Deep shale rock mechanics and fracture evolution feature coordinated testing system and method

Abstract

The present application belongs to the technical field of rock mechanics and oil and gas development, and particularly relates to a deep shale rock mechanics and fracture evolution feature cooperative testing system and method, which comprises a full-diameter triaxial high-pressure kettle, a hydraulic fracturing experimental mechanism, a high-temperature fracturing experimental mechanism, a strain monitoring mechanism and an acoustic emission signal monitoring mechanism; the method comprises the following steps: testing the mechanical properties of the same shale, conducting a thermal fracturing feature experiment, conducting a hydraulic fracturing experiment, analyzing the thermal fracturing process and the hydraulic fracturing process, and analyzing and inferring the generation position, generation time and complexity of the thermal fracturing cracks and the hydraulic fracturing cracks of the shale. The present application simulates the real occurrence environment of the deep shale reservoir, tests the mechanical properties of the shale, monitors the generation of the high-temperature shale thermal fracturing micro-cracks and the extension or development state of the cracks in the hydraulic fracturing process, provides a crack evaluation method, and provides data support for improving the high-temperature thermal fracturing and hydraulic fracturing effects of the deep shale.

Description

Technical Field

[0001] This invention belongs to the field of rock mechanics and oil and gas development technology, specifically relating to a collaborative testing system and method for deep shale rock mechanics and fracture evolution characteristics. Background Technology

[0002] Shale is widely distributed in my country, possessing enormous resource potential. As a layered claystone, shale exhibits significant heterogeneity, anisotropy, and low permeability. Deep reservoirs are characterized by high temperature, high pressure, and high stress states, underdeveloped fractures, and strong rock plasticity, making fracture propagation and extension difficult. Shale thermal fracturing refers to the phenomenon where changes in the internal stress state of shale rock under high temperature conditions lead to the formation or propagation of fractures. In shale gas extraction, the impact of high temperature on deep shale becomes more significant with increasing depth. High-temperature thermal fracturing has important application and research value in geological engineering, oil and gas extraction, and geothermal energy development.

[0003] Existing rock mechanics testing devices typically only perform pure mechanical tests and lack temperature environment simulation modules, making it impossible to study the dynamic effects of temperature on parameters such as rock strength and elastic modulus. For example, the testing device disclosed in Chinese invention patent "Rock Mechanical Property Testing Device and Method Based on Acoustic Emission Detection Technology" (patent number: CN201910468694.4) includes a frame with a sample loading chamber, a confining pressure loading system, a first axial pressure loading system, a second axial pressure loading system, and an acoustic emission detection device. This provides a rock mechanical property testing device and method based on acoustic emission detection technology capable of simulating the real stress environment around a rock sample. The experimental device disclosed in Chinese invention patent "An Experimental Device and Testing Method for Rock Mechanical Properties under High Confining Pressure" (patent number: CN202110006331.6) includes a hydraulic thrust mechanism, a rock confining pressure application mechanism, and a rock mechanical property testing system. The device simultaneously applies pressure and displacement boundary conditions to the rock sample surface. The confining pressure is provided by the mechanical thrust output by the hydraulic cylinder. The axial thrust is converted into radial confining pressure on the rock sample through the steel confining pressure applicator. The aluminum V-shaped clamping block is squeezed by the steel confining pressure applicator, which can uniformly apply the confining pressure to the rock surface.

[0004] Existing experiments on high-temperature thermal fracturing of rocks only involve a single thermal fracturing process or a hydraulic fracturing process, which cannot accurately distinguish between thermal fracturing microcracks and hydraulic fracturing fractures. Furthermore, there is a lack of quantitative evaluation methods for the development process and complexity of fractures. For example, the rock thermal shock experimental device disclosed in the Chinese invention patent "Rock Thermal Shock Experimental Device, Experimental Method and Rock Fracturing Evaluation Method" (Patent No.: CN 202110967800.0) includes a true triaxial system, a liquid supply system and a temperature measurement system. The true triaxial system is used to apply confining pressure and heat the rock sample to a first temperature. A liquid supply pump is used to inject liquid at a second temperature into the borehole. After the temperature stabilizes, the temperature difference is recorded. The rock sample is taken out for CT scanning, and the formed microcracks are recorded. The flow rate is changed and multiple experiments are conducted to establish a functional relationship between temperature difference and microcracks. The experimental equipment disclosed in the Chinese invention patent "Equipment and Method for Simulating Temperature and Pressure Conditions of Deep Rocks in Formations and Performing Hydraulic Fracturing" (Patent No.: 202010684086.X) includes a temperature and pressure regulation system, a water injection system and a data collection system. The temperature and pressure regulation system includes a metal vessel, a temperature control device, and a pressurization device; the water injection system delivers the mixture to the metal vessel; the data collection system includes a control console, a data collector, and sensors. The temperature and pressure conditions of the rock samples in deep formations were reconstructed, and hydraulic fracturing experiments were conducted on the rock samples.

[0005] However, the experimental devices and methods proposed in the above-mentioned prior art have failed to realize the mechanical properties and fracture evolution experiments on the same platform. They have not reflected the temperature effect when testing rock mechanical properties, and cannot accurately simulate the real occurrence environment of deep shale reservoirs (high temperature, high ground stress, high pore pressure). They cannot comprehensively distinguish between the thermal fracturing process and the hydraulic fracturing process of shale, and thus cannot accurately identify the initial thermal fracturing micro-fractures and hydraulic fracturing fractures. There is a lack of experimental devices and methods that can be used to dynamically monitor and analyze factors such as stress, deformation, acoustic emission fracture signals and fluid pressure during the rock thermal fracturing process and hydraulic fracturing process.

