Method and device for obtaining crustal stress of rock core

Abstract

The invention discloses a rock core crustal stress obtaining method and device, and relates to the technical field of rock detection, and the method comprises the steps: determining the maximum horizontal principal stress SH direction, the minimum horizontal principal stress Sh direction and the vertical principal stress SV direction of a to-be-detected rock core based on the sound wave velocity anisotropy; rock core columns are drilled in the SH direction, the Sh direction and the SV direction of the rock core to be measured respectively, and Kaiser stress in the SH direction, the Sh direction and the SV direction is obtained through a Kaiser acoustic emission device; and obtaining the crustal stress of the rock core according to the obtained Kaiser stress in the SH direction, the Sh direction and the SV direction. The method is clear in testing principle, accurate and effective, the drilling number of small rock cores is reduced, the problem that in a conventional Kaiser crustal stress testing method, due to the fact that the mother rock length is not enough, small rock cores in the enough direction cannot be drilled, and testing cannot be conducted can be solved, and basic geological data are provided for oil and gas field exploration and development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of rock detection, and particularly relates to a method and device for obtaining the size of in-situ stress of a rock core. BACKGROUND

[0002] Due to changes in the speed of celestial bodies, the earth's interior, the outside and the earth's rotation, different parts of the crust are unbalanced in stress, and rock layers are subjected to extrusion, stretching, torsion and other forces, which promotes the deformation of the rock layers in the crust. At the same time, the rock layers generate a force resisting deformation, which is generated inside the rock and acts on the unit area of the crust, and is called in-situ stress.

[0003] In-situ stress plays an important role in oil and gas exploration and development, and is often applied to wellbore stability in the drilling process, fracturing breakdown pressure and extension pressure, activation of natural fractures or faults, and sand production problems in the production process, etc. Therefore, determining the size of in-situ stress is crucial to solving the above engineering problems.

[0004] At present, the size of in-situ stress can be measured in the field and in the laboratory. Field measurement methods include hydraulic fracturing, wellbore collapse, acoustic logging, etc. Laboratory measurement methods include acoustic emission, differential strain, etc. However, field testing has many disadvantages such as great construction difficulty, long measurement time and high cost, while laboratory measurement methods have the advantages of simplicity, speed and economy, and are increasingly valued, especially the acoustic emission in-situ stress size testing method based on Kaiser effect is a commonly used laboratory testing method.

[0005] For straight well coring, since the horizontal principal stress orientation cannot be determined in advance, three principal stress sizes need to be measured. Usually, two horizontal principal stress sizes are measured by taking cores in three directions of full-diameter rock core radial counterclockwise 0°, 45° and 90°, and the vertical principal stress size is measured by drilling a core along the full-diameter rock core axis. For example, the in-situ stress testing method based on the Kaiser effect of a rock core disclosed in the application No. 201911336714.9, which drills a lot of cores and requires a large length of full-diameter rock core. For reservoirs that cannot drill enough length of full-diameter rock core, it is impossible to drill enough amount of small rock core, resulting in that the three principal stress sizes cannot be completely determined. Therefore, how to measure the three principal stress sizes while reducing the number of drilled small rock cores has become a problem to be solved. SUMMARY

[0006] The present application aims to provide a method and device for obtaining the size of in-situ stress of a rock core to solve the above technical problems.

[0007] To achieve the above-mentioned purpose, the present application provides a method for obtaining the size of in-situ stress of a rock core, comprising:

[0008] Based on the anisotropy of acoustic wave velocity, the maximum horizontal principal stress S of the to-be-measured core is determined H direction, the minimum horizontal principal stress S h direction and the vertical principal stress S V direction;

[0009] The core columns are drilled in the S H direction, S h direction and S V direction respectively, and the Kaiser stress sizes in the S H direction, S h direction and S V direction are obtained respectively by using Kaiser acoustic emission devices.

[0010] According to the Kaiser stress sizes in the S H direction, S h direction and S V direction obtained respectively, the in-situ stress size of the core is obtained.

