Ground stress measurement method

Abstract

The invention discloses a crustal stress measurement method, which belongs to the field of petroleum and natural gas exploration, and comprises the following steps: processing a rock core into a hexagonal prism sample; measuring acoustic velocity anisotropy characteristics of the rock core sample; determining a first maximum horizontal crustal stress direction and a first minimum horizontal crustal stress direction based on a measured sound wave velocity result, and judging a sequence of historical stress values borne by three pairs of side surface normal directions of the hexagonal prism; single-axis loading is sequentially carried out on the three pairs of side faces according to the sequence of historical stress values from small to large, historical maximum stress values in all directions are determined based on the Kaiser effect, then a second maximum horizontal crustal stress direction and a second minimum horizontal crustal stress direction are determined, detection results of the first maximum horizontal crustal stress direction and detection results of the second maximum horizontal crustal stress direction are compared, and the detection results of the first maximum horizontal crustal stress direction and the second minimum horizontal crustal stress direction are obtained. And the two are fused to determine the final maximum horizontal crustal stress direction. The method solves the problems that the coring yield of shale oil gas, coal bed gas and the like is low, and indoor rock core ground stress evaluation is difficult.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and more specifically to a method for measuring ground stress. Background Art

[0002] Geostress is the natural stress existing in the stratum that is not disturbed by engineering. It is also called initial stress of the rock mass, absolute stress or original rock stress. Its size, direction, distribution law and evolution history are important contents of oil and gas field exploration and development, affecting and controlling the migration and accumulation of oil. Traditional methods for measuring geostress in indoor cores mainly include differential strain analysis, wave velocity anisotropy measurement, and acoustic emission (Kaiser) measurement. Acoustic emission experiment is the most commonly used. It requires drilling to obtain a full-size core, and then at least 4 cylindrical rock specimens with a diameter of 2.5 cm and a height of 5 cm are taken from the full-size core, of which one is taken in the vertical direction and at least three are taken in different horizontal directions. Then, the stress value of the Kaiser effect characteristic point under uniaxial compression is measured as the stress component to calculate the three principal stress vectors. Traditional geostress measurement requires large-size integrity cores and small-size rock specimens.

[0003] The article "A New Method for Deep Geostress Measurement" in the July 2004 issue of Volume 23, Issue 14 of the Chinese Journal of Rock Mechanics and Engineering studied the anisotropy of acoustic wave velocity of deep formation cores and the acoustic emission Kaiser effect under recovery loading conditions, and proposed a simple new method for deep formation geostress measurement. After the full-size core is drilled, the anisotropy of its stress unloading leads to the anisotropy of acoustic wave velocity. This principle can be used to determine the relative positions of the maximum and minimum horizontal geostresses. The cores at the above positions are sampled and the acoustic emission Kaiser experiment is performed under confining pressure to measure the magnitude of the horizontal main geostress. This method improves the geostress testing method for ultra-deep well formations. However, it requires large-sized integrity cores, which is difficult to promote and apply in difficult-to-cored reservoirs.

[0004] Invention patent CN 108918682 A discloses an indoor test and analysis method for the current natural ground stress of deep valley slope rock body. Through the rock samples obtained in six directions on site, indoor tests are carried out to test the acoustic characteristic parameters of the samples in the six directions, and the multiple compressive stress values ​​in the geological history are memorized. The maximum principal stress value and the maximum principal stress direction within the maximum principal direction range, as well as the intermediate principal stress and its direction and the minimum principal stress value and its direction are calculated using elastic mechanics theory and methods, so as to achieve the purpose of determining the three principal stress values ​​and their directions of the current ground stress of the rock body. However, this method requires samples in six directions, and coring is difficult.

