A method for evaluating the compressibility of tight reservoirs based on cyclic loading and unloading tests

Abstract

The embodiments of this specification relate to the technical field of oil and gas extraction, and provide a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, the method comprising: performing multiple cyclic loading and unloading tests on a tight rock sample to obtain stress-strain data; drawing a stress-strain curve according to the stress-strain data, marking a closed loop formed by the unloading curve obtained by the first test and the loading curve obtained by the next test as a first hysteresis loop; marking a closed loop formed by the loading curve obtained by the last test and the unloading curve obtained by the previous test as a second hysteresis loop; calculating the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop, and evaluating the compressibility of the tight rock sample according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop. Through the embodiments of this specification, the real performance of the reservoir under complex geological stress conditions can be accurately reflected, and the accuracy of the evaluation of the compressibility of the tight reservoir can be improved.

Description

Technical Field

[0001] The embodiments of this specification relate to the technical field of oil and gas extraction, and in particular to a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test. Background Art

[0002] Tight reservoirs refer to reservoirs with low permeability such as sandstone, carbonate rock, mixed rock, tuff and shale. Tight reservoir compressibility refers to the ability of shale reservoirs to form complex fracture networks during fracturing development. Since shale gas reservoirs have low porosity and permeability, they can only be effectively developed through horizontal well volume fracturing transformation. According to field experience, when shale compressibility is good, complex fracture networks are easily generated during fracturing, and the production capacity of shale gas wells after fracturing is relatively high. When shale compressibility is poor, shale is prone to plastic deformation during fracturing, and complex fracture networks are not easily generated. The production capacity of shale gas wells after fracturing is relatively low. By evaluating the compressibility of reservoirs, the permeability and gas storage capacity of underground rocks can be predicted, thereby determining the distribution and reserves of oil and gas reservoirs, which in turn helps geologists and petroleum engineers develop more effective exploration and development strategies and improve the efficiency and success rate of resource extraction.

[0003] With the increasing demand for the development of unconventional oil and gas resources, efficient and accurate assessment of the compressibility of reservoir rocks has become the key to improving the efficiency of hydraulic fracturing. At present, most reservoir compressibility evaluation methods are based on a single loading test, which is difficult to accurately reflect the true performance of the reservoir under complex geological stress conditions, resulting in low accuracy in the evaluation of tight reservoir compressibility. Therefore, there is an urgent need for a tight reservoir compressibility evaluation method that can accurately reflect the true performance of the reservoir under complex geological stress conditions, thereby improving the accuracy of the tight reservoir compressibility evaluation and providing a basis for judging whether the reservoir is suitable for fracturing transformation. Summary of the invention

[0004] In view of the above-mentioned problems in the prior art, the purpose of the embodiments of this specification is to provide a method for evaluating the compressibility of tight reservoirs based on cyclic loading and unloading tests, so as to solve the problem that it is difficult to accurately reflect the true performance of the reservoir under complex geological stress conditions in the prior art, resulting in low accuracy in the evaluation of the compressibility of tight reservoirs.

[0005] In order to solve the above technical problems, the specific technical solutions of the embodiments of this specification are as follows:

[0006] On the one hand, the embodiments of this specification provide a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, the method comprising:

[0007] The dense rock sample is placed in a compression testing machine, and multiple cyclic loading and unloading tests are performed at a preset frequency based on a preset confining pressure, and the stress and strain data generated by each cyclic loading and unloading test are recorded;

[0008] Draw a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve;

[0009] The closed loop formed by the unloading curve obtained by the first cyclic loading and unloading test and the loading curve obtained by the next cyclic loading and unloading test is marked as the first hysteresis loop; the closed loop formed by the loading curve obtained by the last cyclic loading and unloading test and the unloading curve obtained by the previous cyclic loading and unloading test is marked as the second hysteresis loop;

[0010] calculating an area of ​​the first hysteresis loop and an area of ​​the second hysteresis loop, and obtaining a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop;

[0011] The compressibility of the dense rock sample is evaluated according to the compressibility characteristic value.

