A method for surveying coal and rock strata structure under water

Abstract

The present invention provides a method for surveying the structure of coal-rock strata under water, which belongs to the field of stratum survey technology, and includes the following steps: S1: dividing the survey area into array grids and determining the drilling points; S2: using drilling equipment to perform drilling operations, sampling the rock strata in the borehole, and detecting the data of its physical and mechanical parameters; S3: placing an acoustic wave transmitting transducer and an acoustic wave receiving transducer in two symmetrical drilling points respectively, detecting the strata between the two symmetrical drilling points and generating data of acoustic wave spectra; S4: regarding the strata as a continuous medium, calculating the gravity stress values ​​of the strata at different depths by integration; S5: constructing a stratum structure model; S6: in the stratum structure model, forming a change interval with a dynamic water gushing area. The present invention provides a method for surveying the structure of coal-rock strata under water, which can predict the water gushing area of ​​the coal-rock strata under water, and reduces the problem of water inrush disasters in the process of coal mining.

Description

Technical Field

[0001] The invention belongs to the technical field of stratum surveying, and more specifically, relates to a method for surveying coal rock stratum structure under water. Background Art

[0002] In the field of coal resource development, coal mining under water has always been a very challenging task. With the continuous increase in the depth and intensity of coal mining, a large amount of coal resources are covered by water. Accurately surveying the coal rock strata structure under water is crucial to ensure safe coal mining, improve resource recovery rate and protect the water environment.

[0003] At present, there are many methods for the survey of coal and rock strata structure. In the study of the occurrence law of coal and rock strata, scholars mainly focus on the study of coalfield structure, starting from the relationship between tectonic movement and coal accumulation, and revealing the occurrence law of coal seams by analyzing factors such as regional tectonic deformation and geotectonic evolution. For example, the relevant theories of structural geology are used to analyze the structural framework of coal basins, study the influence of basin-mountain coupling on coal seams, and use the plate tectonic theory to explain the formation and evolution of coalfield structures. At the same time, in the three-dimensional exploration of the geological structure of coal and rock strata, both underground detection and water detection methods are used. Underground detection uses the difference in the properties of coal seams and surrounding rocks, and uses transient electromagnetic method, slot wave seismic, parallel electrical method, radio wave perspective technology, etc. to explore underground structures based on different physical principles. However, although these methods have their own advantages, they face many problems when applied under water. For example, the transient electromagnetic method is affected by groundwater shielding, and the accuracy of the detection results is limited; although trough wave seismic can overcome some shielding, it is restricted by the stability of the underground structure and deep detection is difficult; underwater detection is difficult to construct due to the presence of water bodies and has an impact on the ecological environment. Although there are methods such as underwater three-dimensional seismic and transient electromagnetic exploration, there are problems such as complex signal processing, high cost, and current shielding, which make it difficult to meet the detection accuracy requirements.

[0004] In terms of analysis, processing and interpretation of multi-source massive geological information, the existing data fusion and joint inversion methods have promoted the development of geological information processing technology to a certain extent. However, the accurate fusion and efficient inversion of multi-source information in complex environments under water bodies still need to be improved. The interference of water factors on information collection and processing has not been fully considered, and it is difficult to accurately obtain stratigraphic structural information. In the study of coal-rock stratigraphic structure, lithology and stress distribution, the evaluation of aquifer water richness has focused on information fusion methods and geophysical exploration methods based on the weight of multiple factors. However, the research on the water control law of pores and fracture structures of coal-rock stratigraphic formations under water bodies is not detailed enough, and there is a lack of in-depth understanding of the structural water control mechanism under the interaction between water bodies and strata. The consideration of factors related to the water-inrush area of ​​coal-rock strata under water bodies is not comprehensive enough. For example, the relationship between the prediction of the water-inrush area and the dynamic changes of the stratigraphic structure has not been fully integrated, and the model is difficult to accurately reflect the dynamic changes of the water-inrush area under the influence of engineering activities such as mining.

[0005] In summary, the existing technology has many shortcomings in the structural survey of coal rock strata under water bodies, especially in clearly reflecting the water gushing areas of coal rock strata under water bodies, which makes it difficult to effectively prevent water inrush disasters during coal mining. Summary of the invention

[0006] The purpose of the present invention is to provide a method for surveying the structure of coal and rock strata under water, which can predict the water gushing area of ​​coal and rock strata under water and reduce the problem of water inrush disasters in the process of coal mining.