[0005] With the exploration and development of shale oil and gas, coalbed methane, and deep-sea oil and gas, the cost of coring is getting higher and higher, the core recovery rate is low, and it is becoming more and more difficult to obtain large-sized and complete cores. How to use a small amount of small cores to accurately measure the ground stress value is becoming more and more important. Summary of the invention

[0006] The purpose of the present invention is to provide a method for measuring geostress to solve the problem that the core recovery rate of shale oil and gas, coalbed methane, etc. is low and indoor core stress evaluation is difficult or even impossible.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0008] According to one aspect of the present invention, a method for measuring ground stress is provided, comprising the following steps:

[0009] Step S1: Processing the core into a hexagonal prism-shaped sample;

[0010] Step S2: using an acoustic wave detection device to measure the acoustic wave velocity anisotropy characteristics of the core sample;

[0011] Step S3: based on the measured acoustic wave velocity results, determine the first maximum horizontal geostress direction and the first minimum horizontal geostress direction, and judge the order of historical stress values ​​in the normal directions of three pairs of side surfaces of the hexagonal prism;

[0012] Step S4: uniaxially load the three pairs of side surfaces of the hexagonal prism in order of historical stress values ​​from small to large, and determine the historical maximum stress values ​​in each direction based on the Kaiser effect;

[0013] Step S5: determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in each direction;

[0014] Step S6: Compare the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction, and merge the two to determine the final maximum horizontal geostress direction.

[0015] According to one embodiment of the present invention, in step S2, measuring the anisotropic characteristics of the acoustic wave velocity of the core sample using an acoustic wave detection device includes:

[0016] Step S2-1: Select the center position of one of the prism sides and draw a marking line;

[0017] Step S2-2: placing the core sample on the acoustic wave detection device, taking the mark line as the starting point, rotating the core sample, changing the phase according to a predetermined step length and collecting the first wave time of the transmitted acoustic wave arriving at the receiving point;

[0018] Step S2-3: Calculate the rock acoustic wave propagation velocity at each phase angle based on the acoustic wave propagation distance in the medium and rock and the first wave arrival time;

[0019] Step S2-4: Fit the relationship between the rock acoustic wave propagation velocity and phase angle to obtain the maximum and minimum wave velocity phase angle values.

[0020] According to one embodiment of the present invention, the acoustic wave detection device includes an annular bracket, an acoustic wave transmitting probe and an acoustic wave receiving probe. During testing, the acoustic wave transmitting probe and the acoustic wave receiving probe are assembled on the annular bracket and are on the same horizontal line, the core sample is placed at the center of the annular bracket, and the marking line and the acoustic wave transmitting probe are placed on the same horizontal line.

[0021] According to one embodiment of the present invention, the diameter of the annular bracket is 5 cm, and the size of the core sample is a regular hexagonal prism with a side length of 2 cm and a height of 4 cm.

[0022] According to one embodiment of the present invention, during testing, the acoustic wave detection device is placed in a working fluid medium that does not physically or chemically react with the core.

[0023] According to one embodiment of the present invention, the working fluid medium is hydraulic oil.

[0024] According to an embodiment of the present invention, the step length is 15°, and the measured phase angle ranges from 0° to 180°.

[0025] According to one embodiment of the present invention, the rock acoustic wave propagation velocity at the 1st to 12th phase angles is calculated using the following formula:

[0026] The sound wave velocity V at the initial phase a0a0’ :

[0027] The velocity of the sound wave V at a phase angle of 15° a1a1’ :

[0028] The velocity of the sound wave V at a phase angle of 30° a2a2’ :

[0029] The velocity of the sound wave with a phase angle of 45° is V a3a3’ :

[0030] The velocity of the sound wave with a phase angle of 60° is V a4a4’ :

[0031] The velocity of the sound wave with a phase angle of 75° is V a5a5’ :

[0032] The velocity of the sound wave with a phase angle of 90° is V a6a6’ :

[0033] The velocity of the sound wave V at a phase angle of 105° a7a7’ :

[0034] The velocity of the sound wave V when the phase angle is 120° a8a8’ :

[0035] The velocity of the sound wave V at a phase angle of 135° a9a9’ :

[0036] The velocity of the sound wave V at a phase angle of 150° a10a10’ :

[0037] The velocity of the sound wave V at a phase angle of 165° a11a11’ :

[0038] In the above formula, V f is the sound wave propagation speed of the medium, in m / s;

[0039] t a0 ,t a1 ,t a2 ,t a3 ,t a4 ,t a5 ,t a6 ,t a7 ,t a8 ,t a9 ,t a10 ,t a11 They are the first wave time from the acoustic wave transmitting probe to the acoustic wave receiving probe at the 1st to 12th phase angles respectively.

