Ground stress orientation evaluation system and method considering influence of ground stress release

Abstract

The invention provides a crustal stress orientation evaluation system and method considering crustal stress release influence, and belongs to the field of petroleum exploration and developing.The evaluation system comprises an objective table, a frame, a pressurizing mechanism and an acoustic emission detection device.The frame and the objective table are used for fixing the acoustic emission detection device and a rock core sample; the pressurizing mechanism is used for applying three-way pressure to the rock core sample to simulate a real stratum environment, and the acoustic emission detection device is used for measuring acoustic wave data. The evaluation method comprises the steps that a rock core sample is placed in the frame and makes contact with the acoustic emission detection device, three-way pressure is applied to the rock core sample through the pressurization mechanism, the three-way pressure can be determined as the minimum crustal stress or 70%-90% of the uniaxial strength of the sample, the wave velocities of different positions in the same test plane are calculated, and therefore the crustal stress orientation is determined. According to the method provided by the invention, the theoretical defects existing in the current testing process adopting a sound wave anisotropy mode can be overcome, and the principal stress orientation in a real stratum environment can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum exploration and development, and in particular to a ground stress orientation evaluation system and a ground stress orientation evaluation method considering the influence of ground stress release. Background Art

[0002] During oil and gas exploration and development, determining geostress orientation plays a crucial role in guiding well pattern adjustment, wellbore trajectory optimization, and hydraulic fracturing design. Currently, methods for determining geostress orientation, both domestically and internationally, are primarily categorized as field testing and analysis methods and laboratory testing and analysis methods. Field testing and analysis methods are often complex and costly, significantly hindering their widespread application. However, laboratory testing methods for geostress orientation, due to their high precision, ease of operation, and low cost, are gaining increasing recognition within the industry.

[0003] Indoor experimental analysis methods primarily utilize paleomagnetic core orientation, differential strain analysis, acoustic emission Kaiser effect, and wave velocity anisotropy. These methods offer advantages such as high precision, simplicity, and low cost, and have therefore been widely adopted. In 1967, Zijderveld et al. separated and obtained viscous remanent magnetization using a step-by-step heating method. The horizontal component of this viscous remanent magnetization indicates the direction of the geographic North Pole, enabling core orientation. In 1990, Lowrie W et al. conducted triaxial isothermal viscous remanent magnetization testing on magnetite cores, further developing paleomagnetic core orientation techniques. In 1999, Hou Shouxin et al. combined paleomagnetic core orientation testing with differential strain testing to achieve the first indoor measurement of geostress orientation. However, the difficulties in sample preparation and cumbersome experimental procedures hindered widespread adoption of differential strain testing. In 2004, Shi Lin et al. used wave velocity anisotropy testing to determine the relative orientation of geostress, but these measurements failed to provide a true orientation relative to the geographic North Pole, presenting certain limitations. In 2011, Lu Yunhu et al. developed a new method for measuring geostress orientation by combining paleomagnetic core orientation with the Ksaier effect of acoustic emission. However, the test results for some rock samples showed significant deviations. In 2017, Han Yannong, Chen Junhai et al. used paleomagnetic, acoustic emission, and wave velocity anisotropy methods to conduct laboratory measurements of rock geostress orientation.

[0004] Through research and laboratory experiments, it has been determined that the current method for measuring rock in-situ stress orientation mostly uses acoustic anisotropy. This method generally assumes that faster acoustic wave velocity corresponds to the direction of compaction, meaning that the greater the in-situ stress orientation, the greater the density. However, this method currently has theoretical flaws. Some literature also suggests that cores retrieved from underground undergo a stress release process, which means that the density decreases in directions with greater in-situ stress, indicating slower acoustic wave velocity. These two theories present inconsistencies, severely restricting the widespread use of wave velocity anisotropy to measure rock in-situ stress orientation.

