In-situ coal rock mechanical property testing device and method for coal-bed gas well

Abstract

The invention relates to the technical field of coal bed gas development and geomechanical testing, in particular to an in-situ coal rock mechanical property testing device and method for a coal bed gas well. The invention aims to solve the technical problem that the real in-situ state and heterogeneous distribution mechanical parameters of a coal seam cannot be accurately obtained due to sampling disturbance, environmental distortion and limited measuring points in the existing laboratory rock core test. According to the device, the functions of underground polishing, macro imaging, in-situ indentation and flocculating settling are integrated, so that continuous and high-definition imaging and micromechanical testing on the inner wall of a coal seam in a real stratum environment are realized; according to the method, by comparing high-definition images before and after indentation, mechanical parameters are accurately associated with specific coal rock components and failure morphology, so that spatial distribution data capable of truly reflecting coal seam heterogeneity and in-situ mechanical behaviors are obtained, and a direct basis is provided for optimizing fracturing design.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane development and geomechanical testing technology, and in particular to an in-situ coal and rock mechanical property testing device and method for coalbed methane wells. Background Technology

[0002] Coalbed methane (CBM), as an important unconventional natural gas resource, plays a crucial role in optimizing the energy structure and achieving low-carbon development. CBM production efficiency is directly related to the effectiveness of reservoir fracturing, and the mechanical properties of coal and rock are key geological factors controlling the initiation, propagation morphology, and overall fracturing effect. Therefore, accurately obtaining the true mechanical parameters of the coal seam under in-situ stress is crucial for optimizing fracturing design and increasing single-well production.

[0003] Currently, the conventional method for obtaining coal and rock mechanical parameters mainly relies on laboratory testing of cored samples. This method has several inherent drawbacks: First, the coring process itself causes severe mechanical disturbance and stress release to the coal and rock, damaging its original structure and geostress state. Second, the laboratory environment cannot fully replicate the multi-field coupling conditions of underground reservoirs, such as temperature, triaxial geostress, and pore pressure. Furthermore, macroscopic coal and rock components can be divided into macroscopic coal and rock types and interbedded rock. The macroscopic coal and rock types consist of bright coal, semi-bright coal, semi-dull coal, and dull coal, whose mechanical properties exhibit strong differences and directions at the microscopic scale. Laboratory testing typically uses samples of limited size and has few measuring points, resulting in highly discrete and unrepresentative test results that fail to reflect the continuous distribution characteristics of coal seam mechanical properties in the well perimeter direction.

[0004] These limitations often lead to discrepancies between fracturing designs based on indoor experimental data and actual conditions, thus hindering the production enhancement effect of coalbed methane wells, and therefore improvements are needed. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide an in-situ coal and rock mechanical property testing device and method for coalbed methane wells, which can perform high-precision polishing, simultaneous imaging and indentation of the inner wall of the coal seam to be tested in a real downhole environment, and realize the precise spatial correlation between the indentation position and the coal and rock components, thereby obtaining component-specific micromechanical parameters.

[0006] Based on the above objectives, the present invention provides an in-situ coal and rock mechanical property testing device for coalbed methane wells, which is used to conduct in-situ mechanical testing on the inner wall of the coal seam in an existing coalbed methane well. The coalbed methane well includes a wellbore, an artificial well bottom located at the bottom of the wellbore, and the coal seam to be tested, and includes wellhead equipment, drill pipe, downhole equipment, and a computer.

[0007] The wellhead equipment is connected to the drill pipe, and the bottom end of the drill pipe is connected to the downhole equipment. The downhole equipment is lowered into the coal seam to be tested inside the wellbore through the drill pipe, and from top to bottom it includes an upper macro camera, an indenter, a lower macro camera, a temperature and pressure sensor, a flocculant chamber, and a polishing machine, and the components are connected by a rotary quick connector.

[0008] The polishing machine includes a driver, an airbag, and a polishing ring, and is used to perform in-situ polishing of the inner wall of the coal seam to be tested inside the well shaft. The airbag is fitted outside the driver, and the polishing ring is fitted outside the airbag.

[0009] The flocculant silo is used to store and release flocculant into the wellbore to promote the settling of pulverized coal within the wellbore.

