Drilling disturbance coal rock damage-stress field in-situ reconstruction method and device

Abstract

The invention provides a drilling disturbance coal rock damage-stress field in-situ reconstruction method and device.The drilling disturbance coal rock damage-stress field in-situ reconstruction method comprises the steps that a sample model is built based on a coal rock sample of coal rock to be measured; the physical properties of the sample model are consistent with those of the to-be-tested coal rock; performing mechanical testing on the coal rock sample of the to-be-tested coal rock and the corresponding sample model to obtain basic mechanical parameters of the coal rock sample of the to-be-tested coal rock; drilling is carried out on each sample model in sequence, at least one time of stress freezing and digital photoelastic testing are carried out, and the damage-stress field evolution process of the to-be-tested coal rock in the drilling process is obtained; drilling is conducted on all the sample models in sequence, and a hydraulic fracturing test is conducted. By means of the method and device, the hydraulic fracturing mechanism of disturbed coal rock can be effectively detected, and the problem that the hydraulic fracturing effect is poor in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of coal and rock detection, and in particular to a method and device for in-situ reconstruction of a coal and rock damage-stress field disturbed by borehole drilling. Background Art

[0002] my country has abundant coal resources, and gas, as a byproduct of coal, is not only the main source of disasters in coal mines, but also a non-renewable energy source and a strong greenhouse gas. High-gas mines account for more than 50% of the total number of mines in my country. Efficient gas extraction can not only reduce mine disasters, but also has important significance for optimizing my country's energy structure and helping "carbon neutrality". The effect of gas extraction depends on the permeability of the coal seam. The internal fractures of coal seams with good permeability are more developed, and the through-fracture network is conducive to the desorption of adsorbed gas and the migration of free gas. my country's coal seam structure is complex, and the permeability of coal rock is generally low. With the increasing depletion of shallow coal resources, coal development has shifted to deep areas and gradually become the norm. The characteristics of high ground stress, high gas pressure and low permeability in deep coal seams have led to increasingly prominent coal-rock gas dynamic disasters. Therefore, it is urgent to construct a through-fracture network inside the coal seam through artificial intervention to improve the gas extraction efficiency of deep low-permeability coal seams.

[0003] Borehole hydraulic fracturing is one of the important means to improve the permeability of low-permeability coal seams in my country, and plays a key role in the rapid pre-extraction of coal seam gas. However, the disturbance caused by drilling in the coal seam before hydraulic fracturing causes the coal rock to be depressurized, breaking the original stress state of the coal seam and releasing the elastic energy accumulated in the coal rock around the hole, which in turn causes the coal rock to deform, break and redistribute stress. In the subsequent hydraulic fracturing process, the deformation and destruction of the coal rock around the deep hole is not only affected by the ground stress, borehole pressure and pore pressure, but also controlled by the damage-stress field induced by the drilling process, which significantly increases the complexity of the hydraulic fracturing process of coal rock.

[0004] Although a large number of researchers have conducted a series of basic studies on hydraulic fracturing of coal and rock boreholes, they mainly use the method of "drilling first and then loading geostress" to simulate the damage-stress state induced by drilling, and then implement drilling hydraulic fracturing on coal and rock. This is obviously fundamentally different from actual engineering, because deep coal and rock are already under high geostress. When simulating drilling, it should be carried out in the manner of "loading geostress first and then drilling".

[0005] There is no effective solution to the problem of poor hydraulic fracturing effect in existing related technologies. Summary of the invention

[0006] The present invention provides a method and device for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling a hole, which are used to solve the defect of poor hydraulic fracturing effect existing in the prior art.