[0040] According to an embodiment of the present invention, in step S2-4, the relationship between the rock acoustic wave propagation velocity and the phase angle is fitted using the least square method, and the maximum and minimum wave velocity phase angle values ​​are determined.

[0041] According to one embodiment of the present invention, in step S3, the first maximum horizontal geostress direction and the first minimum horizontal geostress direction are determined by the following method: based on the phase angle values ​​corresponding to the maximum and minimum wave velocities, the direction with the minimum sound wave propagation velocity is taken as the first maximum horizontal geostress direction, and the direction with the maximum sound wave propagation velocity is taken as the first minimum horizontal geostress direction.

[0042] According to one embodiment of the present invention, in step S4, uniaxial loading is performed on three pairs of side surfaces of the hexagonal prism, and the historical maximum stress values ​​in each direction are determined based on the Kaiser effect, including: uniaxial loading is performed along the direction of a selected pair of side surfaces, acoustic emission signals are monitored, an acoustic emission stress curve is drawn, concentrated cluster points of acoustic emission are obtained, loading is stopped, and corresponding stress values ​​are recorded to obtain the historical maximum stress values ​​in the corresponding directions.

[0043] According to one embodiment of the present invention, in step S5, determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in various directions includes performing elliptical regression analysis on the acoustic emission detection results of three pairs of side surfaces to obtain the directions and values ​​of the major axis and minor axis of the ellipse, taking the direction of the major axis of the ellipse as the second maximum horizontal geostress direction and the stress value corresponding to the major axis of the ellipse as the second maximum horizontal geostress value, taking the direction of the minor axis of the ellipse as the second minimum horizontal geostress direction and the stress value corresponding to the minor axis of the ellipse as the second minimum horizontal geostress value.

[0044] According to one embodiment of the present invention, comparing the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction in step S6 includes determining whether the error between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction is below 5%. If the error is below 5%, the result is reliable, and the middle direction between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction is taken as the final maximum horizontal geostress direction.

[0045] Due to the adoption of the above technical solution, the ground stress measurement method provided by the present invention has at least one of the following beneficial effects compared with the prior art:

[0046] (1) The measurement of geostress is achieved by using a small-sized single core sample in the shape of a regular hexagonal prism. Compared with the traditional method, it saves a large number of cores and boreholes, and can effectively solve the problems of low core recovery rate of shale oil and gas, coalbed methane, deep-sea oil and gas, etc., difficulty in obtaining large-sized integrity cores, and limited geostress evaluation;

[0047] (2) The method of the present invention carries out acoustic wave testing in a working fluid medium that does not undergo physical and chemical reactions with rocks, measures the propagation time of the first wave of acoustic waves of different phase angles in the working fluid and rocks, and establishes a method for calculating the propagation speed of acoustic waves of rocks at different phase angles in combination with the propagation speed of acoustic waves of the working fluid and the propagation distance of acoustic waves in the working fluid and rocks, thereby ensuring the accuracy and reliability of acoustic wave measurement and calculation;

[0048] (3) The anisotropic characteristics of the acoustic wave propagation velocity were used to determine the historical maximum stress sequence in the normal direction of the three side surfaces of the regular hexagonal prism, and uniaxial compression and acoustic emission experiments were carried out in sequence from small to large. This avoided applying a large load first, which would cause signal interference from the acoustic emission cluster point and make it impossible to effectively obtain the Kaiser points of each prism surface, thereby improving the accuracy of the in-situ stress interpretation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0050] Figure 1 is an example process of measuring ground stress of a small-sized single core sample according to an embodiment of the present invention;

