Testing device and testing method for increasing loss and strengthening hydraulic fracturing fracture network expansion by utilizing microwave radiation

Abstract

The invention provides a test device and a test method for increasing loss and strengthening hydraulic fracturing fracture network expansion by utilizing microwave radiation. The test device can perform microwave radiation, hydraulic fracturing and ultrasonic detection on a test piece so as to simulate and evaluate the process and effect of strengthening the expansion of a hydraulic fracturing fracture net by utilizing microwave radiation loss increase. The test device comprises a microwave radiation furnace, a temperature acquisition device, a large-size true triaxial pressure tank, a shaft confining pressure loading servo system, a constant-speed constant-pressure fracturing fluid servo system, an acoustic emission-strain acquisition device, an ultrasonic transmitter, a sensor, a clamp, an acoustic wave acquisition control device and the like. According to the test method, the initial damage of the test piece is evaluated through ultrasonic detection, then damage treatment is increased through microwave radiation, and finally hydraulic fracturing is performed and the fracturing effect is evaluated. According to the testing device and method, multiple testing means can be effectively integrated, the testing stability and applicability are improved, and scientific testing and evaluation are provided for shale gas exploitation through microwave radiation-assisted hydraulic fracturing.

Description

Technical Field

[0001] The invention relates to the technical field of shale gas exploitation methods, and in particular to a test device and a test method for utilizing microwave radiation gain and loss to enhance the expansion of a hydraulic fracturing network. Background Art

[0002] China's shale gas reserves rank first in the world. Shale gas development is of great significance to alleviating the shortage of coal and oil resources and the sustainable and healthy development of the national economy. Due to the low porosity and low permeability characteristics of my country's shale gas reservoirs, only a very small number of shale gas wells with particularly developed natural fractures can be directly put into production. Most shale gas wells need to be hydraulically fractured to obtain a relatively ideal output. The purpose of hydraulic fracturing of reservoirs is to form a large number of fracture networks, but due to the high strength, high hardness and construction conditions of shale, the fracturing effect is often not ideal. How to produce an effective fracture network has become a key issue in reservoir transformation research. Since hydraulic fracturing transformation also faces problems such as lack of water resources and groundwater pollution, emerging production-increasing methods have become one of the development directions of shale gas mining research.

[0003] Microwave radiation fracturing technology has the characteristics of rapid heating, selectivity and no secondary pollution, which makes it show certain advantages in shale gas reservoir transformation. However, microwave radiation fracturing transformation technology is restricted by factors such as high cost and limited radiation range. The effective combination of microwave technology and traditional hydraulic fracturing methods is an effective breakthrough to solve the above problems. How to effectively combine microwave radiation technology and hydraulic fracturing to produce rich fracture networks, expand the range of fracture networks, and effectively control economic costs is a key issue in the research.

[0004] At present, there are still certain limitations in the technical research in this area: combining the microwave radiation heating fracturing effect with hydraulic fracturing requires a lot of energy consumption and has poor economic efficiency; due to equipment limitations, it is impossible to observe and evaluate the effect of microwave radiation on the expansion of the fracture network. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a test device and test method for strengthening the expansion of hydraulic fracturing network by microwave radiation loss. The test device is complete and highly controllable, and the test results and evaluation analysis under various construction conditions can be completed through test operation.