[0006] Therefore, there is an urgent need to design a system and method for the coordinated testing of the mechanical properties and fracture evolution characteristics of deep shale, to conduct coordinated testing of the mechanical properties and fracture evolution characteristics of the same shale sample, to study the mechanical properties of deep shale under the influence of high temperature, high pressure and high stress, and to dynamically monitor the development, propagation and formation of complex fracture networks of deep shale during thermal fracturing and hydraulic fracturing processes. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention proposes a collaborative testing system and method for the rock mechanics and fracture evolution characteristics of deep shale. This system simulates the real occurrence environment of deep shale reservoirs, tests the mechanical properties of shale, monitors the generation of micro-fractures in high-temperature shale thermal fracturing, and monitors the extension or development of fractures during hydraulic fracturing. It also provides a fracture evaluation method, offering data support for improving the effectiveness of high-temperature thermal fracturing and hydraulic fracturing in deep shale.

[0008] The present invention adopts the following technical solution:

[0009] A collaborative testing system for deep shale rock mechanics and fracture evolution characteristics includes: a full-diameter triaxial autoclave for mounting samples and applying axial and confining pressure loads; the full-diameter triaxial autoclave is connected to a hydraulic fracturing test mechanism, a high-temperature fracturing test mechanism, a strain monitoring mechanism, and an acoustic emission signal monitoring mechanism; the hydraulic fracturing test mechanism includes a servo water pump and a liquid injection pipe; the strain monitoring mechanism records stress and strain data of the sample under different confining pressure conditions and performs mechanical property analysis on the sample; the high-temperature fracturing test mechanism includes a temperature sensor for detecting the sample temperature, a heating component for heating the sample, and a temperature control unit for controlling the heating process and displaying the real-time temperature; during the high-temperature fracturing experiment and the hydraulic fracturing experiment, liquids of different colors are injected into the sample, and the strain signal and acoustic emission signal of the sample are recorded to comprehensively determine the fracture type and complexity.

[0010] Preferably, the sample is a cylindrical deep shale sample. The sample is located at the center of the full-diameter triaxial autoclave. The sample is covered with a sealing sleeve. The full-diameter triaxial autoclave containing the sealing sleeve has a confining pressure loading chamber. The bottom and top of the sealing sleeve have axial loading chambers. An axial loading head is located in the axial loading chamber. An axial loading plate is connected to the end of the axial loading head. Driven by hydraulic oil, the axial loading head applies axial pressure to the deep shale sample through the axial loading plate. At the same time, the confining pressure loading chamber provides confining pressure loading to the sample through hydraulic oil.

[0011] Preferably, the hydraulic oil is supplied to the full-diameter triaxial autoclave via oil pipes. The outer end of the oil pipes used for confining pressure and axial pressure is connected to a high-pressure servo oil pump. The oil inlet end of the high-pressure servo oil pump is connected to an oil tank. The confining pressure loading chamber and the axial loading chamber are respectively connected to a liquid pressure display instrument.

[0012] Preferably, the hydraulic fracturing experimental apparatus includes a liquid injection pipe that penetrates the axial loading head and axial loading plate along the axial direction and is slidably connected to the axial loading head and axial loading plate. The top of the sample opposite the liquid injection pipe has an injection hole of the same inner diameter along the axial direction. The other end of the liquid injection pipe penetrates the outer wall of a full-diameter triaxial autoclave and is connected to a water storage tank 1 and a water storage tank 2 via a tee connector. The tee connector is equipped with a valve 1 on the pipe body connecting to water storage tank 1 and water storage tank 2, respectively, to control the liquid flow. The water storage tank 1 and... The other end of the second water tank is connected to a water inlet pipe. The water inlet pipe of the first water tank is equipped with valve two, and the water inlet pipe of the second water tank is equipped with valve three. The other ends of the two water inlet pipes are connected to a six-way valve. The six-way valve is also connected to a servo water pump. The water inlet of the water pump is connected to a water source. The liquid injection pipe is equipped with a pressure sensor for measuring water pressure. The pressure sensor is connected to a liquid pressure display through a wire that passes through the liquid injection pipe and is sealed to the liquid injection pipe. The liquids in the first and second water tanks are different colors.

[0013] Preferably, the heating assembly includes several thermocouples evenly distributed on the outer wall of the confining pressure loading cavity, the temperature sensor is in close contact with the outer wall of the sealing sleeve, the temperature sensor and the thermocouples are electrically connected to the temperature control unit through wires, and the thermocouples are provided with an insulation sleeve on the outside.

[0014] Preferably, the strain monitoring mechanism includes a strain gauge attached to the outer surface of the sample and a dynamic strain gauge located on the outside of a full-diameter triaxial autoclave, wherein the strain gauge is connected to the dynamic strain gauge via a wire.

[0015] Preferably, the acoustic emission signal monitoring mechanism includes several acoustic emission probes disposed on the outer wall of the sealing sleeve, with coupling agent filling the space between the acoustic emission probes and the sealing sleeve. The acoustic emission probes are connected to a signal amplifier disposed on the outside of the full-diameter triaxial autoclave via wires. The signal amplifier is connected to an acoustic emission collector via wires, and the acoustic emission collector is connected to a computer via wires.