[0007] To achieve the above object, the technical solution adopted by the present invention is: to provide a method for surveying coal rock strata structure under water, comprising the following steps:

[0008] S1: Divide the survey area into array grids, construct a three-dimensional coordinate system with the center of the array grid as the origin, define the X-axis and Y-axis in the vertical direction of the horizontal plane where the origin is located, define the Z-axis in the vertical direction where the origin is located, and determine the drilling point at the center point of each grid;

[0009] S2: Use drilling equipment to perform drilling operations along the drilling points in the Z-axis direction, and after drilling a hole of a preset depth, sample the rock layer in the hole, and bring the sample back to the ground to test the data of its physical and mechanical parameters;

[0010] S3: placing the acoustic wave transmitting transducer and the acoustic wave receiving transducer in two symmetrical drilling points respectively, the two symmetrical drilling points are symmetrical about the origin center, and within the same height range, detecting the stratum between the two symmetrical drilling points and generating acoustic wave spectrum data;

[0011] S4: Considering the stratum as a continuous medium, the gravity stress values ​​of the stratum at different depths are calculated by integration. , the integral formula is ,in, is the function of formation density changing with depth, is the acceleration due to gravity;

[0012] Discretize the deformation process of the stratum and analyze the strain values ​​at different time steps and spatial positions , the difference formula is ,in is the change in formation depth, and is the total depth of formation L;

[0013] S5: Physical and mechanical parameter data of multiple samples, data of multiple acoustic wave spectra, and gravity stress value data And strain value data All were input into 3D geological modeling software to construct stratigraphic structural models;

[0014] S6: Measure the hydraulic head and water storage rate of groundwater in the survey area, simulate the flow characteristics of groundwater in strata at different depths, and predict the possible water-gushing areas of groundwater in cracks and fault structures in combination with the pore structure parameters and structural characteristics in the stratigraphic structure model. In the stratigraphic structure model, determine the changing positions of cracks and faults in the strata using the time axis to form a changing interval with dynamic water-gushing areas.

[0015] In a possible implementation, in step S1, in a three-dimensional coordinate system, a plurality of radial construction lines are defined in a horizontal plane where the origin is located, and the plurality of radial construction lines are arranged radially with the origin as the intersection point, and each radial construction line passes through at least four drilling points, and the four drilling points are grouped in pairs, and each group of drilling points is arranged symmetrically with the origin as the center;

[0016] The distance between two adjacent drilling points in the same quadrant on the same radial structural line is 10 to 30 meters, and the distance between two drilling points in the same quadrant on the same radial structural line is 30 to 50 meters.

[0017] In a possible implementation, in step S2, during the drilling operation, the drilling parameters are monitored in real time, and the vertical deviation value of the drilling does not exceed ±0.5°, and the depth error does not exceed ±0.5m;

[0018] When the drilling equipment reaches the predetermined depth, the hole wall is processed to remove loose materials and impurities on the hole wall surface so that the hole wall surface roughness is less than ±1cm.

[0019] In a possible implementation, in step S2, the drilling equipment uses a core drill bit, the single drilling depth of the drilling equipment is no more than 30m, coal and rock samples are collected at different depth intervals, and no less than 5 samples are collected from each hole, and the length of the sample is 2 to 2.5m;

[0020] After the collected samples reach the ground, they are sealed and transported to the laboratory for physical and mechanical experiments:

[0021] a. Weigh and measure the sample and calculate the density of the sample, with the error controlled within ±0.5%;

[0022] b. Use a compressive strength testing machine and a tensile strength testing machine to test the uniaxial compressive strength and tensile strength of the sample. The loading rate is controlled at 0.05-0.5 mm / min and the test accuracy is within ±1%;

[0023] c. Use ultrasonic pulse method to measure the elastic modulus and Poisson's ratio of the sample. The measurement frequency range is 50-500kHz and the measurement accuracy is within ±3%;

[0024] d. The pore distribution of the sample is measured by mercury injection test. The mercury injection pressure range is 10-100MPa. The porosity measurement accuracy is within ±0.1%, and the pore size distribution measurement accuracy is within ±0.01mm.

[0025] e. Use the steady-state method or pulse decay method to measure the permeability of the sample. Nitrogen or helium is used as the gas. The permeability measurement range is 5 to 100 mD, and the test accuracy is within ±5%.

