipment, the oil pressure device serves as a confining pressure control device of the fracturing equipment to apply triaxial stress to the rock sample. The triaxial stress can be independently set by the acquisition equipment in three directions. The pressure acquisition box can monitor and collect the triaxial stress and transmit the final data to the data acquisition end and the data processing end.

[0100] Furthermore, the fracturing equipment is a confining pressure autoclave made of metal, and a cubic inner cavity for placing rock samples is provided inside the confining pressure autoclave. The outermost layer of the inner cavity is provided with thermal insulation cotton to prevent the temperature of the rock sample from dropping after heating. Different sizes of pads are fitted to the inner side of the thermal insulation cotton, and the side lengths of the pads are 300mm, 200mm, and 100mm respectively.

[0101] Specifically, the pads can be placed in combination according to the different sizes of rock samples to adjust the size of the inner cavity. When the side length of the rock sample to be fractured is 100 mm, the three sizes of pads are placed in the center of the confining pressure vessel from large to small. When the side length of the rock sample to be fractured is 200 mm, take out the 100 mm pad, and so on.

[0102] Furthermore, the acid fracturing process of the formation rock sample can be realized by the indoor experimental measurement system of the formation rock sample acid fracturing as follows:

[0103] S1: The outcrops on the ground at the research site were collected, cut, drilled and cemented as simulated to form cubic rock samples with a side length of 100 mm to 300 mm.

[0104] S2: Add acid fracturing fluid and hydraulic fracturing fluid of designed concentration and viscosity into the #1 intermediate container and the #2 intermediate container respectively, and connect the injection equipment and the fracturing equipment through acid-resistant pipelines.

[0105] S3: Apply triaxial stress to the rock sample through the oil pressure device in the acquisition equipment.

[0106] S4: Adjust the valve switch status of the acid-resistant pipeline, adjust the fracturing fluid medium to hydraulic fracturing fluid through the acquisition equipment, and set the fluid parameters.

[0107] S5: Inject hydraulic fracturing fluid into the water injection port of the rock sample to crack the rock, record the fluid pressure curve, and stop injecting the hydraulic fracturing fluid.

[0108] S6: clean water is injected into the rock sample after fracturing. The fluid pressure curve after pressure start will be kept at a horizontal stage. After the fluid pressure curve is stable for a preset time, the injection system is closed, the fluid pressure curve is recorded, and the average value of the fluid pressure curve in the stable stage is taken as the first average value. The conductivity of the rock sample before acidizing is calculated based on the first average value.

[0109] Specifically, the conductivity of the rock sample before acidizing can be calculated according to the following formula:

[0110]

[0111] Among them, KW b is the conductivity of the fractures on the rock sample before acidizing, q b is the flow rate of the injected fluid before acidification, μ b is the viscosity of the injected fluid before acidizing, r e is the effective radius of the rock sample, i.e. half the length of the side of the rock sample, r w is the radius of the wellbore, Δp wb is the pressure difference value at the injection port, that is, the first average value mentioned above.

[0112] S7: Adjust the switch state of the acid-resistant pipeline valve, set the fracturing fluid medium to acidized fracturing fluid, open the injection system, inject the acidified fracturing fluid into the water injection port of the rock sample, and stop injecting the acidified fracturing fluid after the rock sample is acidified.

[0113] S8: injecting clean water into the rock sample after fracturing and acidification, recording the fluid pressure curve, taking the average value of the fluid pressure curve in the stable stage as the second average value, and calculating the conductivity of the rock sample after acidification based on the second average value.

[0114] Specifically, the conductivity of the rock sample after acidizing can be calculated according to the following formula:

[0115]

[0116] Among them, KW a is the conductivity of the fractures on the rock sample after acidification, q a is the flow rate of the injected fluid after acidification, μ ais the viscosity of the injected fluid after acidification, r e is the effective radius of the rock sample, i.e. half the length of the side of the rock sample, r w is the radius of the wellbore, Δp wa is the pressure difference value at the injection port, that is, the second average value mentioned above.

[0117] S9: Compare the difference in conductivity of the rock samples before and after acidizing to evaluate the effect of acidizing and fracturing of the rock samples.