[0016] The testing method for a combined testing system of rock mechanics and fracture evolution characteristics in deep shale includes the following steps:

[0017] Step 1, Preparation of deep shale samples: The shale formation to be tested is processed into cylindrical shale samples required for the experiment;

[0018] Step 2, Connect the experimental equipment;

[0019] Step 3: After the experimental equipment is connected, turn on the strain monitoring mechanism;

[0020] Step 4, shale mechanical property testing;

[0021] The thermocouple was activated, and the sample was heated to the target temperature of 100℃ at a constant heating rate of 2℃ / min. During the stress loading stage, a first-level confining pressure and axial pressure of 5MPa were applied to the sample. After stabilization, the axial pressure was further applied to 10MPa at a loading rate of 0.01MPa / s, and stress-strain data were recorded in real time during the loading process from 5MPa to 10MPa. A second-level loading was applied, increasing the confining pressure and axial pressure to 10MPa. After stabilization, the axial pressure was further adjusted to 15MPa, maintaining constant temperature-pressure coupling conditions throughout the loading process, and stress-strain data were recorded during the loading process from 10MPa to 15MPa. A third-level loading was applied, increasing the confining pressure and axial pressure to 15MPa. After stabilization, the axial pressure was further adjusted to 20MPa, and stress-strain data were recorded during the loading process from 15MPa to 20MPa. During the experiment, strain gauges were used to dynamically monitor sample deformation to ensure the sample remained in an elastic state.

[0022] Based on multi-level loading stress-strain data, the elastic modulus and Poisson's ratio of shale under different confining pressures at a temperature of 100℃ were measured, and the calculation formulas are as follows:

[0023] E=Δσ1

[0024] Δε1

[0025] υ=- Δε3

[0026] Δε1

[0027] In the formula, E is the elastic modulus, GPa; Δσ1 is the axial stress change in the linear elastic stage, MPa; Δε1 is the axial strain change in the linear elastic stage; υ is Poisson's ratio; Δε3 is the radial strain change in the linear elastic stage.

[0028] Step 5: Perform a thermal cracking characteristic test on the sample;

[0029] After completing the mechanical property tests, the acoustic emission monitoring system was activated to record the ambient noise value, set the acoustic emission channel threshold, and filter out positioning errors caused by ambient noise. A confining pressure of 30 MPa and an axial pressure of 30 MPa were applied to the shale sample. During the loading process, the temperature was maintained at 100°C. Room temperature liquid was injected into the sample through a water storage tank via a liquid injection hole at a rate of 0.1 ml / min. The pressure of the injected liquid was monitored in real time by a pressure sensor to ensure that the liquid pressure did not exceed 30 MPa, thus ensuring that the sample had not started the hydraulic fracturing process. The acoustic emission waveform, spatial location of the fracture point, and acoustic emission energy monitoring data collected by the acoustic emission monitoring system were recorded.

[0030] Step 6: Inject high-pressure liquid into the sample to conduct a hydraulic fracturing experiment;

[0031] After completing the preparation for the hydraulic fracturing experiment, the axial pressure was rapidly increased to the target value. The confining pressure and axial pressure were kept stable. Valve 1 was switched, and high-pressure fluid was injected into the sample through water tank 2 to achieve a constant injection rate of 5 ml / min. The acoustic emission monitoring system was used to record the acoustic emission waveform, spatial location of the fracture point, and acoustic emission energy monitoring parameters of the shale sample during the hydraulic fracturing process, and the pressure of the injected liquid was monitored in real time.

[0032] Step 7: After the shale sample is broken, stop the water pump and close valve one, and save the recorded data;

[0033] Step 8: Analyze the thermal fracturing process and the hydraulic fracturing process;

[0034] Based on the acoustic emission monitoring system, a ring count-time curve was plotted during the thermal fracturing process of the shale sample; a ring count-time curve was plotted during the hydraulic fracturing process of the shale sample based on the acoustic emission monitoring system.

[0035] By using the ring count-time curve, amplitude, rise time, duration, ring count, and energy information can be obtained. The acoustic emission signal generated by thermal fracturing is relatively dispersed, propagates relatively slowly, has a long duration, and relatively low energy; the acoustic emission signal of hydraulic fracturing propagates rapidly, has a short duration, and is accompanied by a large amount of energy release. This information can be used to determine the fracture mechanism and characterize the complexity of the fracture.

[0036] Step 9: Analyze and predict the location, time of occurrence, and complexity of thermal fracturing and hydraulic fracturing fractures in shale.

[0037] Based on the corresponding times of the thermal fracturing and hydraulic fracturing processes, and using the obtained time as a variable, the ring count-time curves and strain-time curves are compared and analyzed to distinguish between thermal fracturing fractures and hydraulic fracturing fractures. The RA and AF values ​​are calculated to differentiate fracture types. The calculation formulas are as follows:

[0038]

[0039] For tension cracks, RA / AF < 1; for shear cracks, RA / AF > 1.

[0040] By combining acoustic emission localization maps, the locations of fractures generated by thermal fracturing and hydraulic fracturing are inferred. The complexity of the formed fractures is quantitatively characterized by calculating the acoustic emission b-value; the calculation formula is as follows:

[0041] lnN=a-bM

[0042] Where M is the amplitude of the acoustic emission event, N is the number of events with an amplitude greater than or equal to M, a is a constant representing the overall activity of the acoustic emission event, and b is the parameter we want to calculate, used to describe the energy distribution characteristics. A b value < 1.0 indicates a simple crack, and a b value > 1.5 indicates a complex crack network.

[0043] Step 10: Observe the sample slices;

[0044] After the thermal fracturing and hydraulic fracturing processes are completed, the shale samples are sliced ​​to observe the crack color and crack propagation morphology.

