Multifunctional rock core shear strength testing device and testing method

Abstract

The invention discloses a multifunctional rock core shear strength testing device and a testing method. The device comprises a base body, a testing cavity located in the base body, a step surface located at the bottom end of the testing cavity and a containing cavity communicated with the testing cavity and located below the testing cavity, and the containing cavity is adjacent to the step surface; the axial positioning assembly is matched with the step surface; the shearing shaft is positioned in the testing cavity and is over against the accommodating cavity; the axial positioning assembly is used for axially positioning one end or two ends of a tested rock core, and the shearing shaft is used for loading the tested rock core in the radial direction. The invention provides a multifunctional rock core shear strength testing device and a multifunctional rock core shear strength testing method. The problem that in the prior art, a rock shear strength testing device is poor in adaptability to rock cores in the petroleum industry is solved.

Description

Technical Field

[0001] The invention relates to the field of petroleum engineering, and in particular to a multifunctional rock core shear strength testing device and a testing method. Background Art

[0002] In most cases, rock damage is accompanied by shear damage. In almost every link of the oil and gas development field, formation damage caused by shear deformation will occur, which in severe cases will endanger the safety of drilling, completion and oil and gas production. Therefore, rock shear strength is one of the important characteristics of rock mechanics research. Compared with the compressive strength and tensile strength of rocks, it has more important practical engineering significance; and accurately obtaining the shear strength parameters of rocks is of great operational significance for oil and gas engineering.

[0003] The existing rock shear strength testing devices and related standards are designed for ground geotechnical engineering, and there is no special specification for the shear strength of rocks deep in the formation specifically for the oil industry. The rock shear strength testing devices in the prior art have at least the following disadvantages when used for core shear strength testing in the oil industry:

[0004] (1) Most of the rock shear strength test devices in the prior art are suitable for testing large-sized rock samples with square cross-sections and rectangular shapes (generally standard rock samples with a length of at least 5 cm and a cross-sectional size of 5 cm×5 cm). Unlike the acquisition methods of samples of rock mass, mountain mines and civil engineering projects, the core samples in petroleum engineering come from deep in the stratum. With the development of the international petroleum industry and the increasing demand for oil, the stratum depth of oil and gas exploration continues to increase, and the scale of drilling of deep wells and ultra-deep wells is expanding. Formation coring is extremely difficult and costly, and the extracted cores need to be used for various tests and research. This has led to a particularly short supply and high price of cores that can be used to study shear strength. Therefore, restricted by the conditions and costs of core acquisition, conventional shear strength test devices for rectangular samples can no longer meet the growing needs of petroleum engineering technology.

[0005] (2) In the field of petroleum engineering, since the coring depth is often several thousand meters, various strata of different lithologies may be encountered, and various brittle cores with low shear strength may be extracted, such as loose sandstone, sandstone layers with rich bedding, rock layers after acid fracturing, loose carbonate rock, coal rock in the process of coalbed methane mining, shale after hydration and expansion by external fluids, etc. The applicant found in a large number of research processes that when using existing shear strength test devices to test such brittle cores, the cores are very likely to be broken as a whole under the shear load, resulting in too little test data being collected, which not only fails to accurately obtain the required shear strength, but also causes a waste of expensive formation cores.

[0006] (3) Existing shear strength test devices are all conducted without confining pressure, which cannot truly simulate the three-dimensional stress state of deep rock formations and cannot obtain the true strength characteristics. This is relatively effective for measuring the shear strength of rock masses in ground or shallow projects with low or even no confining pressure, such as civil engineering, tunnel mining, etc., but it cannot simulate the geological operating environment requirements of several thousand meters in the oil and gas field. Because only under accurate underground confining pressure conditions, the shear failure of rocks deep in the formation along the most vulnerable surface determined by the microstructure and stress state can accurately reflect the failure mode of the on-site core, and the shear strength obtained in the test can truly reflect the core's ability to resist shear failure.

[0007] In summary, the rock shear strength testing device in the prior art has poor adaptability to the rock cores of the petroleum industry. It is necessary to develop a special testing device specifically for the shear strength testing of rocks in the deep formations of the petroleum industry. Summary of the invention

[0008] The invention provides a multifunctional rock core shear strength test device and a test method, so as to solve the problem that the rock shear strength test device in the prior art has poor adaptability to the rock cores in the petroleum industry.

