Rock triaxial test system and test method

Abstract

The invention discloses a rock triaxial test system. The rock triaxial test system comprises a host, a hydraulic control system, an industrial camera and a data acquisition instrument, the main machine comprises a pressure loading device and a triaxial pressure chamber; a rock sample is arranged in the triaxial pressure chamber, electrode plates are arranged on the surface of the rock sample in an array mode in the axial direction and the circumferential direction, the surfaces of the electrode plates are coated with insulating films, and mark grids are arranged on the insulating films in an array mode in the axial direction and the circumferential direction. The hydraulic control system is used for injecting confining pressure liquid into the triaxial pressure chamber or injecting fracturing liquid into the rock sample; the triaxial pressure chamber is provided with a window, and the industrial camera shoots a deformation image of the rock sample in the test process through the window. According to the invention, the electrodes are arranged in a layered manner, and the insulating film with the marked grid is arranged on the periphery of the rock sample, so that the resistivity change trend in the triaxial loading damage process can be recorded in real time; a sub-pixel angular point identification technology of a digital image is adopted, and angular point changes are compared in real time so as to obtain deformation of the rock and realize deformation control fracturing of the rock.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering, and particularly relates to a rock triaxial test system and a test method. BACKGROUND

[0002] Rock triaxial test is a basic means for analyzing rock strength and deformation, and is a basis for evaluating rock deformation behavior under conditions such as excavation, displacement and fracturing, and then carrying out safety analysis of rock mass structure. In the process of deep geotechnical engineering disturbance, more reasonable rock mechanics property analysis should be carried out to realize disaster prevention and control in the process of engineering construction.

[0003] The existing rock mechanics unit test often analyzes the deformation of rock as a whole, and the deformation obtained by testing in the test process is the vertical overall deformation or the radial deformation on the partial section of the ring, which cannot analyze the local deformation of the rock sample at different positions in the loading process, and cannot analyze the non-uniform deformation characteristics of the rock unit in the loading process.

[0004] Rock fracturing is a prerequisite for the in-situ mining of special resources such as thermal energy, oil and gas resources or uranium in rock mass, and different scale cracks in rock appear by applying a large fluid pressure to realize the extraction of thermal energy, oil and gas resources or rock combination in the pore. However, the existing research shows that the fluid injection rate in the fracturing process will significantly affect the crack propagation and volume change evolution process of rock. The relationship between the fracturing fluid pumping pressure and rate and the deformation characteristics of rock has important technical value for optimizing the uniformity of rock cracks and then improving the efficiency of energy resource extraction.

[0005] In summary, the controllable implementation of the mechanical test process such as rock fracturing needs to overcome the following problems: (1) to realize the observation of the overall deformation and local deformation of rock; (2) to realize the controllable deformation and fracturing fluid discharge rate in the test process; (3) to realize the evaluation of the fracturing fluid expansion process to evaluate the rock crack development process; (4) to quantify the relationship between the fracturing fluid rate and the deformation.

[0006] Therefore, the development of a rock triaxial test system and test method considering local deformation has important scientific and engineering value for disaster prevention and control in the process of engineering construction. SUMMARY

[0007] The main purpose of the present application is to provide a rock triaxial test system and test method, which adopts layered electrode arrangement and insulating film arrangement around the rock sample to avoid the influence of confining pressure liquid on resistivity measurement, and can record the resistivity change trend in the triaxial loading and failure process in real time; adopts sub-pixel corner point recognition technology of digital image to compare the corner point change in real time to obtain the deformation of rock and realize the deformation control fracturing of rock.

[0008] The technical scheme adopted by the present application is: A rock triaxial test system, comprising a host computer, a hydraulic control system and a data and image acquisition system; the host computer comprises a counterforce frame, a pressure loading device and a triaxial pressure chamber installed on the counterforce frame; a cylindrical rock sample is installed in the triaxial pressure chamber, the surface of the rock sample is arrayed with a plurality of electrode pieces in the axial and circumferential directions, an insulating film is coated on the surface of the electrode pieces for fixing the electrode pieces and isolating the rock sample pores from the external environment, and a mark grid is arrayed on the insulating film in the axial and circumferential directions; the pressure loading device is used to apply pressure load to the rock sample; the hydraulic control system is used to inject confining pressure liquid into the triaxial pressure chamber or to inject fracturing liquid into the rock sample; the data and image acquisition system comprises an industrial camera and a data acquisition instrument; a viewing window is arranged on the triaxial pressure chamber, the industrial camera shoots the deformation image of the rock sample in the test process through the viewing window, and the industrial camera and the data acquisition instrument are signal connected; the signal line of the electrode piece passes through the gap under the insulating film and is connected with the data acquisition instrument outside the triaxial pressure chamber.

[0009] In the above scheme, the insulating film on the surface of the electrode piece is coated with an N-layer × G-column mark grid; during the test, the deformation rate of the rock sample V p The calculation method specifically comprises the following steps: The horizontal distance between the corner points at the same horizontal height in the mark grid and the horizontal distance between the corner points at the same horizontal height outside the mark grid are observed by the industrial camera, and the rock sample diameter at the center of each layer of mark grid is calculated according to formula (1): D n ) / π(1) In formula (1), D n is the rock sample diameter at the center of the nth layer of mark grid; l nxj is the horizontal distance between the corner points at the same horizontal height in the nth layer of mark grid; l nxi is the horizontal distance between the corner points at the same horizontal height outside the nth layer of mark grid; G is the total number of columns of the mark grid; i represents the horizontal distance between the corner points at the same horizontal height outside the ith mark grid, and takes values from 1, 2, 3, ···, G-1; j represents the horizontal distance between the corner points at the same horizontal height in the jth mark grid, and takes values from 1, 2, 3, ···, G; π represents the circular constant; N The average diameter of the rock sample at the center of the nth layer of mark grid D 0, calculated according to formula (2):​ D0= (2) In formula (2), N is the total number of layers of the marking grid; deformation rate of the rock sample V p , calculated by formula (3): (3) In formula (3), D is the diameter of the cylindrical rock sample; T is the total test time.