[0051] Figure 2 It is an example structure of a regular hexagonal geostress core specimen;

[0052] Figure 3a This is a schematic diagram of the core sample and equipment assembly. Figure 3b This is a top view of the core sample and equipment assembly. Figure 3c This is a schematic diagram of the rotation angle of the sound wave velocity characteristic test;

[0053] Figure 4 It is a graph of the speed of sound waves at different phase angles;

[0054] Figure 5 It is a schematic diagram of the historical load sorting and annotation in the normal direction of three pairs of side surfaces of the regular hexagonal prism core. DETAILED DESCRIPTION

[0055] The specific implementation of the present disclosure is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present disclosure, and is not used to limit the present disclosure.

[0056] In addition, reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0057] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined as in the embodiments of this application.

[0058] The present invention provides a method for measuring ground stress, which generally comprises the following steps:

[0059] Step S1: Processing the core into a hexagonal prism-shaped sample;

[0060] Step S2: using an acoustic wave detection device to measure the acoustic wave velocity anisotropy characteristics of the core sample;

[0061] Step S3: based on the measured acoustic wave velocity results, determine the first maximum horizontal geostress direction and the first minimum horizontal geostress direction, and judge the order of historical stress values ​​in the normal directions of three pairs of side surfaces of the hexagonal prism;

[0062] Step S4: uniaxially load the three pairs of side surfaces of the hexagonal prism in order of historical stress values ​​from small to large, and determine the historical maximum stress values ​​in each direction based on the Kaiser effect;

[0063] Step S5: determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in each direction;

[0064] Step S6: Compare the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction, and merge the two to determine the final maximum horizontal geostress direction.

[0065] The measurement of geostress is achieved by using a small-sized single core sample in the shape of a regular hexagonal prism. Compared with the traditional method, it saves a large number of cores and boreholes, and can effectively solve the problems of low core recovery rate of shale oil and gas, coalbed methane, deep-sea oil and gas, etc., difficulty in obtaining large-sized integrity cores, and limited geostress evaluation.

[0066] In some embodiments, in step S2, measuring the anisotropic characteristics of the acoustic wave velocity of the core sample using an acoustic wave detection device includes:

[0067] Step S2-1: Select the center position of one of the prism sides and draw a marking line;

[0068] Step S2-2: placing the core sample on the acoustic wave detection device, taking the mark line as the starting point, rotating the core sample, changing the phase according to a predetermined step length and collecting the first wave time of the transmitted acoustic wave arriving at the receiving point;

[0069] Step S2-3: Calculate the rock acoustic wave propagation velocity at each phase angle based on the acoustic wave propagation distance in the medium and rock and the first wave arrival time;

[0070] Step S2-4: Fit the relationship between the rock acoustic wave propagation velocity and phase angle to obtain the maximum and minimum wave velocity phase angle values.

[0071] In some embodiments, the acoustic wave detection device includes an annular bracket, an acoustic wave transmitting probe and an acoustic wave receiving probe. During the test, the acoustic wave transmitting probe and the acoustic wave receiving probe are assembled on the annular bracket and are on the same horizontal line, the core sample is placed in the center of the annular bracket, and the marking line and the acoustic wave transmitting probe are placed on the same horizontal line. In some embodiments, the diameter of the annular bracket is 5 cm, and the size of the core sample is a regular hexagonal prism with a side length of 2 cm and a height of 4 cm. During the test, the acoustic wave detection device is placed in a working fluid medium that does not physically and chemically react with the core. In some embodiments, the working fluid medium is hydraulic oil.

[0072] In some embodiments, the step size is 15°, and the measured phase angle ranges from 0° to 180°.