[0009] The present invention is achieved through the following technical solutions:

[0010] A multifunctional rock core shear strength testing device comprises a base, a test cavity located in the base, a step surface located at the bottom end of the test cavity, and an accommodating cavity connected to the test cavity and located below the test cavity, wherein the accommodating cavity is adjacent to the step surface; further comprising an axial positioning component matching the step surface, and a shear axis located in the test cavity and facing the accommodating cavity; the axial positioning component is used for axially positioning one or both ends of a rock core to be tested, and the shear axis is used for radially loading the rock core to be tested; further comprising a force sensor for monitoring the loading force of the shear axis, and a displacement sensor for monitoring the loading displacement of the shear axis.

[0011] In view of the problem that the rock shear strength test device in the prior art is poorly adaptable to the cores of the petroleum industry, the present invention first proposes a multifunctional core shear strength test device, which includes a base body, a test cavity and a receiving cavity are arranged inside the base body, and the receiving cavity is located below the test cavity, and is used to provide a travel space for the tested core to move downward. A step surface is arranged next to the receiving cavity, and the height of the step surface is exactly at the height of the intersection surface of the test cavity and the receiving cavity. The axial positioning assembly is used to position the tested core, and the shear axis is used to apply a shear load to the tested core.

[0012] The device can be applied to the shear strength test of conventional hard rock cores or fragile rock cores.

[0013] When the tested rock core is a conventional hard rock core, a single shear surface test method is used to carry out the test, and the specific process includes: placing one end of the tested rock core on the step surface and the other end hanging on the accommodation cavity; positioning the axial ends of the tested rock core by the axial positioning assembly so that the end surface of the tested rock core hanging on the accommodation cavity is coplanar with the side surface of the shear axis away from the step surface; loading downward through the shear axis, and recording the loading force and loading displacement;

[0014] When the tested core is a fragile core, a double shear surface test method is used to carry out the test, and the specific process includes: one end of the tested core is located on the step surface and the other end is located on the accommodating cavity; the axial ends of the tested core are positioned by the axial positioning assembly so that the two ends of the tested core are located on both sides of the shear axis respectively; the shear axis is loaded downward, and the loading force and loading displacement are recorded.

[0015] The force sensor and displacement sensor in this application can be set at any suitable position according to the actual working conditions, as long as the force sensor can monitor the loading force and the displacement sensor can monitor the displacement during the loading process; they can be set on the shear shaft or on the press matched with the shear shaft, and no specific limitation is made here. In addition, both the force sensor and the displacement sensor can be implemented using existing finished products, and their specific models are not specifically limited here. Based on the monitoring results of the force sensor and the displacement sensor, this application can draw a relationship diagram between the shear load and the displacement, that is, draw a force-displacement curve, and then intuitively obtain the process and peak value of the shear failure, and can also be used to evaluate the shear failure characteristics of different rock types.

[0016] It should be noted that the axial positioning component in the present device can axially position one or both ends of the measured core. When the axial positioning component positions one end of the measured core, the other end of the measured core is located on the step surface and can be axially positioned through the inner wall of the substrate or other structures relatively fixed to the substrate.

[0017] It can be seen that the device has two different shear test modes, which can simultaneously meet the shear strength test requirements of conventional hard cores and fragile cores; when conducting shear strength tests on fragile cores, the present application can multiply the shear surface area compared to the traditional shearing method, that is, multiply the force-bearing area, so that the rock sample is not easy to break under the shear load, thereby collecting more and more accurate test data, which is conducive to obtaining more accurate and reliable core shear strength results. The inventor has confirmed through experiments that the device has an excellent anti-crushing effect on common fragile cores (such as loose sandstone, sandstone layers with rich stratification, rock layers after acid fracturing, loose carbonate rocks, coal rocks in the process of coalbed methane mining, and shale after hydration and expansion by external fluids), and can completely obtain the force-displacement data in the shear process, so it can solve the problem of core waste caused by traditional shearing devices and avoid the waste of scarce deep formation cores. In addition, unlike traditional shearing devices that can only be used for testing large-volume rectangular rock samples, the present application can carry out shear tests on small-sized, cylindrical rock cores, and can directly adapt to rock samples obtained after deep coring in petroleum engineering, avoiding the engineering difficulties caused by the need to take large-sized cores from deep layers, significantly reducing the difficulty and engineering risks of coring operations, and avoiding the waste of precious rock samples.