[0007] In a first aspect, the present invention provides a method for in-situ reconstruction of the damage-stress field of coal and rock disturbed by drilling, comprising: A sample model is constructed based on a coal rock sample of the coal rock to be tested; the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested; Performing mechanical tests on the coal rock sample and the corresponding sample model of the coal rock to be tested to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested; Drilling is performed on each of the sample models in turn, and at least one stress freezing and digital photoelastic test is performed to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process; Each sample model is drilled in turn, a hydraulic fracturing test is carried out, and stress freezing and digital photoelastic tests are performed to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

[0008] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, obtaining the coal rock sample to be tested comprises: Determining the sample structure of the coal rock sample; the sample structure includes a cubic type, a cylindrical type and a Brazilian disc type; According to the sample structure, the coal rock to be tested is prepared into a plurality of coal rock samples, and the coal rock samples are screened.

[0009] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, a sample model is constructed based on a coal rock sample of the coal rock to be tested, comprising: Digitally reconstructing the coal rock sample of the coal rock to be tested, and establishing a three-dimensional coal rock digital core model of the coal rock to be tested; The sample model is generated by printing based on the three-dimensional coal rock digital core model of the coal rock to be tested.

[0010] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, the model matrix of the sample model adopts VeroClear material, the model particles of the sample model adopt RGD525 material, and the model pores and model cracks of the sample model adopt Fullcure705 support material.

[0011] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, a mechanical test is performed on a coal rock sample of the coal rock to be tested and a corresponding sample model to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested, including: Conducting observation tests on the coal rock sample and the corresponding sample model of the coal rock to be tested to determine the microstructure and mineral component characteristics of the coal rock to be tested; Performing a uniaxial compression test on the cylindrical coal-rock sample, and taking an average of the test results to determine basic mechanical parameters of the cylindrical coal-rock sample; Conducting a Brazilian splitting test on the Brazilian disc-shaped coal-rock sample, and taking an average of the test results to determine basic mechanical parameters of the Brazilian disc-shaped coal-rock sample; The basic mechanical parameters include the compressive strength, tensile strength, elastic modulus and Poisson's ratio of the coal rock sample.

[0012] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, drilling is performed on each of the sample models in turn, and at least one stress freezing and digital photoelastic test is performed, including: Determine the stress state of the coal rock to be tested based on the sampling depth of the coal rock to be tested, and apply the corresponding stress state to the sample model; Determine the end depth and several stress freezing sections, and when drilling into each stress freezing section, stop drilling and perform a stress freezing and digital photoelastic test until the end depth is reached.

[0013] According to a method for in-situ reconstruction of the damage-stress field of coal rock disturbed by drilling provided by the present invention, drilling is performed on each sample model in turn, a hydraulic fracturing test is performed, and stress freezing and digital photoelastic tests are performed, including: Performing drilling on each of the sample models to obtain a plurality of drilled sample models; A water pressure stress freezing point is set, water is injected into the borehole sample model according to the water pressure stress freezing point, and stress freezing and digital photoelastic tests are performed.

[0014] According to a method for in-situ reconstruction of the damage-stress field of coal and rock disturbed by drilling provided by the present invention, the stress freezing comprises: Applying a preset load to the sample model and keeping it constant; The ambient temperature of the sample model is lowered at a segmented gradient rate until the target temperature is reached, and then the temperature is lowered at a constant rate.

[0015] According to a method for in-situ reconstruction of the damage-stress field of coal and rock disturbed by drilling provided by the present invention, the digital photoelastic test comprises: Slicing the sample model after stress freezing to obtain model slices; performing pulsed laser processing on the model slices and capturing an arithmetic fringe pattern; The equidistant stress at the crack tip and the vicinity of the sample model is determined based on the equidistant fringe diagram.

[0016] In a second aspect, the present invention further provides an in-situ reconstruction device for the damage-stress field of coal and rock disturbed by drilling, comprising: A construction module, used to construct a sample model based on a coal rock sample of the coal rock to be tested; the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested; A testing module, used for performing mechanical testing on the coal rock sample and the corresponding sample model of the coal rock to be tested, so as to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested; The first processing module is used to perform drilling on each of the sample models in turn, and perform at least one stress freezing and digital photoelastic test to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process; The second processing module is used to carry out drilling on each of the sample models in turn, conduct hydraulic fracturing tests, and perform stress freezing and digital photoelastic tests to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The in-situ reconstruction method of the damage-stress field of coal rock disturbed by drilling provided by the present invention, by adopting the process of first loading and then drilling, truly reproduces the damage-stress distribution of coal rock around the hole during the drilling process under the deep in-situ ground stress state, and can effectively explore the hydraulic fracturing mechanism of disturbed coal rock, thus solving the problem of poor hydraulic fracturing effect existing in the existing related technologies.

