Rock core shear strength tester for petroleum field

Abstract

The utility model discloses a rock core shear strength tester for the petroleum field, which comprises a shear shaft, a base body and an upper cover detachably connected onto the base body. A first arc-shaped groove is formed in the top surface of the base body, and a first shearing hole is formed in the groove bottom of the first arc-shaped groove; a second arc-shaped groove is formed in the bottom surface of the upper cover, a second shearing hole is formed in the top of the second arc-shaped groove, the first shearing hole and the second shearing hole are both matched with the shearing shaft, and the second shearing hole penetrates through the upper cover; when the upper cover is connected with the base body, the first arc-shaped groove and the second arc-shaped groove are spliced into a cylindrical cavity, and the first shearing hole and the second shearing hole are opposite to each other; a third arc-shaped groove is formed in the bottom end of the shearing shaft; and the inner diameters of the first arc-shaped groove, the second arc-shaped groove and the third arc-shaped groove are equal. The rock shear strength testing device is used for solving the problem that a rock shear strength testing device in the prior art is poor in adaptability to rock cores in the petroleum industry, and the purposes of improving the utilization rate of the rock cores, reducing waste of the rock cores and the like are achieved.

Description

Technical Field

[0001] The utility model relates to the field of petroleum engineering, in particular to a rock core shear strength tester used in the petroleum field. Background Art

[0002] Rock failure is often accompanied by shear failure. Formation failure due to shear deformation occurs in nearly every phase of oil and gas development, and in severe cases can endanger the safety of drilling, completion, and oil and gas production. Therefore, rock shear strength is a key characteristic in rock mechanics research, possessing greater practical engineering significance than rock compressive and tensile strengths. Accurately determining rock shear strength parameters is crucial for oil and gas engineering.

[0003] Existing rock shear strength testing devices and related standards are designed for surface geotechnical engineering. There are no dedicated specifications specifically for the oil industry, specifically for testing the shear strength of rocks deep within the formation. Existing rock shear strength testing devices have at least the following drawbacks when used for core shear strength testing in the oil industry:

[0004] (1) The rock shear strength test devices in the existing technology are mostly suitable for testing large-sized rock samples with square cross-sections and overall 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 in rock masses, 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 continuous increase in demand for oil, the stratum depth of oil and gas exploration has continued to increase, and the scale of drilling deep wells and ultra-deep wells has been 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, due to the constraints of core acquisition conditions and costs, conventional shear strength test devices for rectangular samples have been unable to meet the growing needs of petroleum engineering technology.

[0005] (2) In the field of petroleum engineering, due to the fact that the coring depth can easily reach several thousand meters, various strata with 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 during coalbed methane extraction, and shale after hydration and expansion by external fluids. During extensive research, the applicant found that when using existing shear strength testing equipment to test such brittle cores, the cores are very likely to break as a whole under the action of shear load, resulting in too little test data being collected. Not only can the required shear strength not be accurately obtained, but also expensive formation cores are wasted.

[0006] Therefore, the rock shear strength testing device in the existing technology has poor adaptability to rock cores in the oil field. It is necessary to develop a special testing instrument specifically for the shear strength test of rocks in the oil field and deep in the surface strata. Utility Model Content

[0007] The utility model provides a rock core shear strength tester for the petroleum field, so as to solve the problem that the rock shear strength test device in the prior art is poorly adaptable to the rock cores of the petroleum industry, thereby achieving the purposes of improving the utilization rate of the rock cores and reducing the waste of the rock cores.

[0008] The utility model is achieved through the following technical solutions:

[0009] A core shear strength tester for use in the petroleum field comprises a shear shaft, a base, and an upper cover detachably connected to the base; a first arcuate groove is provided on the top surface of the base, a first shear hole is provided at the bottom of the first arcuate groove; a second arcuate groove is provided on the bottom surface of the upper cover, a second shear hole is provided at the top of the second arcuate groove, the first and second shear holes both match the shear shaft, and the second shear hole passes through the upper cover;

[0010] When the upper cover is connected to the base, the first arc-shaped groove and the second arc-shaped groove are combined into a cylindrical cavity, and the first shearing hole and the second shearing hole are opposite to each other;

[0011] A third arc-shaped groove is provided at the bottom end of the shear shaft; the inner diameters of the first arc-shaped groove, the second arc-shaped groove and the third arc-shaped groove are all equal.