[0012] Furthermore, the method further comprises:

[0013] The stress-strain curves of each cyclic loading and unloading test are summarized to obtain the total stress-strain curve;

[0014] The elastic modulus of the dense rock sample in the elastic deformation stage is calculated according to the total stress-strain curve, wherein the elastic modulus is calculated by the following formula:

[0015]

[0016] Among them, E d represents the elastic modulus, σ d,max represents the maximum stress on any hysteresis loop on the total stress-strain curve, σ d,min represents the minimum stress on any hysteresis loop on the total stress-strain curve, ε d,max Represents σ d,max The corresponding strain, ε d,min Represents σ d,min The corresponding strain.

[0017] Furthermore, the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop are calculated by the following formula:

[0018]

[0019]

[0020] Among them, s 1 is the area of ​​the first hysteresis loop, s 2 is the area of ​​the second hysteresis loop, ε d1,max is the maximum strain on the first hysteresis loop; ε d1,min is the minimum strain on the first hysteresis loop; ε d2,maxis the maximum strain on the second hysteresis loop; ε d2,min is the minimum strain on the second hysteresis loop; σ i1 is the stress of the loading process on the first hysteresis loop; σ u1 is the stress of the unloading process on the first hysteresis loop; σ i2 is the stress of the loading process on the second hysteresis loop; σ u2 is the stress of the unloading process on the second hysteresis loop.

[0021] Furthermore, the compressibility of the dense rock sample is evaluated according to the compressibility characteristic value, including: the larger the compressibility characteristic value is, the better the compressibility of the dense rock sample is.

[0022] Furthermore, the method for determining the preset confining pressure, preset frequency and number of cycles includes:

[0023] The preset confining pressure, preset frequency and number of cycles are continuously adjusted until the difference between the first hysteresis loop area and the second hysteresis loop area in the corresponding stress-strain curve exceeds a preset threshold.

[0024] Furthermore, the method further comprises:

[0025] Obtaining the compression difficulty of the dense rock sample according to the elastic modulus;

[0026] The compressibility of the dense rock sample is evaluated according to the compression difficulty and the compressibility characteristic value.

[0027] On the other hand, the embodiment of this specification provides a device for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, the device comprising:

[0028] The test module is used to place the dense rock sample in the compression testing machine, perform multiple cyclic loading and unloading tests at a preset frequency based on a preset confining pressure, and record the stress and strain data generated by each cyclic loading and unloading test;

[0029] A drawing module, used for drawing a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve;

[0030] A hysteresis loop marking module is used to mark the closed loop formed by the unloading curve obtained by the first cyclic loading and unloading test and the loading curve obtained by the next cyclic loading and unloading test as the first hysteresis loop; and mark the closed loop formed by the loading curve obtained by the last cyclic loading and unloading test and the unloading curve obtained by the previous cyclic loading and unloading test as the second hysteresis loop;

[0031] a calculation module, configured to calculate an area of ​​the first hysteresis loop and an area of ​​the second hysteresis loop, and obtain a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop;

[0032] An evaluation module is used to evaluate the compressibility of the dense rock sample according to the compressibility characteristic value.

[0033] On the other hand, an embodiment of the present specification further provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein when the computer program is executed by the processor, the instructions of any one of the above methods are executed.

[0034] On the other hand, an embodiment of the present specification further provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor of a computer device, the computer program executes instructions of any one of the above-described methods.

[0035] On the other hand, the embodiments of this specification further provide a computer program product, which, when executed by a processor of a computer device, executes instructions of any one of the above methods.

[0036] One or more technical solutions provided by some embodiments of this specification have at least the following technical effects:

[0037] The embodiment of this specification performs multiple cyclic loading and unloading tests on dense rock samples under preset confining pressure and preset frequency, thereby analyzing the cyclic loading and unloading behavior of dense rock samples under simulated geological conditions, and then generates a stress-strain curve based on the stress-strain data generated in each test, from which the stress-strain characteristics of the dense rock sample are analyzed, and the area ratio of the hysteresis loop of the curve is calculated, which is used as an evaluation index of the rock compressibility. Therefore, the above scheme can more comprehensively reflect the true performance of the reservoir under complex geological stress conditions, thereby improving the accuracy of the evaluation of the compressibility of the dense reservoir, and providing a basis for judging whether the reservoir is suitable for fracturing transformation.