[0026] In a possible implementation, in step S3, an acoustic wave transmitting transducer and an acoustic wave receiving transducer are respectively placed in two symmetrical boreholes and synchronously lowered to multiple sampling areas in sequence to perform acoustic wave detection respectively;

[0027] The acoustic wave transmitting transducer and the acoustic wave receiving transducer are both located in the middle of the sampling area, and the acoustic wave transmitting transducer and the acoustic wave receiving transducer synchronously transmit and receive acoustic waves to generate a horizontal acoustic wave spectrum;

[0028] The acoustic wave transmitting transducer and the acoustic wave receiving transducer are respectively located at the top and the bottom of the sampling area, and the acoustic wave transmitting transducer and the acoustic wave receiving transducer synchronously transmit and receive acoustic waves to generate two inclined acoustic wave spectra respectively;

[0029] The propagation time, amplitude attenuation and phase change parameters of a horizontal acoustic wave spectrum and two inclined acoustic wave spectrums in the same symmetrical boreholes are measured. The propagation time measurement accuracy reaches ±0.05ms, the amplitude attenuation measurement accuracy reaches ±0.05dB, and the phase change measurement accuracy reaches ±0.1°. The parameters of propagation time, amplitude attenuation and phase change are used to construct the acoustic wave velocity image of the stratum where the sampling area is located through tomography technology. The tomography algorithm uses an iterative reconstruction algorithm to perform fine imaging of the stratum, and the image resolution reaches ±0.5m. According to the acoustic wave velocity image, the structural interface and distribution characteristics of the abnormal body in the stratum are identified, and the spatial morphology and extension direction of the structural stratum within the height of the sampling area are analyzed.

[0030] In a possible implementation, after completing the sonic wave detection of multiple sampling areas of two symmetrical boreholes in the same group, the sonic wave detection is alternately performed on two adjacent sampling areas of the two symmetrical boreholes in the same group;

[0031] When performing acoustic wave detection in an alternating manner, the acoustic wave transmitting transducer and the acoustic wave receiving transducer are both located in the middle of the sampling area, forming a plurality of acoustic wave spectra at the first angle and a plurality of acoustic wave spectra at the second angle, respectively. The plurality of acoustic wave spectra at the first angle are coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in the two adjacent sampling areas, respectively, and the plurality of acoustic wave spectra at the second angle are coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in the two adjacent sampling areas, respectively. After taking a weighted average of the two, the structural interface and the distribution characteristics of the abnormal body in the stratum between the two adjacent sampling areas are simulated, and the spatial morphology and extension direction of the structural stratum are analyzed.

[0032] In a possible implementation, in step S5, when constructing the stratigraphic structural model, the strata are divided into sequences of different levels, each sequence consisting of a relatively integrated set of strata, whose top and bottom interfaces are unconformities or comparable conformities, the stratigraphic sequence boundaries of the strata are determined by identifying lithological changes and sedimentary cycle marks, the locations of the coal seams and the trends of changes in the thickness of the coal seams are used for comparative tracking, and a basic framework is provided for the stratigraphic structural model, a number of three-dimensional grid units are divided within the basic framework, and a stratigraphic interface model is constructed in the three-dimensional grid unit using an interpolation method, and for each stratigraphic interface model, the interface elevation value of each three-dimensional grid unit is obtained by interpolation calculation based on the depth information of the stratigraphic interface in the drilling and sampling areas.

[0033] In a possible implementation, when dividing a number of three-dimensional grid units within the basic framework, the grid sizes are divided according to the importance of the area where the stratum is located and the stability of the area where the stratum is located:

[0034] In important and unstable areas of the formation, the grid size is (2-5) m × (2-5) m × (2-5) m;

[0035] In non-important and stable areas of the stratum, the grid size is (5-20) m×(5-20) m×(5-20) m.

[0036] In a possible implementation, in step S6, when simulating the flow characteristics of groundwater in formations at different depths, a flow equation of groundwater in coal and rock formations is established: ;

[0037] in, and are the permeability coefficients in the X-axis and Y-axis directions respectively, h is the water head, S is the water storage rate, and t is the time. When solving the flow equation, the integral transformation and numerical calculation methods in calculus are used.

[0038] In a possible implementation, in step S6, the risk level is divided according to the water gushing area, and the ratio of the hydraulic gradient of the water gushing area to the critical hydraulic gradient of the formation is calculated. When the ratio is greater than 1, it is defined as an active area, and when the ratio is less than or equal to 1, it is defined as an inactive area; the fault activity rate value is simulated, and if the fault activity rate value is greater than 1 cm / year, it is defined as an active area, and if the fault activity rate value is less than or equal to 1 cm / year, it is defined as an inactive area;

[0039] The water-gushing area where two active areas overlap is a high-risk area, the water-gushing area where an active area and an inactive area overlap is a medium-risk area, and the water-gushing area where two inactive areas overlap is a low-risk area. In the stratigraphic structure model, the dynamic change areas of high-risk areas, medium-risk areas and low-risk areas are marked with different colors.