[0010] The indenter includes a main unit, multiple radially symmetrically arranged electric telescopic rods, and a diamond indenter. The fixed end of the electric telescopic rod is installed at the bottom of the main unit, and the telescopic end of the electric telescopic rod is connected to the diamond indenter, which is used to push the indenter radially out to contact the inner wall of the coal seam to be tested.

[0011] The upper macro camera is used to perform circumferential scanning and imaging of the inner wall of the polished coal seam before the indentation operation, so as to obtain a first image sequence;

[0012] The lower macro camera is used to perform circumferential scanning and imaging of the inner wall of the same coal seam with indentations after the indentation operation, so as to obtain a second image sequence.

[0013] The temperature and pressure sensor is used to monitor the temperature and pressure inside the coal seam under test in real time.

[0014] The computer is connected to an upper macro camera, a lower macro camera, an indenter, and a temperature and pressure sensor. The computer receives and processes a first image sequence and a second image sequence, reconstructs the inner wall development of the coal seam to be tested based on the first image sequence, and identifies and divides the distribution areas of different macroscopic coal and rock types and interbedded rock. It also spatially registers the second image sequence with the first image sequence so that each indentation is precisely associated with the specific coal and rock type region in which it is located. In addition, it can calculate the micromechanical parameters of the coal and rock type where each indentation point is located based on the indentation morphology in the registered second image sequence.

[0015] Preferably, the computer can also determine the failure modes of different coal and rock components by analyzing the morphological features of the indentation and the secondary cracks generated around it in the registered image.

[0016] Preferably, both the upper macro camera and the lower macro camera are equipped with multiple lenses, which are evenly distributed in a ring in the same radial plane to achieve circumferential shooting without blind spots.

[0017] Preferably, the diamond indenter is a Vickers indenter with a face angle of 136°, and the predetermined load is 0.98N.

[0018] A method for testing the mechanical properties of coal and rock in situ for coalbed methane wells includes the following steps:

[0019] S1. Add flocculant into the wellbore to promote the settling of coal powder in the dynamic liquid column inside the wellbore to the bottom of the artificial well.

[0020] S2. After the coal powder settles, the downhole equipment is lowered to below the bottom boundary of the coal seam to be tested. The polishing machine is started and the flocculant is released simultaneously. The wellhead equipment is controlled to drive the downhole equipment to slowly lift from the bottom boundary to the top boundary of the coal seam to be tested, thus completing the in-situ polishing of the inner wall of the coal seam to be tested.

[0021] S3. After polishing is completed, keep the downhole equipment below the bottom boundary of the coal seam to be tested, and start the upper macro camera, indenter and lower macro camera.

[0022] S4. Control the wellhead equipment to continuously lift the downhole equipment from the bottom boundary to the top boundary of the coal seam to be measured at a constant speed, while simultaneously performing the following steps:

[0023] S4.1. The upper macro camera performs a circumferential scan of the inner wall of the coal seam to be tested that is not indented, and obtains the first image sequence;

[0024] S4.2. Apply an indentation to the inner wall of the coal seam to be tested at the current location using an indenter.

[0025] S4.3. Use a macro camera to perform a circumferential scan of the inner wall of the coal seam to be tested after indentation is completed, and obtain the second image sequence;

[0026] S5. During step S4, temperature and pressure data are recorded synchronously by the temperature and pressure sensor;

[0027] S6. Transmit the first image sequence and the second image sequence to the computer and perform the following processing:

[0028] S6.1 Generate an inner wall unfolded map of the coal seam to be tested based on the first image sequence, and identify the distribution areas of bright coal, semi-bright coal, semi-dark coal, dull coal and interbedded gangue based on color, texture and gloss characteristics.

[0029] S6.2. Spatial registration is performed between the second image sequence and the unfolded inner wall diagram of the coal seam to be tested generated in step S6.1;

[0030] S6.3 Extract the geometric features of each indentation in the registered image, and calculate the in-situ microhardness, contact stiffness and elastic modulus in combination with the coal and rock type region where it is located.

[0031] S6.4. Based on the clarity of the indentation boundary, whether secondary cracks are generated, and the crack morphology, determine whether the failure mode of each coal and rock component is brittle failure, plastic failure, or transitional failure.