[0018] 2. The present invention provides an in-situ three-dimensional reconstruction method for the hydraulic fracturing damage-stress field of coal rock disturbed by deep drilling, which combines CT scanning and 3D printing technology, uses a transparent printing material VeroClear for the matrix part, a non-transparent white material RGD525 for the particle part, and a support material Fullcure705 for the pore and fracture part to prepare a model consistent with the structural characteristics of natural coal rock, and then conducts a mechanical property test, thereby improving the authenticity and validity of the test results.

[0019] 3. The present invention provides an in-situ three-dimensional reconstruction method for the hydraulic fracturing damage-stress field of coal rock disturbed by deep drilling, in which the target temperature is set at 125°C and then dropped to room temperature at a constant rate after reaching the target temperature at a segmented gradient rate, which can reduce the disturbance during the drilling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a flow chart of the in-situ reconstruction method of the coal rock damage-stress field disturbed by borehole drilling provided by the present invention; Figure 2 is a schematic diagram of a process for obtaining the damage-stress evolution process during coal and rock drilling in an embodiment of the present invention; Figure 3 is a schematic diagram of setting a stress freezing section in an embodiment of the present invention; Figure 4 It is a schematic diagram of a process for obtaining the evolution of a three-dimensional damage-stress field during hydraulic fracturing of coal and rock in an embodiment of the present invention; Figure 5 Schematic diagram of a water pressure-time curve of a sample model in an embodiment of the present invention; Figure 6 is a schematic diagram of a temperature-time curve for stress freezing in an embodiment of the present invention; Figure 7 It is a structural block diagram of the in-situ reconstruction device for the damage-stress field of coal and rock disturbed by drilling provided by the present invention. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides a method for in-situ reconstruction of the damage-stress field of coal and rock disturbed by drilling. Figure 1 Flow chart of the in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling provided by the present invention, such as Figure 1 As shown, the method comprises the following steps: Step S101, constructing a sample model based on a coal rock sample of the coal rock to be tested; the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested.

[0024] Step S102, performing mechanical testing on the coal rock sample of the coal rock to be tested and the corresponding sample model to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested.

[0025] Step S103, drilling is performed on each sample model in turn, and at least one stress freezing and digital photoelastic test is performed to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process.

[0026] Step S104, drilling is performed on each sample model in turn, a hydraulic fracturing test is performed, and stress freezing and digital photoelastic tests are performed to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

[0027] In this method, first, a sample model corresponding to the coal rock sample of the coal rock to be tested is constructed. It is worth noting that in order to more realistically represent the structure and parameters of the coal rock to be tested, the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested, so that the final test results are more real and effective. Then, mechanical tests are performed on each sample model and coal rock sample to determine its basic mechanical parameters for subsequent experiments and tests. Then, each sample model is drilled, and stress freezing and digital photoelastic tests are performed, and hydraulic fracturing tests are performed to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process and the three-dimensional damage-stress field evolution process during the hydraulic fracturing process. This method adopts the process of loading first and then drilling, and truly reproduces the damage-stress distribution of the coal rock around the hole during the drilling process under the deep in-situ ground stress state, which can effectively explore the hydraulic fracturing fracture mechanism of the disturbed coal rock, and solve the problem of poor hydraulic fracturing effect in the existing related technologies. In the above process, the order of step S103 and step S104 can be adjusted as needed.

[0028] In some of the embodiments, obtaining a coal rock sample of the coal rock to be tested includes: determining the sample structure of the coal rock sample; the sample structure includes a cubic type, a cylindrical type and a Brazilian disc type; according to the sample structure, preparing the coal rock to be tested into a plurality of coal rock samples, and screening the coal rock samples.