[0040] The beneficial effect of the coal rock stratum structure survey method under water provided by the present invention is that: compared with the prior art, the method comprises the following steps S1: dividing the survey area into array grids and determining the drilling points; S2: using drilling equipment to perform drilling operations, sampling the rock strata in the borehole, and detecting the data of its physical and mechanical parameters; S3: placing the sound wave transmitting transducer and the sound wave receiving transducer in two symmetrical drilling points respectively, detecting the stratum between the two symmetrical drilling points and generating the data of the sound wave spectrum; S4: regarding the stratum as a continuous medium, calculating the gravity stress values ​​of the stratum at different depths by integration ; S5: constructing a stratigraphic structure model; S6: forming a changing interval with a dynamic water inrush area in the stratigraphic structure model. The present invention provides a method for surveying coal rock stratigraphic structures under water, which can predict the water inrush area of ​​coal rock stratigraphic structures under water, and reduces the problem of water inrush disasters in the coal mining process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, 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 only 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.

[0042] Figure 1 A flow chart of a method for surveying coal rock strata structure under water provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] See also Figure 1 Now, a method for surveying the structure of coal and rock formations under water provided by the present invention is described. The method for surveying the structure of coal and rock formations under water comprises the following steps:

[0045] S1: Divide the survey area into array grids, construct a three-dimensional coordinate system with the center of the array grid as the origin, define the X-axis and Y-axis in the vertical direction of the horizontal plane where the origin is located, define the Z-axis in the vertical direction where the origin is located, and determine the drilling point at the center point of each grid;

[0046] S2: Use drilling equipment to perform drilling operations along the drilling points in the Z-axis direction, and after drilling a hole of a preset depth, sample the rock layer in the hole, and bring the sample back to the ground to test the data of its physical and mechanical parameters;

[0047] S3: placing the acoustic wave transmitting transducer and the acoustic wave receiving transducer in two symmetrical drilling points respectively, the two symmetrical drilling points are symmetrical about the origin center, and within the same height range, detecting the stratum between the two symmetrical drilling points and generating acoustic wave spectrum data;

[0048] S4: Considering the stratum as a continuous medium, the gravity stress values ​​of the stratum at different depths are calculated by integration. , the integral formula is ,in, is the function of formation density changing with depth, is the acceleration due to gravity;

[0049] Discretize the deformation process of the stratum and analyze the strain values ​​at different time steps and spatial positions , the difference formula is ,in is the change in formation depth, and is the total depth of formation L;

[0050] S5: Physical and mechanical parameter data of multiple samples, data of multiple acoustic wave spectra, and gravity stress value data And strain value data All were input into 3D geological modeling software to construct stratigraphic structural models;

[0051] S6: Measure the hydraulic head and water storage rate of groundwater in the survey area, simulate the flow characteristics of groundwater in strata at different depths, and predict the possible water-gushing areas of groundwater in cracks and fault structures in combination with the pore structure parameters and structural characteristics in the stratigraphic structure model. In the stratigraphic structure model, determine the changing positions of cracks and faults in the strata using the time axis to form a changing interval with dynamic water-gushing areas.

[0052] Compared with the prior art, the present invention provides a method for surveying coal rock strata structure under water, which includes the following steps S1: dividing the survey area into array grids and determining the drilling points; S2: using drilling equipment to perform drilling operations, sampling the rock strata in the borehole, and detecting the data of its physical and mechanical parameters; S3: placing an acoustic wave transmitting transducer and an acoustic wave receiving transducer in two symmetrical drilling points respectively, detecting the strata between the two symmetrical drilling points and generating data of acoustic wave spectra; S4: regarding the strata as a continuous medium, calculating the gravity stress values ​​of the strata at different depths by integration. ; S5: constructing a stratigraphic structure model; S6: forming a changing interval with a dynamic water inrush area in the stratigraphic structure model. The present invention provides a method for surveying coal rock stratigraphic structures under water, which can predict the water inrush area of ​​coal rock stratigraphic structures under water, and reduces the problem of water inrush disasters in the coal mining process.