[0038] The above description is only an overview of the technical solutions of some embodiments of this specification. In order to more clearly understand the technical means of some embodiments of this specification, they can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiments of this specification more obvious and easy to understand, the following specifically cites the preferred embodiments and describes them in detail in conjunction with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A schematic flow chart of a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test in some embodiments of this specification is shown;

[0041] Figure 2 A schematic diagram showing a hysteresis loop in a stress-strain curve in some embodiments of the present specification;

[0042] Figure 3 A schematic diagram of a total stress-strain curve in some embodiments of this specification is shown;

[0043] Figure 4 A schematic diagram of the structure of a tight reservoir compressibility evaluation device based on a cyclic loading and unloading test in some embodiments of this specification is shown;

[0044] Figure 5 A schematic diagram of the structure of a computer device in this specification is shown.

[0045] Description of the accompanying symbols:

[0046] 401. Experimental module;

[0047] 402, drawing module;

[0048] 403. Hysteresis loop marking module;

[0049] 404. Calculation module;

[0050] 405. Evaluation module;

[0051] 502. Computer equipment;

[0052] 504, processor;

[0053] 506. Memory;

[0054] 508, driving mechanism;

[0055] 510, input / output module;

[0056] 512. Input devices;

[0057] 514. Output device;

[0058] 516. Presentation equipment;

[0059] 518. Graphical user interface;

[0060] 520, network interface;

[0061] 522, communication link;

[0062] 524. Communication bus. DETAILED DESCRIPTION

[0063] The following will be combined with the drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this specification.

[0064] In order to solve the above problems, the embodiments of this specification provide a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test. Figure 1 This is a flow chart of a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test provided in an embodiment of this specification. This specification provides method operation steps as described in the embodiment or flow chart, but more or fewer operation steps may be included based on conventional or non-creative labor. The order of steps listed in the embodiment is only one way of executing the order of many steps and does not represent the only execution order. When the system or device product is executed in practice, it can be executed in the order of the method shown in the embodiment or the drawings or in parallel.

[0065] It should be noted that the terms "first", "second", etc. in this specification and claims and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of this specification described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0066] Reference Figure 1 As shown, the embodiment of this specification provides a method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, the method comprising:

[0067] S101: placing the dense rock sample in a compression testing machine, performing multiple cyclic loading and unloading tests at a preset frequency based on a preset confining pressure, and recording stress and strain data generated by each cyclic loading and unloading test;

[0068] S102: drawing a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve;

[0069] S103: marking a closed loop formed by an unloading curve obtained from the first cyclic loading and unloading test and a loading curve obtained from the next cyclic loading and unloading test as a first hysteresis loop; marking a closed loop formed by a loading curve obtained from the last cyclic loading and unloading test and an unloading curve obtained from the previous cyclic loading and unloading test as a second hysteresis loop;

[0070] S104: calculating the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop, and obtaining a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop;

[0071] S105: Evaluate the compressibility of the dense rock sample according to the compressibility characteristic value.

[0072] The embodiment of this specification performs multiple cyclic loading and unloading tests on dense rock samples under preset confining pressure and preset frequency, thereby analyzing the cyclic loading and unloading behavior of dense rock samples under simulated geological conditions, and then generates a stress-strain curve based on the stress-strain data generated in each test, from which the stress-strain characteristics of the dense rock sample are analyzed, and the area ratio of the hysteresis loop of the curve is calculated, which is used as an evaluation index of the rock compressibility. Therefore, the above scheme can more comprehensively reflect the true performance of the reservoir under complex geological stress conditions, thereby improving the accuracy of the evaluation of the compressibility of the dense reservoir, and providing a basis for judging whether the reservoir is suitable for fracturing transformation.