[0029] For example, a field survey of the coal seam was conducted to collect relevant engineering test data and the coal rock to be tested. Using the large pieces of coal rock to be tested, three samples of different sizes were processed: a cubic coal rock sample with an edge length of 100 mm, a cylindrical coal rock sample with a diameter of 50 mm and a height of 100 mm, and a Brazilian disc-shaped coal rock sample with a diameter of 50 mm and a thickness of 25 mm. The coal rock samples were screened by combining surface macroscopic observation and ultrasonic detection tests to control the test error.

[0030] In some of the embodiments, step S101, constructing a sample model based on a coal rock sample of the coal rock to be tested, includes: digitally reconstructing the coal rock sample of the coal rock to be tested to establish a three-dimensional coal rock digital core model of the coal rock to be tested; and printing the three-dimensional coal rock digital core model of the coal rock to be tested to generate a sample model.

[0031] On this basis, the model matrix of the specimen model adopts VeroClear material, the model particles of the specimen model adopt RGD525 material, and the model pores and model cracks of the specimen model adopt Fullcure705 support material.

[0032] For example, an industrial CT with a scanning accuracy of 0.5 μm was used to scan and test the processed cubic coal and rock samples, and 250 CT slices were obtained. The CT slices were imported into AVIZO software, and a three-dimensional coal and rock digital core model was established after noise reduction and segmentation, and an STL format file representing the three-dimensional structure was exported. A high-precision layered multi-material stereoscopic molding system such as Object Connex500 3D printing equipment was used to prepare three different sizes of sample models: a cubic sample with an edge length of 100 mm, a cylindrical sample with a diameter of 50 mm and a height of 100 mm, and several Brazilian disc samples with a diameter of 50 mm and a thickness of 25 mm. Among them, the model matrix part uses the transparent printing material VeroClear, the model particle part uses the non-transparent white material RGD525, and the model pore and fracture part uses the support material Fullcure705, so that the sample model has physical and mechanical properties similar to the real coal and rock to be tested.

[0033] In some embodiments, step S102, mechanical testing is performed on the coal rock sample and the corresponding sample model of the coal rock to be tested to obtain the basic mechanical parameters of the coal rock sample of the coal rock to be tested, including: performing observation tests on the coal rock sample and the corresponding sample model of the coal rock to be tested to determine the microstructure and mineral component characteristics of the coal rock to be tested; performing uniaxial compression tests on cylindrical coal rock samples, and taking the average of the test results to determine the basic mechanical parameters of the cylindrical coal rock sample; performing Brazilian splitting tests on Brazilian disc-shaped coal rock samples, and taking the average of the test results to determine the basic mechanical parameters of the Brazilian disc-shaped coal rock sample. The basic mechanical parameters include the compressive strength, tensile strength, elastic modulus and Poisson's ratio of the coal rock sample.

[0034] For example, observation and X-ray diffraction analysis experiments were carried out on coal rock samples and corresponding sample models with the help of scanning electron microscope to analyze their microstructure and mineral composition characteristics. Coal rock samples in cylindrical and Brazilian disc form were subjected to uniaxial compression and Brazilian splitting tests in a rock triaxial servo multi-field coupling test system. In both tests, loads were applied through vertical displacement, and the displacement rate was controlled to 0.05 mm / min. Three or more samples were tested in each group of tests and the average was taken to obtain the basic mechanical parameters of the samples, such as compressive strength, tensile strength, elastic modulus and Poisson's ratio.

[0035] In some of the embodiments, step S103, drilling is performed on each sample model in turn, and at least one stress freezing and digital photoelastic test is performed, including: based on the collection depth of the coal rock to be tested, the stress state of the coal rock to be tested is determined, and the corresponding stress state is applied to the sample model; the terminal depth and several stress freezing sections are determined, and when drilling each stress freezing section, the drilling is stopped and a stress freezing and digital photoelastic test is performed until the terminal depth is reached.