[0053] In the field of geological exploration, the three-dimensional coordinate system plays a vital role. In the three-dimensional coordinate system, multiple radial structural lines are precisely defined by the horizontal plane where the origin is located. These radial structural lines are like a precise large net, spreading out from the origin to the surrounding areas. The origin is set at the center of the estimated mineral vein enrichment area, like the center of a circle, and the radial structural lines are the radius. At least four drilling points are arranged on each radial structural line, which are the key nodes of the drilling. For example, in the first quadrant divided by one of the radial structural lines and the coordinate axis, two adjacent drill holes are located at (5, 3, 0) and (15, 3, 0), with a spacing of 10m. They are at the same height and have a moderate lateral distance, which ensures the continuity of ore sample collection in this small area. Key information will not be missed due to the long distance, and the samples will not lack representativeness due to being too close. The points in the corresponding quadrants of this line, such as (-20, 3, 0) in the second quadrant and (20, 3, 0) in the fourth quadrant, are 40m apart. This larger spacing setting takes into account the possible geological structural differences in different quadrants. One side is close to the folds of the mountain rock strata, and the other side is close to the underground river erosion area. Such a layout can comprehensively cover diverse geological environments and accurately capture key information such as the direction of the veins and changes in ore composition.

[0054] This layout brings significant advantages. On the one hand, the drilling points are arranged in pairs and symmetrically around the origin, so that the collected data can verify each other. If there is a deviation in the data such as ore hardness and mineral content obtained from the symmetrical points, the measurement error or special geological structure changes can be detected in time, which greatly improves the accuracy of the data. On the other hand, the specific spacing design of adjacent points in the same quadrant and close points in the opposite quadrant not only ensures the detailed exploration of local areas, but also takes into account the comprehensive exploration under different environments, providing a solid guarantee for the efficient and accurate exploration of the reserves and quality distribution of the ore veins, greatly improving the exploration efficiency, reducing the exploration cost, and allowing resource development to be planned in an orderly manner.

[0055] When drilling operations are started, real-time monitoring becomes a key link to ensure the accuracy of the project. Through high-precision monitoring instruments, the vertical deviation of the borehole is strictly controlled and must not exceed ±0.5°. This means that in actual operations, even a slight tilt trend can be detected and corrected in time. A slight vertical deviation may cause the collected samples to lose their scientific research value and fail to accurately reflect the formation information.

[0056] The depth error is also limited to an extremely strict range, not exceeding ±0.5m. In the early stage of mining, drilling detection requires accurate knowledge of the buried depth of the ore body. Accurate depth data is the cornerstone of the subsequent construction plan.

[0057] When the drilling equipment reaches the predetermined depth, the hole wall is subsequently processed to make the surface roughness of the hole wall less than ±1cm. The smooth and regular hole wall is conducive to the smooth installation and efficient operation of various subsequent detection equipment and support materials, and provides a relatively smooth surface for subsequent ultrasonic testing. When the ultrasonic probe is detected along the hole wall, if the hole wall roughness is too large, a large amount of irregular scattering and reflection will occur during the propagation of the ultrasonic wave, causing the signal received by the receiving end to be chaotic and difficult to accurately interpret the rock and soil information contained therein. The smooth surface of the finely processed hole wall allows the ultrasonic wave to propagate in a nearly straight line, reducing energy loss, ensuring that the detection personnel can clearly capture the reflected signal, accurately determine whether there are cracks, cavities and other defects inside the rock and soil body, and provide a reliable basis for the safety assessment of the project.

[0058] The drilling equipment uses a core barrel drill bit, which, with its unique structure, can effectively obtain core samples during the drilling process, ensuring that the collected coal and rock samples have good integrity and representativeness. In order to ensure the efficiency and accuracy of the drilling operation, the single drilling depth of the equipment is strictly limited to no more than 30m. On the one hand, a single drilling depth that is too long can easily lead to increased wear of the drill bit, reduced drilling efficiency, and increase the risk of accidents such as drill sticking; on the other hand, a reasonable drilling depth range helps to accurately collect samples at different formation depths.

[0059] During the drilling process, coal and rock samples are collected at different depth intervals according to the predetermined plan. No less than 5 samples are collected in each hole, and the length of the samples is controlled at 2 to 2.5 meters. Taking the preliminary exploration of a large coal mine as an example, in the expected coal-bearing strata within the depth range of 50m to 150m from the surface, sampling points are selected every 20m or so according to the changes in the strata. Such stratified sampling can fully reflect the various characteristics of coal and rock at different depths. These samples carry key information deep in the strata. Once the collection is completed, subsequent proper processing is crucial.

[0060] When the collected samples reach the ground, they are immediately sealed to prevent long-term contact with the outside air, which may cause physical and chemical changes such as oxidation and water loss, thus affecting the accuracy of the test data. Then, the sealed samples are quickly transported to the laboratory for a series of physical and mechanical experiments.