[0073] In the embodiments of this specification, the dense rock sample can be a standard core cylindrical rock sample with a diameter of 25 mm and a length of 50 mm. Obtaining a core cylinder of this size usually involves a drilling process to extract the original core from the underground rock, and then use professional cutting equipment in the laboratory or on-site to cut it into a cylindrical sample of standard size. During the cutting process, it is necessary to ensure the surface finish and flatness of the core to facilitate subsequent testing and analysis. Due to its moderate size, the standard core cylinder of φ25mm×50mm is suitable for experiments such as permeability testing, porosity analysis, rock microstructure observation, and compressibility testing. Through these tests, the oil storage capacity, permeability and microstructural characteristics of the rock can be understood, providing a scientific basis for the evaluation and exploitation of oil and gas resources.

[0074] In some embodiments, the compression tester can be a uniaxial compression tester or a triaxial compression tester. The main difference between uniaxial compression and triaxial compression is the direction and amount of the applied force. Uniaxial compression refers to applying axial pressure to the sample in one direction, that is, the direction of the maximum principal stress, while the stress in the other directions is zero. Its test device is simple, low-cost, easy to operate, and can perform high-temperature and high-pressure tests, with a wide range of applications. Triaxial compression applies external pressure to uniformly squeeze the rock sample in three mutually perpendicular directions, simulating a more complex stress state to more fully understand the mechanical properties of the rock sample. In practical applications, appropriate compression conditions can be selected according to the research purpose and rock sample characteristics.

[0075] In some embodiments, a standard core cylinder of φ25mm×50mm is placed in a triaxial compression testing machine, and multiple cyclic loading and unloading tests are performed based on a preset confining pressure and a preset frequency. The loading and unloading test is a test method for testing the mechanical response and performance changes of rock samples under different stress conditions. In the loading stage, the test machine gradually increases the pressure applied to the rock sample to observe and record the deformation and stress changes of the rock sample. In the unloading stage, the applied pressure is gradually reduced to observe the deformation recovery and stress release of the rock sample during the unloading process. By comparing the data during the loading and unloading processes, the elasticity, plasticity and possible damage or failure mechanisms of the rock sample can be evaluated. Through multiple cyclic loading and unloading tests, the stress change characteristics of rocks under complex geological conditions can be simulated, providing a scientific basis for the evaluation of rock compressibility. By recording the stress-strain data generated in each cyclic loading and unloading test, the corresponding stress-strain curve can be drawn to reflect the relationship between stress and strain of the rock under the action of external force. The abscissa of the stress-strain curve represents strain, that is, the degree of deformation of the rock sample under stress, represented by ε, and the ordinate of the curve represents stress, that is, the force per unit area of ​​the rock sample, represented by σ.

[0076] Reference Figure 2As shown in the figure, each stress-strain curve consists of a loading curve and an unloading curve, where the loading curve represents the process of the deformation of the dense rock sample changing with the gradual increase of the external force, and the unloading curve represents the process of the deformation of the dense rock sample changing with the gradual decrease of the external force. When the rock sample is loaded to the set value of the axial strain, the path of the unloading curve does not follow the curve during loading, but is slightly lower than the loading curve when unloading. When unloading to the set value, a certain amount of irreversible plastic deformation occurs, which indicates that elastic deformation and plastic deformation occur simultaneously during loading. When the next loading and unloading test is continued, the reloading curve and the unloading curve intersect to form a closed loop. The closed loop is a specific part of the stress-strain curve obtained under the reciprocating action of the cyclic force, which reflects the deformation characteristics, stiffness degradation and energy consumption of the rock sample during repeated stress. When the rock sample has elastic-plastic properties and the stress is greater than a certain level, residual deformation will occur during unloading, that is, the load is zero but the deformation does not return to zero. This phenomenon is called "hysteresis", so the closed loop is called a hysteresis loop. A closed loop formed by an unloading curve obtained from a first cyclic loading and unloading test and a loading curve obtained from a next cyclic loading and unloading test is marked as a first hysteresis loop; a closed loop formed by a loading curve obtained from a last cyclic loading and unloading test and an unloading curve obtained from a previous cyclic loading and unloading test is marked as a second hysteresis loop, the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop are calculated, a compressibility characteristic value is obtained according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop, and the compressibility of the dense rock sample is evaluated according to the compressibility characteristic value.

