In-situ stress borehole solid core confining pressure calibration method, system, device and medium

Abstract

The patent application discloses a kind of ground stress borehole solid core confining pressure calibration method, system, equipment and medium, related to ground stress measurement technical field.Complete solid core is drilled, resistance strain gauge is pasted on the surface of core, is placed in confining pressure calibrator and is applied confining pressure, strain data generated in the process of pressurization is read using resistance strain gauge, while recording confining pressure value, the elastic modulus and poisson's ratio of core are calculated.The method realizes the determination of the elastic modulus and poisson's ratio of ground stress test borehole solid core, and provides more reliable data support for ground stress measurement.At the same time, it can effectively overcome the problem that the core is broken and the stress meter is damaged when using hollow core stress meter, and the experiment cannot be carried out.The properties of the core drilled at adjacent positions do not change, and the calculated elastic modulus and poisson's ratio data are the required rock parameters, which effectively improve the success rate of ground stress test.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of in-situ stress measurement, in particular to a method, system, device and medium for calibrating the confining pressure of a solid core in a borehole. BACKGROUND

[0002] In the process of in-situ stress testing, in addition to testing the strain of the core after stress relief, the elastic modulus and Poisson's ratio of the core after stress relief are also needed to be obtained, so as to further calculate the in-situ stress. At present, the elastic modulus and Poisson's ratio of the stress relief core are obtained through confining pressure calibration experiment, that is, after stress relief, the core with stress meter is taken back to the laboratory, and the elastic modulus and Poisson's ratio are tested by using confining pressure calibration instrument. However, in actual testing, the stress relief core is easily damaged, it is difficult to obtain the core with stress meter, and if the core has weak surfaces such as joints, cracks or the core tube is mechanically vibrated too much during coring, it may cause cracking or even breaking of the rock.

[0003] During the stress relief process, the signal line of the stress meter needs to be pulled tight with appropriate force to prevent it from being twisted off due to rotation of the drill rod. The signal line of the stress meter has 14 lines, corresponding to 12 measurement channels, 1 ground and 1 temperature compensation. Once it is twisted off, it will lead to failure of the in-situ stress test, and even if the core is obtained, the subsequent steps cannot be performed. In addition, the signal line of the stress meter is usually disconnected at the tail, and it is difficult to reconnect later. Even if it is reconnected, it is difficult to find the corresponding relationship between the strain gauge and the strain value, so that the experimental data cannot be obtained.

[0004] If the confining pressure experiment cannot be performed normally, the core adjacent to the relief position will be taken back to the laboratory, cut and processed into a standard Φ50*100 cylindrical sample, and then strain gauges are attached to perform uniaxial compression experiment to obtain the elastic modulus and Poisson's ratio of the core, but the process of processing the sample is time-consuming and laborious.

[0005] The prior art with publication number CN111855422A discloses a confining pressure calibration test device and test method. The test device includes a confining pressure calibration cabin, a lifting component and a rubber sleeve component. The confining pressure calibration cabin is a hollow structure, and a pressure cavity is arranged in the confining pressure calibration cabin. The rubber sleeve component and the pressure cavity are coaxially arranged, and the outer side wall of the rubber sleeve component is in communication with the pressure cavity. The cylindrical core is a cylindrical core with a strain gauge. The lifting component includes a circular ring positioning plate installed in the pressure cavity, and the circular ring positioning plate is lifted along the height direction of the rubber sleeve component. The test method includes the following steps: 1. adjustment of the lifting component; 2. installation of the cylindrical core and the plunger rod; 3. confining pressure test; and 4. mechanical parameter processing of the cylindrical core. The overall scheme is complex, the sample processing is troublesome, and the detection efficiency is low.