[0018] Furthermore, the axial positioning assembly includes a linear drive mechanism with a bottom end having the same height as the step surface, and a power device for providing power to the linear drive mechanism; the output end of the linear drive mechanism is located on the accommodating cavity.

[0019] When one end of the core to be tested is placed on the step surface, the linear drive mechanism applies force from the other end to push the core to be tested until it cannot move axially, so that the core to be tested maintains axial stability. The linear drive mechanism in this solution can be implemented by any existing device with linear drive function, including but not limited to hydraulic, pneumatic or electric drive, and its supporting power equipment can provide it with corresponding power.

[0020] Furthermore, the axial positioning assembly also includes a pressure head movably placed on the step surface, and the pressure head is distributed relative to the output end of the linear drive mechanism.

[0021] In different shear test modes, the present application can use cores of different lengths to complete the required tests from the perspective of saving cores, such as using shorter cores for single shear surface tests and longer cores for double shear surface tests. One end of the core suspended in the accommodating cavity is held in place by a linear drive mechanism, and the other end of the core located on the step surface is positioned by a pressure head in this solution. Since the position of the shear axis remains unchanged relative to the substrate, in different shear test modes or for rock samples of different lengths, it is only necessary to replace pressure heads of different lengths to match them with the corresponding cores, so that one end of the pressure head abuts against the inner wall of the test cavity and the other end abuts against the end of the core located on the step surface, thereby ensuring effective shear tests in different shear test modes or for cores of different lengths, which significantly improves the flexibility and versatility of the present application.

[0022] Furthermore, it also includes a thermoplastic tube for accommodating the measured rock core, and the two ends of the thermoplastic tube are respectively connected to the pressure head and the output end of the linear drive mechanism.

[0023] The presence of the thermoplastic tube makes it easier to apply confining pressure to simulate formation stress, and prevents the confining pressure medium from penetrating into the pores inside the core to interfere with the shear strength. In addition, the thermoplastic tube can also avoid direct contact between the measured core and the shear shaft, reduce wear on the end of the shear shaft, and extend the service life of the shear shaft.

[0024] Furthermore, it also includes a pressurizing component for pressurizing the test cavity and the accommodating cavity, and a first pressure monitoring device for monitoring the pressure in the test cavity and the accommodating cavity.

[0025] The inventors of this case also found in the process of in-depth research that the existing rock shear strength test devices are all carried out under no confining pressure conditions, and cannot truly simulate the triaxial stress state of the core in the deep formation, and cannot obtain the true shear strength characteristics. This is relatively effective for the shear strength measurement of rock masses in ground or shallow projects with low or even no confining pressure, such as civil engineering, tunnel mines, etc., but it cannot meet the simulation of geological operating environments of several thousand meters in the field of oil and gas. For the core deep in the formation, only under confining pressure conditions can the shear failure of the rock deep in the formation along the most easily broken surface determined by the microstructure and stress state be simulated, and the failure mode of the underground rock can be accurately reflected. Based on this, this scheme specially sets up a pressurizing component to apply pressure to the test cavity and the accommodating cavity, thereby simulating the confining pressure conditions deep in the formation, so that the shear failure process of the tested core is more in line with the real failure mode of the underground rock, thereby obtaining a more realistic shear strength that is more valuable for actual engineering mining.

[0026] The pressurizing component in this solution can pressurize the test cavity and the containing cavity as a whole by hydraulic pressure, air pressure or other pressurizing methods that can be realized by those skilled in the art. It should be noted that in this solution, the tested core is located in the thermoplastic tube, and the thermoplastic tube is used to block the pressurized medium and the tested pressure, so that the pressurized medium cannot enter the tested core and will not interfere with the mechanical properties of the tested core.