[0006] A test device for enhancing the expansion of hydraulic fracturing network by microwave radiation loss and gain is composed of three relatively independent test systems: microwave radiation system, hydraulic fracturing system and ultrasonic detection system, specifically including: A large-capacity adjustable box-type microwave radiation furnace, which can perform microwave radiation of fixed power, fixed time and fixed temperature on the rock specimens in its box; A temperature collection device, which can collect the temperature in the microwave radiation furnace and at the rock sample collection point in real time and throughout the entire process; A large-sized true triaxial pressure tank, which can be used as a rock sample fixing device and an axial confining pressure transmission device, so that the rock sample in the cavity can be fixed and pressurized; Axial confining pressure loading servo system, which is a hydraulic electric control device, used in conjunction with the large-size true triaxial pressure tank, can achieve constant pressure and timing control of the axial confining pressure of the rock sample; A constant speed and constant pressure fracturing fluid servo system, which can deliver high-pressure fracturing fluid to rock samples through a delivery pipeline, and can achieve constant pressure and constant speed control of the fracturing fluid; An acoustic emission-strain acquisition device, which is used in conjunction with the large-size true triaxial pressure tank, can arrange measuring points on the surface of the rock sample in the pressure tank, and can collect acoustic emission and strain signals of the measuring points during the rock sample fracturing process in real time; An ultrasonic transmitter, which is connected to a power source and can realize frequency control and timing emission of P waves and S waves; An ultrasonic sensor, which is connected to a transmitter and consists of two movable probes, one is an excitation end and the other is a receiving end, which are respectively adsorbed on a set of opposite surfaces of the rock sample, and the two surfaces are parallel to the horizontal plane; A fixture, which consists of four clamps and can be placed on two sets of opposite surfaces of the rock specimen, and the two sets of opposite surfaces are perpendicular to the horizontal plane; An acoustic wave acquisition control device, which is composed of a digitally controlled acoustic wave instrument, an oscilloscope, and a controller, and can automatically acquire acoustic signals of P waves and S waves; A computer control system, wherein the computer control system controls the microwave radiation system, the hydraulic fracturing system and the ultrasonic detection system respectively, and can realize the functions of regulating, storing and processing the test data.

[0007] Preferably, the large-capacity adjustable box-type microwave radiation furnace can realize power regulation of 0 to 2000 W, and the box volume is ≥4000 ml; Preferably, the temperature acquisition device comprises a thermocouple, a temperature display and a memory. The temperature acquisition range is 0.1 to 1000°C; Preferably, the large-size true triaxial pressure tank comprises a base, a top plate, a closed cylinder, and built-in clamping plates in the X, Y, and Z directions, which can achieve close fit with rock specimens of different sizes; Preferably, the axle enclosure pressure loading servo system adopts electric hydraulic control, including a hydraulic station, pipelines, and a controller, and can achieve 0-5000kN pressure control; Preferably, the constant speed and constant pressure fracturing fluid servo system comprises a fracturing fluid storage tank, an injection pump, a pipeline, and a controller, and the fracturing fluid delivery pressure can be 0 to 140 MPa; Preferably, the acoustic emission-strain acquisition device comprises an acoustic emission probe, an acoustic emission analyzer, a strain gauge, a connection line, a strain signal analyzer, and a controller; Preferably, the ultrasonic transmitter has a transmission frequency of 20 to 500 kHz and a power range of 10 to 5000 W; Preferably, the ultrasonic sensor probe is mobile, and can realize multi-point guided wave signal testing; Preferably, the acoustic wave acquisition control device is an automatic data acquisition device with full closed-loop control to avoid low-frequency noise transmission; Preferably, the clamp is movable and can realize the clamping and fixing of a regular hexahedron, a cylinder or an irregular body.

[0008] The present invention also provides a test method for enhancing the expansion of a hydraulic fracture network by using microwave radiation loss and gain, and uses the test device for enhancing the expansion of a hydraulic fracture network by using microwave radiation loss and gain.

[0009] Step 1: Use ultrasonic testing to evaluate the initial damage of the specimen Fix the shale specimen on the fixture of the ultrasonic detection device, and adsorb the two probes of the ultrasonic sensor on the upper and lower surfaces of the shale specimen; start the computer control system and the sound wave collection control device; receive and process the waveguide signal; Changing the contact position of the ultrasonic sensor, repeating the above process until the ultrasonic detection process of multiple preset measuring points is completed; The mechanical parameters and internal structure of the shale specimens are analyzed through acoustic information such as wave velocity, amplitude, and waveform, and the initial damage of the specimens is evaluated.

[0010] Step 2: Microwave radiation enhanced damage treatment Place the shale specimen in the microwave radiation furnace cavity; start the computer control system, set the microwave radiation power, time or target temperature, and insulation time, start the temperature acquisition device and the microwave radiation furnace, and start microwave radiation; collect and store temperature data until the radiation process ends.