[0045] Preferably, in the aforementioned testing method, the room-temperature mechanical properties of shale are obtained by conducting synergistic testing of room-temperature rock mechanics and fracture evolution characteristics. Through room-temperature hydraulic fracturing experiments, acoustic emission signals, stress, strain, and fluid pressure of shale samples are obtained, and RA values, AF values, and acoustic emission b values ​​are calculated to analyze fracture development, propagation, and complex fracture network formation during the hydraulic fracturing process.

[0046] Preferably, in the aforementioned testing method, by comparing the mechanical properties and fracture evolution characteristics of shale samples at room temperature and high temperature, the influence law of temperature on the mechanical properties of shale is clarified, and the thermal fracturing characteristics caused by high temperature and the key role of temperature in fracture evolution during hydraulic fracturing are analyzed.

[0047] The beneficial effects of the integrated testing system and method for deep shale rock mechanics and fracture evolution characteristics of this invention are as follows:

[0048] This invention enables experiments on mechanical properties and fracture evolution to be conducted on a single platform. Collaborative testing saves experimental costs and allows for the measurement of rock mechanical properties of deep shale under different confining pressures influenced by temperature. Based on the measurement of rock mechanical properties of deep shale under different confining pressures influenced by temperature, further experiments on high-temperature thermal fracturing and hydraulic fracturing of deep shale are conducted. Dynamic data such as acoustic emission signals, stress, strain, and fluid pressure of shale samples are obtained. RA values, AF values, and acoustic emission b-values ​​are calculated, and fracture color is observed. This allows for accurate differentiation of fracture types and accurate analysis of fracture development, propagation, and complex fracture network formation during thermal fracturing and hydraulic fracturing processes. This provides data support for improving the effectiveness of high-temperature thermal fracturing and hydraulic fracturing of deep shale and offers a reliable means for research on high-temperature thermal fracturing and hydraulic fracturing of deep shale. Attached Figure Description

[0049] Figure 1 The flowchart of the testing method for the collaborative testing system for deep shale rock mechanics and fracture evolution characteristics provided by this invention;

[0050] Figure 2 Schematic diagram of a collaborative testing system for deep shale rock mechanics and fracture evolution characteristics;

[0051] Figure 3 1. Arrangement diagram of acoustic emission probe and strain gauge;

[0052] In the diagram: 1. Full-diameter triaxial autoclave; 2. Sample; 3. Strain gauge; 4. Injection port; 5. Water tank one; 6. Valve two; 7. Water tank two; 8. Valve three; 9. Six-way valve; 10. Servo water pump; 11. High-pressure servo oil pump A; 12. High-pressure servo oil pump B; 13. Oil tank; 14. Valve one; 15. Confining pressure loading chamber; 16. Triaxial autoclave cover; 17. Axial loading head; 18. Axial loading plate; 19. Sealing sleeve; 20. Liquid injection pipe; 21. Signal amplifier; 22. Acoustic emission acquisition device; 23. Computer; 24. Acoustic emission probe; 25. Liquid pressure display; 26. Temperature control unit; 27. Dynamic strain gauge; 28. Radial strain gauge; 29. ​​Axial strain gauge; 30. Thermocouple. Detailed Implementation

[0053] The following description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0054] The following embodiments can be understood as illustrating a part of the structure or method of the present invention individually, or as combining the embodiments to explain the broader structure or method of the present invention.

[0055] Example 1

[0056] This invention provides a collaborative testing system for the rock mechanics and fracture evolution characteristics of deep shale, such as... Figure 2 As shown, the apparatus includes: a full-diameter triaxial autoclave 1 for mounting the sample 2 and providing axial loading and confining pressure loading to the sample 2; the full-diameter triaxial autoclave 1 is connected to a hydraulic fracturing test mechanism, a high-temperature fracturing test mechanism, a strain monitoring mechanism, and an acoustic emission signal monitoring mechanism; the hydraulic fracturing test mechanism includes a servo water pump 10 and a liquid injection pipe 20; the high-temperature fracturing test mechanism includes a temperature sensor for detecting the sample temperature, a heating component for heating the sample, and a temperature control unit 26 for controlling the heating process and displaying the real-time temperature; during the high-temperature fracturing test and the hydraulic fracturing test, liquids of different colors are injected into the sample respectively, and the strain signal and acoustic emission signal of the sample are recorded to comprehensively determine the type and complexity of the crack.

[0057] Example 2

[0058] Based on Example 1, this example discloses that: the sample 2 is a cylindrical deep shale sample (sample diameter is 80mm, height is 200mm), the sample 2 is located at the center of the full-diameter triaxial autoclave 1, the sample 2 is covered with a sealing sleeve 19, the full-diameter triaxial autoclave 1 containing the sealing sleeve 19 is provided with a confining pressure loading chamber 15, the bottom and top of the sealing sleeve 19 are provided with axial loading chambers, the axial loading chamber is provided with an axial loading head 17, the end of the axial loading head 17 is connected to an axial loading plate 18, under the drive of hydraulic oil, the axial loading head 17 applies axial pressure to the sample 2 through the axial loading plate 18, and at the same time, the confining pressure loading chamber 15 provides confining pressure loading to the sample 2 through hydraulic oil.

[0059] like Figure 2 As shown, the hydraulic oil is supplied to the full-diameter triaxial autoclave 1 through oil pipes. The outer ends of the oil pipes used for confining pressure and axial pressure are respectively connected to high-pressure servo oil pumps (11, 12). The oil inlet of the high-pressure servo oil pump is connected to an oil tank 13. The confining pressure loading chamber 15 and the axial loading chamber are respectively connected to liquid pressure display instruments to display the oil pressure in the confining pressure loading chamber 15 and the axial loading chamber in real time.