[0027] Furthermore, the pressurizing assembly includes an upper cover sealed with the base, and an oil pump for injecting hydraulic oil into the test cavity and the accommodating cavity; the two ends of the thermoplastic tube are respectively sealed with the pressure head and the output end of the linear drive mechanism.

[0028] In this solution, the top of the test chamber is closed by the upper cover, and hydraulic oil is injected through the oil pump to simulate the formation confining pressure. When in use, first put the tested rock core into the thermoplastic tube, and then put the two ends of the thermoplastic tube on the pressure head and the output end of the linear drive mechanism respectively, and seal them. The sealing can be achieved by using a sealing ring. This solution uses hydraulic oil to simulate the formation confining pressure, which can apply great pressure and simulate the confining pressure of deep formations, which is more in line with the actual working conditions of petroleum engineering.

[0029] Furthermore, a mounting groove is provided on the bottom surface of the accommodating cavity, and a support member matching the mounting groove is also included, wherein the support member is used to support the bottom of the measured core; along the axial direction, the shear axis is located between the support member and the step surface.

[0030] During the in-depth research, the inventor of this case also found that when the device of this application is used to perform a double shear surface test, one end of the tested core suspended in the accommodating chamber lacks support, and longitudinal displacement is prone to occur when the thrust of the axial positioning component is insufficient, affecting the accuracy of the test results. In order to overcome the above problems, this solution also provides an installation groove on the bottom surface of the accommodating chamber, and the support member is detachably connected in the installation groove; when performing a double shear surface test, one end of the tested core is located on the step surface and the other end is located on the support member. At this time, the shear axis is facing the middle area of ​​the tested core, which can stably achieve double shear surface shearing of the tested core and avoid longitudinal displacement of the tested core, which is beneficial to improve the stability and result accuracy of the double shear surface test. In addition, when the device of this application is used to perform a single shear surface test, the support member can be removed.

[0031] Furthermore, it also includes a holding member for holding the top of the measured core; along the axial direction, the shear axis is located on the side of the holding member away from the step surface.

[0032] The inventor of this case also found in the process of in-depth research that when the device of this application is used to perform a single shear plane test, the end of the tested core located on the step surface is prone to warp up, causing the core to deflect as a whole and affecting the accuracy of the test results. In order to overcome this problem, this solution also provides a holding member that matches the tested core. When performing a single shear plane test, the holding member is used to hold the tested core and then start the shear axis loading, which can avoid the core from deflecting and warping up, and is conducive to improving the stability of the single shear plane test and the accuracy of the results. In addition, when the device of this application is used to perform a double shear plane test, the support member can be omitted.

[0033] A multifunctional core shear strength test method, including a single shear plane test method and a double shear plane test method;

[0034] The single shear plane test method comprises:

[0035] One end of the core to be tested is located on the step surface, and the other end is suspended on the accommodation cavity;

[0036] The axial ends of the tested rock core are positioned by the axial positioning assembly so that an end surface of the tested rock core suspended above the accommodating cavity is coplanar with the side surface of the shear axis away from the step surface;

[0037] Load downward through the shear axis and record the loading force and loading displacement;

[0038] The double shear plane test method comprises:

[0039] One end of the tested rock core is located on the step surface, and the other end is located on the accommodating cavity;

[0040] Positioning the two axial ends of the measured rock core by the axial positioning assembly so that the two ends of the measured rock core are located on both sides of the shear axis respectively;

[0041] The shear axis is loaded downward, and the loading force is recorded by a force sensor, and the loading displacement is recorded by a displacement sensor.

[0042] Furthermore, before the downward loading is performed through the shear axis, the test chamber and the accommodating chamber are pressurized to a set pressure through a pressurizing assembly; the set pressure may be a formation pressure corresponding to the coring depth.

[0043] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0044] 1. The present invention provides a multifunctional rock core shear strength testing device and testing method, which have two different shear test modes, and can simultaneously meet the shear strength test requirements of conventional hard rock cores and fragile rock cores; when conducting shear strength tests on fragile rock cores, compared with traditional shear methods, the present application can multiply the shear surface area, that is, multiply the force-bearing area, thereby making it difficult for the rock sample to break under the shear load, thereby collecting more and more accurate test data, which is conducive to obtaining more accurate and reliable rock core shear strength results.