[0006] In order to improve the success rate of the ground stress test, for the case of stress meter damage in the core, the confining pressure calibration method cannot be directly used, but the mechanical parameters of this core are the best choice for calculating the ground stress. Therefore, in the case of obtaining the core intact but the sensor damaged, a new calibration method should be developed. SUMMARY

[0007] In view of the shortcomings of the prior art, a ground stress borehole solid core confining pressure calibration method, system, equipment and medium are provided, which only needs to drill a solid core at the adjacent position of the stress meter, paste resistance strain gauges on the surface of the core, connect the strain gauges with strain gauges through wires, put the core with pasted strain gauges into a confining pressure calibrator, the confining pressure calibrator applies confining pressure to the core, the strain gauge reads the strain data in the strain gauge during the pressure process, and records the confining pressure value, and then the elastic modulus and Poisson's ratio of the core can be calculated through the formula, which is simple in steps and convenient to detect.

[0008] To achieve the above technical purposes, the present application discloses a ground stress borehole solid core confining pressure calibration method, which regularly arranges a plurality of circumferential and axial strain gauges on the solid core, uniformly loads the side wall of the solid core with the strain gauges, obtains the circumferential strain value through the circumferential strain gauges, obtains the axial strain value through the axial strain gauges, and obtains the elastic modulus and Poisson's ratio of the solid core in combination with the loaded confining pressure value.

[0009] Further, the specific steps are as follows:

[0010] Use the drilling machine to connect the core tube, drill the solid core in the rock mass ground stress test borehole;

[0011] Paste a plurality of groups of strain flowers around the side surface of the solid core at equal intervals, each group of strain flowers includes two strain gauges, and the two strain gauges are arranged perpendicular to each other: one strain gauge is arranged along the axial direction of the core, and the other strain gauge is arranged along the circumferential direction of the core;

[0012] After connecting all the strain gauges on the solid core with the strain gauges, load the solid core into the sample chamber of the confining pressure calibrator, and keep the strain gauges in the middle of the sample chamber;

[0013] Pressurize the confining pressure calibrator, uniformly apply uniform confining pressure to the solid core at a constant speed to a preset maximum pressure, and collect the strain value of the strain gauge by using the strain gauge;

[0014] Calculate the elastic modulus and Poisson's ratio of the solid core.

[0015] Further, the solid core outside where the strain rosettes are pasted is wrapped with cling film, and a layer of lubricating oil is applied outside the cling film before slowly inserting it into the sample chamber of the confining pressure calibrator to prevent the strain gauge wires from being damaged when inserting into the confining pressure calibrator, reduce the friction between the solid core and the inner wall of the sample chamber, and make the confining pressure uniformly distributed on the surface of the solid core.

[0016] Further, the strain gauges are resistance strain gauges, and the positions where the strain gauges are pasted need to avoid joints and weak planes, and each group of strain rosettes is uniformly arranged at an interval of 120°.

[0017] Further, the strain gauges are pasted tightly on the surface of the solid core, and in the case of extremely small deformation of the solid core, the strain gauges deform synchronously with the solid core without dislocation or falling off from the surface of the solid core. An oil pump is used to pressurize the solid core through the confining pressure calibrator. When the reading of the pressure gauge provided on the confining pressure calibrator starts to change, uniform pressure is applied. The strain values of the strain gauges are collected by the strain gauge. The average value of the readings of all circumferentially arranged strain gauges in each strain rosette is recorded as the average circumferential strain value of the solid core, and the average value of the readings of all axially arranged strain gauges is recorded as the average axial strain value of the solid core. The preset maximum pressure for applying uniform confining pressure to the solid core is 5-10 MPa.

[0018] Further, the elastic modulus and Poisson's ratio of the solid core are calculated by the following formula:

[0019] , ,

[0020] In the formula, E is the elastic modulus of the solid core, μ is the Poisson's ratio of the solid core, P is the confining pressure value loaded by the confining pressure calibrator, ε θ is the average circumferential strain value of the solid core, and ε z is the average axial strain value of the solid core.

[0021] A system for a method of confining pressure calibration of a borehole solid core of in-situ stress includes a loading device, a sample, and a stress reading device.