[0073] In some embodiments, the rock acoustic wave propagation velocity at the 1st to 12th phase angles is calculated using the following formula:

[0074] The sound wave velocity V at the initial phase a0a0’ :

[0075] The velocity of the sound wave V at a phase angle of 15° a1a1’ :

[0076] The velocity of the sound wave V at a phase angle of 30° a2a2’ :

[0077] The velocity of the sound wave with a phase angle of 45° is V a3a3’ :

[0078] The velocity of the sound wave with a phase angle of 60° is V a4a4’ :

[0079] The velocity of the sound wave with a phase angle of 75° is V a5a5’ :

[0080] The velocity of the sound wave with a phase angle of 90° is V a6a6’ :

[0081] The velocity of the sound wave V at a phase angle of 105° a7a7’ :

[0082] The velocity of the sound wave with a phase angle of 120° is V a8a8’ :

[0083] The velocity of the sound wave V at a phase angle of 135° a9a9’ :

[0084] The velocity of the sound wave V at a phase angle of 150° a10a10’ :

[0085] The velocity of the sound wave V at a phase angle of 165° a11a11’ :

[0086] In the above formula, V f is the sound wave propagation speed of the medium, in m / s;

[0087] t a0 ,t a1 ,t a2 ,t a3 ,t a4 ,t a5 ,t a6 ,t a7 ,t a8 ,t a9 ,t a10 ,t a11 They are the first wave time from the acoustic wave transmitting probe to the acoustic wave receiving probe at the 1st to 12th phase angles respectively.

[0088] In some embodiments, in step S2-4, the least square method is used to fit the relationship between the rock acoustic wave propagation velocity and the phase angle, and the maximum and minimum wave velocity phase angle values ​​are determined.

[0089] In some embodiments, in step S3, the first maximum horizontal geostress direction and the first minimum horizontal geostress direction are determined by the following method: based on the phase angle values ​​corresponding to the maximum and minimum wave velocities, the direction with the minimum sound wave propagation velocity is taken as the first maximum horizontal geostress direction, and the direction with the maximum sound wave propagation velocity is taken as the first minimum horizontal geostress direction.

[0090] In some embodiments, in step S4, uniaxial loading is performed on three pairs of side surfaces of the hexagonal prism, and the historical maximum stress values ​​in each direction are determined based on the Kaiser effect, including: uniaxial loading is performed along the direction of a selected pair of side surfaces, the acoustic emission signal is monitored, an acoustic emission stress curve is drawn, concentrated cluster points of the acoustic emission are obtained, loading is stopped, and corresponding stress values ​​are recorded to obtain the historical maximum stress values ​​in the corresponding directions.

[0091] In some embodiments, in step S5, determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in each direction includes performing an elliptical regression analysis on the acoustic emission detection results of three pairs of side surfaces to obtain the directions and values ​​of the major and minor axes of the ellipse, taking the direction of the major axis of the ellipse as the second maximum horizontal geostress direction and the stress value corresponding to the major axis of the ellipse as the second maximum horizontal geostress value, taking the direction of the minor axis of the ellipse as the second minimum horizontal geostress direction and the stress value corresponding to the minor axis of the ellipse as the second minimum horizontal geostress value.

[0092] In some embodiments, comparing the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction in step S6 includes determining whether the error between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction is less than 5%. If the error is less than 5%, the result is reliable, and the middle direction between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction (i.e., the arithmetic mean of the phase angle) is taken as the final maximum horizontal geostress direction.

[0093] In some embodiments, the second maximum horizontal geostress value and the second minimum horizontal geostress value determined in step S5 are used as the final maximum and minimum horizontal geostress values.

[0094] The method is described in detail below with a specific example and in conjunction with the accompanying drawings.

[0095] Figure 1 The following is an example process of measuring the in-situ stress of a small-sized single core sample according to an embodiment of the present invention. Figure 2 It is an example structure of a regular hexagonal geostress core specimen. Figure 3a This is a schematic diagram of the core sample and equipment assembly. Figure 3b This is a top view of the core sample and equipment assembly. Figure 3c It is a schematic diagram of the rotation angle of the sound wave velocity characteristic test. Figure 4 It is a graph of sound wave velocity at different phase angles. Figure 5 It is a schematic diagram of the historical load sorting and annotation in the normal direction of three pairs of side surfaces of the regular hexagonal prism core.