[0045] 2. The multifunctional rock core shear strength testing device and testing method of the present invention have an excellent anti-crushing effect on common fragile rock cores, and can completely obtain the force-displacement data during the shearing process. Therefore, it can solve the problem of core waste caused by traditional shearing devices and avoid the waste of scarce deep formation cores.

[0046] 3. The multifunctional core shear strength testing device and testing method of the present invention can carry out shear tests on small-sized, cylindrical cores, and can directly adapt to rock samples obtained after deep coring in petroleum engineering, solving the engineering problems caused by the need to take large-sized cores from deep layers, significantly reducing the difficulty and engineering risks of coring operations, and avoiding the waste of precious rock samples.

[0047] 4. The present invention provides a multifunctional core shear strength testing device and testing method. In different shear test modes or for rock samples of different lengths, it is sufficient to replace the pressure heads of different lengths accordingly. This can ensure effective shear tests in different shear test modes or for rock cores of different lengths, significantly improving the flexibility and versatility of the present application.

[0048] 5. The multifunctional core shear strength testing device and testing method of the present invention can simulate the confining pressure conditions deep in the formation, so that the shear failure process of the tested core is more consistent with the actual failure mode of the underground rock, which is conducive to obtaining more realistic and more valuable shear strength data for actual engineering mining.

[0049] 6. The present invention provides a multifunctional core shear strength testing device and testing method. By using a thermoplastic tube, the confining pressure medium can be prevented from penetrating into the pores inside the core to cause distortion of the shear strength. The device can also avoid direct contact between the tested core and the shear shaft, reduce wear on the end of the shear shaft, and extend the service life of the shear shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0051] Figure 1is a cross-sectional view of a specific embodiment of the present invention;

[0052] Figure 2 A schematic diagram of a shear axis in a specific embodiment of the present invention;

[0053] Figure 3 A schematic diagram of a pressure head in a specific embodiment of the present invention;

[0054] Figure 4 A schematic diagram of a support member in a specific embodiment of the present invention;

[0055] Figure 5 A schematic diagram of a pressing member in a specific embodiment of the present invention;

[0056] Figure 6 It is a schematic diagram of the connection of the thermoplastic pipe in a specific embodiment of the present invention;

[0057] Figure 7 It is a schematic diagram of a single shear plane test according to a specific embodiment of the present invention;

[0058] Figure 8 It is a schematic diagram of a double shear plane test according to a specific embodiment of the present invention.

[0059] Marks and corresponding parts names in the attached drawings:

[0060] 1-substrate, 101-test cavity, 102-accommodating cavity, 103-step surface, 2-shear axis, 3-linear driving mechanism, 4-power device, 5-pressure head, 501-cylindrical part, 502-square part, 6-thermoplastic tube, 7-first pressure monitoring device, 8-upper cover, 9-oil pump, 10-installation groove, 11-support member, 12-pressing member, 13-second pressure monitoring device, 14-tested core. DETAILED DESCRIPTION

[0061] In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the examples and the accompanying drawings. The schematic embodiments of the present invention and the description thereof are only used to explain the present invention and are not intended to limit the present invention. In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present application.

[0062] Embodiment 1:

[0063] like Figures 1 to 5A multifunctional core shear strength testing device shown in the figure comprises a substrate 1, a test cavity 101 located in the substrate 1, a step surface 103 located at the bottom end of the test cavity 101, and a receiving cavity 102 connected to the test cavity 101 and located below the test cavity 101, wherein the receiving cavity 102 is adjacent to the step surface 103; further comprising an axial positioning component matching the step surface 103, and a shear shaft 2 located in the test cavity 101 and facing the receiving cavity 102; the axial positioning component is used to axially position one or both ends of the tested core, and the shear shaft 2 is used to radially load the tested core; further comprising a force sensor for monitoring the loading force and a displacement sensor for monitoring the loading displacement.

[0064] The axial positioning assembly in this embodiment includes a linear drive mechanism 3 whose bottom end is at the same height as the step surface 103 , and a power device 4 for providing power to the linear drive mechanism 3 ; the output end of the linear drive mechanism 3 is located on the accommodating cavity 102 .