[0118] In the above example, hydraulic fracturing fluid and acid fracturing fluid are alternately injected into the rock sample to achieve fracturing and acidizing of the rock sample. The conductivity of the rock sample before and after acidizing is determined based on the seepage pressure difference, hydraulic parameters and parameters of the rock sample to be tested. This scheme can accurately determine the influence of the fracture network morphology of the formation rock sample after fracturing on the conductivity of the acid-etched fracture under complex stress conditions, thereby solving the problem that the acid fracturing experiment cannot consider the integrated simulation of fracturing and acidizing.

[0119] The acid fracturing method for the three-dimensional fractures of the above-mentioned formation rock sample is described as follows by taking a specific example:

[0120] S1: First, rock samples are collected. Rock samples from the ground outcrops in the on-site block are used as standard samples. Since acid fracturing is currently mostly used in carbonate rock and sandstone reservoirs, it is more appropriate to use such samples. After the outcrop rock samples are collected, they are cut and processed. According to the experimental plan, cube rock samples with a side length of 100mm to 300mm are selected, and simulated drilling is performed on the rock samples to form a wellbore with a fixed length and diameter in the middle of the rock sample. The wellbore and the metal wellbore are bonded with high-strength adhesive materials. At this time, the fracturing rock sample is ready. After the rock sample is heated to the required temperature, it is placed in a confining pressure autoclave. The obtained rock sample can be Figure 3 As shown in (a).

[0121] S2: Prepare two types of fracturing fluid media. According to the experimental plan, respectively prepare the concentration, viscosity and additive composition of the acid fracturing fluid and the hydraulic fracturing fluid. After preparation, add the acid fracturing fluid and the hydraulic fracturing fluid into the #1 intermediate container and the liquid storage tank, respectively. Then connect the injection equipment to the fracturing equipment through the acid-resistant pipeline.

[0122] S3: According to the experimental plan, triaxial confining pressure is applied to the rock sample. Since the triaxial pressure on site is relatively large, it cannot be applied to the indoor experiment. Therefore, the stress difference coefficient of the on-site confining pressure is calculated, and the confining pressure is set and simulated by the stress difference coefficient in the indoor experiment. The above stress difference coefficient is calculated according to the following formula:

[0123]

[0124] Among them, K his the stress difference coefficient, σ H is the maximum horizontal stress, σ h is the minimum horizontal stress.

[0125] S4: Condition setting. First, adjust the switch state of the valve next to the #1 intermediate container, close the valves at the upper and lower interfaces of the #1 intermediate container, and open the valve on the line between the water injection port and the #2 intermediate container. At this time, the fluid supply is the hydraulic fracturing fluid in the upper part of the #2 intermediate container. The general collection equipment sets the pumping flow rate of the hydraulic fracturing fluid.

[0126] S5: Creating fractures in rock samples. The pumping of hydraulic fracturing fluid is controlled by the acquisition equipment. At this time, the hydraulic fracturing fluid will be injected into the injection port of the rock sample at a constant flow rate through the #2 intermediate container and the acid-resistant pipeline. The data acquisition end in the acquisition equipment will monitor and record the fluid pressure curve. The fluid pressure in the rock sample will first continue to rise until it reaches a certain value, then suddenly drop. After dropping to a certain value, it will remain constant. After 300s, the injection system is closed and the fluid pressure curve is recorded. The highest value is the fracture initiation pressure of this rock sample. The fractures of the rock sample after fracture can be shown as follows: Figure 3 As shown in (b).

[0127] S6: The first diversion test, open the injection system again, pump clean water into the cracked rock sample at a constant flow rate, observe and record the fluid pressure curve through the acquisition equipment, because at this time the rock sample has formed a seepage channel, when the fluid pressure rises to a certain value, the cracks of the rock sample will remain open, prompting clean water to seep out from the cracks at the boundary of the rock sample, at this time the fluid pressure will remain at a fixed value and will not change, and this fixed value is the seepage pressure difference of the crack at this time, the value of the horizontal stage of the fluid pressure curve is averaged and calculated as the first average value, and the conductivity of the crack before acidification can be calculated according to the following formula based on the determined first average value:

[0128]

[0129] Among them, KW b is the conductivity of the fractures on the rock sample before acidizing, q b is the flow rate of the injected fluid before acidification, μ b is the viscosity of the injected fluid before acidizing, r e is the effective radius of the rock sample, i.e. half the length of the side of the rock sample, r w is the radius of the wellbore, Δp wb is the pressure difference value at the injection port, that is, the first average value mentioned above.