[0012] In response to the problem that the rock shear strength test device in the prior art is poorly adaptable to the cores of the oil industry, the utility model proposes a core shear strength tester for the oil field, wherein the shear shaft is used to connect to the press and provide a shear load to the core to be tested. The application has a base body, and a top cover is detachably connected to the base body; when the top cover is connected to the base body, the first arc-shaped groove and the second arc-shaped groove face each other and fit together to form a cylindrical cavity, which matches the size of the core to be tested. The core to be tested is stably placed inside the cylindrical cavity, and then the shear shaft enters the second shear hole and acts on the surface of the core to be tested, so that the shear load can be loaded downward. In the present application, the inner diameters of the first arc-shaped groove, the second arc-shaped groove and the third arc-shaped groove are all equal, which are equal to the outer diameter of the tested rock core, thereby making the present application extremely adaptable to deep formation rock samples taken out in petroleum engineering. Shear strength tests can be carried out directly on the small-sized, cylindrical rock cores taken out, without the need for secondary processing of the rock cores and avoiding the engineering difficulties caused by the need to take out large-sized rock cores. This significantly reduces the difficulty and engineering risks of coring operations and avoids the waste of precious rock samples.

[0013] Furthermore, the axis of the cylindrical cavity is perpendicular to and intersects with the axis of the shear axis, and the axis of the third arc-shaped groove is also perpendicular to and intersects with the axis of the shear axis, to ensure that the shear axis is uniformly loaded downward from the top center position of the measured core.

[0014] Furthermore, the shear shaft is square, and the first shear hole and the second shear hole are both square holes that match the shear shaft, which is convenient for preventing the shear shaft from rotating, and is beneficial for ensuring the lateral stability of the shear shaft, and further ensuring the stability of loading.

[0015] Furthermore, it also includes 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.

[0016] The force sensor and displacement sensor in this solution 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 that matches the shear shaft, and no specific restrictions are made here. In addition, the force sensor and 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 displacement sensor, this solution 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. It can also be used to evaluate the shear failure characteristics of different rock types.

[0017] Furthermore, the invention also includes an axial positioning assembly for axially positioning the core being tested, wherein the axial positioning assembly matches the cylindrical cavity. This solution uses the axial positioning assembly to position the core being tested axially, which is beneficial to improving the stability of the shearing process.

[0018] Furthermore, the axial positioning assembly includes a positioning bolt and an axial pressure head respectively located at both ends of the cylindrical cavity; the axis of the positioning bolt is collinear with the axis of the cylindrical cavity, and the axial pressure head is detachably connected to the cylindrical cavity; the axial positioning assembly also includes an axial pressure mechanism abutting against the axial pressure head, and the axial pressure mechanism is located at the end of the axial pressure head away from the positioning bolt.

[0019] This solution uses an axial positioning assembly to ensure the axial stability of the core being tested, while an axial pressure mechanism provides the axial stress required for the shear test. The positioning bolt can be rotated within the cylindrical cavity, and the axial pressure head can be removed from the cylindrical cavity.

[0020] Furthermore, the axial pressure mechanism includes a linear drive device and a power device for providing power to the linear drive device. Providing the axial stress required for the shear test through the linear drive device is beneficial to improving the accuracy of the test results.

[0021] Furthermore, there is a gap between the base and the axial pressure mechanism for accommodating the shear shaft.

[0022] This solution provides two different shear test modes, which can meet the shear strength test requirements of both conventional hard core and brittle core:

[0023] When the core being tested is a conventional hard core, a single shear plane test method is used for testing. The specific process includes: removing the axial pressure head from the cylindrical cavity; placing the core being tested of a specified length into the cylindrical cavity, and pushing the core being tested until it abuts against the axial pressure mechanism by adjusting the positioning bolts; moving the shear axis to above the gap, applying load downward through the shear axis, and recording the loading force and loading displacement.

[0024] When the tested core is brittle, a dual shear surface test method is used. The specific process includes: placing an axial pressure head into a cylindrical cavity; using a tested core of a specified length and placing it into the cylindrical cavity, pushing the tested core by adjusting the positioning bolts so that the axial pressure head abuts against the axial pressure mechanism, and the two ends of the tested core abut against the positioning bolts and the axial pressure head respectively; moving the shear shaft to above the second shear hole, loading downward through the shear shaft, and recording the loading force and loading displacement.