[0032] Preferably, in step S6.1, feature recognition is automatically completed using an image processing algorithm.

[0033] Preferably, in step S6.3, the specific calculation steps are as follows:

[0034] Indentation Projection Area Contact depth with indentation The relationship between them is as follows:

[0035]

[0036] In the formula, The constant is taken as 24.56 for the Vickers indenter, and the projected area of ​​the indentation is... It can be determined by the length of the indentation diagonal. , The calculation yielded:

[0037]

[0038] For the indentation contact area Knowing the face angle of the diamond indenter, the contact area of ​​the indentation can be calculated. With indentation projected area The relationship between them:

[0039]

[0040] For a Vickers indenter with a face angle of 136°, the Vickers hardness is calculated using the following formula when the peak load is 0.98 N:

[0041]

[0042] In the formula, Vickers hardness It is a constant, with a value of 0.102; The peak load is 0.98 N.

[0043] Contact stiffness is calculated by the following formula:

[0044]

[0045] In the formula, For contact stiffness, For peak depth, The parameter is related to the shape of the indenter and is set to 0.75.

[0046] elastic modulus Calculated by the following formula:

[0047]

[0048] In the formula, This is a constant related to the shape of the indenter, with a value of 1.034.

[0049] Preferably, the

[0050] The beneficial effects of this invention are as follows:

[0051] First, by conducting tests directly in the underground reservoir environment, the disturbance caused by coring and the distortion caused by indoor environmental simulation are avoided. The mechanical parameters obtained are most representative of the actual formation state. Furthermore, continuous and large-scale in-situ tests can be conducted on coal seams that are several meters or even tens of meters thick, obtaining a massive amount of data points, far exceeding the limited samples at the millimeter-centimeter level in indoor experiments.

[0052] II. This invention employs a synchronous operation process of "continuous and uniform upward lifting from the bottom boundary to the top boundary of the coal seam." During a single lifting operation, it sequentially completes imaging of the upper region (first image sequence), indentation at the current position, and re-imaging of the lower region (second image sequence). This ensures that the same coal seam location experiences three states: "imaging without indentation → indentation → imaging after indentation," fundamentally solving the spatial misalignment problem caused by traditional step-by-step operations. Combined with a high-precision image registration algorithm based on equipment geometric parameters and geological characteristics, it achieves accurate correlation between the indentation and the macroscopic coal and rock type (such as bright coal, semi-bright coal, etc.). Thus, for the first time, it obtains component-specific in-situ microhardness, elastic modulus, and failure mode in a real coalbed methane well environment, providing a direct basis for evaluating the fracturability of coal seams and optimizing engineering parameters. Attached Figure Description

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0054] Figure 1 This is a schematic diagram of the overall operation of the testing device of the present invention in a coalbed methane well;

[0055] Figure 2 This is a schematic diagram of the downhole equipment of the present invention;

[0056] Figure 3 This is a top view of the airbag on the polishing machine of the present invention in an inflated state;

[0057] Figure 4This is a front view of the macro camera in this invention;

[0058] Figure 5 This is a front view of the indentation instrument of the present invention;

[0059] Figure 6 This is a schematic diagram showing the distribution of the indentations of the present invention on the unfolded well wall;

[0060] Figure 7 This is a schematic diagram of an indentation image captured by a macro camera according to the present invention;

[0061] Figure 8 This is a schematic diagram showing the projected area and contact depth of a single indentation in this invention;

[0062] Figure 9 This is a schematic diagram of the vertical depth of a single indentation in this invention.

[0063] In the diagram: 1. Wellbore; 2. Wellhead equipment; 3. Drill pipe; 4. Downhole equipment; 5. Computer; 6. Upper macro camera; 7. Indenter; 71. Main unit; 72. Electric telescopic rod; 73. Diamond indenter; 8. Lower macro camera; 9. Temperature and pressure sensor; 10. Flocculant chamber; 11. Polishing machine; 111. Driver; 112. Airbag; 113. Polishing ring; 12. Rotary quick coupling. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0065] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this invention should have the ordinary meaning understood by those skilled in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0066] like Figures 1 to 9As shown, an in-situ coal and rock mechanical property testing device for coalbed methane wells is used to conduct in-situ mechanical tests on the inner wall of the coal seam in an existing coalbed methane well. The coalbed methane well includes a wellbore 1, an artificial well bottom located at the bottom of the wellbore 1, and the coal seam to be tested. The device includes wellhead equipment 2, drill pipe 3, downhole equipment 4, and computer 5.