[0130] S7: Acidizing fractures. First, adjust the switch status of the valve next to the #1 intermediate container, open the valves of its upper and lower interfaces, and close the valve on the line between the water injection port and the #2 intermediate container. At this time, the fracturing fluid medium is the acidizing fracturing fluid. Start the pumping program. The acidizing fracturing fluid in the upper part of the #1 intermediate container will be pushed by the hydraulic fracturing fluid in the lower part and enter the rock sample after the fracture. It will continuously acid-etch the cracks in the rock sample to form a special etching structure. According to the experimental plan, when the acidizing fracturing fluid reaches the required dosage, the pumping program is closed. The cracks in the rock sample after acidizing can be as follows. Figure 3 As shown in (c).

[0131] S8: The second diversion test, close the inlet valve of the #1 intermediate container, open the valve of the hydraulic pump, and conduct the conductivity test after acidification according to the process of the first conductivity test. The surface of the crack after acidification forms an uneven etching structure, and a rough surface is formed between the insoluble rock particles and the soluble rock particles. At this time, the crack is still difficult to close completely under the confining pressure condition, and the seepage capacity of the crack is greatly increased. The fluid pressure curve at this time is collected, and the values ​​of the horizontal stage of the fluid pressure curve are averaged and calculated as the second average value. According to the determined second average value, the conductivity of the crack after acidification can be calculated according to the following formula:

[0132]

[0133] Among them, KW a is the conductivity of the fractures on the rock sample after acidification, q a is the flow rate of the injected fluid after acidification, μ a is the viscosity of the injected fluid after acidification, r e is the effective radius of the rock sample, i.e. half the length of the side of the rock sample, r w is the radius of the wellbore, Δp wa is the pressure difference value at the injection port, that is, the second average value mentioned above.

[0134] S9: Figure 4 is the curve of fluid pressure changing with time before and after acidizing, such as Figure 5 The figure shows the relationship between the conductivity and the closure stress before and after acidizing. The calculation results of the two conductivity are processed. The conductivity is compared through the fluid pressure curve before acidizing, the fluid pressure curve after acidizing, the conductivity curve before acidizing and the conductivity curve after acidizing. The effect of acid fracturing on the rock sample can be clearly observed.

[0135] In the above embodiments, a true triaxial stress loading device is used to apply triaxial confining pressure to a cubic rock sample, and hydraulic fracturing fluid and acid fracturing fluid are alternately injected into the rock sample through a fluid injection device to achieve fracturing and acidification of the rock sample. The experimental system also includes a collection device that can monitor and record the fluid pressure curve in real time, and determine the fracturing pressure of the rock sample and the seepage pressure difference of the crack according to the change value of the fluid pressure curve. The seepage pressure difference, hydraulic parameters and rock sample parameters are input into the radial flow conductivity calculation formula, and the conductivity of the rock sample before and after acidification can be calculated. This method can quantitatively compare the effect of the acid fracturing fluid on the three-dimensional cracks of the rock sample.

[0136] The method embodiments provided in the above embodiments of the present application can be executed in a mobile terminal, a computer terminal or a similar computing device. Taking running on an electronic device as an example, Figure 6 This is a hardware structure block diagram of an electronic device for an acid fracturing method for three-dimensional fractures in a formation rock sample provided by the present application. Figure 6 As shown, the electronic device 10 may include one or more (only one is shown in the figure) processors 02 (the processor 02 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA), a memory 04 for storing data, and a transmission module 06 for communication functions. It can be understood by those skilled in the art that Figure 6 The structure shown is only for illustration and does not limit the structure of the above electronic device. Figure 6 More or fewer components as shown, or with Figure 6 Different configurations are shown.

[0137] The memory 04 can be used to store software programs and modules of application software, such as program instructions / modules corresponding to the acid fracturing method for three-dimensional fractures of formation rock samples in the embodiment of the present application. The processor 02 executes various functional applications and data processing by running the software programs and modules stored in the memory 04, that is, the acid fracturing method for three-dimensional fractures of formation rock samples of the above-mentioned application program is realized. The memory 04 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory 04 may further include a memory remotely arranged relative to the processor 02, and these remote memories may be connected to the electronic device 10 via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0138] The transmission module 06 is used to receive or send data via a network. The specific example of the above network may include a wireless network provided by a communication provider of the electronic device 10. In one example, the transmission module 06 includes a network adapter (Network Interface Controller, NIC), which can be connected to other network devices through a base station so as to communicate with the Internet. In one example, the transmission module 06 can be a radio frequency (Radio Frequency, RF) module, which is used to communicate with the Internet wirelessly.