[0025] It can be seen that when conducting shear strength tests on fragile rock cores, the present application can multiply the shear surface area, that is, multiply the force-bearing area, compared to the traditional shearing method, so that the rock sample is not easily broken 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. The inventor's experiments have confirmed that the present application has an excellent anti-crushing effect on common fragile rock cores (such as loose sandstone, sandstone layers with rich stratification, rock layers after acid fracturing, loose carbonate rocks, coal rocks in the coalbed methane mining process, and shales after hydration and expansion by external fluids), and can fully obtain force-displacement data during the shear process. Therefore, it can solve the problem of core waste caused by traditional shearing devices and avoid the waste of scarce deep formation cores.

[0026] Furthermore, the invention further comprises a base, the base body being fixedly mounted on the base; a bolt seat being provided on the base, the positioning bolt passing through the bolt seat and being threadedly engaged with the bolt seat, and the bolt seat ensuring that the positioning bolt cannot move freely in the axial direction.

[0027] Furthermore, the shear shaft is slidably connected to the bracket, and the sliding direction of the shear shaft is parallel to the axial direction of the cylindrical cavity. The shear shaft can adopt any existing sliding method to achieve cooperation with the bracket.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] 1. The core shear strength tester of the utility model is used in the petroleum field and is well adapted to deep formation rock samples taken in petroleum engineering. It can directly carry out shear strength tests on small-sized, cylindrical rock cores taken out, without the need for secondary processing of the rock cores and avoiding the engineering difficulties caused by the need to take out large-sized rock cores. It significantly reduces the difficulty and engineering risks of coring operations and avoids the waste of precious rock samples.

[0030] 2. The core shear strength tester of the utility model used in the petroleum field can provide two different shear test modes, which can simultaneously meet the shear strength test requirements of conventional hard cores and fragile cores.

[0031] 3. The utility model is a core shear strength tester used in the petroleum field. When conducting shear strength tests on fragile cores, compared with traditional shearing methods, the utility model 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 core shear strength results.

[0032] 4. The utility model is a core shear strength tester used in the petroleum field. It has an excellent anti-crushing effect on common fragile cores, can fully obtain the force-displacement data during the shearing process, can solve the problem of core waste caused by traditional shearing devices, and can avoid the waste of scarce deep formation cores. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying 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 accompanying drawings:

[0034] Figure 1 A cross-sectional view of a specific embodiment of the present utility model;

[0035] Figure 2 This is a schematic diagram of a partial structure in which the positioning bolts are omitted in a specific embodiment of the present utility model;

[0036] Figure 3 This is a schematic diagram of a single shear plane test according to a specific embodiment of the present invention;

[0037] Figure 4Schematic diagram of a double shear plane test according to a specific embodiment of the present invention.

[0038] Markings and corresponding parts names in the accompanying drawings:

[0039] 1- shear shaft, 2- base, 3- upper cover, 4- first shear hole, 5- second shear hole, 6- third arc groove, 7- positioning bolt, 8- axis pressure head, 9- linear drive device, 10- power device, 11- base, 12- measured core, 13- gap, 14- bolt seat, 15- bracket. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the examples and drawings. The schematic implementation methods of the present invention and their descriptions 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 orientations or positional relationships indicated by terms such as "front", "back", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inside", "outside", etc. are based on the orientations or positional relationships shown in the accompanying drawings, and are 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.

[0041] Example 1:

[0042] like Figure 1 and Figure 2 The core shear strength tester shown for use in the petroleum industry includes a shear shaft 1, a base 2, and an upper cover 3 detachably connected to the base 2. The base 2 has a first arcuate groove on its top surface, with a first shear hole 4 defined at its bottom. The upper cover 3 has a second arcuate groove on its bottom surface, with a second shear hole 5 defined at its top. Both the first and second shear holes 4 and 5 match the shear shaft 1, and the second shear hole 5 extends through the upper cover 3.

[0043] When the upper cover 3 is connected to the base 2, the first arc-shaped groove and the second arc-shaped groove are combined into a cylindrical cavity, and the first shearing hole 4 and the second shearing hole 5 are opposite to each other;

[0044] A third arc-shaped groove 6 is provided at the bottom end of the shear shaft 1 ; the inner diameters of the first arc-shaped groove, the second arc-shaped groove and the third arc-shaped groove 6 are all equal.