[0005] For example, a Chinese patent document with a publication date of June 27, 2012 and publication number CN102519784A proposes a method for determining the conjugate damage strength of rock using ultrasound. The specific operation of this method is as follows: a pair of longitudinal wave probes are arranged at each end of two mutually perpendicular diameters on a cross-section in the middle of the rock sample. During the loading process of the rock sample, the rock acoustic wave velocity between the two mutually perpendicular diameters of the rock sample is continuously tested at very short time intervals (e.g., 1 to 3 seconds) until the rock sample is damaged. After the test is completed, the change process of the longitudinal wave velocity of the two mutually perpendicular radial directions of the rock sample with the axial stress of the rock sample is sorted out. The axial stress corresponding to the significant reduction of the radial longitudinal wave velocity is the conjugate damage strength of the rock.

[0006] A Chinese patent application, published on September 7, 2016, with publication number CN105136362A, proposes a device and method for determining the direction of geostress based on rock velocity anisotropy. The device comprises a base, a support, a top plate, a rotating table, a synchronous rotating table, a pressure rod, an acoustic wave device, and multiple handwheels. Rotating the handwheels controls the rotating table to rotate the rock core 360 ​​degrees, the acoustic wave device to move up and down, and the pressure applied by the acoustic wave device to the rock core, thereby accurately measuring acoustic wave data at different heights and directions in the rock core.

[0007] A Chinese patent document with a publication date of April 10, 2020 and publication number CN110987674A proposes a stress testing method based on the Kaiser effect of rock cores. The testing method includes: drilling multiple core samples on the parent rock along the core axis of the parent rock and in multiple directions perpendicular to the core axis of the parent rock; performing an acoustic emission test on each core sample, determining the Kaiser effect point on the core sample through the acoustic emission count, acoustic emission count accumulation, and / or acoustic emission count rate increment of the core sample, and determining the stress at the Kaiser effect point on the core sample; based on the stress at the Kaiser effect point on the core sample, determining the maximum horizontal principal stress, minimum horizontal principal stress, and the angle between the maximum horizontal principal stress and the marker line of the parent rock.

[0008] Analysis of the aforementioned patent documents reveals that current methods for measuring geostress direction based on wave velocity anisotropy generally ignore the impact of the stress release process on the core. Instead, they test cores directly from downhole, determining the stress direction based on the theory that locations with high wave velocity correspond to locations with high stress, and locations with slow wave velocity correspond to locations with low stress. While this method can measure the stress direction, the results obtained still exhibit a certain degree of error compared to the actual stress direction in the underlying formation. Summary of the Invention

[0009] In response to the technical problem that the existing methods for measuring the direction of geostress based on acoustic anisotropy do not take into account the influence of geostress release, the present invention provides a geostress orientation evaluation method and system that take into account the influence of geostress release. This method and system can overcome the theoretical defects in the current process of testing the geostress orientation of rock using acoustic anisotropy, and obtain the principal stress orientation in a real formation environment.

[0010] To achieve the above-mentioned objectives, the present invention provides, on the one hand, a ground stress orientation evaluation system that takes into account the influence of ground stress release, the evaluation system comprising: a stage, a frame, a pressurizing mechanism, and an acoustic emission detection device; the stage is used to support the frame, the pressurizing mechanism, and the acoustic emission detection device; the frame is used to fix the acoustic emission detection device and the core sample; the pressurizing mechanism is used to apply three-dimensional pressure to the core sample to simulate the real formation environment; and the acoustic emission detection device is used to measure the acoustic wave data of the core sample.

[0011] In an exemplary embodiment of the present invention, the evaluation system may further include a computer device for controlling the operation of the pressurizing mechanism and the acoustic emission detection device, and processing the measured acoustic wave data.

[0012] In an exemplary embodiment of the present invention, a plurality of limiting grooves may be provided at intervals in the circumferential direction of the frame, and the limiting grooves are used for installing the acoustic emission detection device.

[0013] In an exemplary embodiment of the present invention, an elastic connecting member may be provided between the frame and the acoustic emission detection device.

[0014] In an exemplary embodiment of the present invention, the pressurizing mechanism may include: a confining pressure bearing device and a hydraulic control cabinet.