[0067] Wellhead equipment 2 is connected to drill pipe 3. The bottom end of drill pipe 3 is connected to downhole equipment 4. Downhole equipment 4 is lowered into the coal seam to be tested in wellbore 1 through drill pipe 3. From top to bottom, it includes upper macro camera 6, indenter 7, lower macro camera 8, temperature and pressure sensor 9, flocculant chamber 10 and polishing machine 11. All components are connected by rotary quick connector 12.

[0068] The two macro cameras are identical in model and parameters, and both consist of a camera body, a lens, and a ring light. The function of the macro camera is to take pictures of the coal seam to be measured on the inner wall of shaft 1. Since the inside of shaft 1 is dark, a ring light is arranged in a ring around the outside of the lens. The number of ring lights can be set as needed.

[0069] Wellhead equipment 2 is a hoisting-rotation composite drive device, integrating a hydraulic hoisting system and a servo rotary motor. Its output end is connected to the drill pipe 3 via a universal joint, enabling axial movement and circumferential rotation (which can be used to assist the upper macro camera 6 and the lower macro camera 8 in circumferential scanning).

[0070] The polishing machine 11 includes a driver 111, an airbag 112, and a polishing ring 113, and is used to perform in-situ polishing of the inner wall of the coal seam to be tested inside the shaft 1. The airbag 112 is sleeved on the outside of the driver 111, and the polishing ring 113 is sleeved on the outside of the airbag 112.

[0071] The driver 111 consists of a rotary motor and a miniature air pump arranged coaxially. The output shaft of the rotary motor is connected to the polishing ring 113. The miniature air pump is connected to the air bag 112 through a built-in air passage and is used to adjust the expansion degree of the air bag 112 to control the polishing pressure.

[0072] The output shaft of the rotary motor of the driver 111 is hollow and has an independent air passage inside. The micro air pump is connected to the air bag 112 through the air passage. A rotary sealing ring is provided between the air passage and the motor bearing to ensure that the gas does not leak during the inflation process and does not affect the rotation of the motor.

[0073] In its initial state, the airbag 112 is in a contracted state. At this time, the polishing machine 11 has a small overall volume, making it easy to lower from the wellhead to the designated location of the coal seam to be tested without colliding or rubbing against the well shaft 1. During operation, the driver 11 inflates the airbag 112, allowing it to expand as needed. The inflated airbag 112 compresses the polishing ring 113. Driven by the rotation of the driver 111, the airbag 112 and the polishing ring 113 rotate, achieving the purpose of uniformly polishing the inner wall of the coal seam to be tested. Because the airbag 112 expands uniformly in all radial directions, it ensures uniform force in all directions, thereby achieving synchronous polishing of the coal wall in all directions within the well shaft.

[0074] The flocculant silo 10 is used to store and release flocculant into the wellbore 1 to promote the settling of pulverized coal in the wellbore 1;

[0075] The flocculant is a mixture of polyaluminum chloride and polyacrylamide.

[0076] The flocculant chamber 10 is a component for storing flocculants and can slowly release flocculants into the wellbore 1. The specific release method can be a screw propulsion type (using a screw or screw conveyor, driven by a motor or hydraulic system to rotate slowly and push the flocculant out evenly) or a piston extrusion type (using a slowly moving piston to push the flocculant out under pressure difference or chemical dissolution).

[0077] The indenter 7 includes a main unit 71, multiple radially symmetrically arranged electric telescopic rods 72, and a diamond indenter 73. The fixed end of the electric telescopic rod 72 is installed at the bottom of the main unit 71, and the telescopic end of the electric telescopic rod 72 is connected to the diamond indenter 73. The multiple electric telescopic rods 72 are evenly distributed around the circumference of the main unit 71 and can extend radially synchronously to press the diamond indenter 73 against the well wall.

[0078] The diamond indenter 73 is a Vickers indenter with a face angle of 136° and a predetermined load of 0.98N.

