Crustal stress drilling solid rock core confining pressure calibration method, system, equipment and medium

Abstract

The invention discloses a ground stress drilling solid rock core confining pressure calibration method, system and equipment and a medium, and relates to the technical field of ground stress measurement. A complete solid rock core is drilled, a resistance strain gauge is pasted on the surface of the rock core, the rock core is put into a confining pressure calibration instrument to apply confining pressure, the resistance strain gauge is used for reading strain data generated in the pressurization process, meanwhile, the confining pressure value is recorded, and the elastic modulus and the Poisson's ratio of the rock core are calculated. According to the method, the elasticity modulus and the Poisson ratio of the solid rock core of the ground stress test drill hole are measured, and more reliable data support is provided for ground stress measurement. And simultaneously. The problem that an experiment cannot be carried out due to the fact that a rock core with a hollow inclusion stressometer is broken and the stressometer is damaged can be effectively solved, the properties of the drilled rock cores at adjacent positions are not changed, the calculated elastic modulus and Poisson's ratio data are the required rock parameters, and the success rate of a ground stress test is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of geostress measurement technology, specifically to a method, system, equipment, and medium for determining the confining pressure ratio of solid rock cores from geostress boreholes. Background Technology

[0002] In geostress testing, besides measuring the strain of the rock core upon stress relief, it is also necessary to obtain the elastic modulus and Poisson's ratio of the core after stress relief to further calculate the geostress. Currently, the elastic modulus and Poisson's ratio of stress-relieved rock cores are obtained through confining pressure calibration experiments. This involves bringing the core, equipped with a stress gauge, back to the laboratory after stress relief and using a confining pressure calibrator to measure the elastic modulus and Poisson's ratio. However, in actual testing, stress-relieved rock cores are easily damaged, making it difficult to obtain cores with stress gauges. The presence of weak surfaces such as joints and fissures in the core, or excessive mechanical vibration of the core tube during core extraction, can lead to rock cracking or even breakage.

[0003] During stress relief, the stress gauge's signal wires need to be pulled taut with appropriate force to prevent them from being broken as the drill pipe rotates. The stress gauge has 14 signal wires, corresponding to 12 measurement channels, 1 grounding point, and 1 temperature compensation point. If one is broken, the geostress test will fail, and even if a core sample is obtained, subsequent steps cannot be performed. Furthermore, the stress gauge's signal wires often break at the tail end, making rewiring difficult. Even if rewiring is successful, it is hard to establish the correspondence between strain gauges and strain values, thus preventing the acquisition of experimental data.

[0004] If the confining pressure test cannot be performed normally, the rock core adjacent to the release location is usually brought back to the laboratory, cut and processed into a Φ50×100 standard cylindrical specimen, and then strain gauges are attached to conduct a uniaxial compression test to obtain the elastic modulus and Poisson's ratio of the rock core. However, the process of processing the specimen is time-consuming and labor-intensive.

[0005] Prior art, disclosed in publication number CN111855422A, provides a confining pressure calibrating test apparatus and method. The apparatus includes a confining pressure calibrating chamber, a lifting component, and a rubber sleeve component. The chamber is hollow and contains a pressure chamber. The rubber sleeve component is coaxially arranged with the pressure chamber, and its outer wall communicates with the pressure chamber. The cylindrical rock core is equipped with a strain gauge. The lifting component includes a circular positioning plate installed within the pressure chamber, which moves up and down along the height of the rubber sleeve component. The test method includes the following steps: 1. Adjustment of the lifting component; 2. Installation of the cylindrical rock core and plunger rod; 3. Confining pressure test; 4. Processing of the mechanical parameters of the cylindrical rock core. The overall design is complex, sample preparation is cumbersome, and testing efficiency is low.