[0015] On the other hand, the present invention provides a method for evaluating the orientation of ground stress taking into account the influence of ground stress release. The evaluation method is implemented by the evaluation system as described above, and includes the following steps: determining a test plane of a core sample; placing a frame along the test plane of the core sample, and making several acoustic emission detection devices in the frame closely contact the core sample to form multiple test positions; applying three-dimensional pressure to the core sample through a pressurizing mechanism, and calculating the sound wave velocity at different test positions in the same test plane; on the same test plane, determining the angle corresponding to the position with the maximum sound wave velocity as the maximum principal stress orientation, and determining the angle corresponding to the position with the minimum sound wave velocity as the minimum principal stress orientation.

[0016] In another exemplary embodiment of the present invention, the core sample may be spherical or cylindrical.

[0017] In another exemplary embodiment of the present invention, determining the test plane of the core sample may include: when the core sample is cylindrical, determining at least one cross-section of the core sample in the height direction as the test plane; when the core sample is spherical, determining two cross-sections of the core sample passing through the center of the sphere and perpendicular to each other as the test planes.

[0018] In another exemplary embodiment of the present invention, the calculating of the sound wave velocity at different test positions within the same test plane may include: on the same test plane, calculating the sound wave velocity at different test positions based on the sound wave arrival time and core sample length collected at different test positions.

[0019] In another exemplary embodiment of the present invention, the evaluation method may further include: before pressurization, based on geological data, determining the minimum ground stress value as the three-dimensional pressure applied by the pressurization mechanism.

[0020] In another exemplary embodiment of the present invention, the evaluation method may further include: before pressurization, taking 70% to 90% of the uniaxial strength of the core sample to determine the three-dimensional pressure applied by the pressurization mechanism.

[0021] The technical solution provided by the present invention has at least the following technical effects:

[0022] (1) The present invention applies three-dimensional pressure to the core sample by setting a pressure mechanism, thereby simulating the stress release process experienced by the core when it is taken out from the well, and obtains the acoustic wave velocity at different test positions of the core sample based on the test of the acoustic emission detection mechanism, so as to determine the principal stress orientation obtained based on the wave velocity anisotropy. This method overcomes the theoretical defects of the current use of acoustic wave anisotropy to test the rock stress orientation, and can obtain the principal stress orientation in the real formation environment, which has important guiding significance for well network deployment adjustment, wellbore trajectory optimization and hydraulic fracturing design;

[0023] (2) The device of the present invention has a light structure, simple operation, and low manufacturing cost. The test results obtained using the device are reliable and highly applicable.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following detailed description, they are used to explain the embodiments of the present invention, but do not constitute a limitation of the embodiments of the present invention. In the accompanying drawings:

[0026] Figure 1 A schematic diagram of the structure of a geostress orientation evaluation system provided by an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the partial structure of the frame and acoustic emission detection device provided in an embodiment of the present invention.

[0028] Description of Reference Numerals

[0029] 1- loading platform, 2- frame, 3- confining pressure bearing device, 4- computer equipment, 5- hydraulic control cabinet, 6- fixing pin of acoustic emission detection device, 7- acoustic emission detection device, 8- core sample. DETAILED DESCRIPTION

[0030] The following describes the specific implementation of the embodiment of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the embodiment of the present invention and is not used to limit the embodiment of the present invention.

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] In the present invention, unless otherwise specified, directional words such as "up, down, top, bottom" are usually used to describe the relative positions of components in the directions shown in the drawings or in the vertical, perpendicular or gravity directions.

[0033] It should also be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "installation" and "connection" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integrated connection; direct connection, indirect connection, wired connection, or wireless connection. Those skilled in the art will understand the specific meanings of the above terms in the present invention depending on the specific circumstances.