[0060] Example 3

[0061] Based on Embodiment 2, this embodiment discloses: the hydraulic fracturing experimental mechanism includes a liquid injection pipe 20 that axially penetrates an axial loading head 17 and an axial loading plate 18 and is slidably connected to the axial loading head 17 and the axial loading plate 18. The top of the sample 2, opposite to the liquid injection pipe 20, has an injection hole 4 (70mm deep, 6mm diameter) with the same inner diameter along the axial direction. The other end of the liquid injection pipe 20 penetrates the outer wall of a full-diameter triaxial autoclave 1 and is connected to a water storage tank 5 and a water storage tank 7 via a three-way connector. A valve for controlling the liquid outflow is provided on the pipe body connecting the three-way connector to the water storage tank 5 and the water storage tank 7. Door 14, the other ends of the water storage tank 1 5 and water storage tank 2 7 are respectively connected to water inlet pipes. The water inlet pipe of water storage tank 1 5 is equipped with valve 2 6 and the water inlet pipe of water storage tank 2 7 is equipped with valve 3 8. The other ends of the two water inlet pipes are connected to a six-way valve 9. The six-way valve 9 is also connected to a servo water pump 10. The water inlet end of the servo water pump 10 is connected to a water source. The liquid injection pipe 20 is equipped with a pressure sensor for measuring water pressure. The pressure sensor is connected to a liquid pressure display 25 through a wire that passes through the liquid injection pipe 20 and is sealed to the liquid injection pipe 20. The liquids in water storage tank 1 and water storage tank 2 are different colors.

[0062] Example 4

[0063] like Figure 2As shown, the heating assembly includes several thermocouples 30 evenly distributed on the outer wall of the confining pressure loading cavity 15. The temperature sensor is in close contact with the outer wall of the sealing sleeve. The temperature sensor and the thermocouples 30 are electrically connected to the temperature control unit 26 through wires. The thermocouples 30 are provided with an insulation sleeve on the outside.

[0064] like Figure 2 , 3 As shown, the strain monitoring mechanism includes a strain gauge 3 attached to the outer surface of the sample 2 and a dynamic strain gauge 27 located on the outside of the full-diameter triaxial autoclave 1. The strain gauge 3 is connected to the dynamic strain gauge 27 via wires. Figure 3 As shown, the strain gauges include a radial strain gauge 28 that is attached to the outer wall of the specimen and an axial strain gauge 29 that is embedded in the bottom of the specimen.

[0065] like Figure 2 As shown, the acoustic emission signal monitoring mechanism includes several acoustic emission probes 24 disposed on the outer wall of the sealing sleeve 19. The acoustic emission probes 24 and the sealing sleeve 19 are filled with coupling agent (to conduct acoustic wave signals). The acoustic emission probes 24 are connected to a signal amplifier 21 disposed on the outside of the full-diameter triaxial autoclave 1 via wires. The signal amplifier 21 is connected to an acoustic emission collector 22 via wires. The acoustic emission collector 22 is connected to a computer 23 via wires.

[0066] Example 5

[0067] Based on the above embodiments, this embodiment discloses a testing method for a collaborative testing system for deep shale rock mechanics and fracture evolution characteristics, such as... Figure 1 As shown, it includes the following steps:

[0068] Step 1, Preparation of deep shale samples 2: The shale formation to be tested is processed into cylindrical shale samples required for the experiment;

[0069] Step 2, Connect the experimental equipment;

[0070] Strain gauge 3 is tightly attached to the outer surface of the shale sample and connected to dynamic strain gauge 27 via wires; acoustic emission probe 24 is tightly attached to the surface of sealing sleeve 19 covering shale sample 2 using coupling agent (other fixing methods may be used if necessary); acoustic emission probe 24 is electrically connected to signal amplifier 21; signal amplifier 21 is electrically connected to acoustic emission signal acquisition device 22; acoustic emission signal acquisition device 22 is electrically connected to computer 23; sample 2 is placed inside sealing sleeve 19 of full-diameter triaxial autoclave 1; sample 2 is fixed by axial loading head 17 tightly attached to loading plate 18; fluid injection end of full-diameter triaxial autoclave is connected to water storage tank 5 and water storage tank 7 via valve 1; water storage tank 5 and water storage tank 7 are connected to the outlet end of six-way valve 9 via valve 2 6 and valve 3 8 respectively; inlet end of six-way valve 9 is connected to servo water pump 10; thermocouple 30 is connected to the outer surface of full-diameter triaxial autoclave 1 and connected to temperature controller 26 via wires;

[0071] Step 3: After the experimental equipment is connected, turn on the strain monitoring mechanism;

[0072] Step 4, shale mechanical property testing;

[0073] The thermocouple was activated, and the sample 2 was heated to the target temperature of 100℃ at a constant heating rate of 2℃ / min. During the stress loading stage, a first-level confining pressure and axial pressure of 5MPa were applied to the sample 2. After stabilization, the axial pressure was further applied to 10MPa at a loading rate of 0.01MPa / s. The stress and strain data during the loading process from 5MPa to 10MPa were recorded in real time. A second-level loading was applied to the sample 2, increasing the confining pressure and axial pressure to 10MPa. After stabilization, the axial pressure was further adjusted to 15MPa. During the loading process, the temperature-pressure coupling conditions were kept constant, and the stress and strain data during the loading process from 10MPa to 15MPa were recorded. A third-level loading was applied to the sample 2, increasing the confining pressure and axial pressure to 15MPa. After stabilization, the axial pressure was further adjusted to 20MPa, and the stress and strain data during the loading process from 15MPa to 20MPa were recorded. During the experiment, strain gauge 3 was used to dynamically monitor the deformation of the sample 2 to ensure that the sample remained in an elastic state.