[0006] To improve the success rate of geostress testing, the confining pressure calibration method cannot be directly applied when the stress gauge in the rock core is damaged, even though the mechanical parameters of this rock core are optimal for calculating geostress. Therefore, when an intact rock core is obtained but the sensor is damaged, a new calibration method should be developed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, a method, system, equipment, and medium for determining the confining pressure of solid rock cores from boreholes under in-situ stress are provided. This method requires drilling a complete solid rock core adjacent to the stress gauge, attaching resistance strain gauges to the core surface, and connecting the strain gauges to the strain gauge via wires. The core with the attached strain gauges is then placed in the confining pressure calibrator, which applies confining pressure. The strain gauge reads the strain data from the strain gauges during the pressurization process and records the confining pressure value. The elastic modulus and Poisson's ratio of the rock core can then be calculated using formulas. The process is simple and convenient.

[0008] To achieve the above technical objectives, this invention discloses a method for determining the confining pressure of a solid rock core from a geostress borehole. By regularly arranging multiple circumferential and axial strain gauges on the solid rock core, uniform confining pressure is applied to the sidewall of the solid rock core with strain gauges. The circumferential strain value is obtained through the circumferentially arranged strain gauges, and the axial strain value is obtained through the axially arranged strain gauges. Combined with the applied confining pressure value, the elastic modulus and Poisson's ratio of the solid rock core can be obtained.

[0009] Furthermore, the specific steps are as follows: A core tube is connected to a drilling rig, and a solid core is drilled from a test borehole for rock mass stress. Multiple sets of strain rosettes are attached at equal intervals around the side of the solid rock core. Each set of strain rosettes contains two strain gauges, which are set perpendicular to each other: one strain gauge is set along the axial direction of the rock core, and the other strain gauge is set along the circumference of the rock core. After connecting all the strain gauges on the solid rock core to the strain gauge, install them into the sample chamber of the confining pressure calibrator, and keep the strain gauges in the middle of the sample chamber. Pressurize the confining pressure calibrator and apply uniform confining pressure to the solid rock core at a constant speed until the preset maximum pressure is reached. At the same time, use a strain gauge to collect the strain value of the strain gauge. The elastic modulus and Poisson's ratio of the solid rock core were calculated.

[0010] Furthermore, the solid rock core with the strain gauge attached was wrapped with plastic wrap, and a layer of lubricating grease was applied to the outside of the plastic wrap before it was slowly inserted into the sample chamber of the confining pressure calibrator. This was done to prevent damage to the strain gauge wires when inserting the core into the confining pressure calibrator, reduce friction between the solid rock core and the inner wall of the sample chamber, and ensure that the confining pressure was evenly distributed on the surface of the solid rock core.

[0011] Furthermore, the strain gauges are resistance strain gauges, and the positions where the strain gauges are pasted need to avoid joints, cracks, and weak surfaces. Each group of strain gauges is evenly distributed at a 120° angle.

[0012] Furthermore, the strain gauges are tightly bonded to the surface of the solid rock core. Even with extremely small deformations in the solid rock core, the strain gauges deform synchronously with the solid rock core, preventing misalignment or detachment from the surface. An oil pump is used to pressurize the solid rock core via a confining pressure calibrator. Once the pressure gauge reading on the confining pressure calibrator begins to change, pressure is increased at a constant rate. The strain gauge collects the strain values ​​of the strain gauges. For every 1 MPa increase in the pressure gauge reading, the average readings of all circumferentially arranged strain gauges in each strain rosette are recorded as the average circumferential strain value of the solid rock core. The average readings of all axially arranged strain gauges are also recorded as the average axial strain value of the solid rock core. The preset maximum pressure for applying uniform confining pressure to the solid rock core is 5~10 MPa.

[0013] Furthermore, the elastic modulus and Poisson's ratio of the solid rock core were calculated using the following formulas: , , In the formula, E is the elastic modulus of the solid rock core; μ is the Poisson's ratio of the solid rock core; P is the confining pressure value applied by the confining pressure calibrator; ε θ ε represents the average circumferential strain value of a solid rock core. z This represents the average axial strain value of the solid rock core.