[0079] The main unit 71 has a rotation function, which can rotate the electric telescopic rods 72 below the main unit 71. Multiple electric telescopic rods 72 rotate synchronously. The electric telescopic rods 72 shorten during rotation, and after reaching the target point, they extend and drive the diamond indenter 73 to insert into the coal seam to be tested inside the shaft 1. After the indentation operation is completed, the electric telescopic rods 72 shorten, causing the diamond indenter 73 to be pulled out from the coal seam to be tested, and then move to the next target point with the rotation of the electric telescopic rods 72. The main purpose of the indenter 7 is to leave an indentation on the inner wall of the coal seam to be tested.

[0080] The upper macro camera 6 is used to perform circumferential scanning and imaging of the inner wall of the polished coal seam before the indentation operation to obtain the first image sequence;

[0081] The lower macro camera 8 is used to perform circumferential scanning and imaging of the inner wall of the same coal seam with indentations after the indentation operation, so as to obtain a second image sequence;

[0082] Both the upper macro camera 6 and the lower macro camera 8 are equipped with multiple lenses, which are evenly distributed in a ring in the same radial plane to achieve circumferential shooting without blind spots.

[0083] Temperature and pressure sensor 9 is used to monitor the temperature and pressure inside the coal seam under test in real time;

[0084] Computer 5 is connected to the upper macro camera 6, the lower macro camera 8, the indenter 7, and the temperature and pressure sensor 9. Computer 5 is used to receive and process the first image sequence and the second image sequence, and to reconstruct the inner wall development diagram of the coal seam to be tested based on the first image sequence, and to identify and divide the distribution areas of different macroscopic coal and rock types and interbedded rock. It also performs spatial registration between the second image sequence and the first image sequence, so that each indentation is accurately associated with the specific coal and rock type region where it is located. In addition, it can calculate the micromechanical parameters of the coal and rock type where each indentation point is located based on the indentation morphology in the registered second image sequence. Computer 5 can also determine the failure mode of different coal and rock components by analyzing the morphological characteristics of the indentation and the secondary cracks generated around it in the registered image.

[0085] The computer can be an industrial control computer, an embedded processor, or a cloud server. It is internally equipped with an image processing module, a spatial registration module, and a mechanical inversion module, and stores a database of coal and rock optical characteristics and a library of indentation mechanical models. These modules work collaboratively, as detailed below:

[0086] The image processing module (which has internal image processing algorithms) receives the first image sequence transmitted from the macro camera and performs the following operations:

[0087] Lens distortion correction and illumination equalization are performed on each frame of the image;

[0088] The vertical spacing between adjacent frames is calculated based on the drill rod lifting speed and the camera frame rate. Matching point pairs are extracted in the overlapping area of ​​adjacent frames using feature point matching algorithms (such as SIFT or ORB).

[0089] The circumferential image is unfolded into a rectangle by cylindrical projection transformation, and then stitched along the axis to generate a continuous 360° unfolded image of the inner wall of the coal seam to be tested.

[0090] Extract the color histogram (HSV space), texture features (contrast and entropy of the gray-level co-occurrence matrix), and surface reflection intensity (as a gloss index) of each region in the unfolded image. Input these features into a pre-trained classifier (such as a support vector machine, SVM). Combined with the built-in coal and rock component template library (containing typical optical features of bright coal, semi-bright coal, semi-dark coal, dull coal, and interbedded rock), output the coal and rock type label of each pixel or block, thereby completing the macroscopic regional division of coal and rock types and interbedded rock.

[0091] The spatial registration module establishes the spatial correspondence between the second image sequence and the unfolded inner wall diagram of the coal seam to be tested generated based on the first image sequence. Specifically, it includes:

[0092] Obtain the fixed distance between the upper and lower macro cameras in the downhole equipment;

[0093] Based on the parameter of uniform upward movement of the drill pipe, it is estimated that when the lower camera captures a certain position, the upper camera has already moved upward, and the initial phase offset of the two sequences is determined accordingly.

[0094] Identify stable geological markers (such as natural fissures, highly reflective mineral bands, or coal-rock interfaces) in the unfolded diagram and the second image sequence as registration anchors;

[0095] A non-rigid transformation model using thin plate spline (TPS) is employed to perform local deformation correction on the second image sequence, enabling it to achieve sub-millimeter-level alignment with the unfolded image at both the global and local scales.