[0074] Based on multi-level loading stress-strain data, the elastic modulus and Poisson's ratio of shale under different confining pressures at a temperature of 100℃ were measured, and the calculation formulas are as follows:

[0075] E=Δσ1

[0076] Δε1

[0077] υ=- Δε3

[0078] Δε1

[0079] In the formula, E is the elastic modulus, GPa; Δσ1 is the axial stress change in the linear elastic stage, MPa; Δε1 is the axial strain change in the linear elastic stage; υ is Poisson's ratio; Δε3 is the radial strain change in the linear elastic stage.

[0080] Step 5: Perform a thermal cracking characteristic test on the sample;

[0081] After completing the mechanical property test, the acoustic emission monitoring system was turned on, the environmental noise value was recorded, the acoustic emission channel threshold was set, and the positioning error caused by environmental noise was filtered out. A confining pressure of 30 MPa and an axial pressure of 30 MPa were applied to the shale sample. During the loading process, the temperature was kept at 100℃. Room temperature liquid (or cryogenic liquid carbon dioxide) was injected into the sample through the liquid injection hole at a rate of 0.1 ml / min through the water storage tank. The pressure of the injected liquid was monitored in real time by the pressure sensor to ensure that the liquid pressure did not exceed 30 MPa, so as to ensure that the sample had not started the hydraulic fracturing process. The acoustic emission waveform, spatial location of the fracture point, and acoustic emission energy monitoring data collected by the acoustic emission monitoring system were recorded.

[0082] Step 6: Inject high-pressure liquid into the sample to conduct a hydraulic fracturing experiment;

[0083] After completing the preparation for the hydraulic fracturing experiment, the axial pressure was rapidly increased to the target value (to achieve different stress differential loading). While maintaining stable confining pressure and axial pressure, valve one was switched, and high-pressure fluid was injected into the sample through water tank two at a constant rate of 5 ml / min. (The model and prototype fluid properties are the same; using the similarity criterion, the geometric scale is 1:100, and the model injection rate of 5 ml / min represents the prototype injection rate of 5 ml / min.) 3 / min) injection; using an acoustic emission monitoring system to record acoustic emission waveforms, spatial location of fracture points, and acoustic emission energy monitoring parameters of the shale sample hydraulic fracturing process, and to monitor the pressure of the injected liquid in real time;

[0084] Step 7: After the shale sample is broken, stop the water pump and close valve one, and save the recorded data;

[0085] Step 8: Analyze the thermal fracturing process and the hydraulic fracturing process;

[0086] Based on the acoustic emission monitoring system, a ring count-time curve was plotted during the thermal fracturing process of the shale sample; a ring count-time curve was plotted during the hydraulic fracturing process of the shale sample based on the acoustic emission monitoring system.

[0087] By using the ring count-time curve, amplitude, rise time, duration, ring count, and energy information can be obtained. The acoustic emission signal generated by thermal fracturing is relatively dispersed, propagates relatively slowly, has a long duration, and relatively low energy; the acoustic emission signal of hydraulic fracturing propagates rapidly, has a short duration, and is accompanied by a large amount of energy release. This information can be used to determine the fracture mechanism and characterize the complexity of the fracture.

[0088] Step 9: Analyze and predict the location, time of occurrence, and complexity of thermal fracturing and hydraulic fracturing fractures in shale.

[0089] Based on the corresponding times of the thermal fracturing and hydraulic fracturing processes, and using the obtained time as a variable, the ring count-time curves and strain-time curves are compared and analyzed to distinguish between thermal fracturing fractures and hydraulic fracturing fractures. The RA and AF values ​​are calculated to differentiate fracture types. The calculation formulas are as follows:

[0090]

[0091] For tension cracks, RA / AF < 1; for shear cracks, RA / AF > 1.

[0092] By combining acoustic emission localization maps, the locations of fractures generated by thermal fracturing and hydraulic fracturing are inferred. The complexity of the formed fractures is quantitatively characterized by calculating the acoustic emission b-value; the calculation formula is as follows:

[0093] lnN=a-bM

[0094] Where M is the amplitude of the acoustic emission event, N is the number of events with an amplitude greater than or equal to M, a is a constant representing the overall activity of the acoustic emission event, and b is the parameter we want to calculate, used to describe the energy distribution characteristics. A b value < 1.0 indicates a simple crack, and a b value > 1.5 indicates a complex crack network.

[0095] Step 10: Observe the sample slices;

[0096] After the thermal fracturing and hydraulic fracturing processes were completed, the shale samples were sliced ​​to observe the color and propagation morphology of the fractures. During the slice observation, because the thermal fracturing experiment was performed first, a temperature difference existed between the injected liquid and the sample, causing cracks to form at the contact point. These thermal fracturing cracks were initially stained by the liquid in water tank one. Although the colored liquid from water tank two also passed through this crack during the subsequent hydraulic fracturing process, the staining did not completely cover the previous staining. Therefore, color differentiation allowed for the identification of the initial thermal fracturing cracks and the hydraulic fracturing cracks.