[0045] The axis of the cylindrical cavity is perpendicular to and intersects with the axis of the shear axis 1 , and the axis of the third arc-shaped groove 6 is also perpendicular to and intersects with the axis of the shear axis 1 .

[0046] The shear shaft 1 is square, and the first shear hole 4 and the second shear hole 5 are both square holes matching the shear shaft 1 .

[0047] This embodiment further includes a force sensor for monitoring the loading force of the shear shaft 1 and a displacement sensor for monitoring the loading displacement of the shear shaft 1 .

[0048] This embodiment further includes a base 11 , and the base 2 is fixedly mounted on the base 11 .

[0049] Example 2:

[0050] A core shear strength tester for the oil field, based on Example 1, as Figures 1 to 4 As shown, it also includes an axial positioning component for axially positioning the measured core, and the axial positioning component matches the cylindrical cavity.

[0051] In this embodiment, the axial positioning assembly includes a positioning bolt 7 and an axial pressure head 8, respectively located at both ends of the cylindrical cavity; the axis of the positioning bolt 7 is collinear with the axis of the cylindrical cavity, and the axial pressure head 8 is detachably connected to the cylindrical cavity; the axial positioning assembly also includes an axial pressure mechanism that abuts the axial pressure head 8 and is located at the end of the axial pressure head 8 away from the positioning bolt 7. The axial pressure mechanism includes a linear drive device 9 and a power device 10 for providing power to the linear drive device 9.

[0052] A gap 13 is defined between the base 2 and the axial pressure mechanism to accommodate the shear shaft 1. A bolt seat 14 is also provided on the base 11, through which the positioning bolt 7 passes and is threadedly engaged. The shear shaft 1 is slidably connected to the bracket 15, with the sliding direction of the shear shaft 1 being parallel to the axial direction of the cylindrical cavity.

[0053] It should be noted that this embodiment is Figure 2 The positioning bolts, brackets and other structures are omitted. When used, the positioning bolts need to be screwed into the bolt seat 14.

[0054] Preferably, the linear drive device 9 is a hydraulic cylinder, and the power device 10 is a hydraulic pump. A pressure sensor for monitoring the pressure in the hydraulic cylinder is also included.

[0055] The working process of the tester of this embodiment can refer to the following steps:

[0056] Step 1: Determine whether the core 12 to be tested is brittle and decide on the shear mode to be used:

[0057] If the core being tested is not brittle, use the single shear plane test mode;

[0058] If the core being tested is brittle, use the double shear plane test mode.

[0059] 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.

[0060] Step 2: Conduct shear strength test.

[0061] (1) For non-brittle cores, the single shear plane test mode process is as follows Figure 3 As shown, the following steps are included:

[0062] Remove the axial pressure head from the cylindrical cavity; place the core to be tested of a specified length into the cylindrical cavity, and push the core to be tested until it abuts against the axial pressure mechanism by adjusting the positioning bolts; move the shear shaft to above the gap;

[0063] Load downward through the shear axis 1, record the loading force through the force sensor, and record the loading displacement through the displacement sensor to obtain a force-displacement curve.

[0064] Calculate the shear stress τ: τ = P / A; where P is the load force when the core is sheared, and A is the cross-sectional area of ​​the core.

[0065] The internal friction angle φ can also be calculated based on the shear stress: τ = c + σ·tanφ, where c is the cohesion and σ is the normal stress.

[0066] 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 1 is located at 1 / 4 of the length of the core being tested, that is, the distance between the centerline of the shear axis 1 and one end of the core being tested is 1 / 4 of the total length of the core being tested, and the distance between the centerline of the shear axis 1 and the other end of the core being tested is 3 / 4 of the total length of the core being tested.

[0067] (2) For fragile cores, the process of the double shear plane test mode is as follows Figure 4 As shown, the following steps are included:

[0068] Place the axial pressure head into the cylindrical cavity; take a rock core of a specified length and place it into the cylindrical cavity, and push the rock core by adjusting the positioning bolts so that the axial pressure head abuts against the axial pressure mechanism, and the two ends of the rock core abut against the positioning bolts and the axial pressure head respectively; move the shear shaft to above the second shear hole;

[0069] Load downward through shear axis 1 and record the loading force and loading displacement.

[0070] Calculate the shear stress τ: τ = P / 2A; where P is the load force when the core is sheared, and A is the cross-sectional area of ​​the core.