[0011] The application further provides a device for obtaining the in-situ stress size of a core, comprising:

[0012] A determination unit is configured to determine the maximum horizontal principal stress S of the to-be-measured core based on the anisotropy of acoustic wave velocity H direction, the minimum horizontal principal stress S h direction and the vertical principal stress S V direction;

[0013] A drilling unit is configured to drill core columns in the S H direction, S h direction and S V direction respectively, and obtain the Kaiser stress sizes in the S H direction, S h direction and S V direction respectively by using Kaiser acoustic emission devices.

[0014] An obtaining unit is configured to obtain the in-situ stress size of the core according to the Kaiser stress sizes in the S H direction, S h direction and S V direction obtained respectively.

[0015] The application further provides an electronic device, comprising a processor coupled with a memory;

[0016] The processor is configured to read and execute a computer program stored in the memory to implement the method according to any one of the preceding embodiments.

[0017] The application also provides a computer readable storage medium, wherein a program or instruction is stored, and the program or instruction is executed by a processor to realize the method according to any one of the above.

[0018] Technical effects and advantages of the application:

[0019] The three-directional main ground stress test of the application is divided into two aspects, one is the basic principle of determining the ground stress direction based on the anisotropy of rock wave velocity, and the maximum and minimum horizontal principal stress directions of the mother rock drilled from the vertical well are obtained through the radial acoustic wave velocity anisotropy testing device; the other is based on Kaiser effect, and the Kaiser stress point of the core drilled from the mother rock in three principal stress directions is identified, so as to calculate the size of the three-directional main ground stress. The test principle of the method is clear, accurate and effective, the number of small cores drilled is reduced, and the problem that the test cannot be performed due to the insufficient length of the mother rock and the inability to drill enough directional small cores in the conventional Kaiser ground stress test method can be solved, thereby providing basic geological data for oil and gas field exploration and development.

[0020] Other features and advantages of the application will be set forth in the following description of the application, and in part will become apparent to those skilled in the art from the description, or recognized by practicing the application as described herein. The aims and other advantages of the application will be realized and attained by the structure particularly pointed out in the written description and claims. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Flow chart for obtaining the size of the core ground stress;

[0022] Figure 2 Schematic diagram of the radial acoustic wave velocity anisotropy core sample;

[0023] Figure 3 Graph of the radial acoustic wave velocity changing with the test angle;

[0024] Figure 4 Schematic diagram of the three principal stress coordinates and the drilled core in the core to be tested;

[0025] Figure 5 Graph of the cumulative acoustic emission count and the stress;

[0026] Figure 6 Graph of the real-time acoustic emission count and the stress. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, but not all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0028] It should be noted that the structure, proportion, size and the like shown in the drawings attached to the present specification are only used to cooperate with the content disclosed in the specification, so as to be understood and read by those skilled in the art, and do not have technical significance, and any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effect and purpose that can be achieved by the present application, should still fall within the scope covered by the disclosed technology. Meanwhile, the terms such as "upper", "lower", "left", "right", "middle" and "one" in the present specification are only for the convenience of clear description, and are not used to limit the scope of the present application, and the change or adjustment of the relative relationship, without substantially changing the technical content, is also considered as the scope of the present application.

[0029] In order to solve the problems in the prior art, the present application discloses a method for obtaining the in-situ stress of a core, as shown in Figure 1 The method comprises the following steps:

[0030] 1. Based on the anisotropy of acoustic wave velocity, the maximum horizontal principal stress S H of the measured core, the minimum horizontal principal stress S h and the vertical principal stress S V are determined.

[0031] Specifically, the steps include: 1) cutting the end face of a cylindrical core drilled in a vertical well flat, and drawing a starting line representing a central angle of 0° as a 0° line for testing the anisotropy of radial acoustic wave velocity, as shown in Figure 2 . The diameter of the measured core is measured at the middle position of the height, and the diameters at 0°, 45°, 90° and 135° are measured, and then the average value is taken as the diameter r of the measured core, and the diameter data r is input into the acoustic wave test control software.