[0034] In the existing technology, the most common method for measuring rock in-situ stress orientation is acoustic anisotropy. The testing principle of this method is as follows: the rock in the formation is subjected to triaxial stress. During core drilling and coring, the rock is freed from stress, resulting in stress release. During this stress release process, microcracks appear in the core proportional to the degree of unloading. The core relaxes and deforms the most in the direction of maximum horizontal in-situ stress. Therefore, these small cracks are perpendicular to the direction of maximum horizontal in-situ stress and are filled with air. The wave resistance values ​​of rock and air differ significantly, and the speed of sound waves in rock is much faster than in air. The tiny cracks in the core cause the speed of sound waves propagating in different directions in the core to have significant anisotropy. In other words, the existing acoustic anisotropy testing method assumes that the location with a high acoustic wave velocity (referred to as wave velocity) corresponds to the direction of compaction, which can be regarded as the direction of high in-situ stress. Conversely, the location with a slow acoustic wave velocity corresponds to the direction of low density, which can be regarded as the direction of low in-situ stress. However, some literature suggests that cores retrieved from underground undergo a process of in-situ stress release. This means that the azimuthal density decreases in locations with high in-situ stress, resulting in slower acoustic wave velocity, while the azimuthal density increases in locations with low in-situ stress, resulting in faster acoustic wave velocity. Clearly, these two theories contradict each other, and the measured in-situ stress azimuthal results are also contradictory.

[0035] Currently, the most widely accepted acoustic anisotropy measurement theory is still the former. This method, when measuring rock in-situ stress orientation, assigns locations with high wave speeds to the orientation of maximum principal stress, and locations with slow wave speeds to the orientation of minimum principal stress. However, this measurement method selectively ignores the effects of in-situ stress release, resulting in a certain degree of error between the obtained results and the principal stress orientation in the actual formation environment.

[0036] Given the technical problem that existing methods for measuring geostress direction based on acoustic anisotropy fail to account for the effects of geostress release, the present invention provides a method and system for evaluating geostress orientation that takes into account the impact of geostress release. This method takes into account the influence of the geostress release process. During the process of measuring geostress orientation based on acoustic anisotropy, three-dimensional pressure is applied to the core sample to simulate the geostress experienced by the core underground. Compared to existing rock geostress orientation measurement methods, this method can obtain the principal stress orientation in a real formation environment, which is conducive to the promotion of methods for measuring geostress orientation based on rock wave velocity anisotropy.

[0037] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0038] An embodiment of the present invention provides a ground stress orientation evaluation system that takes into account the influence of ground stress release. The evaluation system includes a loading platform, a frame, a pressurizing mechanism, and an acoustic emission detection device.

[0039] The loading platform is used to carry the frame, the pressure mechanism and the acoustic emission detection device. The loading platform can be a movable platform or a bracket for conveniently loading and unloading the test device and samples.

[0040] Acoustic emission detection devices are used to measure acoustic wave data from core samples. These devices consist of an acoustic wave transmitter and an acoustic wave receiver. The acoustic wave transmitter, such as an acoustic wave transmitter probe, generates acoustic signals. It is typically an acoustic source that stimulates microcracks in rock or other materials by applying electrical signals or other forms of energy, generating sound waves. The acoustic wave receiver, such as a receiver or sensor, receives and records the acoustic wave signals transmitted from the rock or material. The acoustic wave receiver converts the acoustic wave signals into electrical signals for further analysis and processing.

[0041] The frame is used to secure the acoustic emission detector and core sample. Specifically, the acoustic emission detector can be secured within the frame via removable connectors. When testing is required, the core sample is placed within the frame, in close contact with the acoustic emission detector, securing the device and core sample. Furthermore, the frame's radial dimensions should be greater than or equal to the sum of the radial dimensions of the acoustic emission detector and core sample, ensuring stable placement of the core sample and device within the frame.

[0042] The pressurizing mechanism applies triaxial pressure to the core sample to simulate a realistic formation environment. This mechanism applies uniform pressure to the core sample, subjecting it to stresses from different directions and thereby simulating the pressure environment of actual rock underground. During operation, the pressurizing mechanism can be controlled to apply varying triaxial pressures to the core sample, simulating varying depths and in-situ stress conditions.

[0043] In the above embodiment, multiple frames can be provided, for fixing at multiple locations on the core sample to form different test planes. Multiple acoustic emission detection devices can also be provided within the frame to form multiple test locations within a test plane, thereby facilitating measurement of acoustic wave velocity at different test locations on the core sample.