[0097] This invention proposes a collaborative testing system and method for the rock mechanics and fracture evolution characteristics of deep shale. It enables experiments on mechanical properties and fracture evolution to be conducted on the same platform, saving experimental costs. Based on the measurement of rock mechanics properties of deep shale under different confining pressures under temperature influence, further experiments on high-temperature thermal fracturing and hydraulic fracturing of deep shale are performed. Dynamic data such as acoustic emission signals, stress, strain, and fluid pressure of shale samples are obtained. RA values, AF values, and acoustic emission b-values ​​are calculated, and fracture color is observed. This allows for accurate differentiation of fracture types and accurate analysis of fracture development, propagation, and complex fracture network formation during thermal fracturing and hydraulic fracturing processes. This provides data support for improving the effectiveness of high-temperature thermal fracturing and hydraulic fracturing of deep shale and offers a reliable means for research on high-temperature thermal fracturing and hydraulic fracturing of deep shale.

Claims

1. A testing method for a collaborative testing system for deep shale rock mechanics and fracture evolution characteristics, wherein the collaborative testing system for deep shale rock mechanics and fracture evolution characteristics includes: A full-diameter triaxial autoclave is used to mount specimens and apply axial and confining pressure loads to them. The full-diameter triaxial autoclave is connected to a hydraulic fracturing test mechanism, a high-temperature fracturing test mechanism, a strain monitoring mechanism, and an acoustic emission signal monitoring mechanism. The hydraulic fracturing test mechanism includes a servo water pump and a liquid injection pipe. The strain monitoring mechanism records stress and strain data of the specimen under different confining pressure conditions and performs mechanical property analysis on the specimen. The high-temperature fracturing test mechanism includes a temperature sensor for detecting the specimen temperature, a heating component for heating the specimen, and a temperature control unit for controlling the heating process and displaying the real-time temperature. During the high-temperature fracturing test and the hydraulic fracturing test, liquids of different colors are injected into the specimen, and the strain signal and acoustic emission signal of the specimen are recorded to comprehensively determine the type and complexity of the crack. The sample is a cylindrical deep shale sample. The sample is placed at the center of the full-diameter triaxial autoclave. The sample is covered with a sealing sleeve. The full-diameter triaxial autoclave containing the sealing sleeve has a confining pressure loading chamber. The bottom and top of the sealing sleeve have axial loading chambers. An axial loading head is placed in the axial loading chamber. An axial loading plate is connected to the end of the axial loading head. Driven by hydraulic oil, the axial loading head applies axial pressure to the deep shale sample through the axial loading plate. At the same time, the confining pressure loading chamber provides confining pressure loading to the sample through hydraulic oil. The hydraulic oil is supplied to the full-diameter triaxial autoclave via oil pipes. The outer end of the oil pipes used for confining pressure and axial pressure is connected to a high-pressure servo oil pump. The oil inlet of the high-pressure servo oil pump is connected to an oil tank. The confining pressure loading chamber and the axial loading chamber are respectively connected to a liquid pressure display instrument. The hydraulic fracturing experimental apparatus includes a liquid injection pipe that runs axially through an axial loading head and an axial loading plate and is slidably and sealingly connected to them. The top of the sample opposite the liquid injection pipe has an injection hole of the same inner diameter along the axial direction. The other end of the liquid injection pipe passes through the outer wall of a full-diameter triaxial autoclave and is connected to a water storage tank (tank 1) and a water storage tank (tank 2) via a tee connector. The pipe body connecting the tee connector to water storage tanks 1 and 2 is equipped with a valve (valve 1) for controlling the liquid flow. The water storage tank 1 and water storage tank 2... The other end of tank 2 is connected to a water inlet pipe. The water inlet pipe of water tank 1 is equipped with valve 2, and the water inlet pipe of water tank 2 is equipped with valve 3. The other ends of the two water inlet pipes are connected to a six-way valve. The six-way valve is also connected to a servo water pump. The water inlet of the water pump is connected to a water source. The liquid injection pipe is equipped with a pressure sensor for measuring water pressure. The pressure sensor is connected to a liquid pressure display through a wire that passes through the liquid injection pipe and is sealed to the liquid injection pipe. The liquids in water tank 1 and water tank 2 are different colors. The heating assembly includes several thermocouples evenly distributed on the outer wall of the confining pressure loading cavity. The temperature sensor is in close contact with the outer wall of the sealing sleeve. The temperature sensor and the thermocouples are electrically connected to the temperature control unit through wires. The thermocouples are provided with heat insulation sleeves on the outside. The strain monitoring mechanism includes strain gauges attached to the outer surface of the sample and a dynamic strain gauge located on the outside of a full-diameter triaxial autoclave. The strain gauges are connected to the dynamic strain gauge via wires. The acoustic emission signal monitoring mechanism includes several acoustic emission probes located on the outer wall of the sealing sleeve. Coupling agent is filled between the acoustic emission probes and the sealing sleeve. The acoustic emission probes are connected to a signal amplifier located on the outside of the full-diameter triaxial autoclave via wires. The signal amplifier is connected to an acoustic emission collector via wires. The acoustic emission collector is connected to a computer via wires. Its characteristics are: The testing method includes the following steps: Step 1, Preparation of deep shale samples: The shale formation to be tested is processed into cylindrical shale samples required for the experiment; Step 2, Connect the experimental equipment; Step 3: After the experimental equipment is connected, turn on the strain monitoring mechanism; Step 4, shale mechanical property testing; The thermocouple was activated, and the sample was heated to the target temperature of 100℃ at a constant heating rate of 2℃ / min. During the stress loading stage, a first-level confining pressure and axial pressure of 