[0032] 2) Coupling agent is applied on the acoustic wave probe, and the acoustic wave probe is directly connected together, the propagation time t1 of the acoustic wave in the probe is tested and input into the control software; the measured core is placed on the radial acoustic wave velocity anisotropy testing device, the position of the acoustic wave probe is adjusted, the acoustic wave probe is aligned with the 0° line of the measured core at the middle position of the height of the measured core, the scale disc of the testing device is adjusted, the angle of the base scale disc is 0°, the base rotating table is tightened to clamp the measured core; coupling agent is applied on the acoustic wave probe, the starting valve is opened to tightly couple the acoustic wave probe with the measured core, the acoustic wave velocity at 0° position is tested, then the base is rotated clockwise by 15°, the acoustic wave velocity at 15° position is tested, and so on, until the acoustic wave velocity at 180° position is tested.

[0033] 3) According to the acoustic wave velocity data obtained by testing, the curve graph of acoustic wave velocity with test angle is drawn, as shown inFigure 3 The horizontal axis is the angle with the marker line, i.e. the test angle, and the vertical axis is the sound wave velocity. The data is fitted using a trigonometric function, and the relative angles of the maximum and minimum horizontal principal stress directions are determined according to the horizontal axis values corresponding to the minimum and maximum positions of the curve velocity.

[0034] 4) Marking and establishing a coordinate system on the end face of the core to be tested, wherein the direction consistent with the minimum wave velocity direction is the X axis direction, which is the maximum horizontal principal stress S H ; the direction consistent with the maximum wave velocity direction is the Y axis direction, which is the minimum horizontal principal stress S h ; and the axial direction of the core to be tested is the Z axis direction, which is the vertical principal stress S V .

[0035] 2) Drilling core columns in the S H direction, the S h direction and the S V direction, respectively, and using the Kaiser acoustic emission device to obtain the Kaiser stress in the S H direction, the S h direction and the S V direction, respectively.

[0036] Specifically, cylindrical small cores are drilled along the X axis, the Y axis and the Z axis directions on the core to be tested for acoustic emission testing, as shown in Figure 4 . During acoustic emission testing, an axial load loading device is used to load at a certain strain rate, and an acoustic emission device (AE) is used to collect acoustic emission signals and stress data in real time to obtain acoustic emission cumulative count and stress change curves, acoustic emission real-time count and stress change curves, as shown in Figure 5 and Figure 6 , respectively. The Kaiser stress point is determined based on the acoustic emission cumulative count and real-time count.

[0037] The Kaiser stress point is determined based on the acoustic emission cumulative count and real-time count, specifically as follows: 1) Based on the AE cumulative count-stress curve, the AE cumulative count growth rate R is calculated by the AE cumulative count growth rate with stress, and the stress corresponding to the R surge point is obtained according to the R stress change trend. The R calculation formula is:

[0038] R = (AE cumulative count (σ + Δσ) - AE cumulative count (σ)) / Δσ

[0039] wherein σ is the axial stress of the core corresponding to the AE cumulative count at the same time, and Δσ is the axial stress increment.

[0040] 2) Based on the AE real-time count-stress curve, the stress point corresponding to the AE instantaneous count surge point is obtained.

[0041] 3) If R and AE real-time count appear surge phenomenon at the same stress point, it is determined that the stress point is a common surge point, that is, the rock core S H Kaiser stress point in the direction.

[0042] 4) Using the same method, the rock core S h and S V Kaiser stress point in the direction.

[0043] 5) Substitute the Kaiser stress points of S H direction, S h direction and S V direction into the acoustic emission cumulative count and stress change curve or acoustic emission real-time count and stress change curve, and obtain the Kaiser stress size of S H direction, S h direction and S V direction.

[0044] 3, according to the Kaiser stress size of S H direction, S h direction and S V direction obtained respectively, the rock core ground stress size is obtained.