[0014] A system for determining the confining pressure ratio of a solid rock core from a geostress borehole includes a loading device, a sample, and a stress reading device. The loading device includes a confining pressure calibrator, which is equipped with a pressure gauge. The confining pressure calibrator is connected to an oil pump via an oil pipe to provide pressure, so as to uniformly apply a confining pressure to the sample placed in the loading chamber of the confining pressure calibrator at a constant speed to the preset maximum pressure. The sample is a solid rock core, which is obtained from the rock mass by sampling equipment and then used to be loaded and tested by the loading device.

[0015] A solid rock core confining pressure grading module for geostress testing boreholes includes a solid rock core detection and acquisition unit, a solid rock core loading unit, and a solid rock core detection unit; Solid rock core detection and acquisition unit, used to extract solid rock cores from the target rock mass for detection; Solid core loading unit is used to apply uniform confining pressure to the sidewalls of the collected solid core. The solid rock core testing unit obtains the strain value of the confining pressure applied to the solid rock core by means of strain gauges circumferentially and circumferentially set on the side wall of the solid rock core; The solid core calculation unit uses the strain values ​​obtained from the solid core detection unit to calculate the elastic modulus and Poisson's ratio of the solid core.

[0016] A computer device includes a processor and a memory, the processor being electrically connected to the memory, the memory being used to store instructions and data, and the processor being used to perform calculations of the elastic modulus and Poisson's ratio in a method for calibrating the confining pressure of a solid rock core from a ground stress borehole.

[0017] A computer-readable storage medium storing a computer program adapted to be loaded by a processor and executed to calculate the elastic modulus and Poisson's ratio in a method for calibrating confining pressure in a solid core borehole under stress.

[0018] Beneficial Effects: Addressing the issues of broken or incomplete rock cores with stress gauges after stress relief, or damaged stress gauge signal lines, in existing methods, this method discloses a process that only requires drilling a complete solid rock core adjacent to the stress gauge. Resistance strain gauges are attached to the core surface and connected to the strain gauge via wires. The core with the attached strain gauges is placed in a confining pressure calibrator, which applies confining pressure. The strain gauge reads the strain data from the strain gauges during pressurization and records the confining pressure value. The elastic modulus and Poisson's ratio of the rock core can then be calculated using formulas. This method complements existing methods for confining pressure calibration of stress-relieved rock cores, improving the success rate of geostress testing. Furthermore, the properties of the rock cores from adjacent locations remain unchanged, and the calculated elastic modulus and Poisson's ratio data are the required rock parameters. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the confining pressure grading system for solid rock cores in geostress drilling, as described in this embodiment of the invention.

[0020] Figure 2 This is a schematic diagram of the strain gauge bonding in an embodiment of the present invention.

[0021] Figure 3 This is a top view of the strain gauge attachment in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of the confining pressure calibrator in an embodiment of the present invention.

[0023] In the figure: 1. Solid rock core; 2. Strain rosette; 3. Strain gauge; 4. Strain meter; 5. Conductor; 6. Confining pressure calibrator; 7. Sample chamber; 8. Oil pump; 9. Oil pipe; 10. Pressure gauge. Detailed Implementation

[0024] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0025] This invention discloses a method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes, using a system such as... Figure 1 As shown, it includes a loading device, a sample, a stress reading device, and a core calculation device; The loading device includes a confining pressure calibrator 6, which is equipped with a pressure gauge 10. The confining pressure calibrator 6 is connected to an oil pump 8 via an oil pipe 9 to provide pressure, so as to uniformly apply a confining pressure to the sample placed in the loading chamber of the confining pressure calibrator 6 at a constant speed to the preset maximum pressure. The sample includes a solid rock core 1, which was used for loading and testing by a loading device after sampling; The stress reading device includes three sets of strain rosettes 2 that are equally spaced on the side surface of the solid rock core 1. Each strain rosette 2 includes two strain gauges 3 that are set perpendicular to each other. All strain gauges 3 are connected to strain gauges 4 via wires 5.