[0065] The axial positioning assembly in this embodiment further includes a pressing head 5 movably placed on the step surface 103 , and the pressing head 5 is arranged opposite to the output end of the linear drive mechanism 3 .

[0066] The bottom surface of the accommodating cavity 102 is provided with a mounting groove 10 , and also includes a support member 11 matching the mounting groove 10 , wherein the support member 11 is used to support the bottom of the measured core; along the axial direction, the shear axis 2 is located between the support member 11 and the step surface 103 .

[0067] It also includes a holding member 12 for holding the top of the core being tested; along the axial direction, the shear axis 2 is located on a side of the holding member 12 away from the step surface 103 .

[0068] In this embodiment, the shear shaft 2 is connected to the press for downward loading.

[0069] The linear drive mechanism 6 in this embodiment is a hydraulic piston, the matching power device 4 is a hydraulic pump, and the pipeline between the hydraulic pump and the hydraulic piston is connected with a second pressure monitoring device 13. A sealing ring is provided between the hydraulic piston and the base 1 for sealing.

[0070] Preferably, a semicircular arc notch matching the outer diameter of the core to be measured is provided at the bottom end of the shear shaft 2, the top end of the support member 11, and the bottom end of the holding member 12.

[0071] The testing device of this embodiment can carry out shear strength tests on cylindrical rock cores with a diameter of 1 inch; compared with the technology in the prior art that requires square standard rock samples with a cross-section of 5cm×5cm, it significantly saves rock samples and has strong adaptability to formation core tests in petroleum engineering.

[0072] In a more preferred embodiment, the step surface 103 can be a plane or a concave arc surface. When the step surface 103 is a plane, the pressure head 5 is square, and the side length of the pressure head is greater than the diameter of the measured core; when the step surface 103 is a concave arc surface, the pressure head 5 is a matching cylindrical shape, and the pressure head diameter is greater than or equal to the diameter of the measured core.

[0073] Embodiment 2:

[0074] A multifunctional core shear strength testing device, based on Example 1, as Figures 6 to 8 The device further comprises a thermoplastic tube 6 for accommodating the core to be tested, and two ends of the thermoplastic tube 6 are respectively connected to the pressure head 5 and the output end of the linear drive mechanism 3 .

[0075] This embodiment further includes a pressurizing component for pressurizing the test chamber 101 and the receiving chamber 102 , and a first pressure monitoring device 7 , such as a pressure gauge, for monitoring the pressure in the test chamber 101 and the receiving chamber 102 .

[0076] The pressurizing assembly in this embodiment includes an upper cover 8 sealed with the base 1, and an oil pump 9 for injecting hydraulic oil into the test cavity 101 and the accommodating cavity 102; both ends of the thermoplastic tube 6 are sealed with the pressure head 5 and the output end of the linear drive mechanism 3 respectively.

[0077] In a more preferred embodiment, the pressure head 5 has a cylindrical portion 501 that matches the thermoplastic tube 6, and the inner diameter of the thermoplastic tube 6 is equal to the diameter of the output shaft of the linear drive mechanism 3 and the diameter of the cylindrical portion 501. Sealing rings are provided at both ends of the thermoplastic tube 6 to achieve sealing at both ends of the axial direction.

[0078] In a more preferred embodiment, when the step surface 103 is a plane, the pressure head 5 further includes a square portion 502 for stably placing on the step surface.

[0079] In a more preferred embodiment, when the upper cover 8 is sealed and connected to the base 1 and a holding piece 12 is installed inside the base 1 , the bottom end of the holding piece 12 presses the core to be tested and the top end of the holding piece 12 abuts against the upper cover 8 .

[0080] Embodiment 3:

[0081] A multifunctional core shear strength test method: based on the test device in embodiment 1 or 2, comprising the following steps:

[0082] Step 1: Determine whether the core being tested is fragile:

[0083] If the core being tested is not brittle, the single shear plane test method is used;

[0084] If the core being tested is brittle, the double shear plane test method is used.

[0085] Among them, the judgment of whether the tested core is fragile can be made by the operating personnel, geological staff, etc. based on experience or based on the lithology; for example, loose sandstone, sandstone layers with rich bedding, rock layers after acid fracturing, loose carbonate rock, coal rock in the process of coalbed methane extraction, shale after hydration and expansion by external fluids, etc. are considered fragile, and the rest of the lithologies are considered non-fragile.