[0096] Output the precise position of each indentation in the unfolded coordinate system and associate it with the corresponding coal and rock component label to establish an "indentation-coal and rock component" mapping table.

[0097] The mechanical inversion module calculates micromechanical parameters based on the registered indentation images.

[0098] The coal seam under test possesses reservoir pressure (fluid pressure within the pores and fractures of the coal seam) in its in-situ state and produces water into wellbore 1. This process indicates that the coal seam is in a state of energy non-equilibrium. Only when the dynamic fluid level of the dynamic fluid column inside wellbore 1 remains stable, and the pressure of the dynamic fluid column near the coal seam equals the reservoir pressure of the coal seam, does the system consisting of the coal seam and wellbore 1 reach an energy equilibrium state. Only under this equilibrium state can it be considered to be in an in-situ stress state. Based on this, the micromechanical properties of the coal seam under test under in-situ stress state can be tested using the downhole equipment of this device.

[0099] A method for testing the mechanical properties of coal and rock in situ for coalbed methane wells includes the following steps:

[0100] S1. Add flocculant into wellbore 1 to promote the settling of coal powder in the dynamic liquid column inside wellbore 1 to the bottom of the artificial well.

[0101] S2. After the coal powder settles, the downhole equipment 4 is lowered to the bottom boundary of the coal seam to be tested. The polishing machine 11 is started and the flocculant is released simultaneously. The wellhead equipment 2 is controlled to drive the downhole equipment 4 to slowly lift from the bottom boundary to the top boundary of the coal seam to be tested, thus completing the in-situ polishing of the inner wall of the coal seam to be tested.

[0102] S3. After polishing is completed, keep the downhole equipment 4 below the bottom boundary of the coal seam to be tested, and start the upper macro camera 6, indenter 7 and lower macro camera 8.

[0103] S4. Control the wellhead equipment 2 to continuously lift the downhole equipment 4 from the bottom boundary to the top boundary of the coal seam to be measured at a constant speed. During this process, the following steps are executed simultaneously:

[0104] S4.1 The upper macro camera 6 performs a circumferential scan of the inner wall of the coal seam to be tested above which there is no indentation, and obtains the first image sequence;

[0105] S4.2 The indenter 7 applies an indentation to the inner wall of the coal seam to be tested at the current location;

[0106] S4.3 The lower macro camera 8 performs a circumferential scan on the inner wall of the coal seam to be tested after the indentation has been completed, and obtains the second image sequence;

[0107] S5. During step S4, temperature and pressure data are recorded synchronously by temperature and pressure sensor 9;

[0108] S6. Transmit the first image sequence and the second image sequence to computer 5, and perform the following processing:

[0109] S6.1 Generate an inner wall unfolded map of the coal seam to be tested based on the first image sequence, and identify the distribution areas of bright coal, semi-bright coal, semi-dark coal, dull coal and interbedded gangue based on color, texture and gloss characteristics.

[0110] In step S6.1, feature recognition is automatically completed using an image processing algorithm.

[0111] S6.2. Spatial registration is performed between the second image sequence and the unfolded inner wall diagram of the coal seam to be tested generated in step S6.1;

[0112] S6.3 Extract the geometric features of each indentation in the registered image, and calculate the in-situ microhardness, contact stiffness and elastic modulus in combination with the coal and rock type region where it is located.

[0113] In step S6.3, the specific calculation steps are as follows:

[0114] Indentation Projection Area Contact depth with indentation The relationship between them is as follows:

[0115]

[0116] In the formula, The constant is taken as 24.56 for the Vickers indenter, and the projected area of ​​the indentation is... It can be determined by the length of the indentation diagonal. , The calculation yielded:

[0117]

[0118] For the indentation contact area Knowing the face angle of the diamond indenter, the contact area of ​​the indentation can be calculated. With indentation projected area The relationship between them:

[0119]

[0120] For a Vickers indenter with a face angle of 136°, the Vickers hardness is calculated using the following formula when the peak load is 0.98 N:

[0121]

[0122] In the formula, Vickers hardness It is a constant, with a value of 0.102; The peak load is 0.98 N.