[0022] The loading device includes a confining pressure calibrator, a pressure gauge provided on the confining pressure calibrator, and an oil pump connected to the confining pressure calibrator through an oil pipe to provide pressure, so as to uniformly apply uniform confining pressure to the sample placed in the loading chamber of the confining pressure calibrator to a preset maximum pressure.

[0023] The sample is a solid core obtained from a rock mass by a sampling device and loaded for detection by the loading device after sampling.

[0024] A confining pressure calibration module for a borehole solid core of in-situ stress testing includes a solid core detection and collection unit, a solid core loading unit, and a solid core detection unit.

[0025] A solid core detection collection unit is used to take out a solid core for detection from a target rock mass;

[0026] A solid core loading unit is used to apply uniform confining pressure to the side wall of the collected solid core;

[0027] A solid core detection unit obtains the strain value of the confining pressure applied to the solid core from the feedback of the solid core through the strain gauges arranged circumferentially and circumferentially on the side wall of the solid core;

[0028] A solid core calculation unit calculates the elastic modulus and Poisson's ratio information of the solid core by using the strain value obtained by the solid core detection unit.

[0029] A computer device includes a processor and a memory, the processor is electrically connected with the memory, the memory is used to store instructions and data, and the processor is used to execute the elastic modulus and Poisson's ratio calculation in the in-situ stress borehole solid core confining pressure calibration method.

[0030] A computer readable storage medium, the computer readable storage medium stores a computer program, the computer program is suitable for being loaded and executed by a processor to perform the elastic modulus and Poisson's ratio calculation in the in-situ stress borehole solid core confining pressure calibration method.

[0031] Beneficial effect: In view of the broken or incomplete core with stress meter after stress relief in the detection process of the existing method, or the damage of the stress meter signal line, the method discloses a solid core which only needs to be drilled at the adjacent position of the stress meter and is complete, a resistance strain gauge is pasted on the surface of the core, the strain gauge is connected with a strain meter through a lead wire, the core with the pasted strain gauge is placed into a confining pressure calibrator, the confining pressure calibrator applies confining pressure to the core, the strain meter reads the strain data in the strain gauge in the pressure process, and the confining pressure value is recorded at the same time, and then the elastic modulus and Poisson's ratio of the core can be calculated through a formula. The method is a supplement to the existing stress relief core confining pressure calibration method, improves the success rate of the in-situ stress test, and the properties of the core drilled at the adjacent position are not changed, and the calculated elastic modulus and Poisson's ratio data are the required rock parameters. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a structure schematic diagram of the in-situ stress borehole solid core confining pressure calibration system in the embodiment of the application.

[0033] Figure 2 It is a pasting schematic diagram of the strain gauge in the embodiment of the application.

[0034] Figure 3 It is a top view of the pasted strain gauge in the embodiment of the application.

[0035] Figure 4It is the structural schematic view of the confining pressure calibrator in the embodiment of the present application.

[0036] In the figure: 1, solid core; 2, strain flower; 3, strain gauge; 4, strain gauge; 5, wire; 6, confining pressure calibrator; 7, sample cabin; 8, oil pump; 9, oil pipe; 10, pressure gauge. DETAILED DESCRIPTION

[0037] The embodiments of the present application will be further described below in combination with the drawings.

[0038] The present application discloses a kind of ground stress borehole solid core confining pressure calibration method, the system used as shown in Figure 1 Including loading device, sample, stress reading device and core computing device;

[0039] Loading device includes confining pressure calibrator 6, confining pressure calibrator 6 is equipped with pressure gauge 10, confining pressure calibrator 6 is connected with oil pump 8 for providing pressure by oil pipe 9, to be loaded in the sample of confining pressure calibrator 6 loading cabin even speed is applied even confining pressure to preset maximum pressure;

[0040] Sample includes solid core 1, after sampling to be loaded by loading device detection;

[0041] Stress reading device includes three groups of strain flowers 2 pasted at equal intervals on the side surface of solid core 1, strain flower 2 includes two mutually perpendicular strain gauges 3, all strain gauges 3 are connected with strain gauge 4 by wire 5.