[0044] Furthermore, in one possible embodiment, the evaluation system may also include a computer device. The computer device is connected to the pressurizing mechanism and the acoustic emission detection device, respectively, to control their operation and process the measured acoustic wave data. For example, at the start of a test, the computer device can send a pressure loading instruction to the pressurizing mechanism to control the pressurizing mechanism to apply three-dimensional pressure to the core sample. Simultaneously, the computer device can send an acoustic emission detection instruction to the acoustic emission detection device to control the acoustic emission detection device to begin measuring the acoustic wave data of the core sample. During the test, a data acquisition system installed on the computer device can be used to acquire the acoustic wave data obtained by the acoustic emission detection device in real time, and the ground stress azimuth calculation results can be obtained through data processing.

[0045] Furthermore, in a possible embodiment, a plurality of limiting grooves may be provided at intervals in the circumferential direction of the frame, and the limiting grooves are used for installing the acoustic emission detection device.

[0046] Furthermore, in one possible embodiment, an elastic connector is provided between the frame and the acoustic emission detection device. The purpose of providing the elastic connector is to ensure close contact between the acoustic emission probe on the acoustic emission device and the core sample. Therefore, the elastic connector is used to achieve flexible control of the fixation of the acoustic emission detection device. For example, the elastic connector may be a spring or a spring.

[0047] Furthermore, in one possible embodiment, the pressurizing mechanism may be composed of a confining pressure bearing device and a hydraulic control cabinet. The hydraulic control cabinet may be connected to the confining pressure bearing device via a hydraulic pump to supply hydraulic oil to the confining pressure bearing device. A confining pressure bearing device is a device used to apply three-dimensional confining pressure, typically used to simulate the ground stress experienced by rock or soil underground. The confining pressure bearing device generally consists of the following main components:

[0048] (1) The pressure vessel used to seal the confining pressure device and the specimen should generally be designed and made of materials that can withstand the high pressure applied and maintain tightness to ensure uniform and controllable pressure loading;

[0049] (2) The pressure transmission medium is responsible for transmitting pressure from the outside to the core sample. Common media include liquids (such as water or oil) or gases (such as nitrogen);

[0050] (3) A hydraulic or pneumatic system that controls pressure and pressure transmission rate. By controlling the pressure system, operations such as applying, unloading, and reloading the sample can be achieved.

[0051] Of course, the present invention is not limited to this. Other devices or structures that can apply three-dimensional pressure to the core sample can be applied to the pressurizing mechanism of the present invention. For example, the pressurizing mechanism can also be configured as a triaxial compression testing machine, which can apply three-dimensional pressure with different loads to the sample. For another example, the pressurizing mechanism can also be configured as a high-pressure solid medium press. This device uses a solid medium (such as salt or certain soft metals) to uniformly apply pressure. The solid medium is compressed and transmits pressure to the sample enclosed therein, which can simulate an extremely high pressure environment.

[0052] An embodiment of the present invention further provides a method for evaluating the orientation of ground stress taking into account the influence of ground stress release. The method comprises the following steps:

[0053] Step S101: determining the test plane of the core sample.

[0054] Step S102 : placing a frame along the test plane of the core sample, and making a plurality of acoustic emission detection devices in the frame closely contact the core sample to form a plurality of test positions.

[0055] Step S103: applying three-dimensional pressure to the core sample through a pressurizing mechanism, and calculating the acoustic wave velocity at different test positions in the same test plane during the pressurizing process.

[0056] Step S104: On the same test plane, the angle corresponding to the position with the maximum acoustic wave velocity is determined as the maximum principal stress orientation, and the angle corresponding to the position with the minimum acoustic wave velocity is determined as the minimum principal stress orientation. Furthermore, in one possible embodiment, the core sample can be spherical or cylindrical.

[0057] If the core sample is cylindrical, at least one cross-section of the core sample in the height direction is determined as a test plane. For example, multiple cross-sections can be taken at regular intervals along the height direction of the core sample, each serving as a test plane to facilitate testing the acoustic wave velocity of the core sample at different heights.