[0077] Specifically, the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop are calculated by the following formula:

[0078]

[0079] Among them, s 1 is the area of ​​the first hysteresis loop, s 2 is the area of ​​the second hysteresis loop, ε d1,max is the maximum strain on the first hysteresis loop; ε d1,min is the minimum strain on the first hysteresis loop; ε d2,max is the maximum strain on the second hysteresis loop; ε d2,min is the minimum strain on the second hysteresis loop; σ i1 is the stress of the loading process on the first hysteresis loop; σ u1 is the stress of the unloading process on the first hysteresis loop; σ i2 is the stress of the loading process on the second hysteresis loop; σ u2 is the stress of the unloading process on the second hysteresis loop.

[0080] During the loading test, it is assumed that there is no energy exchange between the test system and the outside world, and all the energy input by the test system acts on the rock sample, and the heat energy generated between the rock and the system and inside the rock is ignored. Therefore, under the action of cyclic loading and unloading, the total strain energy of the rock increases continuously during the process of loading to the predetermined value, which is converted into elastic energy and plastic energy. When unloading to the specified load, the elastic energy stored in the rock sample is continuously released, and the plastic energy is consumed in the form of plastic deformation. From the calculation formula of the hysteresis loop area, it can be seen that the area enclosed by the unloading curve and the strain axis in the hysteresis loop represents the energy released by the rock in the macroscopic state from the A stress-strain state to the B stress-strain state, and the area enclosed by the loading curve and the strain axis in the hysteresis loop represents the energy required for the rock to be loaded from the B stress-strain state to the A stress-strain state, and the difference between the two represents the energy dissipated by the rock in the conversion between the A and B states. The dissipated energy is dissipated in the form of friction between rock particles and the development of microcracks, and its size is the area of ​​the hysteresis loop. The greater the difference in the area of ​​the two hysteresis loops, the more developed the natural cracks inside the rock are, the better the pore structure is, and the easier it is to store oil and gas. Therefore, the compressibility of the rock sample can be evaluated by obtaining the compressibility characteristic value based on the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop. The larger the compressibility characteristic value, the better the compressibility of the rock sample. Specifically, the compressibility characteristic value can be calculated according to the following formula:

[0081]

[0082] Among them, α is the compressibility characteristic value, s 1 is the area of ​​the first hysteresis loop, s 2 is the area of ​​the second hysteresis loop.

[0083] In order to verify the feasibility of using the compressibility characteristic value to evaluate the compressibility of rock samples, in the embodiment of this specification, two sandstone standard cylindrical cores with a diameter of 25 mm and a height of 50 mm were placed in a triaxial press respectively. The compressive strength of the two sandstone standard cylindrical cores was different. Under a confining pressure of 10 MPa, 100 cycles of loading and unloading were performed. Each time, the rock was loaded to 50% of its compressive strength and then unloaded to its initial state. The loading and unloading frequency was 1 Hz. The stress-strain data generated by each cyclic loading and unloading test were accurately recorded. The areas of the first hysteresis loop and the second hysteresis loop of the two sandstone standard cylindrical cores were calculated according to formula (1). The compressibility characteristic values ​​of the two sandstone standard cylindrical cores were obtained. The comparison results are shown in Table 1.

[0084] Table 1

[0085] serial number Compressive strength(MPa) <![CDATA[s 1 ]]> <![CDATA[s 2 ]]> Compressibility characteristic value 1 136.18 136.92 65.33 0.53 2 79.5 81.79 50.71 0.38

[0086] In some embodiments, through a large number of tests, it is known that the compressibility characteristic value of the rock sample is between 0.4-0.6, indicating that the rock sample has good compressibility, while when it is less than 0.4, it indicates that the rock sample has poor compressibility. From the results in Table 1, it can be seen that the compressibility characteristic value of the No. 1 sandstone standard cylindrical core is 0.53, which is within the range of 0.4-0.6 and is greater than the No. 2 sandstone standard cylindrical core. Therefore, the compressibility of the No. 1 sandstone standard cylindrical core is better than that of the No. 2 sandstone standard cylindrical core.

[0087] In some embodiments, the method for determining the preset confining pressure, the preset frequency and the number of cycles includes:

[0088] The preset confining pressure, preset frequency and number of cycles are continuously adjusted until the difference between the first hysteresis loop area and the second hysteresis loop area in the corresponding stress-strain curve exceeds a preset threshold.