[0042] Solid core computing device, the elastic modulus and poisson's ratio information of solid core are calculated using the strain information obtained by solid core detection device.

[0043] Specifically including the following steps:

[0044] Step 1: use drilling machine to connect core tube with outer diameter of 133mm, drill solid core 1 in rock mass ground stress test borehole, the diameter of solid core 1 is about 117mm, when the length of coring exceeds 500mm, drilling machine stops rotating and drilling, and the solid core 1 is broken by lifting and dropping the drill pipe up and down;

[0045] Step 2: the drilling machine is uniformly withdrawn, and the solid core is taken out from the core tube after the core tube is disassembled and sealed and packaged;

[0046] Step 3: after sending solid core 1 to laboratory, clean the surface, wipe the core surface with cotton dipped in alcohol or acetone, remove the dust on the surface;

[0047] Step 4: According to the installation angle of the triaxial stress meter in the in-situ stress test hole, 3 sets of strain flowers 2 are uniformly pasted on the corresponding positions of the axial middle surface of the core at intervals of 120°, each set of strain flowers 2 contains 2 strain gauges 3, and the 2 strain gauges 3 are arranged perpendicular to each other, one along the axial direction of the core and the other along the circumferential direction of the core; the pasting of the strain flowers 2 and the strain gauges 3 is as shown in Figure 2 and Figure 3 ;

[0048] Step 5: The strain gauges 3 are connected with the strain meter 4 through the lead wires 5, the core is wrapped with plastic wrap, and then a layer of lubricating oil is applied outside the plastic wrap, and the core is slowly inserted into the sample chamber 7 of the confining pressure calibrator 6, so that the strain gauges 3 are located in the middle of the sample chamber 7; the structure of the confining pressure calibrator 6 is as shown in Figure 4 ;

[0049] Step 6: The hydraulic oil pump 8 is pressed to make the hydraulic oil enter the confining pressure calibrator 6 through the oil pipe 9 to pressurize the solid core 1, and the pressure is quickly increased until the reading of the pressure gauge 10 starts to change, then the pressure is uniformly increased, the strain values of the strain gauges 3 are collected by the strain meter 4, and the strain values of the circumferential strain gauges 3 and the axial strain gauges 3 are recorded once every 1 MPa increase of the pressure gauge 10, respectively, and the average circumferential strain of all circumferential strain gauges 3 and the average axial strain of all axial strain gauges 3 are calculated, respectively, the maximum pressure is determined according to the properties and integrity of the solid core 1, and the value is 5-10 MPa;

[0050] Step 7: According to the formula and the formula , the elastic modulus and Poisson's ratio of the solid core 1 are calculated, wherein E is the elastic modulus, μ is Poisson's ratio, and P is the confining pressure value; is the average circumferential strain; is the average axial strain.

[0051] The derivation process of the elastic modulus and Poisson's ratio formula in step 7 is further described as follows:

[0052] 1) Under the action of uniform confining pressure, the stress and constraint state of the core are symmetrical through the plane of Z axis, which can be regarded as the plane axisymmetric problem of the thick-walled cylinder under the action of 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 the stress, strain and deformation displacement are only functions of radius r;

[0053] In polar coordinates, the two components of the stress of the thick-walled cylinder are radial stress , circumferential stress , and shear stress , and the general solution of the stress function is , wherein A, B, C and D are undetermined constants.

[0054] 2) Substitute the stress function into the stress function to calculate:

[0055] radial stress , circumferential stress .

[0056] 3) From the plane strain formula, we get: radial strain , circumferential strain

[0057] radial strain ,

[0058] circumferential strain ;

[0059] In the formula: E is the elastic modulus, μ is the Poisson's ratio.