[0010] In the above scheme, the vertical deformation calculation method of the rock sample during the test specifically includes the following steps: S141, observing the vertical distance between each corner point in the same vertical direction in the marking grid and the vertical distance between each corner point in the same vertical direction outside the marking grid through an industrial camera , and calculating the rock sample height at the center of each column of marking grid according to formula (4) g : H (4) In formula (4), H g is the rock sample height at the center of the gth column of marking grid; is the vertical distance between each corner point in the same vertical direction in the gth column of marking grid; is the vertical distance between each corner point in the same vertical direction outside the gth column of marking grid; e represents the vertical distance between each corner point in the same vertical direction in the e th marking grid, and the value is from 1, 2, 3, ···, N; f represents the vertical distance between each corner point in the same vertical direction outside the f th marking grid, and the value is from 1, 2, 3, ···, N-1; S142, the average height of the rock sample at the center of the Gth column of marking grid is 0, calculated by formula (5): H (5) In formula (5), G is the total number of columns of the marking grid; S143, the vertical deformation H of the rock sample p , calculated by formula (6): H p =H-H0(6) In formula (6), H is the height of the cylindrical rock sample.

[0011] ​​In the above scheme, the electrode pieces are pasted on the surface of the rock sample in a uniform arrangement of 4 rows x 4 columns by conductive adhesive, the 4 rows are respectively a row 1, b row 2, c row 3, d row 4, and the 4 columns are respectively column 1, column 2, column 3 and column 4, and each electrode piece is marked as a 1, a 2, a 3, a 4; b 1, b 2, b 3, b 4; c 1, c 2, c 3, c 4; d 1, d 2, d 3, d 4; The resistivity of the rock sample corresponding to the four-layer electrode pieces is calculated according to formulas (7)-(10): exp(-π d ) + exp(-π d ) = 1 (7) exp(-π d ) + exp(-π d ) = 1 (8) exp(-π d ) + exp(-π d ) = 1 (9) exp(-π d ) + exp(-π d ) = 1 (10) wherein p 1, p 2, p 3, p 4 represent the resistivity of the rock sample corresponding to the four-layer electrode pieces respectively; I a1a2 is the current between electrode pieces a 1 and a 2, and U a3a4 is the voltage between electrode pieces a 3 and a 4, current between the electrode pieces a 1 and a 3, U a2a4 voltage between the electrode pieces a 2 and a 4; I b1b2 current between the electrode pieces b 1 and b 2, U b3b4 voltage between the electrode pieces b 3 and b 4, I b1b3 current between the electrode pieces b 1 and b 3, U b2b4 voltage between the electrode pieces b 2 and b 4; I c1c2 current between the electrode pieces c 1 and c 2, U c3c4 voltage between the electrode pieces c 3 and c 4, I c1c3 current between the electrode pieces c 1 and c 3, U c2c4 voltage between the electrode pieces c 2 and c 4; I d1d2 current between the electrode pieces d 1 and d 2, U d3d4 voltage between the electrode pieces d 3 and d 4, I d1d3 current between the electrode pieces d 1 and d 3, U d2d4 voltage between the electrode pieces d 2 and d 4.

[0012] In the above scheme, the pressure loading device comprises a hydraulic cylinder, a load sensor, and a loading rod, the hydraulic cylinder is installed on the counterforce frame, the upper end of the load sensor is connected with a hydraulic driving device, the lower end of the load sensor is connected with the loading rod, and the loading rod extends into the triaxial pressure chamber through a sealing sleeve to load the rock sample.

[0013] In the scheme, the triaxial pressure chamber comprises a cylindrical pressure chamber body, a front flange cover plate with a window and a rear flange cover plate, the front flange cover plate with a window and the rear flange cover plate are respectively installed at the front end and the rear end of the pressure chamber body to form a sealed triaxial pressure chamber.

[0014] In the scheme, a sealing sleeve is arranged at the upper center of the pressure chamber body for loading rods to pass through; a sample loading base is arranged at the lower center of the pressure chamber body for installing a rock sample; a pressure chamber light source mounting hole is arranged on the lower side wall of the pressure chamber body for installing a light source; an exhaust hole is arranged at the front side of the upper center of the pressure chamber body; the middle part of the front flange cover plate with a window is made of high-pressure-resistant glass, and an annular heating belt is arranged outside the glass to prevent glass window condensation; the rear flange cover plate is provided with a fracturing fluid inlet, a confining pressure inlet and a through-cabin connector mounting hole.

[0015] The rock triaxial test system can effectively avoid the influence of confining pressure liquid on resistivity measurement by arranging electrodes in layers and sleeving an insulating film around the rock sample, and can record the resistivity change trend in the triaxial loading and failure process in real time, and finally form a surface resistivity imaging technology; meanwhile, a mark grid is engraved on the surface of the insulating film, a deformation control fracturing technology is used, sub-pixel corner points are identified through digital image technology, and the deformation of the rock is obtained by real-time comparison of the change of the corner points, so that the deformation control fracturing of the rock is realized.