[0086] Step 2: Conduct shear strength test.

[0087] (1) For non-brittle cores, the process of single shear plane testing is as follows: Figure 7 As shown, the following steps are included:

[0088] Install the pressure head 5 for single shear plane testing, so that one end of the tested core 14 abuts against the pressure head 5 and the other end is flush with the side of the shear axis 2 away from the pressure head 5;

[0089] The other end of the tested core 14 is pushed by the linear drive mechanism 3 until the axial pushing load reaches a set value;

[0090] Install the holding member 12 so that the holding member 12 is located between the shear shaft 2 and the pressure head 5;

[0091] The load is loaded downward through the shear axis 2, the loading force is recorded by the force sensor, and the loading displacement is recorded by the displacement sensor to obtain a force-displacement curve.

[0092] Calculate the shear stress τ: τ = P / A; where: P is the loading force when the measured core 14 is sheared, and A is the cross-sectional area of ​​the measured core 14;

[0093] The internal friction angle φ can also be calculated based on the shear stress: τ = c + σ·tanφ; c is the cohesion and σ is the normal stress.

[0094] (2) For fragile cores, the process of double shear plane testing is as follows: Figure 8 As shown, the following steps are included:

[0095] Install the indenter 5 for double shear surface testing, and install the support member 11 into the installation groove 10;

[0096] Install the tested rock core 14 so that one end of the tested rock core 14 abuts against the pressure head 5 and the other end is located on the support member 11 and flush with the side of the support member 11 away from the pressure head 5;

[0097] The other end of the tested core 14 is pushed by the linear drive mechanism 3 until the axial pushing load reaches a set value;

[0098] Load downward through shear axis 2 and record the loading force and loading displacement.

[0099] Calculate the shear stress τ: τ = P / 2A; where: P is the loading force when the measured core 14 is sheared, and A is the cross-sectional area of ​​the measured core 14;

[0100] The internal friction angle φ can also be calculated based on the shear stress: τ = c + σ·tanφ; c is the cohesion and σ is the normal stress.

[0101] In addition, the present embodiment can also obtain other required shear strength parameters according to Moore's theory, which will not be elaborated here.

[0102] Preferably, when performing a single shear plane test, the dimensions of the core being tested are: 1 inch in diameter and 5 cm in length; the centerline of the shear axis 2 is located at 1 / 4 of the length of the core being tested, that is, the centerline of the shear axis 2 is 1 / 4 of the total length of the core being tested from one end of the core being tested, and is 3 / 4 of the total length of the core being tested from the other end of the core being tested.

[0103] Preferably, when performing a double shear plane test, the dimensions of the tested core are: 1 inch in diameter and 7.5 cm in length; the centerline of the shear axis 2 passes through the axial center of the tested core.

[0104] Embodiment 4:

[0105] A multifunctional core shear strength test method, based on Example 3, in this embodiment, whether a single shear plane test or a double shear plane test is performed, before the shear shaft 2 is loaded downward, the test chamber 101 and the accommodating chamber 102 are pressurized to a set pressure through a pressurizing component. Specifically:

[0106] Before installing the measured rock core 14, the measured rock core 14 is placed in a thermoplastic tube 6 with both ends open, and the inner diameter of the thermoplastic tube 6 is equal to or slightly larger than the diameter of the measured rock core 14;

[0107] The outer wall of the pressure head 5 and the outer wall of the output end of the linear drive mechanism 3 are both sleeved with sealing rings;

[0108] One end of the thermoplastic tube 6 is sleeved on the outer wall of the pressure head 5 used, and the other end is sleeved on the outer wall of the output end of the linear drive mechanism 3, and the sealing rings at both ends are inserted into the thermoplastic tube 6;

[0109] Start the linear drive mechanism 3 until the axial thrust load reaches a set value;

[0110] Heat the two ends of the thermoplastic tube 6, such as by blowing hot air, so that the two ends of the thermoplastic tube 6 are stably attached to the outer wall of the corresponding component;

[0111] Install the upper cover 8 and seal it;

[0112] Hydraulic oil is injected into the test chamber 101 and the accommodating chamber 102 through the oil pump 9 until the required pressure is reached.