[0026] The solid rock core calculation device uses strain information obtained from the solid rock core detection device to calculate the elastic modulus and Poisson's ratio of the solid rock core.

[0027] Specifically, the following steps are included: Step 1: Use a drilling rig to connect a core tube with an outer diameter of 133mm and drill solid core 1 in the rock mass stress test borehole. The diameter of solid core 1 is about 117mm. When the core length exceeds 500mm, stop the drilling rig from rotating and drilling. Break solid core 1 by raising and lowering the drill rod. Step 2: The drilling rig retracts the drill rod at a constant speed, and after removing the core tube, the solid core is taken out of the core tube and sealed and packaged. Step 3: After delivering solid core 1 to the laboratory, clean the surface of the core and wipe it with a cotton cloth soaked in alcohol or acetone to remove dust. Step 4: Based on the installation angle of the triaxial stress gauge in the geostress testing borehole, evenly attach three sets of strain rosettes 2 at 120° intervals to the corresponding positions on the axial center surface of the rock core. Each set of strain rosettes 2 contains two strain gauges 3, which are set perpendicular to each other, one along the rock core axis and the other along the rock core circumference; the attachment of the strain rosettes 2 and strain gauges 3 is as follows. Figure 2 and Figure 3 As shown; Step 5: Connect strain gauge 3 to strain meter 4 via wire 5, wrap the rock core with plastic wrap, then apply a layer of lubricating grease to the outside of the plastic wrap, and slowly insert it into the sample chamber 7 of the confining pressure calibrator 6, keeping strain gauge 3 in the middle of the sample chamber 7; the structure of the confining pressure calibrator 6 is as follows. Figure 4 As shown; Step 6: Press the oil pump 8 to allow hydraulic oil to enter the confining pressure calibrator 6 through the oil pipe 9, thereby pressurizing the solid rock core 1. Pressurize rapidly until the reading of the pressure gauge 10 begins to change, and then pressurize at a constant speed. The strain gauge 4 collects the strain value of the strain gauge 3. For every 1 MPa increase in the reading of the pressure gauge 10, record the strain value of the circumferential strain gauge 3 and the axial strain gauge 3, respectively. Calculate the average circumferential strain of all circumferential strain gauges 3 and the average axial strain of all axial strain gauges 3. Determine the maximum pressure based on the properties and integrity of the solid rock core 1, and take a value of 5~10 MPa. Step 7: According to the formula and formula Calculate the elastic modulus and Poisson's ratio of solid rock core 1, where E is the elastic modulus; μ is the Poisson's ratio; and P is the confining pressure. The mean circumferential strain; The mean axial strain is given.

[0028] The derivation process of the formulas for the elastic modulus and Poisson's ratio in step 7 will be further explained: 1) Under uniform confining pressure, the rock core is subjected to stress and constraint state through the plane symmetry of the Z-axis. It can be regarded as a plane axisymmetric problem of a thick-walled cylinder subjected to internal and external pressure. The internal pressure is p1, the external pressure is p2, the inner diameter of the thick-walled cylinder is a, the outer diameter is b, and its stress, strain, deformation and displacement are only functions of the radius r. In polar coordinates, the stress on a thick-walled cylinder consists of two components: radial stress. Circumferential stress shear stress The general solution of its stress function is In the formula, A, B, C and D are constants to be determined.

[0029] 2) Substituting the general solution of the stress function into the stress function yields the following result: Radial stress Circumferential stress .

[0030] 3) Radial strain is obtained from the plane strain formula: Circumferential strain Substituting the plane stress formula, we get: radial strain , Circumferential strain ; In the formula: E is the elastic modulus, and μ is Poisson's ratio.