5MPa were applied to the sample. After stabilization, the axial pressure was further applied to 10MPa at a loading rate of 0.01MPa / s, and stress-strain data were recorded in real time during the loading process from 5MPa to 10MPa. A second-level loading was applied, increasing the confining pressure and axial pressure to 10MPa. After stabilization, the axial pressure was further adjusted to 15MPa, maintaining constant temperature-pressure coupling conditions throughout the loading process, and stress-strain data were recorded during the loading process from 10MPa to 15MPa. A third-level loading was applied, increasing the confining pressure and axial pressure to 15MPa. After stabilization, the axial pressure was further adjusted to 20MPa, and stress-strain data were recorded during the loading process from 15MPa to 20MPa. During the experiment, strain gauges were used to dynamically monitor sample deformation to ensure the sample remained in an elastic state. Based on multi-level loading stress-strain data, the elastic modulus and Poisson's ratio of shale under different confining pressures at a temperature of 100℃ were measured, and the calculation formulas are as follows: ； In the formula, E is the elastic modulus, GPa; denoted as the change in axial stress during the linear elastic stage, in MPa; This represents the change in axial strain during the linear elastic stage. Poisson's ratio; This represents the change in radial strain during the linear elastic stage. Step 5: Perform a thermal cracking characteristic test on the sample; After completing the mechanical property tests, the acoustic emission monitoring system was activated to record the ambient noise value, set the acoustic emission channel threshold, and filter out positioning errors caused by ambient noise. A confining pressure of 30 MPa and an axial pressure of 30 MPa were applied to the shale sample. During the loading process, the temperature was maintained at 100°C. Room temperature liquid was injected into the sample through a water storage tank via a liquid injection hole at a rate of 0.1 ml / min. The pressure of the injected liquid was monitored in real time by a pressure sensor to ensure that the liquid pressure did not exceed 30 MPa, thus ensuring that the sample had not started the hydraulic fracturing process. The acoustic emission waveform, spatial location of the fracture point, and acoustic emission energy monitoring data collected by the acoustic emission monitoring system were recorded. Step 6: Inject high-pressure liquid into the sample to conduct a hydraulic fracturing experiment; After completing the preparation for the hydraulic fracturing experiment, the axial pressure was rapidly increased to the target value. The confining pressure and axial pressure were kept stable. Valve 1 was switched, and high-pressure fluid was injected into the sample through water tank 2 to achieve a constant injection rate of 5 ml / min. The acoustic emission monitoring system was used to record the acoustic emission waveform, spatial location of the fracture point, and acoustic emission energy monitoring parameters of the shale sample during the hydraulic fracturing process, and the pressure of the injected liquid was monitored in real time. Step 7: After the shale sample is broken, stop the water pump and close valve one, and save the recorded data; Step 8: Analyze the thermal fracturing process and the hydraulic fracturing process; Based on the acoustic emission monitoring system, a ring count-time curve was plotted during the thermal fracturing process of the shale sample; a ring count-time curve was plotted during the hydraulic fracturing process of the shale sample based on the acoustic emission monitoring system. By using the ring count-time curve, amplitude, rise time, duration, ring count, and energy information can be obtained. The acoustic emission signal generated by thermal fracturing is relatively dispersed, propagates relatively slowly, has a long duration, and relatively low energy; the acoustic emission signal of hydraulic fracturing propagates rapidly, has a short duration, and is accompanied by a large amount of energy release. This information can be used to determine the fracture mechanism and characterize the complexity of the fracture. Step 9: Analyze and predict the location, time of occurrence, and complexity of thermal fracturing and hydraulic fracturing fractures in shale. Based on the corresponding times of the thermal fracturing and hydraulic fracturing processes, and using the obtained time as a variable, the ring count-time curves and strain-time curves are compared and analyzed to distinguish between thermal fracturing fractures and hydraulic fracturing fractures. The RA and AF values ​​are calculated to differentiate fracture types. The calculation formulas are as follows: ； For tension cracks, RA / AF < 1; for shear cracks, RA / AF > 1. By combining acoustic emission localization maps, the locations of fractures generated by thermal fracturing and hydraulic fracturing are inferred. The complexity of the formed fractures is quantitatively characterized by calculating the acoustic emission b-value; the calculation formula is as follows: ； Where M is the amplitude of the acoustic emission event, N is the number of events with an amplitude greater than or equal to M, a is a constant representing the overall activity of the acoustic emission event, and b is the parameter we want to calculate, used to describe the energy distribution characteristics. A b value < 1.0 indicates a simple crack, and a b value > 1.5 indicates a complex crack network. Step 10: Observe the sample slices; After the thermal fracturing and hydraulic fracturing processes are completed, the shale samples are sliced ​​to observe the crack color and crack propagation morphology.

2. The testing method of the deep shale rock mechanics and fracture evolution characteristic co-testing system as described in claim 1, characterized in that, By conducting synergistic testing of room-temperature rock mechanics and fracture evolution characteristics, the room-temperature mechanical properties of shale were obtained. Through room-temperature hydraulic fracturing experiments, acoustic emission signals, stress, strain, and fluid pressure of shale samples were obtained. The RA value, AF value, and acoustic emission b value were calculated, and the fracture development, propagation, and formation of complex fracture networks during the hydraulic fracturing process were analyzed.

3. The testing method of the deep shale rock mechanics and fracture evolution characteristic co-testing system as described in claim 1 or 2, characterized in that, By comparing the mechanical properties and fracture evolution characteristics of shale samples at room temperature and high temperature, the influence of temperature on the mechanical properties of shale is clarified, and the characteristics of thermal fracturing caused by high temperature and the key role of temperature in fracture evolution during hydraulic fracturing are analyzed.

Images