[0016] The rock triaxial test system can effectively avoid the influence of confining pressure liquid on resistivity measurement by arranging electrodes in layers and sleeving an insulating film around the rock sample, and can record the resistivity change trend in the triaxial loading and failure process in real time, and finally form a surface resistivity imaging technology; meanwhile, a mark grid is engraved on the surface of the insulating film, a deformation control fracturing technology is used, sub-pixel corner points are identified through digital image technology, and the deformation of the rock is obtained by real-time comparison of the change of the corner points, so that the deformation control fracturing of the rock is realized. S11, a cylindrical rock sample with a diameter D and a height H is prepared, electrodes are arranged on the surface of the rock sample in an axial and circumferential uniform array form of 4 rows x 4 columns, and an insulating film provided with N layers x G columns of mark grids is coated on the surface of the electrodes; S12, the rock triaxial test system of any one of claims 1-7 is assembled, the hydraulic control system is started to fill the triaxial pressure chamber with confining pressure liquid and then apply fluid pressure, the pressure loading device is started to move the loading end downward until it contacts the rock sample; the data and image acquisition system is opened, wherein the industrial camera is used to shoot the sample deformation image in the test process and transmit it to the data acquisition instrument, the data acquisition instrument is also used to acquire the voltage and current signals measured by each electrode in the test process and the load signals measured by the load sensor in the pressure loading device; the target deformation rate V p0 The test is started, and the pressure loading device continues to apply pressure to the rock sample; S13, during the test, the deformation rate of the rock sample is calculated according to the change of the corner point spacing of the mark grid on the insulating film observed by the industrial camera V p ; S14, the deformation rate of the rock sample is used to control the deformation of the rock sample Vp adjusts the loading rate of the pressure loading device according to the relative size of the target deformation rate V p0 , so that the rock sample carries out the loading test according to the target deformation rate V p0 ; until the vertical deformation H ℇ of the rock sample reaches 6% H or is broken, the test is stopped. S15, after the test is stopped, the resistivity of the rock sample corresponding to each layer of electrode sheet is calculated according to the measurement data of each layer of electrode sheet, the point cloud data graph of the resistivity of each layer of rock sample is drawn through calculation, the resistivity of each layer of rock is imaged, the overall resistivity imaging of the rock sample is realized, and the change of the resistivity field of the rock sample in the test process is studied.

[0017] The rock triaxial test system can carry out rock triaxial mechanical test, and the rock sample carries out loading test according to the target deformation rate through deformation control loading, finally, the point cloud data graph of the resistivity of each layer of rock sample is drawn through calculation, the resistivity of each layer of rock is imaged, the overall resistivity imaging of the rock sample is realized, and the change of the resistivity field of the rock sample in the test process is studied.

[0018] The application further provides a controllable fracturing test method for a rock sample. S21, a cylindrical rock sample with a diameter D and a height H is prepared, a fracturing pipe is pre-buried in the rock sample, electrode sheets are pasted on the surface of the rock sample in a uniform array arrangement form of 4 rows x 4 columns along the axial and circumferential directions, and an insulating film provided with N layers x G columns of mark grids is coated on the surface of the electrode sheets; S22, the rock triaxial test system in any one of claims 1-7 is assembled, the hydraulic control system is started to fill the triaxial pressure chamber with confining pressure liquid and then apply fluid pressure, and the data and image acquisition system is opened, wherein the industrial camera is used to shoot sample deformation images in the test process and transmit the images to the data acquisition instrument, the data acquisition instrument is also used to acquire voltage and current signals measured by each electrode sheet in the test process and load signals measured by the load sensor in the pressure loading device; the fracturing fluid is injected into the rock sample through the hydraulic control system, and the test is started; S23, in the test process, the deformation rate of the rock sample is calculated according to the change of the angle point spacing of the mark grids on the insulating film observed by the industrial camera V p ; The resistivity of the rock sample corresponding to each layer of electrode sheet is calculated according to the measurement data of each layer of electrode sheet, the resistivity growth rate is determined by fitting the resistivity curves according to (1, p 1), (2, p 2), (3, p 3), (4, p 4) four coordinatesS i ; S24, adjusting the flow rate of the fracturing fluid by the hydraulic control system so that the rock sample deforms at a target deformation rate V p0 Carrying out a loading test to realize a fracturing test with controllable deformation rate; or making the rock sample's resistivity growth rate S i According to the target resistivity growth rate S i0 Carrying out a loading test to realize a fracturing test with controllable resistivity feedback of fracturing fluid evolution process.

[0019] In step S24 of the above rock sample controllable fracturing test method, the flow rate of the fracturing fluid is adjusted by the hydraulic control system so that the rock sample deforms at a target deformation rate V p0 Carrying out a loading test, and the specific method is: ① When V p ＜V p0 , the hydraulic control system increases the flow rate of the fracturing fluid, so that the deformation rate increases to V p =V p0 ; ② When V p ＞V p0 , the hydraulic control system decreases the flow rate of the fracturing fluid, so that the deformation rate decreases until V p = V p0 ; ③ When V p =V p0 , the hydraulic control system maintains the flow rate of the fracturing fluid; The flow rate of the fracturing fluid is adjusted by the hydraulic control system so that the rock sample's resistivity growth rate S i According to the target resistivity growth rate S i0 Carrying out a loading test, and the specific method is: ① When S i > S i0 , the hydraulic control system decreases the flow rate of the fracturing fluid, so that the resistivity growth rate increases to S i = Si0 ; When S i < S i0 , the hydraulic control system accelerates the flow rate of the fracturing fluid, and promotes the growth rate of the resistivity to slow down until S i = S i0 ; When S i = S i0 , the hydraulic control system maintains the flow rate of the fracturing fluid.

[0020] The rock triaxial test system of the present application can also perform a controllable fracturing test on a rock sample, and realize the controllable fracturing of the rock through digital image technology and resistivity distribution servo feedback. This is beneficial to improve the authenticity of the rock fracturing test parameter acquisition, and provide engineering parameter basis for deep energy resource development.

[0021] The present application has the following beneficial effects: The present application realizes the direct observation of the overall deformation and local deformation of the rock during the loading process through digital image technology; realizes the controllable flow rate of the fracturing fluid based on the deformation during the test process according to the local deformation test calculation results obtained by the digital image; realizes the discrimination of the expansion front of the fracturing fluid in the rock during the fracturing process through resistivity imaging technology, and further realizes the evaluation of the rock fracture development based on the evolution law of the expansion front of the fracturing fluid. The provided technology is beneficial to improve the authenticity of the rock fracturing test parameter acquisition, and provide engineering parameter basis for deep energy resource development. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0023] Figure 1 is a schematic diagram of the overall structure of the rock triaxial test system of the present application; Figure 2 is a schematic diagram of the structure of the host computer of the rock triaxial test system shown in Figure 1 ; Figure 3 is a schematic diagram of the installation of the rock sample of the present application; Figure 4 is a schematic diagram of the local structure of the electrode sheet and the insulating film at A on the rock sample of the present application.