[0036] For example, Figure 2 is a flow chart of obtaining the damage-stress evolution process during coal rock drilling in an embodiment of the present invention, such as Figure 2 As shown in Figure 1, first, based on the collection depth of the coal rock sample, the stress state of the coal rock to be tested is calculated and obtained, and the stress state is applied to the cubic coal rock model on the testing machine. Subsequently, a spiral drill with a diameter of 8 mm is used to carry out drilling while collecting its rotation speed and drill displacement. The drilling pressure is set to 100 N, and the drilling depth is set to 70 mm. With this depth as the end point depth, four stress freezing sections are set at equal intervals, as shown in Figure 1. Figure 3 As shown, Figure 3 1 is a schematic diagram of the setting of the stress freezing section in the embodiment of the present invention, in which 11 represents the stress state, 12 represents the spiral drill bit, 13 represents the cubic sample model, and 14 represents the stress freezing section. Whenever drilling reaches a certain stress freezing section, drilling is stopped and a stress freezing and digital photoelastic test are performed. After the stress freezing and digital photoelastic test are completed, drilling is performed again, and this cycle is repeated until the end depth is reached, and drilling is no longer performed, thereby obtaining the damage-stress evolution process during the coal and rock drilling process.

[0037] In some of the embodiments, step S104, drilling is performed on each sample model in turn, a hydraulic fracturing test is performed, and stress freezing and digital photoelastic tests are performed, including: drilling is performed on each sample model to obtain a number of drilled sample models; a water pressure stress freezing point is set, water is injected into the drilled sample model according to the water pressure stress freezing point, and stress freezing and digital photoelastic tests are performed.

[0038] For example, Figure 4 FIG. 1 is a flow chart of obtaining the evolution process of the three-dimensional damage-stress field during hydraulic fracturing of coal rock in an embodiment of the present invention. Figure 4 As shown in Figure 1, a spiral drill bit with a diameter of 8 mm was used for drilling, the drilling pressure was set to 100 N, the drilling depth was set to 70 mm, and several drilling sample models were prepared. Then, a full-process hydraulic fracturing test was carried out on the true triaxial testing machine, and the water injection rate was set to 60 ml / min, so as to obtain a complete water pressure-time curve, as shown in Figure 1. Figure 5 As shown, Figure 5It is a schematic diagram of the water pressure-time curve of the sample model in the embodiment of the present invention. Based on this curve, four stress freezing points of water pressure are set before the fracture pressure, and the corresponding water pressures are 20%, 40%, 60%, and 80% of the fracture pressure, respectively. Subsequently, four other borehole sample models are selected, corresponding to four different water pressures, and water is injected in sequence. When the water pressure reaches the corresponding water pressure value, it is stopped and stress freezing and digital photoelastic testing are performed to obtain the three-dimensional damage-stress field evolution process during coal rock hydraulic fracturing.

[0039] Based on the above embodiment, stress freezing includes: applying a preset load to the sample model and keeping it constant; and lowering the ambient temperature of the sample model at a segmented gradient rate until the target temperature is reached, and then cooling at a constant rate.

[0040] For example, a cubic coal rock model is placed on a true triaxial testing machine with a temperature chamber, and a specified load is applied and kept constant. Then, the temperature of the temperature chamber is set to 125°C, and after reaching the target temperature at a stepwise gradient rate, the temperature is lowered at a constant rate to reduce disturbance, such as Figure 6 As shown, Figure 6 Schematic diagram of temperature-time curve for stress freezing in an embodiment of the present invention.

[0041] On this basis, the digital photoelastic test includes: slicing the specimen model after stress freezing to obtain model slices; performing pulsed laser processing on the model slices and capturing the arithmetic fringe pattern; and determining the arithmetic stress at the crack tip and nearby areas of the specimen model based on the arithmetic fringe pattern.