[0061] a. In the process of weighing and measuring samples, a high-precision electronic balance is used to accurately weigh the sample mass, and the sample density is calculated by a calculation formula based on the regular size of the sample. The error is strictly controlled within ±0.5%. Even a small weighing error or size measurement deviation may be magnified in subsequent data analysis, thereby misleading the judgment of coal rock quality.

[0062] b. Use a compressive strength tester and a tensile strength tester to test the uniaxial compressive strength and tensile strength of the sample. The loading rate must be precisely controlled within 0.05-0.5 mm / min. This range can ensure that the stress of the sample is evenly distributed during the loading process and truly reflect its strength characteristics, while preventing the sample from being instantly damaged due to excessive loading and making it impossible to obtain complete data. The test accuracy is as high as ±1%, providing a reliable basis for the evaluation of the bearing capacity of coal and rock in engineering applications.

[0063] c. When measuring the elastic modulus and Poisson's ratio of the sample using the ultrasonic pulse method, the measurement frequency range is precisely set to 50-500kHz. In this frequency range, the ultrasonic wave interacts with the internal microstructure of the coal and rock sample, and the generated reflection, refraction and other signals can be accurately captured, and then the elastic modulus and Poisson's ratio of the sample are calculated through complex algorithms. The measurement accuracy is steadily controlled within ±3%, which helps to gain a deeper understanding of the mechanical elastic characteristics of coal and rock.

[0064] d. In the mercury injection test, the mercury injection pressure range is finely adjusted to 10-100 MPa. Under this pressure span, mercury can gradually penetrate into the sample pores. By monitoring the relationship between the injection amount of mercury and the pressure change, the pore distribution of the sample can be accurately measured. The porosity accuracy can reach within ±0.1%, and the pore size distribution measurement accuracy can reach within ±0.01mm, providing high-resolution data support for the study of coal rock permeability, gas storage performance, etc.

[0065] e. Use the steady-state method or pulse decay method to measure the permeability of the sample. Nitrogen or helium is used as the gas. These two gases have small molecules and stable chemical properties. Their flow characteristics in the pores of coal and rock can accurately reflect the permeability of the sample. The permeability measurement range is 5-100mD, and the test accuracy is within ±5%, providing key parameters for engineering practices such as gas extraction and groundwater prevention in coal mining.

[0066] In the advanced stage of coal and rock geological exploration, acoustic wave detection technology plays a vital role and provides a key means for in-depth insight into the internal structure of the strata.

[0067] First, the high-precision acoustic wave transmitting transducer and acoustic wave receiving transducer are placed in two symmetrical boreholes. The selection of these two boreholes should be based on the key detection areas determined by the preliminary drilling layout and preliminary judgment of the stratum. Then, the two are synchronously controlled to descend smoothly to multiple pre-planned sampling areas in turn to start the acoustic wave detection process.

[0068] When the acoustic wave transmitting transducer and the acoustic wave receiving transducer are both precisely positioned in the middle of the sampling area, the two work together to transmit and receive acoustic waves synchronously. At this time, in a uniform medium environment, the acoustic wave propagates in a nearly straight line, and the acquired data can reflect the relatively stable stratigraphic characteristics in the middle of the area, thereby generating a horizontal acoustic wave spectrum. Next, adjust the transducer position so that the acoustic wave transmitting transducer and the acoustic wave receiving transducer are at the top and bottom of the sampling area, respectively. Start the transmitting and receiving functions synchronously again, and since the acoustic wave propagation path becomes inclined, two inclined acoustic wave spectra will be generated respectively. These two spectra scan the sampling area from different perspectives, capturing the differences in the stratigraphic changes from top to bottom, such as possible rock stratification transition zones, local loose areas and other information.

[0069] In the measurement phase, strict measurement accuracy standards are set for the propagation time, amplitude attenuation and phase change parameters of a horizontal acoustic wave spectrum and two inclined acoustic wave spectrums in the same symmetrical borehole. The propagation time measurement accuracy reaches ±0.05ms; the amplitude attenuation measurement accuracy reaches ±0.05dB, and the phase change measurement accuracy reaches ±0.1°.