[0139] The embodiments of the present application also provide a specific implementation of an electronic device capable of implementing all the steps in the acid fracturing method for three-dimensional fractures of formation rock samples in the above-mentioned embodiments, and the electronic device specifically includes the following contents: a processor, a memory, a communication interface, and a bus; wherein the processor, the memory, and the communication interface communicate with each other through the bus; the processor is used to call a computer program in the memory, and when the processor executes the computer program, all the steps in the acid fracturing method for three-dimensional fractures of formation rock samples in the above-mentioned embodiments are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0140] Step 1: Obtain a rock sample of preset size and half side length of the rock sample to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore;

[0141] Step 2: applying triaxial stress to the rock sample to be tested at a preset stress value;

[0142] Step 3: connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameters of the hydraulic fracturing fluid in the second container through a collection device;

[0143] Step 4: injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording the fluid pressure curve during the fracturing process through a collection device, and stopping the injection of the hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first predetermined time;

[0144] Step 5: Inject clean water into the rock sample to be tested after fracturing at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a collection device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches the second preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches the second preset time, and use it as the pressure difference value of the first water injection port. Calculate the conductivity of the rock sample to be tested before acidification according to the determined pressure difference value of the first water injection port;

[0145] Step 6: connecting the acid-resistant pipeline between the first container and the rock sample to be tested, injecting acid fracturing fluid into the rock sample to be tested at a preset flow rate, and stopping the injection of the acid fracturing fluid when the injection amount of the acid fracturing fluid reaches the preset injection amount;

[0146] Step 7: Inject clean water into the rock sample to be tested after fracturing and acidification at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a collection device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than the third preset value and reaches the third preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the third preset value and reaches the third preset time, and use it as the pressure difference value of the second water injection port. Calculate the conductivity of the rock sample to be tested after acidification according to the determined pressure difference value of the second water injection port;

[0147] Step 8: Determine the influence of acid fracturing on the conductivity of the rock sample to be tested according to the conductivity of the rock sample to be tested before acidizing and the conductivity of the rock sample to be tested after acidizing.

[0148] The embodiments of the present application also provide a computer-readable storage medium capable of implementing all the steps in the acid fracturing method for three-dimensional fractures in formation rock samples in the above embodiments. The computer-readable storage medium stores a computer program. When the computer program is executed by a processor, all the steps in the acid fracturing method for three-dimensional fractures in formation rock samples in the above embodiments are implemented. For example, when the processor executes the computer program, the following steps are implemented:

[0149] Step 1: Obtain a rock sample of preset size and half side length of the rock sample to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore;

[0150] Step 2: applying triaxial stress to the rock sample to be tested at a preset stress value;

[0151] Step 3: connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameters of the hydraulic fracturing fluid in the second container through a collection device;

[0152] Step 4: injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording the fluid pressure curve during the fracturing process through a collection device, and stopping the injection of the hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first predetermined time;

[0153] Step 5: Inject clean water into the rock sample to be tested after fracturing at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a collection device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches the second preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the second preset value and reaches the second preset time, and use it as the pressure difference value of the first water injection port. Calculate the conductivity of the rock sample to be tested before acidification according to the determined pressure difference value of the first water injection port;

[0154] Step 6: connecting the acid-resistant pipeline between the first container and the rock sample to be tested, injecting acid fracturing fluid into the rock sample to be tested at a preset flow rate, and stopping the injection of the acid fracturing fluid when the injection amount of the acid fracturing fluid reaches the preset injection amount;

[0155] Step 7: Inject clean water into the rock sample to be tested after fracturing and acidification at a preset flow rate, and record the fluid pressure curve during the clean water injection process through a collection device. When the change amplitude of the fluid pressure curve during the clean water injection process is less than the third preset value and reaches the third preset time, stop the injection of clean water, determine the average value of the curve segment in which the change amplitude of the fluid pressure curve during the clean water injection process is less than the third preset value and reaches the third preset time, and use it as the pressure difference value of the second water injection port. Calculate the conductivity of the rock sample to be tested after acidification according to the determined pressure difference value of the second water injection port;

[0156] Step 8: Determine the influence of acid fracturing on the conductivity of the rock sample to be tested according to the conductivity of the rock sample to be tested before acidizing and the conductivity of the rock sample to be tested after acidizing.