[0096] refer to Figures 1 to 5 First, the core was taken from the south section 1 of X3 well in the TM8 block. The core was processed into a hexagonal prism by wire cutting and double-sided grinding machine. The side length of the hexagonal prism was 2 cm and the height was 4 cm. The symmetric surface was ground flat, and the center position of a prism side was selected to engrave the marking line S. 0 S 0 ', its corresponding top azimuth line is a 0 a 0 ',like Figure 2 shown.

[0097] like Figure 3a and Figure 3b As shown, assemble the acoustic wave transmitting probe T and the acoustic wave receiving probe R. Place the acoustic wave transmitting probe T and the acoustic wave receiving probe R on a ring bracket with a diameter of 5 cm. The two probes are placed on the same horizontal line, and the distance between the probes is also kept at 5 cm. Place the core sample S in the center of the ring bracket, adjust the position of the sample S, and place the marking line and the transmitting probe T on the same horizontal line.

[0098] Place the assembled sonic probe and core sample in 46# wear-resistant hydraulic oil. The sonic propagation speed of the hydraulic oil is 1380m / s. 0 S 0 ' is the starting point, and the rock specimen is rotated counterclockwise in steps of 15 degrees to measure the time from the first wave of the sound wave emitted by the transmitting probe to the first wave of the receiving probe. Rotate counterclockwise from 0 degrees to 180 degrees. Figure 3c As shown, there are 12 phase points (a 0 a 0 'To a 11 a 11 '), according to the propagation distance of the sound wave in the hydraulic oil medium and the rock and the arrival time of the first wave, the rock sound wave propagation velocity at each phase angle is calculated according to the formula described above. The calculation results of the sound wave velocity are shown in Table 1.

[0099] Table 1 Calculation results of acoustic wave velocity at different phase angles

[0100]

[0101] The relationship between the rock acoustic wave propagation velocity and phase angle is fitted by the least squares method to obtain the maximum and minimum wave velocity phase angle values, such as Figure 4 As shown. After the core is unloaded, the degree of unloading is the highest in the direction of the maximum horizontal geostress, the most micro cracks are developed, and the corresponding sound wave propagation velocity is also the lowest. The degree of unloading is the lowest in the direction of the minimum horizontal geostress, the least micro cracks are developed, and the corresponding sound wave propagation velocity is also the highest. Based on the above principle, according to the phase angle values ​​corresponding to the maximum and minimum wave velocities, the directions of the maximum and minimum horizontal geostress are judged. The directions of the maximum and minimum horizontal geostress are the phase angle directions of 27 degrees and 117 degrees, respectively. The direction with a phase angle of 27 degrees is the first maximum horizontal geostress direction, and the direction with a phase angle of 117 degrees is the first minimum horizontal geostress direction.

[0102] in accordance with Figure 4 The acoustic wave velocity results shown in the figure are used to determine the order of the historical stress values ​​on the three pairs of side surfaces of the hexagonal prism, and are marked 1-1, 2-2, and 3-3 in order from small to large, as shown in Figure 1. Figure 5 shown.

[0103] The 1-1 surface was subjected to uniaxial loading, the acoustic emission signal was monitored, and the acoustic emission-stress curve was drawn to obtain the concentrated group point of acoustic emission, which was the Kaiser effect point in the 1-1 direction. The loading was stopped and the corresponding stress value was recorded to obtain the historical maximum stress value corresponding to the 1-1 direction.

[0104] The 2-2 surface is subjected to uniaxial loading, the acoustic emission signal is monitored, and the acoustic emission-stress curve is drawn to obtain the second concentrated group point of the acoustic emission, which is the Kaiser effect point in the 2-2 direction. The loading is stopped and the corresponding stress value is recorded, which is the historical maximum stress value corresponding to the 2-2 direction.