[0031] 4) The strain component equation in polar coordinates for the strain generated in a thick-walled cylinder under uniform confining pressure is: Radial strain Circumferential strain After integration, the displacement produced by the thick-walled cylinder under axisymmetric stress state is obtained: radial displacement , Circumferential displacement , In the formula, I, K, and H are undetermined constants. It is expressed as the angle with the polar coordinate axis; due to the circumferential displacement u θ In the expression The term is multivalued, and there should be no difference in circumferential displacement at the same point in a thick-walled cylinder. Due to the requirement of single-valued displacement, B must be 0. The axisymmetric problem only depends on r, therefore K and I are both 0. From this, we can obtain the axisymmetric stress components and radial displacement as follows: , , .

[0032] 5) The boundary conditions for the internal and external stresses of a thick-walled cylinder are: the stress on the inner wall of the thick-walled cylinder... Stress on the outer wall The geometric equation for strain in polar coordinates is: Radial stress , Circumferential stress ; 6) Obtained by transforming Lamé's solution formula: radial strain ; Circumferential strain .

[0033] 7) For plane stress problems, the axial stress on the rock core =0, axial strain ≠0: .

[0034] 8) Since the core is solid at this time and is only subjected to external stress, i.e., internal pressure p1=0 and external pressure p2=p, the circumferential strain generated by solid core 1 under pressure can be derived from the above formula: axial strain ,at this time , Since both p and are measured parameters, it is possible to deduce the elastic modulus of solid rock core 1 when it is subjected to external pressure only. Poisson's ratio .

[0035] Example: Table 1 shows the data comparison results of measuring the same rock core using two methods: the solid confining pressure ratio determination method and the uniaxial compression method.

[0036] Table 1. Comparison of data from the same rock core measured using two methods: solid confining pressure ratio determination and uniaxial compression method. ,

[0037] Analysis of the test results revealed that, between the solid confining pressure ratio determination method of this invention and the existing uniaxial compression method, the largest difference in Poisson's ratio was 0.033, the smallest was 0.006, and the average difference was 0.019; the largest difference in elastic modulus was 0.888 GPa, the smallest was 0.055 GPa, and the average difference was 0.0487 GPa. The test results indicate that the results obtained by the two methods are close, with a small range of difference. In conclusion, the solid confining pressure ratio determination method is feasible.

Claims

1. A method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes, characterized in that, By regularly arranging multiple circumferential and axial strain gauges (3) on a solid rock core (1), uniform confining pressure is applied to the sidewall of the solid rock core (1) with strain gauges (3) arranged thereon. The circumferential strain value is obtained through the circumferential strain gauges (3), and the axial strain value is obtained through the axial strain gauges (3). Combined with the confining pressure value, the elastic modulus and Poisson's ratio of the solid rock core (1) can be obtained.

2. The method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes according to claim 1, characterized in that, The specific steps are as follows: A solid rock core was drilled in a rock mass stress test borehole by connecting a core tube to a drilling rig (1). Multiple strain rosettes (2) are attached at equal intervals around the side of the solid rock core (1). Each strain rosette (2) contains two strain gauges (3). The two strain gauges (3) are set perpendicular to each other: one strain gauge (3) is set along the axial direction of the rock core, and the other strain gauge (3) is set along the circumference of the rock core. After connecting all the strain gauges (3) on the solid rock core (1) to the strain gauge (4), they are placed into the sample chamber (7) of the confining pressure calibrator (6), and the strain gauges (3) are kept in the middle of the sample chamber (7). Pressurize the confining pressure calibrator (6) and apply uniform confining pressure to the solid rock core (1) at a constant speed until the preset maximum pressure is reached. At the same time, use the strain gauge (4) to collect the strain value of the strain gauge (3). The elastic modulus and Poisson's ratio of the solid rock core (1) were calculated.

3. The method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes according to claim 1, characterized in that: The solid rock core (1) with the strain gauge (2) attached is wrapped with plastic wrap, and a layer of lubricating grease is applied to the outside of the plastic wrap before it is slowly inserted into the sample chamber (7) of the confining pressure calibrator (6) to prevent damage to the wires (5) of the strain gauge (3) when inserted into the confining pressure calibrator (6), reduce the friction between the solid rock core (1) and the inner wall of the sample chamber (7), and make the confining pressure evenly distributed on the surface of the solid rock core (1).