[0045] Specifically, according to the Kaiser stresses of the three principal stress directions obtained by the Kaiser acoustic emission test, combined with the formation pressure of the target layer of the test, the ground stress size is calculated according to the following formula:

[0046] Si=SKi+αpp

[0047] In the formula: S Ki is the Kaiser stress, MPa; i=H, h, V respectively corresponds to the maximum horizontal principal stress, the minimum horizontal principal stress, and the vertical principal stress; alpha is the pore elastic coefficient, dimensionless; p p is the formation pressure, MPa.

[0048] The application also provides a rock core ground stress size obtaining device, comprising:

[0049] A determination unit is configured to determine the maximum horizontal principal stress S H direction, the minimum horizontal principal stress S h direction and the vertical principal stress S V direction of the rock core to be tested based on the acoustic wave velocity anisotropy.

[0050] A drilling unit is configured to drill a core column in the rock core to be tested S H direction, S h direction and S V direction respectively, and obtain S Hdirection, S h direction and S V Kaiser stress magnitude of the direction;

[0051] obtaining unit, configured to obtain the core in-situ stress magnitude according to the respectively obtained S H direction, S h direction and S V Kaiser stress magnitude of the direction, and obtaining the core in-situ stress magnitude.

[0052] Since the content protected by the device is similar to the content protected by the method, no more details are given here, and the detailed description is referred to the description of the method.

[0053] The present application also provides an electronic device. The electronic device comprises at least one processor, at least one communication interface, at least one memory and at least one communication bus; optionally, the communication interface can be the interface of a communication module, such as the interface of a GSM module; the processor can be a processor CPU, or a specific integrated circuit ASIC (Application Specific Integrated Circuit), or one or more integrated circuits configured to implement the embodiments of the present application. The memory can contain a high-speed RAM memory, and can also include a non-volatile memory, such as at least one disk memory. The memory stores a program, and the processor calls the program stored in the memory to execute the method provided in the above embodiments of the present application.

[0054] Corresponding to the method of the present application, the present application also provides a computer storage medium. The computer storage medium stores a computer program, which is run by a processor to execute the method provided in the above embodiments of the present application.

[0055] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the present application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still can modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A method for obtaining the magnitude of geostress in a rock core, characterized in that, include: Based on the anisotropy of acoustic wave velocity, the maximum horizontal principal stress S in the core sample was determined. H Direction, minimum horizontal principal stress S h Direction and vertical principal stress S V direction; In the rock core S to be tested H Direction, S h Direction and S V Core columns were drilled in different directions, and S values ​​were obtained using a Kaiser acoustic emission device. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction; Based on the S obtained respectively H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction is used to obtain the magnitude of the geostress in the rock core.

2. The method for obtaining the magnitude of core in-situ stress according to claim 1, characterized in that, Based on the anisotropy of acoustic wave velocity, the maximum horizontal principal stress S in the core sample was determined. H Direction, minimum horizontal principal stress S h Direction and vertical principal stress S V Directions, including: Cut the end face of the rock core to be tested flat and draw a starting line along the axis to indicate that the central angle is 0°; Based on the anisotropy of acoustic wave velocity, the radial wave velocity and central angle curves on the same horizontal plane of the rock core under test are obtained. Based on the radial wave velocity and central angle curve, determine the maximum and minimum central angles corresponding to the maximum and minimum wave velocities; A coordinate system is established with the end face of the rock core to be tested as the origin, the endpoint of the largest central angle as the Y-axis, the endpoint of the smallest central angle as the X-axis, and the axis of the rock core to be tested as the Z-axis. Wherein, the Y-axis direction represents the minimum horizontal principal stress S. h Direction; the X-axis direction is the direction of maximum horizontal principal stress S. H Direction; the Z direction is perpendicular to the principal stress S. V direction.

3. The method for obtaining the magnitude of core in-situ stress according to claim 1, characterized in that, In the rock core S to be tested H Direction, S h Direction and S V Core columns were drilled in different directions, and S values ​​were obtained using a Kaiser acoustic emission device. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction includes: Acoustic emission tests were performed on the three drilled cores to obtain the relationship curves between the cumulative acoustic emission count and stress for each core, as well as the relationship curves between the real-time acoustic emission count and stress. Based on the cumulative acoustic emission count and real-time acoustic emission count of each core column, the Kaiser stress point of each core column is determined. Substitute the Kaiser stress points of each core column into the relationship curve between acoustic emission cumulative count and stress, or the relationship curve between acoustic emission real-time count and stress, to determine S. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction.