[0113] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0114] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In addition, the term "connected" used in this article can be directly connected or indirectly connected via other components without special explanation.

Claims

1. A multifunctional core shear strength testing device, characterized in that: The invention comprises a base (1), a test cavity (101) located in the base (1), a step surface (103) located at the bottom end of the test cavity (101), and a receiving cavity (102) connected to the test cavity (101) and located below the test cavity (101), wherein the receiving cavity (102) is adjacent to the step surface (103); further comprises an axial positioning component matching the step surface (103), and a shear shaft (2) located in the test cavity (101) and facing the receiving cavity (102); the axial positioning component is used for axially positioning one end or both ends of a tested rock core, and the shear shaft (2) is used for radially loading the tested rock core; further comprises a force sensor for monitoring the loading force of the shear shaft (2), and a displacement sensor for monitoring the loading displacement of the shear shaft (2).

2. A multifunctional core shear strength testing device according to claim 1, characterized in that: The axial positioning assembly comprises a linear drive mechanism (3) whose bottom end is at the same height as the step surface (103) and a power device (4) for providing power to the linear drive mechanism (3); the output end of the linear drive mechanism (3) is located on the accommodating cavity (102).

3. A multifunctional core shear strength testing device according to claim 2, characterized in that: The axial positioning assembly further comprises a pressure head (5) movably placed on the step surface (103), and the pressure head (5) is arranged opposite to the output end of the linear drive mechanism (3).

4. A multifunctional core shear strength testing device according to claim 3, characterized in that: It also comprises a thermoplastic tube (6) for accommodating the rock core to be tested, and the two ends of the thermoplastic tube (6) are respectively connected to the pressure head (5) and the output end of the linear drive mechanism (3).

5. A multifunctional core shear strength testing device according to claim 4, characterized in that: It also includes a pressurizing component for pressurizing the test chamber (101) and the accommodating chamber (102), and a first pressure monitoring device (7) for monitoring the pressure in the test chamber (101) and the accommodating chamber (102).

6. A multifunctional core shear strength testing device according to claim 5, characterized in that: The pressurizing assembly comprises an upper cover (8) sealed with the base (1), and an oil pump (9) for injecting hydraulic oil into the test cavity (101) and the accommodating cavity (102); the two ends of the thermoplastic tube (6) are respectively sealed with the pressure head (5) and the output end of the linear drive mechanism (3).

7. A multifunctional core shear strength testing device according to claim 1, characterized in that: The bottom surface of the accommodating cavity (102) is provided with a mounting groove (10), and also includes a support member (11) matching the mounting groove (10), wherein the support member (11) is used to support the bottom of the measured core; along the axial direction, the shear axis (2) is located between the support member (11) and the step surface (103).

8. A multifunctional core shear strength testing device according to claim 1, characterized in that: It also comprises a holding piece (12) for holding the top of the core to be tested; along the axial direction, the shear axis (2) is located on a side of the holding piece (12) away from the step surface (103).

9. A testing method based on a multifunctional core shear strength testing device according to any one of claims 1 to 8, characterized in that: Including single shear plane test method and double shear plane test method; The single shear plane test method comprises: One end of the rock core to be tested is located on the step surface (103), and the other end is suspended in the accommodation cavity (102); The axial ends of the rock core to be measured are positioned by the axial positioning assembly so that the end surface of one end of the rock core to be measured suspended in the accommodating cavity (102) is coplanar with the side surface of the shear axis (2) in the direction away from the step surface (103); Load downwards through the shear axis (2), and record the loading force and loading displacement; The double shear plane test method comprises: One end of the rock core to be tested is located on the step surface (103), and the other end is located on the accommodating cavity (102); The axial ends of the measured rock core are positioned by the axial positioning assembly so that the two ends of the measured rock core are located on both sides of the shear axis (2) respectively; The shear axis (2) is loaded downward, and the loading force is recorded by a force sensor, and the loading displacement is recorded by a displacement sensor.

10. The testing method according to claim 9, characterized in that: Before the shear shaft (2) is loaded downward, the test chamber (101) and the accommodating chamber (102) are pressurized to a set pressure through a pressurizing component.

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