[0060] 4) The strain component equation of thick-walled cylinder under uniform confining pressure in polar coordinates is: radial strain , circumferential strain

[0061] radial displacement ,

[0062] circumferential displacement ,

[0063] In the formula, I, K, H are undetermined constants, is the angle between the polar coordinate axis and the displacement θ The expression of the circumferential displacement u is multi-valued, but there should be no difference in the circumferential displacement at the same point in the thick-walled cylinder. According to the single-valued displacement condition, B must be 0; The axisymmetric problem only relates to r, so K and I are both 0. Thus, the stress components and radial displacement of axisymmetric are: , , .

[0064] 5) The boundary conditions of the inner and outer stresses of the thick-walled cylinder are: radial stress , circumferential stress

[0065] radial stress ,

[0066] circumferential stress ;

[0067] 6) Convert from the Lame solution formula:

[0068] radial strain ;

[0069] Circumferential strain .

[0070] 7) For the plane stress problem, the axial stress =0, the axial strain ≠0:

[0071] .

[0072] 8) Since the core is a solid core at this time, and only external stress is applied, that is, the internal pressure p1=0, and the external pressure p2=p, the circumferential strain of the solid core 1 after being compressed, the axial strain , at this time , and p are all measured parameters, so the elastic modulus of the solid core 1 under only external pressure can be derived .

[0073] Example: The data comparison results of the same core measured by the solid confining pressure calibration method and the uniaxial compression method shown in Table 1.

[0074] Table 1 Data comparison results of the same core measured by the solid confining pressure calibration method and the uniaxial compression method

[0075] ,

[0076] Through the analysis of the test results, it is found that the maximum difference of the Poisson's ratio in the test results obtained by the solid confining pressure calibration method and the existing uniaxial compression method is 0.033, the minimum difference is 0.006, and the average difference is 0.019; the maximum difference of the elastic modulus is 0.888 GPa, the minimum difference is 0.055 GPa, and the average difference is 0.0487 GPa. The test results show that the test results obtained by the two methods are close, and the difference range is small. Comprehensive analysis shows that the solid confining pressure calibration method is practical.

Claims

1. A method of calibrating a confining pressure ratio of a borehole in-situ stress solid core, characterized by, The elastic modulus and Poisson's ratio of the solid core (1) can be obtained by regularly arranging a plurality of circumferential and axial strain gauges (3) on the solid core (1), uniformly loading the side wall of the solid core (1) arranged with the strain gauges (3), obtaining the circumferential strain value through the circumferential strain gauges (3), obtaining the axial strain value through the axial strain gauges (3), and combining the circumferential strain value, the axial strain value and the loading confining pressure value; The elastic modulus and Poisson's ratio of the solid core (1) can be calculated by the following formula: ， ， In the formula, E is the solid core elastic modulus; μ is the solid core Poisson's ratio; P is the confining pressure value loaded by the confining pressure rate device (6); is the average circumferential strain value of the solid core; is the average axial strain value of the solid core.

2. The in-situ stress borehole solid core stress calibrating method according to claim 1, characterized in that, The specific steps are as follows: Connect the core tube with the drilling machine, drill the solid core (1) in the rock mass in-situ stress test borehole; Paste a plurality of groups of strain flowers (2) on the side surface of the solid core (1) at equal intervals, each group of strain flowers (2) includes two strain gauges (3), and the two strain gauges (3) are arranged perpendicularly: one strain gauge (3) is arranged along the axial direction of the core, and the other strain gauge (3) is arranged along the circumferential direction of the core; After connecting all the strain gauges (3) on the solid core (1) with the strain gauge (4), the solid core (1) is loaded into the sample chamber (7) of the confining pressure rate setting instrument (6), and the strain gauges (3) are kept in the middle of the sample chamber (7); The confining pressure rate setting instrument (6) is pressurized, and the solid core (1) is uniformly and slowly applied with uniform confining pressure to a preset maximum pressure, while the strain values of the strain gauges (3) are collected by the strain gauge (4); The elastic modulus and Poisson's ratio of the solid core (1) are calculated.