[0157] From the above description, it can be seen that the method described in the embodiment of the present application includes: obtaining a rock sample to be tested of a preset size and a half-side length of the rock sample to be tested, performing rock surface drilling and simulated cementing and obtaining the radius of the wellbore; applying triaxial stress to the rock sample to be tested with a preset stress value; connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameter of the hydraulic fracturing fluid in the second container through a collection device; injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording the fluid pressure curve during the fracturing process through the collection device, and stopping the injection of hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first preset time length; injecting clean water into the rock sample to be tested after fracturing at a preset flow rate, and recording the fluid pressure curve during the injection of clean water through the collection device, and stopping the injection of clean water when the change amplitude of the fluid pressure curve during the injection of clean water is less than a second preset value and reaches a second preset time length, and determining that the change amplitude of the fluid pressure curve during the injection of clean water is less than the second preset value and reaches a second preset time length. The average value of the curve segment of a predetermined time length is used as the pressure difference value of the first water injection port, and the conductivity of the rock sample to be tested before acidification is calculated according to the determined pressure difference value of the first water injection port; the acid-resistant pipeline between the first container and the rock sample to be tested is connected, and the acid fracturing fluid is injected into the rock sample to be tested, and when the injection amount of the acid fracturing fluid reaches a preset injection amount, the injection of the acid fracturing fluid is stopped; clean water is injected into the rock sample to be tested after fracturing and acidification at a preset flow rate, and the fluid pressure curve during the injection of clean water is recorded by a collection device, and the pressure curve of the fluid during the injection of clean water is recorded. When the change amplitude of the fluid pressure curve in the process is less than the third preset value and reaches the third preset time, the injection of clean water is stopped, and the average value of the curve segment in which the change amplitude of the fluid pressure curve in the process of injecting clean water is less than the third preset value and reaches the third preset time is determined as the pressure difference value of the second water injection port, and the conductivity of the rock sample to be tested after acidification is calculated according to the determined pressure difference value of the second water injection port; according to the conductivity of the rock sample to be tested before acidification and the conductivity of the rock sample to be tested after acidification, the influence of acid fracturing on the conductivity of the rock sample to be tested is determined. Through the above scheme, the influence of the fracture network morphology of the formation rock sample after fracturing on the conductivity of the acid-etched fracture can be accurately determined under complex stress conditions, thereby solving the problem that the acid fracturing experiment cannot consider the integrated simulation of fracturing and acidification.

[0158] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the hardware + program embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0159] The above is a description of a specific embodiment of the specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in an order different from that in the embodiments and still achieve the desired results. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0160] Although the present application provides method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-creative labor. The order of steps listed in the embodiments is only one way of executing the order of many steps and does not represent the only execution order. When the actual device or client product is executed, it can be executed in the order of the method shown in the embodiments or the drawings or in parallel (for example, in a parallel processor or multi-threaded processing environment).

[0161] Although the present specification embodiment provides the method operation steps as described in the embodiment or flow chart, more or less operation steps may be included based on conventional or non-creative means. The order of steps listed in the embodiment is only one way in the order of execution of many steps, and does not represent a unique execution order. When the device or terminal product in practice is executed, it can be executed in sequence or in parallel (such as a parallel processor or a multi-threaded processing environment, or even a distributed data processing environment) according to the method shown in the embodiment or the accompanying drawings. The term "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, product or equipment including a series of elements not only includes those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, product or equipment. In the absence of more restrictions, it is not excluded that there are other identical or equivalent elements in the process, method, product or equipment including the elements.

[0162] For the convenience of description, the above devices are described in various modules according to their functions. Of course, when implementing the embodiments of this specification, the functions of each module can be implemented in the same or more software and / or hardware, or the module implementing the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0163] Those skilled in the art also know that, in addition to implementing the controller in a purely computer-readable program code, the controller can be made to implement the same function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, such a controller can be considered as a hardware component, and the devices for implementing various functions included therein can also be considered as structures within the hardware component. Or even, the devices for implementing various functions can be considered as both software modules for implementing the method and structures within the hardware component.