[0105] The 3-3 surface was subjected to uniaxial loading, the acoustic emission signal was monitored, and the acoustic emission-stress curve was drawn to obtain the third concentrated group point of acoustic emission, which was the Kaiser effect point in the 3-3 direction. The loading was stopped and the corresponding stress value was recorded, which was the historical maximum stress value corresponding to the 3-3 direction.

[0106] Based on the acoustic emission test results of the 1-1, 2-2 and 3-3 surfaces, ellipse regression analysis was performed to obtain the values ​​and directions of the major and minor axes of the ellipse. The stress value corresponding to the major axis was calculated as σ H , the major axis corresponds to the stress direction as α H , the stress value corresponding to the short axis is calculated as σ h , the stress direction corresponding to the minor axis is α h .generally

[0107]

[0108] With α H as the second maximum horizontal stress direction, and σ H As the second maximum horizontal stress value, α h as the second minimum horizontal stress direction, and σ h as the second minimum horizontal stress value.

[0109] The anisotropic characteristics of the sound wave propagation velocity are used to determine the historical maximum stress ranking in the normal direction of the three side surfaces of the regular hexagonal prism, and uniaxial compression and acoustic emission experiments are carried out in sequence from small to large. This avoids applying a large load first, which would cause signal interference from the acoustic emission cluster point and make it impossible to effectively obtain the Kaiser points of each prism surface, thereby improving the accuracy of ground stress interpretation.

[0110] Comparing the first maximum horizontal geostress direction with the second maximum horizontal geostress direction, the error between the two is less than 3%, and the detection result is considered reliable. The arithmetic mean of the two is taken as the maximum horizontal geostress direction. The final interpretation results of geostress are shown in Table 2.

[0111] Table 2 Interpretation results of geostress

[0112]

[0113] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0114] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0115] In addition, 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 method for measuring ground stress, It is characterized in that The following steps are involved: Step S1: Processing the core into a hexagonal prism-shaped sample; Step S2: using an acoustic wave detection device to measure the acoustic wave velocity anisotropy characteristics of the core sample; Step S3: based on the measured acoustic wave velocity results, determine the first maximum horizontal geostress direction and the first minimum horizontal geostress direction, and judge the order of historical stress values ​​in the normal directions of three pairs of side surfaces of the hexagonal prism; Step S4: uniaxially load the three pairs of side surfaces of the hexagonal prism in order of historical stress values ​​from small to large, and determine the historical maximum stress values ​​in each direction based on the Kaiser effect; Step S5: determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in each direction; Step S6: Compare the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction, and merge the two to determine the final maximum horizontal geostress direction.

2. The method according to claim 1, It is characterized in that In step S2, measuring the anisotropic characteristics of the acoustic wave velocity of the core sample using an acoustic wave detection device includes: Step S2-1: Select the center position of one of the prism sides and draw a marking line; Step S2-2: placing the core sample on the acoustic wave detection device, taking the mark line as the starting point, rotating the core sample, changing the phase according to a predetermined step length and collecting the first wave time of the transmitted acoustic wave arriving at the receiving point; Step S2-3: Calculate the rock acoustic wave propagation velocity at each phase angle based on the acoustic wave propagation distance in the medium and rock and the first wave arrival time; Step S2-4: Fit the relationship between the rock acoustic wave propagation velocity and phase angle to obtain the maximum and minimum wave velocity phase angle values.

3. The method according to claim 2, It is characterized in that The acoustic wave detection device includes an annular bracket, an acoustic wave transmitting probe and an acoustic wave receiving probe. During testing, the acoustic wave transmitting probe and the acoustic wave receiving probe are assembled on the annular bracket and are on the same horizontal line, the core sample is placed at the center of the annular bracket, and the marking line and the acoustic wave transmitting probe are placed on the same horizontal line.

4. The method according to claim 3, It is characterized in that The diameter of the annular bracket is 5 cm, and the size of the core sample is a regular hexagonal prism with a side length of 2 cm and a height of 4 cm.