3. The in-situ stress borehole solid core stress correction method according to claim 1, characterized in that: The solid core (1) with the strain flowers (2) pasted on the outside is wrapped with a plastic wrap, and a layer of lubricating oil is applied outside the plastic wrap before being slowly inserted into the sample chamber (7) of the confining pressure rate setting instrument (6), so as to prevent the lead wires (5) of the strain gauges (3) from being damaged when being inserted into the confining pressure rate setting instrument (6), reduce the friction between the solid core (1) and the inner wall of the sample chamber (7), and make the confining pressure uniformly distributed on the surface of the solid core (1).

4. The in-situ stress borehole solid core stress correction method according to claim 2, characterized in that: The strain gauges (3) are resistance strain gauges, and the positions of the strain gauges (3) need to avoid joints, fractures and weak planes, and each group of strain flowers (2) is arranged at an interval of 120°.

5. The in-situ stress borehole solid core stress correction method according to claim 1, characterized in that: The strain gauges (3) are closely pasted on the surface of the solid core (1), and the strain gauges (3) deform synchronously with the solid core (1) and will not be dislocated or fall off from the surface of the solid core (1), the oil pump (8) is used to pressurize the solid core (1) through the confining pressure rate setting instrument (6), when the reading of the pressure gauge (10) arranged on the confining pressure rate setting instrument (6) starts to change, the pressure is uniformly increased, the strain values of the strain gauges (3) are collected by the strain gauge (4), and the average value of the readings of all the circumferential strain gauges (3) in each strain flower (2) is recorded as the average circumferential strain value of the solid core, and the average value of the readings of all the axial strain gauges (3) is recorded as the average axial strain value of the solid core; the preset maximum pressure of the uniform confining pressure applied to the solid core (1) is 5-10 MPa.

6. The in-situ stress borehole solid core stress correction method according to claim 1, characterized in that, The system used includes a loading device, a sample, and a stress reading device. The loading device comprises a confining pressure calibrator (6), the confining pressure calibrator (6) is provided with a pressure gauge (10), the confining pressure calibrator (6) is connected with an oil pump (8) for providing pressure through an oil pipe (9), and the oil pump (8) is used for uniformly applying uniform confining pressure to a preset maximum pressure to the sample put into the loading cabin of the confining pressure calibrator (6) at a constant speed; The sample is a solid core (1) obtained from a rock mass through a sampling device, and is used for loading detection by the loading device after sampling; The stress reading device comprises three groups of strain flowers (2) pasted on the side surface of the solid core (1) at equal intervals, the strain flower (2) comprises two mutually perpendicular strain gauges (3), and all the strain gauges (3) are connected with a strain meter (4) through a lead wire (5).

7. A module for calibrating the confining pressure of a solid core borehole using the method of claim 1, wherein, The method comprises the following steps: The solid core detection and collection unit is used for taking out the solid core (1) for detection from the target rock mass; The solid core loading unit is used for applying uniform confining pressure to the side wall of the collected solid core (1); The solid core detection unit obtains the strain value of the confining pressure applied to the solid core (1) from the solid core (1) through the strain gauges (3) arranged on the side wall of the solid core (1) in the circumferential direction and the circumferential direction; The solid core calculation unit calculates the elastic modulus and Poisson's ratio information of the solid core (1) by using the strain value obtained by the solid core detection unit.

8. A computer device, comprising: The computer readable storage medium stores a computer program, and the computer program is suitable for being loaded and executed by the processor to calculate the elastic modulus and Poisson's ratio in the in-situ stress borehole solid core confining pressure calibration method of claim 1.

9. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and the computer program is suitable for being loaded and executed by the processor to calculate the elastic modulus and Poisson's ratio in the in-situ stress borehole solid core confining pressure calibration method of claim 1.

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