[0024] Fig. 1, host computer; 11, counterforce frame; 111, bottom fixed table; 112, top fixed table; 12, hydraulic cylinder; 13, load sensor; 14, loading rod; 15, triaxial pressure chamber; 151, pressure chamber body; 1511, pressure chamber light source mounting hole; 1512, exhaust hole; 152, flange front cover plate with window; 153, flange rear cover plate; 1531, fracturing fluid inlet; 1532, confining pressure inlet; 1533, through-chamber connector mounting hole; 1534, sealing sleeve; 154, loading base; 16, rock sample; 161, electrode sheet; 162, insulating film; 17, loading cap; 18, fracturing tube; 19, plane mirror; 2, hydraulic control system; 21, electric control cabinet; 22, hydraulic pump station; 3, data and image acquisition system; 31, industrial camera; 32, data acquisition instrument; 4, host computer system. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0026] It should be noted that the diagrams provided in the embodiments of the present application only illustrate the basic concept of the present application in a schematic manner, and therefore only the components related to the present application are shown in the diagrams, not the number, shape and size of the components when actually implemented. The actual implementation of each component may be a random change in shape, number and proportion, and the layout pattern of the components may also be more complex.

[0027] In the present application, it should also be noted that, if the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like appear, the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, if the terms "first" and "second" appear, they are only for description and distinction purposes, and cannot be understood as indicating or implying relative importance.

[0028] As shown in FIG. 1, a rock triaxial test system is provided, which includes a host computer 1, a hydraulic control system 2 and a data and image acquisition system 3. As shown in FIG. 2, the hydraulic control system 2 includes an electric control cabinet 21 and a hydraulic pump station 22. Figure 1 As shown in FIG. 1, a rock triaxial test system is provided, which includes a host computer 1, a hydraulic control system 2 and a data and image acquisition system 3. As shown in FIG. 2, the hydraulic control system 2 includes an electric control cabinet 21 and a hydraulic pump station 22. Figure 2As shown, the main unit 1 includes a reaction frame 11, a pressure loading device mounted on the reaction frame 11, and a triaxial pressure chamber 15. A cylindrical rock sample 16 is installed inside the triaxial pressure chamber 15. Several electrode plates 161 are arranged in an axial and circumferential array on the surface of the rock sample 16. An insulating film 162 is covered on the surface of the electrode plates 161 to fix the electrode plates 161 and isolate the pores of the rock sample 16 from the external environment. A marking grid is arranged in an axial and circumferential array on the insulating film 162. The pressure loading device is used to apply pressure load to the rock sample 16. The hydraulic control system 2 is used to inject confining fluid into the triaxial pressure chamber 15 or fracturing fluid into the rock sample 16. The data and image acquisition system 3 includes an industrial camera 31 and a data acquisition instrument 32; a viewing window is provided on the triaxial pressure chamber 15, and the industrial camera 31 captures images of the deformation of the rock sample 16 during the test through the viewing window. The industrial camera 31 is connected to the data acquisition instrument 32 via signal. The signal line of the electrode plate 161 passes through the gap on the lower side of the insulating film 162 and is connected to the data acquisition instrument 32 located outside the triaxial pressure chamber 15.

[0029] In one embodiment of the present invention, such as Figures 3-4 As shown, electrode sheets 161 are attached to the surface of rock sample 16 with conductive adhesive in a uniform 4-row × 4-column arrangement. The 4 rows are respectively... a OK, b OK, c OK, d The rows are numbered 1, 2, 3, and 4 respectively, and each electrode piece 161 is labeled as follows: a 1. a 2. a 3. a 4; b 1. b 2. b 3. b 4; c 1. c 2. c 3. c 4; d 1. d 2. d 3. d 4.

[0030] In one embodiment of the present invention, the surface of the insulating film 162 is uniformly printed with N layers × G columns of marking grid, wherein the horizontal distance between each corner point at the same horizontal height within the marking grid is . l nxj The horizontal distance between corner points at the same horizontal height outside the marked grid is... l nxi .

[0031] In one embodiment of the present application, the counterforce frame 11 is gantry type, comprising a bottom fixed platform 111, a top fixed platform 112 and a plurality of optical axis columns supported between the two. The pressure loading device is installed on the top fixed platform 112, and the triaxial pressure chamber 15 is installed on the bottom fixed platform 111.

[0032] In one embodiment of the present application, the pressure loading device comprises a hydraulic cylinder 12, a load sensor 13 and a loading rod 14. The hydraulic cylinder 12 is installed on the top fixed platform 112. The upper end of the load sensor 13 is connected to the loading column of the hydraulic cylinder 12 by threading, and the lower end is connected to the loading rod 14 by threading. The loading rod 14 extends into the triaxial pressure chamber 15 through the sealing sleeve 1534 to load the rock sample 16. The load signal during the test is measured by the load sensor 13, which facilitates observation of the test progress.

[0033] In one embodiment of the present application, the triaxial pressure chamber 15 comprises a cylindrical pressure cabin body 151, a flange front cover plate 152 with a window and a flange rear cover plate 153. The flange front cover plate 152 with a window and the flange rear cover plate 153 are installed on the front end and the rear end of the pressure cabin body 151 respectively to form a sealed triaxial pressure chamber 15. A sealing sleeve 1534 is provided at the center of the upper part of the pressure cabin body 151 for the loading rod 14 to pass through. A sample loading base 154 is provided at the center of the lower part of the pressure cabin body 151. A pressure chamber light source mounting hole 1511 is provided on the side wall of the lower part of the pressure cabin body 151. An exhaust hole 1512 is provided on the front side of the center of the upper part of the pressure cabin body 151. The middle part of the flange front cover plate 152 with a window is made of high-pressure resistant glass material, and an annular heating belt is provided outside the glass to prevent condensation. The flange rear cover plate 153 is made of stainless steel, and the flange rear cover plate 153 is provided with a fracturing fluid inlet 1531, a confining pressure inlet 1532 and a through-cabin connector mounting hole 1533. The through-cabin connector is mounted on the through-cabin connector mounting hole 1533. The electrode sheet 161 is connected to the internal signal terminal of the through-cabin connector through a signal line, and the data acquisition instrument 32 is connected to the external signal terminal of the through-cabin connector.