[0058] When the core sample is spherical, two cross-sections of the core sample that pass through the center of the sphere and are perpendicular to each other are determined as test planes. For example, a three-dimensional rectangular coordinate system can be established with the center of the core sample as the origin, and two cross-sections (such as a horizontal cross-section and a vertical cross-section) that pass through the center of the sphere and are perpendicular to each other are selected as test planes to facilitate testing the acoustic wave velocity of the core sample in different directions.

[0059] Furthermore, in a possible implementation, in step S103, the specific process of calculating the acoustic wave velocity at different test positions within the same test plane is as follows: on the same test plane, the acoustic wave velocity at different test positions is calculated based on the acoustic wave arrival time and core sample length collected at different test positions.

[0060] Furthermore, in one possible implementation, in step S103, before pressurization, the three-dimensional pressure applied by the pressurizing mechanism can be determined based on the results of in-situ stress tests in a real formation environment. For example, the formation height of the core sample and the magnitude of the in-situ stress it experiences can be estimated based on the geological data of the core sample. During the test, the three-dimensional pressure applied by the pressurizing mechanism can be set to the minimum in-situ stress value, thereby simulating the in-situ stress experienced by the rock underground.

[0061] Furthermore, in another possible embodiment, in step S103, before pressurization, the three-dimensional pressure applied by the pressurizing mechanism can also be determined based on the uniaxial strength of the core sample. For example, a cylindrical or cubic core sample can be placed on the loading platform of the uniaxial testing machine, and then an axial load is applied, that is, pressure is applied in a direction perpendicular to the sample. When the sample begins to fail, the loading is stopped, and the load and displacement at this time are recorded. The uniaxial strength of the core sample can be calculated by the load and sample size. Subsequently, during the test, a tensile strength value can be obtained by multiplying the uniaxial strength of the sample with a preset threshold coefficient (such as 0.7 to 0.9), and the tensile strength value is set as the three-dimensional pressure applied by the pressurizing mechanism.

[0062] In order to better understand the above exemplary embodiments of the present invention, they are further described below with reference to specific examples and drawings.

[0063] like Figure 1 and Figure 2 As shown, a ground stress orientation evaluation system considering the influence of ground stress release is composed of a loading platform 1, a frame 2, a confining pressure bearing device 3, a computer device 4, a hydraulic control cabinet 5, an acoustic emission detection device fixing pin 6 and an acoustic emission detection device 7.

[0064] The loading platform 1 is used to carry the frame 2, the acoustic emission detection device 7 and the core sample 8, so as to facilitate the movement of the acoustic emission detection device, the frame and the core sample in and out of the confining pressure bearing device.

[0065] The frame 2 is used to support the acoustic emission detection devices 7 so that the acoustic emission devices are distributed at 45° intervals on each test plane of the core sample.

[0066] The acoustic emission detection device includes an acoustic wave transmitting component and an acoustic wave receiving component, which are used to test the acoustic wave velocity at different positions of the core sample. The acoustic emission detection device 7 is fixed to the frame 2 via the acoustic emission detection device fixing pin 6. In addition, the position of the acoustic emission detection device can be controlled by spring flexibility to facilitate close contact between the acoustic emission probe on the acoustic emission detection device and the rock sample. The confining pressure bearing device 3 is used to apply three-dimensional pressure to the rock sample to simulate the ground stress experienced by the core in the well. The hydraulic control cabinet 5 is connected to the confining pressure bearing device 3 via a hydraulic pump to provide hydraulic oil to the confining pressure bearing device.

[0067] The computer device 4 is used to send acoustic emission detection instructions, control confining pressure loading, and process the acoustic wave speed at different test positions.

[0068] Based on the above system, the ground stress orientation evaluation test considering the influence of ground stress release is carried out. The specific test method includes the following steps:

[0069] Step 1: Test and record the uniaxial strength of the target rock sample. Prepare a spherical core sample with a diameter of 100 mm or a cylindrical core sample with a diameter of 50 mm and a height of 50 mm. The contact surface can be polished according to the test requirements.

[0070] Step 2: Place the core sample in the frame and apply resin glue on the core sample to fix the acoustic emission probe. Under the action of the spring connecting the frame and the acoustic emission probe, the core sample is in close contact with the acoustic emission probe; the stage drags the acoustic emission detection device, frame and rock sample into the confining pressure bearing device.