[0089] Since different types of rocks have different characteristics, the confining pressure, frequency and number of cycles required for loading and unloading tests need to be adjusted according to different rocks. For different types of rocks, set different numbers of cyclic loading and unloading tests, confining pressures, frequencies and loads, etc., until the difference in the area of ​​the first hysteresis loop and the second hysteresis loop can be intuitively seen through the stress-strain curve. Specifically, the threshold can be set to determine whether the confining pressure, frequency, number of cycles and load meet the test conditions.

[0090] In some embodiments, in order to further improve the accuracy of the evaluation of the compressibility of dense rock samples, refer to Figure 3 As shown, the stress-strain curve of each cyclic loading and unloading test is summarized to obtain a total stress-strain curve, and then the elastic modulus of the dense rock sample in the elastic deformation stage is calculated according to the total stress-strain curve, and the compressibility of the dense rock sample is evaluated by combining the elastic modulus and the compressibility characteristic value. The calculation formula of the elastic modulus is as follows:

[0091]

[0092] Among them, E d represents the elastic modulus, σ d,max represents the maximum stress on any hysteresis loop on the total stress-strain curve, σ d,min represents the minimum stress on any hysteresis loop on the total stress-strain curve, ε d,max Represents σ d,max The corresponding strain, ε d,min Represents σ d,min In some embodiments, any hysteresis loop on the total stress-strain curve is a closed loop formed by the intersection of the loading curve and the unloading curve obtained from any two consecutive cyclic loading and unloading tests.

[0093] The elastic modulus is a physical quantity used to describe the elasticity of an object. It indicates the proportional relationship between stress and strain of an object in the elastic deformation stage. Specifically, when an external force is applied to a rock sample, the rock sample will change its shape, i.e., deform. The elastic modulus describes the ratio of stress to strain in the corresponding direction under this unidirectional stress state, reflecting the difficulty of compressing the rock sample. The larger the elastic modulus, the more difficult it is to compress the rock sample. The elastic modulus and hysteresis loop reflect the mechanical properties of the rock sample from different perspectives. The elastic modulus mainly focuses on the stiffness of the rock sample within the elastic range, while the hysteresis loop focuses on the energy dissipation and deformation recovery ability of the rock sample under cyclic loading and unloading. By comprehensively considering these two parameters, the compressibility of the rock sample can be more comprehensively evaluated. For example, a dense rock sample may have a high elastic modulus, i.e., it is difficult to be compressed, but if its hysteresis loop area is large, it means that it can dissipate more energy under cyclic loading and may still have good compressibility.

[0094] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties. And the acquisition, storage, use, and processing of data in the technical solutions described in the embodiments of this application are in compliance with relevant regulations.

[0095] Based on the above-mentioned method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, an embodiment of this specification also provides a corresponding device for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test. The device may include a system (including a distributed system), software (application), module, component, server, client, etc. using the method described in the embodiment of this specification and a device combined with necessary implementation hardware. Based on the same innovative concept, the device in one or more embodiments provided in the embodiment of this specification is as described in the following embodiments. Since the implementation scheme and method of the device to solve the problem are similar, the implementation of the specific device in the embodiment of this specification can refer to the implementation of the aforementioned method, and the repetitions will not be repeated. As used below, the term "unit" or "module" can implement a combination of software and / or hardware with predetermined functions. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0096] Specifically, Figure 4 This is a schematic diagram of the module structure of an embodiment of a tight reservoir compressibility evaluation device based on a cyclic loading and unloading test provided in the embodiments of this specification, with reference to Figure 4 As shown, a device for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test provided in an embodiment of this specification includes:

[0097] The test module 401 is used to place the dense rock sample in a compression testing machine, perform multiple cyclic loading and unloading tests at a preset frequency based on a preset confining pressure, and record stress and strain data generated by each cyclic loading and unloading test;

[0098] A drawing module 402 is used to draw a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve;

[0099] The hysteresis loop marking module 403 is used to mark the closed loop formed by the unloading curve obtained by the first cyclic loading and unloading test and the loading curve obtained by the next cyclic loading and unloading test as the first hysteresis loop; and mark the closed loop formed by the loading curve obtained by the last cyclic loading and unloading test and the unloading curve obtained by the previous cyclic loading and unloading test as the second hysteresis loop;

[0100] A calculation module 404, configured to calculate the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop, and obtain a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop;

[0101] The evaluation module 405 is used to evaluate the compressibility of the dense rock sample according to the compressibility characteristic value.