4. The method for obtaining the magnitude of core in-situ stress according to claim 1, characterized in that, Based on the S obtained respectively H Direction, S h Direction and S V The magnitude of Kaiser stress in the direction is used to obtain the magnitude of geostress in the core, including: Obtain the formation pressure of the target layer; Based on the S obtained respectively H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction and the formation pressure of the target layer are used to obtain the magnitude of the core in-situ stress.

5. The method for obtaining the magnitude of core in-situ stress according to claim 4, characterized in that, The magnitude of the geostress in the rock core can be obtained using the following formula; Si=SKi+αpp In the formula: S Ki Kaiser stress, MPa; i = H, h, V correspond to the maximum horizontal principal stress, minimum horizontal principal stress, and vertical principal stress, respectively; α is the porosity coefficient, dimensionless; p p , where is the formation pressure, MPa.

6. A device for obtaining the magnitude of rock core in-situ stress, characterized in that, include: The determination element is used to determine the maximum horizontal principal stress S in the test core based on the anisotropy of acoustic wave velocity. H Direction, minimum horizontal principal stress S h Direction and vertical principal stress S V direction; Drilling unit, used for drilling core S to be tested H Direction, S h Direction and S V Core columns were drilled in different directions, and S values ​​were obtained using a Kaiser acoustic emission device. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction; The obtaining unit is used to obtain S according to the respective S H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction is used to obtain the magnitude of the geostress in the rock core.

7. The device for obtaining the magnitude of rock core in-situ stress according to claim 6, characterized in that, Based on the anisotropy of acoustic wave velocity, the maximum horizontal principal stress S in the core sample was determined. H Direction, minimum horizontal principal stress S h Direction and vertical principal stress S V Directions, including: Cut the end face of the rock core to be tested flat and draw a starting line along the axis to indicate that the central angle is 0°; Based on the anisotropy of acoustic wave velocity, the radial wave velocity and central angle curves on the same horizontal plane of the rock core under test are obtained. Based on the radial wave velocity and central angle curve, determine the maximum and minimum central angles corresponding to the maximum and minimum wave velocities; A coordinate system is established with the end face of the rock core to be tested as the origin, the endpoint of the largest central angle as the Y-axis, the endpoint of the smallest central angle as the X-axis, and the axis of the rock core to be tested as the Z-axis. Wherein, the Y-axis direction represents the minimum horizontal principal stress S. h Direction; the X-axis direction is the direction of maximum horizontal principal stress S. H Direction; the Z direction is perpendicular to the principal stress S. V direction.

8. The device for obtaining the magnitude of rock core in-situ stress according to claim 6, characterized in that, In the rock core S to be tested H Direction, S h Direction and S V Core columns were drilled in different directions, and S values ​​were obtained using a Kaiser acoustic emission device. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction includes: Acoustic emission tests were performed on the three drilled cores to obtain the relationship curves between the cumulative acoustic emission count and stress for each core, as well as the relationship curves between the real-time acoustic emission count and stress. Based on the cumulative acoustic emission count and real-time acoustic emission count of each core column, the Kaiser stress point of each core column is determined. Substitute the Kaiser stress points of each core column into the relationship curve between acoustic emission cumulative count and stress, or the relationship curve between acoustic emission real-time count and stress, to determine S. H Direction, S h Direction and S V The magnitude of the Kaiser stress in the direction.

9. An electronic device, characterized in that, include: Processor, the processor being coupled to memory; The processor is configured to read and execute a computer program stored in the memory to implement the method as described in any one of claims 1-5.

10. A computer-readable storage medium storing a program or instructions, characterized in that, When the program or instructions are executed by the processor, they implement the method as described in any one of claims 1-5.

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