[0164] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0165] Those skilled in the art will appreciate that the embodiments of this specification may be provided as methods, systems or computer program products. Therefore, the embodiments of this specification may take the form of complete hardware embodiments, complete software embodiments or embodiments combining software and hardware. Moreover, the embodiments of this specification may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0166] The present specification embodiments may be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform specific tasks or implement specific abstract data types. The present specification embodiments may also be practiced in distributed computing environments where tasks are performed by remote processing devices connected through a communication network. In a distributed computing environment, program modules may be located in local and remote computer storage media, including storage devices.

[0167] Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. In the description of this specification, the description of the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, in the absence of contradiction, a person skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0168] The above is only an example of the embodiment of the present specification and is not intended to limit the embodiment of the present specification. For those skilled in the art, the embodiment of the present specification may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiment of the present specification shall be included in the scope of the claims of the embodiment of the present specification.

Claims

1. An acid fracturing system for three-dimensional fractures in formation rock samples, characterized in that: include: Fracturing equipment, a fluid injection system connected to the fracturing equipment, and a collection device electrically connected to the fracturing equipment and the fluid injection system, wherein: The fracturing equipment comprises: a confining pressure kettle body, wherein an inner cavity is provided in the confining pressure kettle body, wherein the inner cavity is used to place a rock sample to be tested, and a water injection port is provided on the rock sample to be tested; The injection system comprises: a first container carrying acid fracturing fluid and a second container carrying hydraulic fracturing fluid, the tops of the first container and the second container being connected to the water injection port on the rock sample to be tested through an acid-resistant pipeline; The collection equipment includes: an oil pressure device and a pressure collection box; the oil pressure device is used to control the confining pressure kettle body to apply triaxial stress to the rock sample to be tested with a preset stress value; the pressure collection box is used to monitor and record the triaxial stress applied by the confining pressure kettle body to the rock sample to be tested.

2. The system according to claim 1, characterized in that The inner cavity in the confining pressure autoclave body is a cube, wherein the six faces of the inner cavity of the cube are composed of six groups of pads and thermal insulation cotton, each group of pads includes a first pad, a second pad and a third pad, the first pad has a side length of 300 mm, the second pad has a side length of 200 mm, the third pad has a side length of 100 mm, the first pad, the second pad and the third pad are all 50 mm thick, the first pad, the second pad and the third pad are placed in sequence from the outside to the inside to form a face of the inner cavity of the confining pressure autoclave body, and the six groups of pads are combined to form the inner cavity of the cube; the thermal insulation cotton is arranged on the outside of the inner cavity of the cube formed by the six groups of pads.

3. The system according to claim 2, characterized in that According to the sizes of different rock samples to be tested, the size of the inner cavity of the cube is adjusted by placing the combination of the pads. When the side length of the rock sample to be tested is 100 mm, the first pad, the second pad and the third pad in the six groups of pads are placed in the confining pressure autoclave from the outside to the inside in sequence to form an inner cavity of the cube with a side length of 100 mm. When the side length of the rock sample to be tested is 200 mm, the first pad and the second pad in the six groups of pads are placed in the confining pressure autoclave from the outside to the inside in sequence to form an inner cavity of the cube with a side length of 200 mm.

4. The system according to claim 1, characterized in that The bottom of the first container is connected to the top of the second container through an acid-resistant pipeline. The upper end of the first container carries acidified fracturing fluid, and the lower end carries hydraulic fracturing fluid provided by the second container. A piston top plate is provided inside the first container to separate the fracturing fluids at the upper and lower ends.

5. The system according to claim 1, characterized in that The liquid injection system also includes: a circulating water device and a liquid storage tank; The bottom of the second container is connected to the circulating water device through an acid-resistant pipeline, and a piston top plate is arranged inside the second container, with hydraulic fracturing fluid carried on the upper end and clean water pumped into the circulating water device carried on the lower end; The top of the second container is also connected to the liquid storage tank, which stores hydraulic fracturing fluid. When the hydraulic fracturing fluid in the second container is insufficient, the liquid storage tank is pressurized by the air compressor at the bottom to drive the hydraulic fracturing fluid in the liquid storage tank into the second container.