5. The method according to claim 4, It is characterized in that During the test, the acoustic wave detection device is placed in a working fluid medium that does not physically or chemically react with the core.

6. The method according to claim 5, It is characterized in that The working fluid medium is hydraulic oil.

7. The method according to claim 6, It is characterized in that The step length is 15°, and the measured phase angle range is 0-180°.

8. The method according to claim 7, It is characterized in that The rock acoustic wave propagation velocity at the 1st to 12th phase angles is calculated using the following formula: The sound wave velocity V at the initial phase a0a0’ : The velocity of the sound wave V at a phase angle of 15° a1a1’ : The velocity of the sound wave V at a phase angle of 30° a2a2’ : The velocity of the sound wave with a phase angle of 45° is V a3a3’ : The velocity of the sound wave with a phase angle of 60° is V a4a4’ : The velocity of the sound wave with a phase angle of 75° is V a5a5’ : The velocity of the sound wave with a phase angle of 90° is V a6a6’ : The velocity of the sound wave V at a phase angle of 105° a7a7’ : The velocity of the sound wave with a phase angle of 120° is V a8a8’ : The velocity of the sound wave V at a phase angle of 135° a9a9’ : The velocity of the sound wave V at a phase angle of 150° a10a10’ : The velocity of the sound wave V at a phase angle of 165° a11a11’ : In the above formula, V f is the sound wave propagation speed of the medium, in m / s; t a0 ,t a1 ,t a2 ,t a3 ,t a4 ,t a5 ,t a6 ,t a7 ,t a8 ,t a9 ,t a10 ,t a11 They are the first wave time from the acoustic wave transmitting probe to the acoustic wave receiving probe at the 1st to 12th phase angles respectively.

9. The method according to claim 2, It is characterized in that In step S2-4, the least square method is used to fit the relationship between the rock acoustic wave propagation velocity and the phase angle, and the maximum and minimum wave velocity phase angle values ​​are determined.

10. The method according to claim 2, It is characterized in that In step S3, the first maximum horizontal geostress direction and the first minimum horizontal geostress direction are determined by the following method: according to the phase angle values ​​corresponding to the maximum and minimum wave velocities, the direction with the minimum sound wave propagation velocity is taken as the first maximum horizontal geostress direction, and the direction with the maximum sound wave propagation velocity is taken as the first minimum horizontal geostress direction.

11. The method according to claim 1, It is characterized in that In step S4, uniaxial loading is performed on three pairs of side surfaces of the hexagonal prism, and the historical maximum stress values ​​in each direction are determined based on the Kaiser effect, including: uniaxial loading is performed along the direction of a selected pair of side surfaces, acoustic emission signals are monitored, acoustic emission stress curves are drawn, concentrated cluster points of acoustic emission are obtained, loading is stopped, and corresponding stress values ​​are recorded to obtain the historical maximum stress values ​​in the corresponding directions.

12. The method according to claim 11, It is characterized in that In step S5, determining the second maximum horizontal geostress direction and the second minimum horizontal geostress direction based on the historical maximum stress values ​​in various directions includes performing elliptical regression analysis on the acoustic emission detection results of three pairs of side surfaces to obtain the directions and values ​​of the major axis and the minor axis of the ellipse, taking the direction of the major axis of the ellipse as the second maximum horizontal geostress direction and the stress value corresponding to the major axis of the ellipse as the second maximum horizontal geostress value, taking the direction of the minor axis of the ellipse as the second minimum horizontal geostress direction and the stress value corresponding to the minor axis of the ellipse as the second minimum horizontal geostress value.

13. The method according to claim 12, It is characterized in that In step S6, comparing the detection results of the first maximum horizontal geostress direction and the second maximum horizontal geostress direction includes determining whether the error between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction is less than 5%. If the error is less than 5%, the result is reliable, and the middle direction between the first maximum horizontal geostress direction and the second maximum horizontal geostress direction is taken as the final maximum horizontal geostress direction.

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