[0102] The beneficial effects obtained by the device provided in the embodiments of this specification are consistent with the beneficial effects obtained by the above method and will not be repeated here.

[0103] Reference Figure 5As shown, based on the above-mentioned method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, a computer device 502 is also provided in an embodiment of the specification, wherein the above-mentioned method is run on the computer device 502. The computer device 502 may include one or more processors 504, such as one or more central processing units (CPUs), each of which may implement one or more hardware threads. The computer device 502 may also include any memory 506, which is used to store any kind of information such as code, settings, data, etc. Non-limitingly, for example, the memory 506 may include any one or more combinations of the following: any type of RAM, any type of ROM, flash memory device, hard disk, optical disk, etc. More generally, any memory may use any technology to store information. Further, any memory may provide volatile or non-volatile retention of information. Further, any memory may represent a fixed or removable component of the computer device 502. In one case, when the processor 504 executes an associated instruction stored in any memory or combination of memories, the computer device 502 may perform any operation of the associated instruction. The computer device 502 also includes one or more drive mechanisms 508 for interacting with any storage, such as a hard disk drive mechanism, an optical disk drive mechanism, etc.

[0104] The computer device 502 may also include an input / output module 510 (I / O) for receiving various inputs (via input devices 512) and for providing various outputs (via output devices 514). A specific output mechanism may include a presentation device 516 and an associated graphical user interface (GUI) 518. In other embodiments, the input / output module 510 (I / O), the input device 512, and the output device 514 may not be included, and the computer device 502 may be used as a computer device in a network. The computer device 502 may also include one or more network interfaces 520 for exchanging data with other devices via one or more communication links 522. One or more communication buses 524 couple the components described above together.

[0105] The communication link 522 may be implemented in any manner, for example, through a local area network, a wide area network (e.g., the Internet), a point-to-point connection, etc., or any combination thereof. The communication link 522 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

[0106] Corresponding to Figures 1 to 3 In addition to the method shown, an embodiment of the specification also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the above method are executed.

[0107] The embodiment of the present specification also provides a computer-readable instruction, wherein when the processor executes the instruction, the program therein causes the processor to execute the following Figures 1 to 3 The method shown.

[0108] The embodiments of the present specification also provide a computer program product, including at least one instruction or at least one program, wherein the at least one instruction or the at least one program is loaded and executed by a processor to implement the following Figures 1 to 3 The method shown.

[0109] It should be understood that in the various embodiments of this specification, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this specification.

[0110] It should also be understood that in the embodiments of this specification, the term "and / or" is only a description of the association relationship of the associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this specification generally indicates that the associated objects before and after are in an "or" relationship.

[0111] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in this specification can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this specification.

[0112] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0113] In the several embodiments provided in this specification, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, or it can be an electrical, mechanical or other form of connection.

[0114] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the embodiments of this specification.

[0115] In addition, each functional unit in each embodiment of this specification may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0116] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this specification is essentially or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of this specification. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0117] Specific embodiments are used in this specification to illustrate the principles and implementation methods of this specification. The description of the above embodiments is only used to help understand the methods and core ideas of this specification. At the same time, for those skilled in the art, according to the ideas of this specification, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on this specification.

Claims

1. A method for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, characterized in that: The method comprises: The dense rock sample is placed in a compression testing machine, and multiple cyclic loading and unloading tests are performed at a preset frequency based on a preset confining pressure, and the stress and strain data generated by each cyclic loading and unloading test are recorded; Draw a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve; The closed loop formed by the unloading curve obtained by the first cyclic loading and unloading test and the loading curve obtained by the next cyclic loading and unloading test is marked as the first hysteresis loop; the closed loop formed by the loading curve obtained by the last cyclic loading and unloading test and the unloading curve obtained by the previous cyclic loading and unloading test is marked as the second hysteresis loop; calculating an area of ​​the first hysteresis loop and an area of ​​the second hysteresis loop, and obtaining a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop; evaluating the compressibility of the dense rock sample according to the compressibility characteristic value; The compressibility characteristic value is calculated according to the following formula: Where α is the compressibility characteristic value, s1 is the area of ​​the first hysteresis loop, and s2 is the area of ​​the second hysteresis loop.