[0034] In one embodiment of the present application, the rock sample 16 is installed on the sample loading base 154, and the loading cap 17 is installed on the top of the rock sample 16. A ball socket is provided at the center of the top surface of the upper part of the loading cap 17 to facilitate contact with the ball head of the loading rod 14. A hole is provided in the lower part of the loading cap 17 which penetrates the side wall, and a hole is provided in the center of the loading base 154 which communicates with the outside of the triaxial pressure chamber 15. These two holes are used to apply pore pressure to the rock sample 16. Test personnel can choose whether to apply pore pressure according to the test conditions to explore the difference in test results under the condition of whether to apply pore pressure.

[0035] In one embodiment of the present application, the rock sample 16 is provided with a mirror 19 on both sides of the back of the rock sample 16, which is used to reflect the image of the back surface of the rock sample 16, so that the industrial camera 31 can monitor the deformation of all the corner points of the mark grid on the surface of the rock sample 16.

[0036] In one embodiment of the present application, the insulating film 162 is a rubber film, which is wrapped on the outer surface of the rock sample 16 by thermoplastic method. The mark grid is printed on the insulating film 162.

[0037] In one embodiment of the present application, the electrode sheet 161 is a titanium foil electrode sheet 161.

[0038] In one embodiment of the present application, the rock triaxial test system further comprises a host computer system 4, and the data acquisition instrument 32 and the host computer system 4 are in communication through Ethernet.

[0039] In one embodiment of the present application, the hydraulic control system 2 comprises an electric control cabinet 21 and a hydraulic pump station 22, wherein the electric control cabinet 21, the hydraulic pump station 22 and the host computer system 4 are in communication through Ethernet, and the hydraulic pump station 22 is connected with the triaxial pressure chamber 15 through high-pressure oil pipes.

[0040] The rock triaxial test system provided by the present application can perform rock triaxial mechanical test and rock sample 16 controllable fracturing test.

[0041] Correspondingly, the present application further provides a rock triaxial mechanical test method, which is characterized by comprising the following steps: S11, preparing a cylindrical rock sample 16 with a diameter of D and a height of H, and pasting electrode sheets 161 on the surface of the rock sample 16 in a uniform array arrangement of 4 rows and 4 columns along the axial and circumferential directions, and wrapping an insulating film 162 on the surface of the electrode sheet 161, and setting a mark grid of N layers and G columns on the insulating film 162.

[0042] S12, assembling the rock triaxial test system, starting the hydraulic control system 2 to fill the triaxial pressure chamber 15 with confining pressure liquid and then applying fluid pressure, starting the pressure loading device to move the loading rod 14 downward until it contacts the rock sample 16, and opening the data and image acquisition system 3, wherein the industrial camera 31 is used to shoot the sample deformation image during the test and transmit it to the data acquisition instrument 32, the data acquisition instrument 32 is also used to collect the voltage and current signals measured by each electrode sheet 161 and the load signal measured by the load sensor 13 in the pressure loading device during the test, and transmit all kinds of signals to the host computer system 4, and set the target deformation rate V p0 and start the test, and continue to apply pressure to the rock sample 16 through the pressure loading device.

[0043] S13, during the test, the host computer system 4 calculates the deformation rate of the rock sample 16 according to the change of the distance between the corner points of the marked grid on the insulating film 162 observed by the industrial camera 31 V p .

[0044] the deformation rate of the rock sample 16 V p The calculation method specifically includes the following steps: S131, the horizontal distance between the corner points at the same height in the marked grid and the horizontal distance between the corner points at the same height outside the marked grid are observed by the industrial camera 31, and the diameter of the rock sample 16 at the center of each layer of the marked grid is calculated according to formula (1): D n = ) / π(1) In formula (1), D n is the diameter of the rock sample 16 at the center of the nth layer of the marked grid; l nxj is the horizontal distance between the corner points at the same height in the nth layer of the marked grid; l nxi is the horizontal distance between the corner points at the same height outside the nth layer of the marked grid; G is the total number of columns of the marked grid; i represents the horizontal distance between the corner points at the same height outside the ith marked grid, taking values from 1, 2, 3, ···, G-1; j represents the horizontal distance between the corner points at the same height in the jth marked grid, taking values from 1, 2, 3, ···, G; π represents the circular constant.

[0045] S132, N the average diameter of the rock sample 16 at the center of the layer of the marked grid D 0, calculated by formula (2): D0= (2) In formula (2), N is the total number of layers of the marked grid.

[0046] S133, the deformation rate of the rock sample 16 V p , calculated by formula (3): (3) In formula (3), D is the diameter of the cylindrical rock sample 16; T is the total test time.

[0047] S14, the host computer system 4 calculates the deformation rate of the rock sample 16 V pWith the target deformation rate V p0 The relative size of the pressure loading device is adjusted to control the loading rate, so that the rock sample 16 deforms at the target deformation rate V. p0 Conduct loading tests until the vertical deformation H of rock specimen 16 is reached. ℇ Stop the test when 6% H is reached or the material breaks down.

[0048] The host computer system 4 adjusts the loading rate of the pressure loading device so that the rock sample 16 deforms at the target rate V. p0 The loading test was conducted using the following method: ①When V p ＜V p0 The control pressure loading device accelerates the movement of the loading rod 14, causing the deformation rate to increase to [a certain value]. V p =V p0 ; ②When V p ＞V p0 The pressure loading device slows down the movement of the loading rod 14, causing the deformation rate to decrease. V p =V p0 ; ③When V p =V p0 The pressure loading device is controlled to maintain the current loading rate.

[0049] The method for calculating the vertical deformation of rock sample 16 specifically includes the following steps: S141. Observe the vertical distance between each corner point in the same vertical direction within the marked grid using industrial camera 31. And the vertical distance between each corner point in the same vertical direction outside the marked grid. The height of rock sample 16 at the center of each marked grid was calculated according to formula (4). H g : (4) In equation (4), H g Mark the height of rock sample 16 at the center of the grid in column g; Mark the vertical distance between each corner point in the same vertical direction within the grid in column g; The vertical distance between the corner points in the same vertical direction outside the gth column of the marking grid is denoted as e, and the vertical distance between the corner points in the same vertical direction inside the e th marking grid is denoted as f, where e and f take values from 1, 2, 3, ···, N and 1, 2, 3, ···, N-1, respectively. S142, the average height of the rock sample 16 at the center of the G-column marking grid is H 0, calculated by formula (5): (5) In formula (5), G is the total number of columns of the marking grid. S143, the vertical deformation H of the rock sample 16 p is calculated by formula (6): H p = H-H0 (6) In formula (6), H is the height of the cylindrical rock sample 16.