[0011] Step 3: Evaluate the specimen strengthening damage Fix the shale specimen after microwave radiation on the fixture of the ultrasonic detection device again, and adsorb the two probes of the ultrasonic sensor on the upper and lower surfaces of the shale specimen; start the computer control system and the sound wave collection control device; receive and process the waveguide signal; Change the contact position of the ultrasonic sensor and repeat the above process until the ultrasonic test process of multiple preset measuring points is completed. The position of the test piece measuring point remains the same as before microwave radiation; Through the acoustic information such as wave velocity, amplitude, waveform, etc., the mechanical parameters and internal structure of the rock specimens before and after microwave radiation are analyzed, and the microwave radiation-enhanced damage of the specimens is evaluated.

[0012] Step 4: Hydraulic fracturing process simulation test Fix the shale specimen in a large-size true triaxial pressure tank, arrange the acoustic emission probe and strain gauge at the set position, and load the configured fracturing fluid into the fracturing fluid storage tank of the constant speed and constant pressure fracturing fluid servo system; set the axis and confining pressure values, and start the axis confining pressure loading servo system; set the fracturing fluid pumping volume on the computer control system, turn on the acoustic emission-strain acquisition device, and monitor the internal situation of the true triaxial pressure tank; finally, turn on the constant speed and constant pressure fracturing fluid servo system and enter the fracturing mode; wait until the pump pressure-time curve displayed on the computer reaches the peak and then drops for a period of time, and then the curve stabilizes near a certain pressure value over time, and when fracturing fluid overflows from the bottom of the specimen, the hydraulic fracturing process is ended and the test system is closed.

[0013] Step 5: Fracturing effect evaluation and data analysis After the test, the morphology and trend of hydraulic cracks on the sample surface were observed, and six surfaces of the sample were photographed and recorded with a SLR camera. Then, the sample was cut along the hydraulic cracks on the sample surface, and the morphology of the hydraulic cracks was analyzed in combination with the acoustic emission positioning results and the pump pressure-time curve. The initiation and expansion mechanism of the hydraulic cracks was analyzed, and the influence of microwave radiation gain and loss on the morphology and expansion of the hydraulic cracks was analyzed.

[0014] The present invention provides a test device and a test method for strengthening the expansion of hydraulic fracture network by microwave radiation loss. Compared with the prior art, the present invention has the following beneficial effects: 1. The technology proposed in the present invention uses microwave radiation to increase rock damage, then hydraulically fractures the rock, and then strengthens the expansion of the fracture network, which can effectively control the cost of microwave radiation and improve the economic efficiency of shale gas extraction technology using microwave radiation in combination with hydraulic fracturing; 2. The present invention effectively integrates three relatively independent test systems (microwave radiation system, hydraulic fracturing system and ultrasonic detection system), realizing a complete set of test devices and test methods for strengthening the expansion of hydraulic fracturing network by microwave radiation gain and loss, which can effectively evaluate the strengthening effect of microwave radiation gain and loss on the expansion of hydraulic fracturing network; 3. The fixture device of the ultrasonic detection equipment and the built-in clamp of the large-size true triaxial pressure tank in the device of the present invention can realize size adjustment and stably cooperate with the test specimens; when used in conjunction with a large-size box-type microwave radiation furnace, it can meet the test conditions for stable loading of large-size and multi-size rock specimens, thereby improving the stability and applicability of the test; 4. The test device of the present invention adopts a computer automatic control acquisition system, which adopts computer automatic control acquisition in ultrasonic transmission acoustic signal acquisition, microwave radiation temperature acquisition, hydraulic fracturing process displacement, acoustic emission signal acquisition, etc., realizing real-time and effective acquisition of whole process monitoring information, effectively avoiding various errors caused by human operation, and improving the reliability of the test device; 5. The present invention provides a complete set of test equipment and test methods for utilizing microwave radiation to increase and decrease the expansion of hydraulic fracturing networks. This method can be widely used in the research work on the transformation of coal and rock structures by microwave radiation.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0017] Figure 1 This is a structural diagram of a test device for enhancing the expansion of a hydraulic fracture network by using microwave radiation loss.