2. The method according to claim 1, characterized in that The method further comprises: The stress-strain curves of each cyclic loading and unloading test are summarized to obtain the total stress-strain curve; The elastic modulus of the dense rock sample in the elastic deformation stage is calculated according to the total stress-strain curve, wherein the elastic modulus is calculated by the following formula: Among them, E d represents the elastic modulus, σ d,max represents the maximum stress on any hysteresis loop on the total stress-strain curve, σ d,min represents the minimum stress on any hysteresis loop on the total stress-strain curve, ε d,max Represents σ d,max The corresponding strain, ε d,min Represents σ d,min The corresponding strain.

3. The method according to claim 1, characterized in that The area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop are calculated by the following formula: Where s1 is the area of ​​the first hysteresis loop, s2 is the area of ​​the second hysteresis loop, and ε d1,max is the maximum strain on the first hysteresis loop; ε d1,min is the minimum strain on the first hysteresis loop; ε d2,max is the maximum strain on the second hysteresis loop; ε d2,min is the minimum strain on the second hysteresis loop; σ i1 is the stress of the loading process on the first hysteresis loop; σ u1 is the stress of the unloading process on the first hysteresis loop; σ i2 is the stress of the loading process on the second hysteresis loop; σ u2 is the stress of the unloading process on the second hysteresis loop.

4. The method according to claim 1, characterized in that: The evaluating the compressibility of the dense rock sample according to the compressibility characteristic value includes: the larger the compressibility characteristic value is, the better the compressibility of the dense rock sample is.

5. The method according to claim 1, characterized in that The method for determining the preset confining pressure, preset frequency and number of cycles includes: The preset confining pressure, preset frequency and number of cycles are continuously adjusted until the difference between the first hysteresis loop area and the second hysteresis loop area in the corresponding stress-strain curve exceeds a preset threshold.

6. The method according to claim 2, characterized in that The method further comprises: Obtaining the compression difficulty of the dense rock sample according to the elastic modulus; The compressibility of the dense rock sample is evaluated according to the compression difficulty and the compressibility characteristic value.

7. A device for evaluating the compressibility of a tight reservoir based on a cyclic loading and unloading test, characterized in that: The device comprises: The test module is used to place the dense rock sample in the compression testing machine, perform multiple cyclic loading and unloading tests at a preset frequency based on a preset confining pressure, and record the stress and strain data generated by each cyclic loading and unloading test; A drawing module, used for drawing a stress-strain curve according to the stress-strain data, wherein the stress-strain curve consists of a loading curve and an unloading curve; A hysteresis loop marking module is used to mark the closed loop formed by the unloading curve obtained by the first cyclic loading and unloading test and the loading curve obtained by the next cyclic loading and unloading test as the first hysteresis loop; and mark the closed loop formed by the loading curve obtained by the last cyclic loading and unloading test and the unloading curve obtained by the previous cyclic loading and unloading test as the second hysteresis loop; a calculation module, configured to calculate an area of ​​the first hysteresis loop and an area of ​​the second hysteresis loop, and obtain a compressibility characteristic value according to the area of ​​the first hysteresis loop and the area of ​​the second hysteresis loop; An evaluation module, used for evaluating the compressibility of the dense rock sample according to the compressibility characteristic value; The compressibility characteristic value is calculated according to the following formula: Where α is the compressibility characteristic value, s1 is the area of ​​the first hysteresis loop, and s2 is the area of ​​the second hysteresis loop.

8. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

10. A computer program product, characterized in that The method comprises at least one instruction or at least one program, wherein the at least one instruction or the at least one program is loaded and executed by a processor to implement the method according to any one of claims 1 to 6.

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