[0050] S15, after the test is stopped, the resistivity of the rock sample 16 corresponding to each layer of the electrode sheet 161 is calculated according to the measurement data of each layer of the electrode sheet 161. The resistivity of each layer of the rock sample 16 obtained by calculation is plotted to image the resistivity of each layer of the rock, so as to realize the whole resistivity imaging of the rock sample 16 and study the change of the resistivity field of the rock sample 16 in the test process.

[0051] The resistivity of the rock sample 16 corresponding to the four-layer electrode sheet 161 is calculated according to formulas (7)-(10): exp(-π d ) + exp(-π d ) = 1 (7) exp(-π d ) + exp(-π d ) = 1 (8) exp(-π d ) + exp(-π d ) = 1 (9) exp(-π d ) + exp(-π d ) = 1 (10) In the formula, p 1, p 2, p 3,p 4 denotes the resistivity of the rock sample 16 corresponding to the four electrode pads 161 ; I a1a2 is the current between the electrode pads 161 a 1 and a 2, U a3a4 is the voltage between the electrode pads 161 a 3 and a 4, is the current between the electrode pads 161 a 1 and a 3, U a2a4 is the voltage between the electrode pads 161 a 2 and a 4; I b1b2 is the current between the electrode pads 161 b 1 and b 2, U b3b4 is the voltage between the electrode pads 161 b 3 and b 4, I b1b3 is the current between the electrode pads 161 b 1 and b 3, U b2b4 is the voltage between the electrode pads 161 b 2 and b 4; I c1c2 is the current between the electrode pads 161 c 1 and c 2, U c3c4 is the voltage between the electrode pads 161 c 3 and c 4, I c1c3 is the current between the electrode pads 161 c 1 and c 3, U c2c4 is the voltage between the electrode pads 161 c 2 and c 4; I d1d2 is the current between the electrode pads 161 d 1 and d 2, U d3d4 is the voltage between the electrode pads 161 d 3 and d 4, I d1d3 is the current between the electrode pads 161 d 1 and d 3, U d2d4 is the voltage between the electrode pads 161 d 2 and d 4.

[0052] Based on the above rock triaxial test system, the application also provides a rock sample 16 controllable fracturing test method, comprising the following steps: S21, a cylindrical rock sample 16 with a diameter D and a height H is prepared, a fracturing pipe 181 is pre-embedded in the rock sample 16, and electrode pieces 161 are pasted on the surface of the rock sample 16 in an axial and circumferential uniform array arrangement form of 4 rows x 4 columns, and an insulating film 162 provided with a mark grid is coated on the surface of the electrode piece 161.

[0053] S22, assemble the above rock triaxial test system, start the hydraulic control system 2 to fill the confining pressure liquid into the triaxial pressure chamber 15, then apply fluid pressure, open the data and image acquisition system 3, wherein the industrial camera 31 is used to shoot the sample deformation image in the test process and transmit to the data acquisition instrument 32, the data acquisition instrument 32 is also used to collect the voltage and current signals measured by each electrode piece 161 in the test process and the load signal measured by the load sensor 13 in the pressure loading device, and transmit various signals to the upper computer system 4; inject fracturing fluid into the rock sample 16 through the hydraulic control system 2, and start the test.

[0054] S23, in the test process, the upper computer system 4 calculates the deformation rate of the rock sample 16 according to the change of the angle point spacing of the mark grid on the insulating film 162 observed by the industrial camera 31 V p ; at the same time, the upper computer system 4 calculates the resistivity of the rock sample 16 corresponding to each layer of electrode piece 161 according to the measurement data of each layer of electrode piece 161 respectively, and determines the resistivity growth rate according to (1, p 1), (2, p 2), (3, p 3), (4, p 4) four coordinate fitting resistivity curve and derivation S i . The calculation method of deformation rate V p and each layer of resistivity has been described above, and will not be repeated here.

[0055] S24, the upper computer system 4 adjusts the liquid outlet rate of the fracturing fluid by controlling the hydraulic control system 2, so that the rock sample 16 carries out loading test according to the target deformation rate V p0 , so as to realize the fracturing test with controllable deformation rate; or make the rock sample 16 carry out loading test according to the target resistivity growth rate S i , so as to realize the fracturing test with controllable resistivity feedback in the evolution process of fracturing fluid. S i0

[0056] ​The hydraulic control system 2 adjusts the flow rate of the fracturing fluid, so that the rock sample 16 deforms at a target deformation rate V p0 The loading test is carried out in the following way: ① When V p ＜V p0 , the hydraulic control system 2 increases the flow rate of the fracturing fluid, so that the deformation rate increases to V p = V p0 ; ② When V p ＞V p0 , the hydraulic control system 2 decreases the flow rate of the fracturing fluid, so that the deformation rate decreases until V p = V p0 ; ③ When V p =V p0 , the hydraulic control system 2 maintains the flow rate of the fracturing fluid.

[0057] The hydraulic control system 2 adjusts the flow rate of the fracturing fluid, so that the rock sample 16 increases in resistivity at a target resistivity growth rate S i at the target resistivity growth rate S i0 The loading test is carried out in the following way: ① When S i > S i0 , the hydraulic control system 2 decreases the flow rate of the fracturing fluid, so that the resistivity growth rate increases to S i = S i0 ; ② When S i < S i0 , the hydraulic control system 2 increases the flow rate of the fracturing fluid, so that the resistivity growth rate decreases until S i = S i0 ; ③ When S i = S i0 , the hydraulic control system 2 maintains the flow rate of the fracturing fluid.

[0058] It should be noted that, according to the needs of implementation, each step / component described in the present application can be split into more steps / components, or two or more steps / components or part of the operation of the steps / components can be combined into a new step / component, to achieve the purpose of the present application.