[0070] Using these highly accurate parameters of propagation time, amplitude attenuation and phase change, the tomography technology is used to construct the acoustic velocity image of the stratum where the sampling area is located. In this process, the tomography algorithm uses an iterative reconstruction algorithm to perform fine imaging of the stratum, so that the final image resolution reaches a high level of ±0.5m, and can accurately present the structural interface and distribution characteristics of abnormal bodies in the stratum. Based on the acoustic velocity image, professionals can clearly identify the structural interface in the stratum, determine its type such as faults and folds, determine the distribution location of abnormal bodies such as caves and dense mineral blocks, and deeply analyze the spatial morphology of the structural stratum within the height of the sampling area, accurately grasp its morphological characteristics such as tilt, upright or curved, and the extension direction, whether it is horizontal extension, vertical penetration or oblique development at a certain angle, providing a solid basis for subsequent coal mining planning and geological disaster warning.

[0071] After the first round of sonic wave detection of multiple sampling areas of two symmetrical boreholes in the same group is completed, the next step is immediately started to alternately perform sonic wave detection on two adjacent sampling areas of the two symmetrical boreholes in the same group.

[0072] During the interlaced detection process, the acoustic wave transmitting transducer and the acoustic wave receiving transducer are controlled to be located in the middle of the sampling area. At this time, with the emission and reception of the acoustic wave, multiple acoustic wave spectra at the first angle and multiple acoustic wave spectra at the second angle are formed respectively. The spectra obtained at these two angles contain signals from different directions in the same formation area, and are closely related to the horizontal acoustic wave spectra and the inclined acoustic wave spectra in the two adjacent sampling areas.

[0073] Specifically, multiple acoustic wave spectra at the first angle are coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in two adjacent sampling areas. This coupling process is like the fusion of information puzzles from different perspectives, integrating the acoustic characteristics of the strata at various angles. Similarly, multiple acoustic wave spectra at the second angle are also coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in two adjacent sampling areas. Through such double coupling, the scattered acoustic wave data are integrated into an organic whole.

[0074] Subsequently, the weighted average of the two coupled atlas data is calculated. This mathematical processing method is not a simple arithmetic addition, but assigns corresponding weights according to the importance of the stratigraphic characteristics reflected in different atlases, thereby accurately simulating the structural interface and distribution characteristics of abnormal bodies in the strata between two adjacent sampling areas. With this simulation result, it is possible to analyze the spatial morphology of the structural strata more deeply, accurately identify whether it is a smooth transition, abrupt change, or a complex distortion; at the same time, accurately grasp its extension direction, and clarify whether it is stably extended along a certain axis or intertwined in multiple directions. Such a sophisticated advancement of the acoustic wave detection process provides richer and more accurate stratigraphic information for coal and rock geological exploration, greatly improves the level of understanding of the complex underground environment, and lays a solid data foundation for many fields such as coal mining and geological research.

[0075] In coal and rock geological exploration, constructing an accurate stratigraphic structure model is a core task.

[0076] First, the strata are finely stratified and divided into sequences of different levels. Each sequence has a unique geological significance. They are composed of a relatively integrated set of strata, and their top and bottom interfaces are very iconic, either clear unconformities or highly comparable conformities. By identifying lithological changes, starting from differences in rock composition, grain size, structural structure, etc., the signals of strata change are captured; at the same time, through sedimentary cycle marks, according to the laws of periodic repetition of sediments in the vertical direction, such as alternation of coarse-grained and fine-grained sediments, changes in color depth, etc., the sequence boundaries of the strata are determined to ensure that the definition of each sequence is accurate.

[0077] Next, we used coal seams, a highly recognizable geological element, to accurately locate the location of the coal seams and conduct in-depth analysis of the trend of coal seam thickness changes, and conduct detailed comparative tracking. Whether it is thinning, thickening, bifurcation, or pinching out of the coal seams, they are all recorded one by one, building a solid basic framework for the stratigraphic structure model, so that the model is rooted in real and reliable geological data from the beginning.

[0078] Within the established basic framework, the operation is further refined and divided into several three-dimensional grid units. These grid units are like sieves, cutting the stratigraphic space into small units that are easy to study and calculate. Subsequently, the stratigraphic interface model is constructed in the three-dimensional grid unit using the interpolation method. For each stratigraphic interface model, the interface elevation value of each three-dimensional grid unit is obtained through interpolation calculation based on the depth information of the stratigraphic interface accurately measured in the drilling and sampling areas, that is, the height coordinates are marked on each three-dimensional grid unit, so that the original stratigraphic interface is gradually visualized in three-dimensional space, clearly showing the complex forms of stratigraphic undulations and dislocations, and providing high-resolution digital maps for subsequent all-round exploration of stratigraphic structure, prediction of coal and rock distribution, and assessment of geological risks.