[0071] The internal friction angle φ can also be calculated based on the shear stress: τ = c + σ·tanφ, where c is the cohesion and σ is the normal stress.

[0072] 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 1 passes through the axial center of the tested core.

[0073] In addition, those skilled in the art can also obtain the remaining required shear strength parameters based on Moore's theory, which will not be described in detail here.

[0074] In addition, when using different shear test modes, if the maximum stroke of the positioning bolt 7 is not sufficient to meet the pushing requirement, the positioning bolt 7 can be replaced with a different length to complete the required test.

[0075] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the utility model in detail. It should be understood that the above description is only a specific implementation method of the utility model and is not intended to limit the scope of protection of the utility model. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the utility model should be included in the scope of protection of the utility model.

[0076] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises", or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In addition, the term "connected" as used in this document, unless otherwise specified, may refer to a direct connection or an indirect connection via other components.

Claims

1. A core shear strength tester for use in the petroleum field, comprising a shear shaft (1), characterized in that: It also includes a base (2) and an upper cover (3) detachably connected to the base (2); a first arc-shaped groove is provided on the top surface of the base (2), and a first shearing hole (4) is provided at the bottom of the first arc-shaped groove; a second arc-shaped groove is provided on the bottom surface of the upper cover (3), and a second shearing hole (5) is provided at the top of the second arc-shaped groove; the first shearing hole (4) and the second shearing hole (5) both match the shearing shaft (1), and the second shearing hole (5) passes through the upper cover (3); When the upper cover (3) is connected to the base (2), the first arc-shaped groove and the second arc-shaped groove are combined into a cylindrical cavity, and the first shearing hole (4) and the second shearing hole (5) are opposite to each other; A third arc-shaped groove (6) is provided at the bottom end of the shear shaft (1); the inner diameters of the first arc-shaped groove, the second arc-shaped groove and the third arc-shaped groove (6) are all equal.

2. The core shear strength tester for use in the petroleum field according to claim 1, characterized in that: The axis of the cylindrical cavity is perpendicular to and intersects with the axis of the shear axis (1), and the axis of the third arc-shaped groove (6) is also perpendicular to and intersects with the axis of the shear axis (1).

3. The core shear strength tester for use in the petroleum field according to claim 1, characterized in that: The shearing shaft (1) is square, and the first shearing hole (4) and the second shearing hole (5) are both square holes that match the shearing shaft (1).

4. The core shear strength tester for use in the petroleum field according to claim 1, characterized in that: It also includes a force sensor for monitoring the loading force of the shear shaft (1) and a displacement sensor for monitoring the loading displacement of the shear shaft (1).

5. The core shear strength tester for use in the petroleum field according to claim 1, characterized in that: It also includes an axial positioning component for axially positioning the measured core, and the axial positioning component matches the cylindrical cavity.

6. The core shear strength tester for use in the petroleum field according to claim 5, characterized in that: The axial positioning assembly includes a positioning bolt (7) and an axial pressure head (8) respectively located at both ends of the cylindrical cavity; the axis of the positioning bolt (7) is colinear with the axis of the cylindrical cavity, and the axial pressure head (8) is detachably connected to the cylindrical cavity; the axial positioning assembly also includes an axial pressure mechanism abutting against the axial pressure head (8), and the axial pressure mechanism is located at an end of the axial pressure head (8) away from the positioning bolt (7).

7. The core shear strength tester for use in the petroleum field according to claim 6, characterized in that: The axial pressurizing mechanism comprises a linear drive device (9) and a power device (10) for providing power to the linear drive device (9).

8. The core shear strength tester for use in the petroleum field according to claim 6, characterized in that: A gap (13) for accommodating the shear shaft (1) is provided between the base body (2) and the axial pressing mechanism.

9. The core shear strength tester for use in the petroleum field according to claim 6, characterized in that: It also includes a base (11), on which the base (2) is fixedly mounted; a bolt seat (14) is also provided on the base (11), and the positioning bolt (7) passes through the bolt seat (14) and is threadedly engaged with the bolt seat (14).

10. The core shear strength tester for use in the petroleum field according to claim 1, characterized in that: The shear shaft (1) is slidably connected to the bracket (15), and the sliding direction of the shear shaft (1) is parallel to the axial direction of the cylindrical cavity.

Images