6. The system according to claim 5, characterized in that Also includes: Controller; A first valve is provided on the acid-resistant pipeline between the first container and the water injection port on the rock sample to be tested, a second valve is provided on the acid-resistant pipeline between the first container and the second container, and a third valve is provided on the acid-resistant pipeline between the second container and the water injection port on the rock sample to be tested; The controller is electrically connected to the acquisition device; the first valve, the second valve and the third valve are electrically connected to the controller; the controller is also electrically connected to the circulating water device; the controller performs on-off control of the first valve, the second valve and the third valve according to the fracturing fluid medium set in the acquisition device, and performs injection control on the circulating water device, so as to alternately inject acid fracturing fluid and hydraulic fracturing fluid into the injection port on the rock sample to be tested; A flow meter and a fluid pressure gauge are also provided on the acid-resistant pipeline between the second container and the third valve, and the flow meter and the fluid pressure gauge are electrically connected to the controller; the controller collects data from the flow meter and the fluid pressure gauge, and controls the flow rate and fluid pressure of the hydraulic fracturing fluid in the second container according to the flow parameters set by the collection equipment.

7. A method for acid fracturing based on the acid fracturing system for three-dimensional fractures in a formation rock sample according to any one of claims 1 to 6, characterized in that: include: Obtain the rock sample to be tested of preset size and half side length of the rock sample to be tested, perform rock surface drilling and simulate cementing, and obtain the radius of the wellbore; Applying triaxial stress to the rock sample to be tested at a preset stress value; Connecting the acid-resistant pipeline between the second container and the rock sample to be tested, and setting the flow parameters of the hydraulic fracturing fluid in the second container through the acquisition equipment; Injecting hydraulic fracturing fluid into the rock sample to be tested at a preset flow rate, fracturing the rock sample to be tested, and recording a fluid pressure curve during the fracturing process through a collection device, and stopping the injection of the hydraulic fracturing fluid when the change amplitude of the fluid pressure curve during the fracturing process is less than a first preset value and reaches a first predetermined time length; Injecting clean water into the rock sample to be tested after fracturing at a preset flow rate, and recording the fluid pressure curve during the injection of clean water through a collection device, stopping the injection of clean water when the change amplitude of the fluid pressure curve during the injection of clean water is less than a second preset value and reaches a second preset time, determining an average value of a curve segment in which the change amplitude of the fluid pressure curve during the injection of clean water is less than the second preset value and reaches a second preset time as the pressure difference value of the first water injection port, and calculating the conductivity of the rock sample to be tested before acidification according to the determined pressure difference value of the first water injection port; Connecting the acid-resistant pipeline between the first container and the rock sample to be tested, injecting acid fracturing fluid into the rock sample to be tested at a preset flow rate, and stopping the injection of the acid fracturing fluid when the injection amount of the acid fracturing fluid reaches the preset injection amount; Injecting clean water into the rock sample to be tested after fracturing and acidification at a preset flow rate, and recording the fluid pressure curve during the injection of clean water through a collection device, stopping the injection of clean water when the change amplitude of the fluid pressure curve during the injection of clean water is less than a third preset value and reaches a third preset time, determining an average value of a curve segment in which the change amplitude of the fluid pressure curve during the injection of clean water is less than the third preset value and reaches a third preset time as the pressure difference value of the second water injection port, and calculating the conductivity of the rock sample to be tested after acidification according to the determined pressure difference value of the second water injection port; The influence of acid fracturing on the conductivity of the rock sample to be tested is determined according to the conductivity of the rock sample to be tested before acidizing and the conductivity of the rock sample to be tested after acidizing.

8. The method according to claim 7, characterized in that Calculating the conductivity of the rock sample to be tested before acidizing according to the determined pressure difference value of the first water injection port includes: Obtaining the flow rate of the injected fluid before acidizing and the viscosity of the injected fluid before acidizing; The conductivity of the rock sample before acidizing was calculated according to the following formula: Among them, KW b is the conductivity of the fractures on the rock sample before acidizing, q b is the flow rate of the injected fluid before acidification, μ b is the viscosity of the injected fluid before acidizing, r e is the half side length of the rock sample to be tested, r w is the radius of the wellbore, Δp wb is the pressure difference value of the first water injection port.

9. The method according to claim 7, characterized in that: Calculating the conductivity of the rock sample after acidification according to the determined pressure difference value of the second water injection port, including: Obtaining the flow rate of the injected fluid after acidizing and the viscosity of the injected fluid after acidizing; The conductivity of the rock sample after acidification is calculated according to the following formula: Among them, KW a is the conductivity of the fractures on the rock sample after acidification, q a is the flow rate of the injected fluid after acidification, μ a is the viscosity of the injected fluid after acidification, r e is the half side length of the rock sample to be tested, r w is the radius of the wellbore, Δp wa is the pressure difference value of the second water injection port.

10. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 7 to 9 are implemented.

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