[0123] Contact stiffness is calculated by the following formula:

[0124]

[0125] In the formula, For contact stiffness, For peak depth, The parameter is related to the shape of the indenter and is set to 0.75.

[0126] elastic modulus Calculated by the following formula:

[0127]

[0128] In the formula, This is a constant related to the shape of the indenter, with a value of 1.034.

[0129] S6.4. Based on the clarity of the indentation boundary, whether secondary cracks are generated, and the crack morphology, determine whether the failure mode of each coal and rock component is brittle failure, plastic failure, or transitional failure.

[0130] In step S6.4, the criteria for determining the damage mode are as follows:

[0131] Brittle fracture: sharp indentation boundaries, accompanied by radial or annular secondary cracks;

[0132] Plastic failure: The indentation boundary is blurred, there are no visible cracks, and the material is obviously raised;

[0133] Transitional failure: It combines some characteristics of brittle failure and plastic failure.

[0134] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0135] The embodiments of this invention are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An in-situ coal and rock mechanical property testing device for coalbed methane wells, used for in-situ mechanical testing of the inner wall of a coal seam in an existing coalbed methane well, wherein the coalbed methane well includes a wellbore (1), an artificial well bottom located at the bottom of the wellbore (1), and the coal seam to be tested, characterized in that, Includes wellhead equipment (2), drill pipe (3), downhole equipment (4), and computer (5); The wellhead equipment (2) is connected to the drill pipe (3), and the bottom end of the drill pipe (3) is connected to the downhole equipment (4). The downhole equipment (4) is lowered into the coal seam to be tested in the wellbore (1) through the drill pipe (3), and from top to bottom it includes an upper macro camera (6), an indenter (7), a lower macro camera (8), a temperature and pressure sensor (9), a flocculant chamber (10) and a polishing machine (11), and the components are connected by a rotary quick connector (12). The polishing machine (11) includes a driver (111), an airbag (112), and a polishing ring (113), which is used to perform in-situ polishing of the inner wall of the coal seam to be tested in the well shaft (1). The airbag (112) is sleeved on the outside of the driver (111), and the polishing ring (113) is sleeved on the outside of the airbag (112). The flocculant silo (10) is used to store and release flocculant into the wellbore (1) to promote the settling of coal powder in the wellbore (1); The indenter (7) includes a main unit (71), multiple radially symmetrically arranged electric telescopic rods (72) and a diamond indenter (73). The fixed end of the electric telescopic rod (72) is installed at the bottom of the main unit (71), and the telescopic end of the electric telescopic rod (72) is connected to the diamond indenter (73) for radially pushing the diamond indenter (73) to contact the inner wall of the coal seam to be tested. The upper macro camera (6) is used to perform circumferential scanning and imaging of the inner wall of the polished coal seam before the indentation operation, so as to obtain the first image sequence; The lower macro camera (8) is used to perform circumferential scanning and imaging of the inner wall of the same coal seam with indentation after the indentation operation, so as to obtain a second image sequence; The temperature and pressure sensor (9) is used to monitor the temperature and pressure in the coal seam under test in real time. The computer (5) is connected to the upper macro camera (6), the lower macro camera (8), the indenter (7), and the temperature and pressure sensor (9). The computer (5) is used to receive and process the first image sequence and the second image sequence, and to reconstruct the inner wall unfolding of the coal seam to be tested based on the first image sequence, and to identify and divide the distribution areas of different macroscopic coal and rock types and interbedded rock. Furthermore, it spatially registers the second image sequence with the first image sequence to accurately associate each indentation with the specific coal and rock type region in which it is located. In addition, it can calculate the micromechanical parameters of the coal and rock type where each indentation point is located based on the indentation morphology in the registered second image sequence.

2. The in-situ coal and rock mechanical property testing device for coalbed methane wells according to claim 1, characterized in that, The computer (5) can also determine the failure modes of different coal and rock components by analyzing the morphological features of the indentation and the secondary cracks generated around it in the registered image.

3. The in-situ coal and rock mechanical property testing device for coalbed methane wells according to claim 1, characterized in that, Both the upper macro camera (6) and the lower macro camera (8) are equipped with multiple lenses, which are evenly distributed in a ring in the same radial plane to achieve circumferential shooting without blind spots.