[0042] Exemplarily, the polarized light field optical path used for digital photoelastic testing includes: a light source, a polarizer, a first quarter wave plate, a temperature chamber, a fixed bracket, a second quarter wave plate, an analysis mirror, and a high-speed camera. Specifically, the frozen sample model is cut into model slices with a thickness of 1.5 mm, and then the digital photoelastic test is started. At this time, the light source emits a pulsed laser with a half-width of 220 ns, which passes through the polarizer and the first quarter wave plate in turn, so that the sample model made of the photosensitive material produces a birefringence phenomenon under stress, and after passing through the second quarter wave plate, interference fringes are formed on the analysis mirror, and an arithmetic fringe pattern is obtained by phase formation with a high-speed camera.

[0043] When the incident light is perpendicular to x - y When the plane is incident, the stress component σ x , σ y and The photoelastic effect is produced on the crack tip. Based on the plane stress theory, by capturing the equal-difference fringe image in the circularly polarized light field, analyzing the order of the equal-difference fringes in the fringe image and bringing it into the three-dimensional photoelastic model stress-optical law formula, the magnitude of the equal-difference stress at the crack tip and the surrounding area can be calculated. The three-dimensional photoelastic model stress-optical law formula is as follows:

[0044] Where σ1' and σ2' are the principal stresses in the plane perpendicular to the incident light, also called secondary principal stresses. f 0' is the fringe value of the material at the stress freezing temperature, t represents the thickness of the slice, m represents the level of equidistant fringe at this point, represents the normal stress in the x-direction, represents the normal stress in the y direction, represents the shear stress on the plane.

[0045] The present invention also provides an in-situ reconstruction device for the damage-stress field of coal rock disturbed by drilling a hole. The in-situ reconstruction device for the damage-stress field of coal rock disturbed by drilling a hole provided by the present invention is described below. The in-situ reconstruction device for the damage-stress field of coal rock disturbed by drilling a hole described below and the in-situ reconstruction method for the damage-stress field of coal rock disturbed by drilling a hole described above can be referred to each other. Figure 7 : is a structural block diagram of the in-situ reconstruction device for the damage-stress field of coal rock disturbed by drilling provided by the present invention, such as Figure 7 As shown, the device comprises: A construction module 701 is used to construct a sample model based on the coal rock sample of the coal rock to be tested; the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested; The testing module 702 is used to perform mechanical testing on the coal rock sample to be tested and the corresponding sample model to obtain basic mechanical parameters of the coal rock sample to be tested; The first processing module 703 is used to perform drilling on each sample model in turn, and perform at least one stress freezing and digital photoelastic test to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process; The second processing module 704 is used to perform drilling on each sample model in turn, conduct hydraulic fracturing tests, and perform stress freezing and digital photoelastic tests to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

[0046] When the device is used, first, the construction module 701 constructs a corresponding sample model according to the coal rock sample of the coal rock to be tested. It is worth noting that in order to more realistically express the structure and parameters of the coal rock to be tested, the physical properties of the sample model are consistent with the physical properties of the coal rock to be tested, so that the final detection result is more real and effective. Then, the test module 702 performs mechanical tests on each sample model and coal rock sample to determine its basic mechanical parameters for subsequent experiments and tests. The first processing module 703 and the second processing module 704 then drill each sample model, and perform stress freezing and digital photoelastic tests, in conjunction with hydraulic fracturing tests, to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process and the three-dimensional damage-stress field evolution process during the hydraulic fracturing process. When the device is used, the process of loading first and then drilling is adopted to truly reproduce the damage-stress distribution of the coal rock around the hole during the drilling process under the deep in-situ ground stress state, which can effectively explore the hydraulic fracturing fracture mechanism of disturbed coal rock, and solve the problem of poor hydraulic fracturing effect in the existing related technologies.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ reconstruction of the damage-stress field of coal and rock disturbed by drilling, characterized in that: include: Constructing a sample model based on the coal rock sample to be tested; The physical properties of the sample model are consistent with the physical properties of the coal rock to be tested; Performing mechanical tests on the coal rock sample and the corresponding sample model of the coal rock to be tested to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested; Drilling is performed on each of the sample models in turn, and at least one stress freezing and digital photoelastic test is performed to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process; Each sample model is drilled in turn, a hydraulic fracturing test is carried out, and stress freezing and digital photoelastic tests are performed to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

2. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1 is characterized in that: Obtaining the coal rock sample of the coal rock to be tested includes: Determining the sample structure of the coal rock sample; the sample structure includes a cubic type, a cylindrical type and a Brazilian disc type; According to the sample structure, the coal rock to be tested is prepared into a plurality of coal rock samples, and the coal rock samples are screened.

3. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1 is characterized in that: A sample model is constructed based on the coal rock sample to be tested, including: Digitally reconstructing the coal rock sample of the coal rock to be tested, and establishing a three-dimensional coal rock digital core model of the coal rock to be tested; The sample model is generated by printing based on the three-dimensional coal rock digital core model of the coal rock to be tested.

4. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1 is characterized in that: The model matrix of the sample model is made of VeroClear material, the model particles of the sample model are made of RGD525 material, and the model pores and model cracks of the sample model are made of Fullcure705 supporting material.

5. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1, characterized in that: Mechanical testing is performed on the coal rock sample and the corresponding sample model of the coal rock to be tested to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested, including: Conducting observation tests on the coal rock sample and the corresponding sample model of the coal rock to be tested to determine the microstructure and mineral component characteristics of the coal rock to be tested; Performing a uniaxial compression test on the cylindrical coal-rock sample, and taking an average of the test results to determine basic mechanical parameters of the cylindrical coal-rock sample; Conducting a Brazilian splitting test on the Brazilian disc-shaped coal-rock sample, and taking an average of the test results to determine basic mechanical parameters of the Brazilian disc-shaped coal-rock sample; The basic mechanical parameters include the compressive strength, tensile strength, elastic modulus and Poisson's ratio of the coal rock sample.

6. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1, characterized in that: Drilling is performed on each of the sample models in turn, and at least one stress freezing and digital photoelastic test is performed, including: Determine the stress state of the coal rock to be tested based on the sampling depth of the coal rock to be tested, and apply the corresponding stress state to the sample model; Determine the end depth and several stress freezing sections, and when drilling into each stress freezing section, stop drilling and perform a stress freezing and digital photoelastic test until the end depth is reached.

7. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1 is characterized in that: Each of the sample models is drilled in turn, a hydraulic fracturing test is performed, and a stress freezing and digital photoelastic test are performed, including: Performing drilling on each of the sample models to obtain a plurality of drilled sample models; A water pressure stress freezing point is set, water is injected into the borehole sample model according to the water pressure stress freezing point, and stress freezing and digital photoelastic tests are performed.

8. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1, characterized in that: The stress freezing comprises: Applying a preset load to the sample model and keeping it constant; The ambient temperature of the sample model is lowered at a segmented gradient rate until the target temperature is reached, and then the temperature is lowered at a constant rate.

9. The in-situ reconstruction method of the coal rock damage-stress field disturbed by drilling according to claim 1, characterized in that: The digital photoelastic test includes: Slicing the sample model after stress freezing to obtain model slices; performing pulsed laser processing on the model slices and capturing an arithmetic fringe pattern; The equidistant stress at the crack tip and the vicinity of the sample model is determined based on the equidistant fringe diagram.

10. An in-situ reconstruction device for the damage-stress field of coal and rock disturbed by drilling, characterized in that: include: A construction module, used for constructing a sample model based on a coal rock sample to be tested; The physical properties of the sample model are consistent with the physical properties of the coal rock to be tested; A testing module, used for performing mechanical testing on the coal rock sample and the corresponding sample model of the coal rock to be tested, so as to obtain basic mechanical parameters of the coal rock sample of the coal rock to be tested; The first processing module is used to perform drilling on each of the sample models in turn, and perform at least one stress freezing and digital photoelastic test to obtain the damage-stress field evolution process of the coal rock to be tested during the drilling process; The second processing module is used to carry out drilling on each of the sample models in turn, conduct hydraulic fracturing tests, and perform stress freezing and digital photoelastic tests to obtain the three-dimensional damage-stress field evolution process of the coal rock to be tested during the hydraulic fracturing process.

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