4. The method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes according to claim 1, characterized in that: The strain gauge (3) is a resistance strain gauge. The position of the strain gauge (3) should avoid joints, cracks and weak surfaces. Each group of strain flowers (2) is evenly arranged at a 120° angle.

5. The method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes according to claim 1, characterized in that: The strain gauge (3) is tightly bonded to the surface of the solid rock core (1). The strain gauge (3) deforms synchronously with the solid rock core (1) and will not be misaligned or fall off the surface of the solid rock core (1). The oil pump (8) pressurizes the solid rock core (1) through the confining pressure calibrator (6). When the reading of the pressure gauge (10) set on the confining pressure calibrator (6) begins to change, the pressure is increased at a constant speed. The strain gauge (4) collects the strain value of the strain gauge (3). For every 1 MPa increase in the reading of the pressure gauge (10), the average value of the readings of all circumferentially set strain gauges (3) in each strain flower (2) is recorded as the average circumferential strain value of the solid rock core. The average value of the readings of all axially set strain gauges (3) is taken as the average axial strain value of the solid rock core. The preset maximum pressure for applying uniform confining pressure to the solid rock core (1) is 5~10 MPa.

6. The method for determining the confining pressure ratio of solid rock cores from in-situ stress boreholes according to claim 4, characterized in that, The elastic modulus and Poisson's ratio of the solid rock core (1) were calculated using the following formulas: ， ， In the formula, E is the elastic modulus of the solid rock core; μ is the Poisson's ratio of the solid rock core; P is the confining pressure value loaded by the confining pressure calibrator (6); ε θ This represents the average circumferential strain value of a solid rock core. ε z This represents the average axial strain value of the solid rock core.

7. A system for determining the confining pressure of solid rock cores from in-situ stress boreholes according to any one of claims 1-5, characterized in that, Includes loading device, specimen, and stress reading device; The loading device includes a confining pressure calibrator (6), which is equipped with a pressure gauge (10). The confining pressure calibrator (6) is connected to an oil pump (8) through an oil pipe (9) to apply uniform confining pressure to the sample placed in the loading chamber of the confining pressure calibrator (6) at a uniform speed to the preset maximum pressure. The sample is a solid rock core (1), which is obtained from the rock mass by sampling equipment and then used to be loaded and tested by the loading device; The stress reading device includes three sets of strain rosettes (2) that are equally spaced on the side surface of a solid rock core (1). Each strain rosette (2) includes two strain gauges (3) that are set perpendicular to each other. All strain gauges (3) are connected to a strain gauge (4) via wires (5).

8. A module for determining the confining pressure ratio of a solid rock core from a borehole used for in-situ stress testing, characterized in that, It includes a solid core detection and acquisition unit, a solid core loading unit, a solid core detection unit, and a solid core calculation unit; Solid rock core detection and acquisition unit, used to extract solid rock cores for detection from the target rock mass (1); Solid core loading unit, used to apply uniform confining pressure to the sidewall of the collected solid core (1); The solid rock core testing unit obtains the strain value of the confining pressure applied to the solid rock core from the solid rock core (1) by means of strain gauges (3) arranged circumferentially on the side wall of the solid rock core (1); The solid core calculation unit uses the strain value obtained from the solid core detection unit to calculate the elastic modulus and Poisson's ratio of the solid core (1).

9. A computer device, characterized in that, It includes a processor and a memory, the processor being electrically connected to the memory, the memory being used to store instructions and data, and the processor being used to perform the calculation of the elastic modulus and Poisson's ratio in the method for determining the confining pressure of a solid rock core from a ground stress borehole as described in claim 6.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program adapted to be loaded by a processor and executed for calculating the elastic modulus and Poisson's ratio in the method for determining the confining pressure of a solid core borehole as described in claim 6.

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