4. The in-situ coal and rock mechanical property testing device for coalbed methane wells according to claim 1, characterized in that, The diamond indenter (73) is a Vickers indenter with a face angle of 136°, and the predetermined load is 0.98N.

5. A method for testing the in-situ mechanical properties of coal and rock in coalbed methane wells using the apparatus described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Add flocculant into the wellbore (1) to cause the coal powder in the moving liquid column inside the wellbore (1) to settle to the bottom of the artificial well. S2. After the coal powder settles, the downhole equipment (4) is lowered to the bottom boundary of the coal seam to be tested. The polishing machine (11) is started and the flocculant is released simultaneously. The wellhead equipment (2) is controlled to drive the downhole equipment (4) to slowly lift from the bottom boundary to the top boundary of the coal seam to be tested, thus completing the in-situ polishing of the inner wall of the coal seam to be tested. S3. After polishing is completed, keep the downhole equipment (4) below the bottom boundary of the coal seam to be tested, and start the upper macro camera (6), indenter (7) and lower macro camera (8). S4. Control the wellhead equipment (2) to drive the downhole equipment (4) at a constant speed to continuously lift it from the bottom boundary to the top boundary of the coal seam to be tested. During this process, the following steps are performed simultaneously: S4.1 The upper macro camera (6) performs a circumferential scan on the inner wall of the coal seam to be tested that is not indented, and obtains the first image sequence; S4.2, The indenter (7) applies an indentation to the inner wall of the coal seam at the current location; S4.

3. The lower macro camera (8) performs a circumferential scan on the inner wall of the coal seam to be tested after the indentation has been completed, and obtains the second image sequence. S5. During step S4, temperature and pressure data are recorded synchronously by the temperature and pressure sensor (9); S6. Transmit the first image sequence and the second image sequence to the computer (5) and perform the following processing: S6.1 Generate an inner wall unfolded map of the coal seam to be tested based on the first image sequence, and identify the distribution areas of bright coal, semi-bright coal, semi-dark coal, dull coal and interbedded gangue based on color, texture and gloss characteristics. S6.

2. Spatial registration is performed between the second image sequence and the unfolded inner wall diagram of the coal seam to be tested generated in step S6.1; S6.3 Extract the geometric features of each indentation in the registered image, and calculate the in-situ microhardness, contact stiffness and elastic modulus in combination with the coal and rock type region where it is located. S6.

4. Based on the clarity of the indentation boundary, whether secondary cracks are generated, and the crack morphology, determine whether the failure mode of each coal and rock component is brittle failure, plastic failure, or transitional failure.

6. The method for testing the in-situ mechanical properties of coal and rock in coalbed methane wells according to claim 5, characterized in that, In step S6.1, feature recognition is automatically completed using an image processing algorithm.

7. The method for testing the in-situ mechanical properties of coal and rock in coalbed methane wells according to claim 5, characterized in that, In step S6.3, the specific calculation steps are as follows: Indentation Projection Area Contact depth with indentation The relationship between them is as follows: ， In the formula, The constant is taken as 24.56 for the Vickers indenter, and the projected area of ​​the indentation is... It can be determined by the length of the indentation diagonal. , The calculation yielded: ， For the indentation contact area Knowing the face angle of the diamond indenter, the contact area of ​​the indentation can be calculated. With indentation projected area The relationship between them: ， For a Vickers indenter with a face angle of 136°, the Vickers hardness is calculated using the following formula when the peak load is 0.98 N: ， In the formula, Vickers hardness It is a constant, with a value of 0.102; The peak load is 0.98 N. Contact stiffness is calculated by the following formula: ， In the formula, For contact stiffness, For peak depth, The parameter is related to the shape of the indenter and is set to 0.

75. elastic modulus Calculated by the following formula: ， In the formula, This is a constant related to the shape of the indenter, with a value of 1.

034.

8. The method for testing the mechanical properties of coal and rock in situ for coalbed methane wells according to claim 5, characterized in that, In step S6.4, the criteria for determining the damage mode are as follows: Brittle fracture: sharp indentation boundaries, accompanied by radial or annular secondary cracks; Plastic failure: The indentation boundary is blurred, there are no visible cracks, and the material is obviously raised; Transitional failure: It combines some characteristics of brittle failure and plastic failure.

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