[0059] The size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0060] It should be understood that, for those skilled in the art, improvements or changes can be made according to the above description, and all these improvements and changes shall fall within the protection scope of the appended claims of the present application.

Claims

1. A rock triaxial testing system, characterized by, The host, a hydraulic control system and a data and image acquisition system are comprised; The host comprises a counterforce frame, a pressure loading device and a triaxial pressure chamber installed on the counterforce frame; a cylindrical rock sample is installed in the triaxial pressure chamber; a plurality of electrode pieces are arranged on the surface of the rock sample in an axial and circumferential array; an insulating film is coated on the surface of the electrode pieces for fixing the electrode pieces and isolating the rock sample pores from the external environment; a mark grid is arranged on the insulating film in an axial and circumferential array; the pressure loading device is used for applying pressure load to the rock sample; The hydraulic control system is used for injecting confining pressure liquid into the triaxial pressure chamber or injecting fracturing liquid into the rock sample; The data and image acquisition system comprises an industrial camera and a data acquisition instrument; a window is arranged on the triaxial pressure chamber; the industrial camera shoots the deformation image of the rock sample in the test process through the window; the industrial camera is signal connected with the data acquisition instrument; the signal line of the electrode piece is connected with the data acquisition instrument outside the triaxial pressure chamber after passing through the gap under the insulating film.

2. The rock triaxial test system of claim 1, wherein, The insulating film with N layers and G columns of mark grids is arranged on the surface of the electrode sheet; during the test, the deformation rate of the rock sample V p The calculation method specifically comprises the following steps: The horizontal distance between the corner points at the same horizontal height in the mark grid and the horizontal distance between the corner points at the same horizontal height outside the mark grid are observed by the industrial camera; the rock sample diameter at the center of each layer of the mark grid is calculated according to formula (1): D n = ） / π（1） In formula (1), D n Dn is the diameter of the rock sample at the center of the n-th layer of marking grid; l nxj Dn is the diameter of the rock sample at the center of the n-th layer of marking grid; l nxi Dn is the diameter of the rock sample at the center of the n-th layer of marking grid;G is the total number of columns of the marking grid; i represents the horizontal distance between the corner points at the same horizontal height outside the i-th marking grid, taking values from 1, 2, 3, ···, G-1; j represents the horizontal distance between the corner points at the same horizontal height inside the j-th marking grid, taking values from 1, 2, 3, ···, G; π represents the circular constant; N Layer marker grid center rock sample average diameter D 0, calculated from equation (2): D0= （2） In formula (2), N is the total number of layers of the mark grid; Deformation rate of rock sample V p is calculated by equation (3): （3） In formula (3), D D is the diameter of the cylindrical rock sample; T T is the total test time.

3. The rock triaxial test system of claim 2, wherein, During the test process, the vertical deformation calculation method of the rock sample comprises the following steps: S141, observing the vertical distance between each corner point in the same vertical direction within the marked grid through the industrial camera and the vertical distance between each corner point in the same vertical direction outside the marked grid , calculating the height of the rock sample at the center of each column of the marked grid according to formula (4) H g : （4） In formula (4), H g Hg is the height of the rock sample at the center of the gth marked grid; Hg is the vertical distance between the corner points in the same vertical direction within the gth marked grid; Hg is the vertical distance between the corner points in the same vertical direction outside the gth marked grid; e represents the vertical distance between the corner points in the same vertical direction within the e th marked grid, taking values from 1, 2, 3, ···, N; f represents the vertical distance between the corner points in the same vertical direction outside the f th marked grid, taking values from 1, 2, 3, ···, N-1; S142, the average height of the rock sample at the center of the G-column marker grid is H 0, calculated from equation (5): （5） In formula (5), G is the total number of columns of the mark grid; S143, vertical deformation H of the rock sample p calculated from equation (6): H p =H-H0(6) In formula (6), H H is the height of the cylindrical rock sample.

4. The rock triaxial test system of claim 1, wherein, The electrode pieces are pasted on the surface of the rock sample in a uniform arrangement of 4 rows x 4 columns, the 4 rows are respectively a row 1, b row 2, c row 3, d row 4, and the 4 columns are respectively column 1, column 2, column 3 and column 4, and each electrode piece is marked as: a 1, a 2, a 3, a 4; b 1, b 2, b 3, b 4; c 1, c 2, c 3, c 4; d 1, d 2, d 3, d 4; The resistivity of the rock sample corresponding to the four electrode pieces is calculated according to formulas (7)-(10): exp(-π d ) + exp(-π d ) = 1 (7) exp(-π d ) + exp(-π d ) = 1 (8) exp(-π d ) + exp(-π d ) = 1 (9) exp(-π d ) + exp(-π d ) = 1 (10) In the formula, The pressure loading device comprises a hydraulic cylinder, a load sensor and a loading rod; the hydraulic cylinder is installed on the counterforce frame; the upper end of the load sensor is connected with a hydraulic driving device and the lower end is connected with the loading rod; the loading rod penetrates through a sealing sleeve and extends into the triaxial pressure chamber to load the rock sample. 1、 The triaxial pressure chamber comprises a cylindrical pressure chamber body, a flange front cover plate with a window and a flange rear cover plate; the flange front cover plate and the flange rear cover plate are respectively installed on the front end and the rear end of the pressure chamber body to form a sealed triaxial pressure chamber. 2、 A sealing sleeve is arranged at the center of the upper part of the pressure chamber body for the loading rod to penetrate through; a sample loading base is arranged at the center of the lower part of the pressure chamber body for installing the rock sample; a pressure chamber light source mounting hole is arranged on the side wall of the lower part of the pressure chamber body for installing a light source; an exhaust hole is arranged on the front side of the center of the upper part of the pressure chamber body; the middle part of the flange front cover plate with a window is made of high-pressure resistant glass; an annular heating belt is arranged outside the glass to prevent glass window condensation; a fracturing liquid inlet, a confining pressure inlet and a through-cabin connector mounting hole are arranged on the flange rear cover plate. 3、 The steps comprise: 4 respectively represent the resistivity of the rock sample corresponding to the four-layer electrode sheet pair; I a1a2 is the current between the electrode pieces a 1 and a 2, a3a4 is the voltage between the electrode pieces a 3 and a 4, is the current between the electrode pieces a 1 and a 3, a2a4 is the voltage between the electrode pieces a 2 and a 4. I b1b2 is the current between the electrode pieces b 1 and b 2, U b3b4 is the voltage between the electrode pieces b 3 and b 4, I b1b3 is the current between the electrode pieces b 1 and b 3, U b2b4 is the voltage between the electrode pieces b 2 and b 4; I c1c2 the current between the electrode pieces c 1 and c 2, U c3c4 the voltage between the electrode pieces c 3 and c 4, I c1c3 the current between the electrode pieces c 1 and c 3, U c2c4 the voltage between the electrode pieces c 2 and c 4; I d1d2 is the current between the electrode pieces d 1 and d 2, U d3d4 is the voltage between the electrode pieces d 3 and d 4, I d1d3 is the current between the electrode pieces d 1 and d 3, U d2d4 is the voltage between the electrode pieces d 2 and d 4.