[0018] Explanation of symbols in the figure: 1-large-capacity adjustable box-type microwave radiation furnace; 2-temperature acquisition device; 3-computer control system-1; 4-large-size true triaxial pressure tank; 5-axis confining pressure loading servo system; 6-constant speed and constant pressure fracturing fluid servo system; 7-acoustic emission-strain acquisition device; 8-computer control system-2; 9-ultrasonic sensor; 10-clamp; 11-acoustic wave acquisition control device; 12-ultrasonic transmitter; 13-computer control system-3

[0019] Figure 2 The present invention is a flow chart of an experimental method for enhancing the expansion of a hydraulic fracture network by using microwave radiation gain and loss. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0021] like Figure 1As shown, a test device for enhancing the expansion of hydraulic fracture network by microwave radiation loss and gain in the present invention comprises three relatively independent test systems: a microwave radiation system, a hydraulic fracturing system and an ultrasonic detection system. The microwave radiation system comprises: a large-capacity adjustable box-type microwave radiation furnace (1), a temperature acquisition device (2), and a computer control system-1 (3); the hydraulic fracturing system comprises: a large-size true triaxial pressure tank (4), an axial confining pressure loading servo system (5), a constant speed and constant pressure fracturing fluid servo system (6), an acoustic emission-strain acquisition device (7), and a computer control system-2 (8); the ultrasonic detection system comprises: an ultrasonic sensor (9), a fixture (10), an acoustic wave acquisition control device (11), an ultrasonic transmitter (12), and a computer control system-3 (13).

[0022] Combination Figure 1 and Figure 2 ,use Figure 1 When the test device shown in the figure studies an implementation scheme of using microwave radiation to increase and decrease the expansion of hydraulic fracture network, the operation process is as follows Figure 2 shown.

[0023] First, ultrasonic testing is performed on the shale specimen to evaluate the initial damage of the specimen. The shale specimen is placed on the base of the fixture 10 of the ultrasonic testing device, and the four clamps of the fixture are used to clamp the two opposite surfaces of the shale specimen perpendicular to the horizontal plane; the two probes of the ultrasonic sensor 9 are respectively adsorbed on the corresponding position measuring points on the upper and lower surfaces of the shale specimen; the computer control system 3 and the sound wave acquisition control device 11 are started; the ultrasonic type and frequency are set, and the ultrasonic transmitter 8 is turned on, and the sound wave acquisition control device 11 automatically receives and processes the waveguide signal. According to the size of the test specimen, multiple measuring points can be arranged, and the contact position of the mobile ultrasonic sensor probe is changed. The above process is repeated until the ultrasonic testing process of multiple preset measuring points is completed. The mechanical parameters and internal structure of the rock specimen are analyzed through acoustic information such as wave velocity, amplitude, and waveform, and the initial damage of the specimen is evaluated.

[0024] Then, the shale specimen is subjected to microwave radiation enhanced damage treatment. The shale specimen is taken out from the ultrasonic detection device and placed in the cavity of a large-capacity adjustable box-type microwave radiation furnace 1; the computer control system 8 and the temperature acquisition device 2 are started; the microwave radiation power, time or target temperature, and insulation time are set, and microwave radiation is started; the temperature acquisition device 2 monitors and stores the test temperature data in real time until the radiation process is completed. The shale specimen is taken out from the microwave radiation furnace 1, cooled to room temperature, and then placed in the ultrasonic detection device again, and ultrasonic detection is performed on the shale specimen after microwave radiation; the microwave radiation enhanced damage is evaluated based on the difference in ultrasonic signals before and after microwave radiation.