[0071] Step 3: Set the confining pressure according to 80% of the uniaxial strength of the sample, pump in hydraulic oil using a hydraulic pump, and apply three-dimensional pressure to the core sample by generating a reaction force through the presence of the confining pressure bearing device.

[0072] Step 4: Sending acoustic emission detection instructions and confining pressure loading instructions through computer equipment, processing the measured acoustic wave data, and determining the ground stress orientation.

[0073] Specifically, the acoustic wave velocity at different locations can be calculated based on the collected acoustic wave arrival time and the length of the rock sample. On the same test plane, the location with the fastest acoustic wave velocity is determined as the maximum principal stress orientation, and the location with the slowest acoustic wave velocity is determined as the minimum principal stress orientation.

[0074] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0075] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0076] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A ground stress orientation evaluation system considering the impact of ground stress release, characterized in that: The evaluation system includes: a stage, a frame, a pressurizing mechanism and an acoustic emission detection device; The loading platform is used to carry the frame, the pressurizing mechanism and the acoustic emission detection device; The frame is used to fix the acoustic emission detection device and the core sample; The pressurizing mechanism is used to apply three-dimensional pressure to the core sample to simulate the real formation environment; The acoustic emission detection device is used to measure the acoustic wave data of the core sample.

2. The ground stress orientation evaluation system considering the impact of ground stress release according to claim 1, characterized in that: A plurality of limiting grooves are arranged at intervals in the circumferential direction of the frame, and the limiting grooves are used for installing the acoustic emission detection device.

3. The ground stress orientation evaluation system considering the impact of ground stress release according to claim 1, characterized in that: An elastic connecting piece is provided between the frame and the acoustic emission detection device.

4. The ground stress orientation evaluation system considering the impact of ground stress release according to claim 1, characterized in that: The pressurizing mechanism includes: a confining pressure bearing device and a hydraulic control cabinet.

5. A method for evaluating the orientation of ground stress taking into account the influence of ground stress release, characterized in that: The evaluation method is implemented by the evaluation system according to any one of claims 1 to 4, comprising the following steps: Determine the test plane of the core sample; A frame is placed along the test plane of the core sample, and a plurality of acoustic emission detection devices in the frame are in close contact with the core sample to form a plurality of test positions; Apply three-dimensional pressure to the core sample through a pressure mechanism, and calculate the acoustic wave velocity at different test positions in the same test plane; On the same test plane, the angle corresponding to the position with the maximum acoustic wave velocity is determined as the maximum principal stress orientation, and the angle corresponding to the position with the minimum acoustic wave velocity is determined as the minimum principal stress orientation.

6. The method for evaluating the orientation of ground stress considering the influence of ground stress release according to claim 5, characterized in that: The core sample is spherical or cylindrical.

7. The method for evaluating the orientation of ground stress considering the influence of ground stress release according to claim 6, characterized in that: Determining the test plane of the core sample includes: When the core sample is cylindrical, at least one cross section of the core sample in the height direction is determined as a test plane; When the core sample is spherical, two cross sections of the core sample that pass through the center of the sphere and are perpendicular to each other are determined as test planes.

8. The method for evaluating the orientation of ground stress considering the influence of ground stress release according to claim 5, characterized in that: The calculating of the sound wave velocity at different test positions in the same test plane includes: On the same test plane, the sound wave velocity at different test positions is calculated based on the sound wave arrival time and core sample length collected at different test positions.

9. The method for evaluating the ground stress orientation considering the influence of ground stress release according to claim 5, characterized in that: The evaluation method further comprises: Before pressurization, the minimum ground stress value is determined as the three-dimensional pressure applied by the pressurization mechanism based on geological data.

10. The method for evaluating the ground stress orientation considering the influence of ground stress release according to claim 5, characterized in that: The evaluation method further comprises: Before pressurization, 70% to 90% of the uniaxial strength of the core sample is determined as the three-dimensional pressure applied by the pressurization mechanism.

Images