5. The rock triaxial test system of claim 1, wherein, S11, preparing a cylindrical rock sample with a diameter of D and a height of H; electrode pieces are pasted on the surface of the rock sample in an axial and circumferential uniform array arrangement of 4 rows x 4 columns; an insulating film with N layers x G columns of mark grids is coated on the surface of the electrode pieces; 6. The rock triaxial test system of claim 1, wherein, ​ 7. The rock triaxial testing system of claim 6, wherein, ​ 8. A rock triaxial mechanics test method, characterized by, ​ ​ S12, assemble the rock triaxial test system of any one of claims 1-7, start the hydraulic control system to fill the confining pressure liquid in the triaxial pressure chamber and then apply fluid pressure, start the pressure loading device to move the loading end downward until it contacts the rock sample; open the data and image acquisition system, wherein the industrial camera is used to take the sample deformation image during the test and transmit it to the data acquisition instrument, and the data acquisition instrument is also used to collect the voltage and current signals measured by each electrode sheet during the test and the load signals measured by the load sensor in the pressure loading device; Setting target deformation rate V p0 After starting the test, the rock sample is continuously subjected to pressure by the pressure loading device; S13, during the test, the deformation rate of the rock sample is calculated according to the change of the distance between the corner points of the mark grid on the insulation film observed by the industrial camera V p ; S14, adjusting the loading rate of the pressure loading device according to the deformation rate of the rock sample V p adjusting the relative size of the target deformation rate V p0 , so that the rock sample is loaded according to the target deformation rate V p0 ; until the vertical deformation H ℇ of the rock sample reaches 6% H or is crushed, the test is stopped; S15, after the test is stopped, the resistivity of the rock sample corresponding to each layer of electrode sheet is calculated according to the measurement data of each layer of electrode sheet, the rock resistivity of each layer is imaged by drawing point cloud data diagram, the whole rock resistivity imaging is realized, and the change of the rock resistivity field during the test is studied.

9. A method of controllable fracturing test of a rock sample, characterized by, The method comprises the following steps: S21, prepare a cylindrical rock sample with a diameter of D and a height of H, embed a fracturing pipe in the rock sample, paste electrode sheets on the surface of the rock sample in a uniform array arrangement form of 4 rows x 4 columns along the axial and circumferential directions, and coat an insulating film with N layers x G columns of mark grids on the surface of the electrode sheets; S22, assemble the rock triaxial test system of any one of claims 1-7, start the hydraulic control system to fill the confining pressure liquid in the triaxial pressure chamber and then apply fluid pressure, open the data and image acquisition system, wherein the industrial camera is used to take the sample deformation image during the test and transmit it to the data acquisition instrument, and the data acquisition instrument is also used to collect the voltage and current signals measured by each electrode sheet during the test and the load signals measured by the load sensor in the pressure loading device; start the test by injecting fracturing fluid into the rock sample through the hydraulic control system; S23, during the test, the deformation rate of the rock sample is calculated according to the change of the distance between the corner points of the mark grid on the insulation film observed by the industrial camera V p ; According to the measured data of each layer electrode sheet, the resistivity of the rock sample corresponding to each layer electrode sheet is calculated, and the resistivity growth rate is determined according to (1, ρ 1), (2, ρ 2), (3, ρ 3), (4, ρ 4) four coordinate fitting resistivity curves and derivation S i ; S24, adjusting the liquid discharge rate of the fracturing fluid by the hydraulic control system, so that the rock sample is in accordance with the target deformation rate V p0 Carrying out loading test to realize the fracturing test with controllable deformation rate; or making the rock sample resistivity growth rate S i According to the target resistivity growth rate S i0 Carrying out loading test to realize the fracturing test with controllable resistivity feedback of fracturing fluid evolution process.

10. The method of claim 9, wherein, In step S24, the hydraulic control system adjusts the flow rate of the fracturing fluid so that the rock sample deforms at the target deformation rate V p0 The loading test is carried out, and the specific method is as follows: ①When V p ＜V p0 , the hydraulic control system accelerates the flow rate of the fracturing fluid, and promotes the deformation rate to V p =V p0 ; ii. when V p ＞V p0 , the hydraulic control system slows the rate of fluid flow of the fracturing fluid, causing the rate of deformation to slow until V p =V p0 ; ③When V p =V p0 , the hydraulic control system maintains the flow rate of the fracturing fluid; The hydraulic control system adjusts the flow rate of the fracturing fluid, so that the rock sample resistivity growth rate S i According to the target resistivity growth rate S i0 The loading test is carried out, and the specific method is: When S i S i0 , the hydraulic control system reduces the flow rate of the fracturing fluid, prompting the rate of resistivity growth to S i = S i0 ;​ ii) when S i < S i0 , the hydraulic control system accelerates the rate of fluid flow of the fracturing fluid, prompting the rate of resistivity growth to slow down until S i = S i0 ; iii. When S i = S i0 , the hydraulic control system maintains the flow rate of the fracturing fluid.

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