[0025] Then, the shale specimen is hydraulically fractured to evaluate its fracturing effect. The shale specimen is placed in the cavity of the large-size true triaxial pressure tank 4, three pairs of built-in clamps are placed on three opposite surfaces of the shale specimen, the acoustic emission probe and strain gauge are arranged at the set position, and the lines are connected; the configured fracturing fluid is loaded into the fracturing fluid storage tank of the constant speed constant pressure fracturing fluid servo system 6; the axis confining pressure value is set, and the axis confining pressure loading servo system 5 is started; the fracturing fluid pumping displacement is set on the computer control system 13, the acoustic emission-strain acquisition device 7 is turned on, and the internal situation of the true triaxial pressure tank 4 is monitored; finally, the constant speed constant pressure fracturing fluid servo system 6 is turned on to enter the fracturing mode; after the pump pressure-time curve displayed by the computer reaches the peak value and falls for a period of time, the curve stabilizes near a certain pressure value over time, and when the fracturing fluid overflows from the bottom of the sample, the hydraulic fracturing process is ended and the test system is closed. The shale specimen was taken out from the large-size true triaxial pressure tank 4, and the morphology and trend of hydraulic fractures on the specimen surface were observed. The six surfaces of the specimen were photographed and recorded with a SLR camera. Then, the specimen was cut along the hydraulic fractures on the specimen surface, and the morphology of the hydraulic fractures was analyzed in combination with the acoustic emission positioning results and the pump pressure-time curve. The initiation and expansion mechanism of the hydraulic fractures was analyzed, and the influence of microwave radiation gain and loss on the morphology and expansion of the hydraulic fractures was analyzed.

[0026] Finally, the above process was repeated by changing microwave radiation power, time, temperature, action position and other conditions for multiple times to comprehensively evaluate the advantages, disadvantages and feasibility of different microwave radiation gain-loss enhanced hydraulic fracturing network expansion implementation plans.

[0027] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the description details of the above specific embodiments. It should also be noted that within the technical concept of the present invention, technicians in the shale field can make several improvements to the present invention, which all belong to the protection scope of the present invention.

Claims

1. A test device and test method for enhancing the expansion of hydraulic fracturing network by microwave radiation loss and gain, wherein the test device comprises: Large-capacity adjustable box-type microwave radiation furnace, used for microwave radiation of fixed power, time effect and temperature to rock specimens; Temperature collection device, used to collect the temperature in the microwave radiation furnace and at the rock sample collection point in real time and throughout the entire process; Large-size true triaxial pressure tank, used to fix rock samples and transmit axial confining pressure; The axial confining pressure loading servo system is a hydraulic electronic control device, which is used in conjunction with the true triaxial pressure tank to achieve constant pressure and timing control of the axial confining pressure of the rock sample; The constant speed and pressure fracturing fluid servo system delivers high pressure fracturing fluid to the rock sample through the delivery pipeline to achieve constant pressure and speed control of the fracturing fluid; Acoustic emission-strain acquisition device, used in conjunction with the true triaxial pressure tank, real-time acquisition of acoustic emission and strain signals at the measuring points during rock sample fracturing; The ultrasonic transmitter is connected to the power supply to realize the frequency control and timing emission of P-wave and S-wave; The ultrasonic sensor consists of two movable probes, one is the excitation end and the other is the receiving end, which are respectively attached to a set of opposite surfaces of the rock sample; The fixture, consisting of four chucks, can be placed on two sets of opposite surfaces of the rock specimen; The acoustic wave acquisition control device is composed of a digitally controlled acoustic wave instrument, an oscilloscope, and a controller, and automatically acquires acoustic signals of P waves and S waves.

2. The test device for enhancing the expansion of hydraulic fracturing network by microwave radiation loss according to claim 1, characterized in that: The computer control system controls the microwave radiation system, hydraulic fracturing system and ultrasonic detection system respectively to realize the regulation, storage and processing of test data; the temperature acquisition device includes a thermocouple, a temperature display and a memory, and the temperature acquisition range is 0.1-1000°C; The large-size true triaxial pressure tank comprises a base, a top plate, a closed cylinder, and built-in clamps in the X, Y, and Z directions, which can achieve close cooperation with rock specimens of different sizes; The axle enclosure pressure loading servo system adopts electric hydraulic control, including a hydraulic station, pipelines, and a controller, and can achieve 0-5000kN pressure control; The constant speed and constant pressure fracturing fluid servo system comprises a fracturing fluid storage tank, an injection pump, a pipeline, and a controller, and the fracturing fluid delivery pressure can be 0 to 140 MPa; The acoustic emission-strain acquisition device comprises an acoustic emission probe, an acoustic emission analyzer, a strain gauge, a connection line, a strain signal analyzer, and a controller; The ultrasonic transmitter can achieve a transmission frequency of 20 to 500 kHz and a power range of 10 to 5000 W; The ultrasonic sensor probe is mobile and can realize multi-point guided wave signal testing; The acoustic wave acquisition control device is to automatically acquire data and perform full closed-loop control to avoid low-frequency noise transmission; The clamp is movable and can realize the clamping and fixing of a regular hexahedron, a cylinder or an irregular body.

3. A test device and test method for enhancing the expansion of hydraulic fracturing network by microwave radiation, using the test device of claims 1 and 2, wherein the test method comprises the following steps: Step 1: Use ultrasonic testing to evaluate the initial damage of the specimen Fix the shale specimen on the fixture of the ultrasonic detection device, and adsorb the two probes of the ultrasonic sensor on the upper and lower surfaces of the shale specimen; start the computer control system and the sound wave collection control device; receive and process the waveguide signal; Changing the contact position of the ultrasonic sensor, repeating the above process until the ultrasonic detection process of multiple preset measuring points is completed; Analyze the mechanical parameters and internal structure of shale specimens and evaluate the initial damage of specimens through acoustic information such as wave velocity, wave amplitude, and waveform; Step 2: Microwave radiation enhanced damage treatment Place the shale specimen in the microwave radiation furnace cavity; start the computer control system, set the microwave radiation power, time or target temperature, and insulation time, start the temperature acquisition device and the microwave radiation furnace, and start microwave radiation; collect and store temperature data until the radiation process ends; Step 3: Evaluate the specimen strengthening damage Fix the shale specimen after microwave radiation on the fixture of the ultrasonic detection device again, and adsorb the two probes of the ultrasonic sensor on the upper and lower surfaces of the shale specimen; start the computer control system and the sound wave collection control device; receive and process the waveguide signal; Change the contact position of the ultrasonic sensor and repeat the above process until the ultrasonic test process of multiple preset measuring points is completed. The position of the test piece measuring point remains the same as before microwave radiation; Through acoustic information such as wave velocity, wave amplitude, and waveform, the mechanical parameters and internal structure of rock specimens before and after microwave radiation are analyzed to evaluate the microwave radiation-enhanced damage of the specimens. Step 4: Hydraulic fracturing process simulation test Fix the shale specimen in a large-size true triaxial pressure tank, arrange the acoustic emission probe and strain gauge at the set position, and load the configured fracturing fluid into the fracturing fluid storage tank of the constant speed and constant pressure fracturing fluid servo system; set the axis and confining pressure values, and start the axis confining pressure loading servo system; set the fracturing fluid pumping volume on the computer control system, turn on the acoustic emission-strain acquisition device, and monitor the internal situation of the true triaxial pressure tank; finally, turn on the constant speed and constant pressure fracturing fluid servo system and enter the fracturing mode; wait until the pump pressure-time curve displayed on the computer reaches the peak value and then drops for a period of time, and then the curve stabilizes near a certain pressure value over time, and when the fracturing fluid overflows from the bottom of the specimen, the hydraulic fracturing process is over, and the test system is closed; Step 5: Fracturing effect evaluation and data analysis After the test, the morphology and trend of hydraulic cracks on the sample surface were observed, and six surfaces of the sample were photographed and recorded with a SLR camera. Then, the sample was cut along the hydraulic cracks on the sample surface, and the morphology of the hydraulic cracks was analyzed in combination with the acoustic emission positioning results and the pump pressure-time curve. The initiation and expansion mechanism of the hydraulic cracks was analyzed, and the influence of microwave radiation gain and loss on the morphology and expansion of the hydraulic cracks was analyzed.

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