[0079] After the basic framework of the stratigraphic model is initially formed, the next step is to divide it into several three-dimensional grid units and customize the grid size based on the two key characteristics of the area where the stratum is located, namely its importance and stability.

[0080] In important stratigraphic areas and unstable areas, such as near fault zones with frequent geological tectonic activities, rock strata are broken, strata dislocation occurs frequently, and the geological conditions are complex; in coal-rich areas, the precise exploration of coal seams plays a decisive role in the subsequent mining benefits. Given that these areas require us to accurately capture every change, the grid size is finely set to (2-5) m×(2-5) m×(2-5) m. Taking a large coalfield that is being prepared for mining as an example, there happens to be a hidden small fault underneath the planned first mining area. After dividing this area into smaller grids, through subsequent monitoring and analysis, it is clearly found that the coal seams have a significant thinning trend near the fault, which provides a key basis for adjusting the mining plan and avoids potential economic losses and safety risks.

[0081] In non-important and stable areas of the strata, the situation is relatively simple and clear. For example, strata that are far away from mining areas, deeply buried underground, have a single geological structure, and are in a stable state for a long time have little impact on the entire exploration and development process. In order to balance computing efficiency without losing key information and reduce unnecessary data processing burden, the grid size is appropriately enlarged to (5-20) m×(5-20) m×(5-20) m. For example, in the deep boundary area of ​​the coalfield, it has been determined through preliminary exploration that there is no mining value and the geology is stable. After using a larger grid division, it is sufficient to meet the macro-level understanding needs of the stratum thickness, lithology distribution, etc. in the area. At the same time, it greatly shortens the model construction time, which speeds up and increases the efficiency of the overall exploration project.

[0082] In the field of coal and rock geological exploration, while the work of accurately constructing stratigraphic structural models is progressing steadily, in-depth research on the flow characteristics of groundwater in strata at different depths is also indispensable.

[0083] When simulating the flow characteristics of groundwater in strata at different depths, the flow equation of groundwater in coal and rock strata was established: .

[0084] in, and They are the permeability coefficients in the X-axis and Y-axis directions, respectively. These two parameters are like indicators of the width of the water vein channels in the strata, which directly determine the difficulty of groundwater penetration on different coordinate axes in the horizontal direction. The larger the permeability coefficient, the smoother the groundwater can flow in the corresponding direction. h is the water head, which represents the mechanical energy per unit weight of liquid and intuitively reflects the energy state contained in groundwater. It is usually measured in height (unit: centimeters). The difference in water head will drive groundwater to flow from high head areas to low head areas, which is one of the power sources of groundwater flow. S is the water storage rate, which characterizes the amount of water released or stored in a unit volume of aquifers when the unit head changes, and is a key measure of the water storage capacity of the stratum. t is time, which records the time course of the groundwater flow process.

[0085] The two terms on the left side of the equation respectively describe the changes in water flow in the X-axis and Y-axis directions in detail. Together, they show the adjustment of groundwater flow trend in the two-dimensional plane. The one term on the right side of the equation accurately represents the change in water head per unit time, reflecting the dynamic impact of formation water storage and release on water head over time.

[0086] In the integral transformation link, tools such as Laplace transform are often used. Laplace transform can instantly convert partial differential equations containing time variables into ordinary differential equations, simplifying the originally complex four-dimensional space-time (three-dimensional space plus time) problem into a three-dimensional space problem, which greatly reduces the difficulty of solving. After Laplace transform, the time dimension in the equation is eliminated, leaving only equations about the spatial variables and, making subsequent processing more convenient. Then enter the numerical calculation stage, usually using efficient means such as finite difference method and finite element method. Taking the finite difference method as an example, it is like cutting the continuous stratum space into a fine grid puzzle. Specifically, the solution area is discretized and differentials are replaced by differential approximations. Through this approximate transformation, the partial differential equation is converted into a set of algebraic equations that can be solved by iteration, and then the head distribution of each node is gradually calculated. The same is true for the finite element method, which divides the solution area into multiple small units (such as triangular or quadrilateral units), assumes an approximate function form of the water head in each unit, and then constructs a set of algebraic equations based on the variational principle or weighted residual method to ultimately solve the distribution of the water head.

[0087] By establishing flow equations and solving them, we can accurately depict the flow path of groundwater in strata at different depths, changes in flow velocity, and the dynamic process of its interaction with coal and rock, providing key support for many practical issues such as preventing mine water disasters and rationally planning water resource utilization, and further improving the scientificity and safety of coal and rock geological exploration and development and utilization.

[0088] In the process of coal and rock geological exploration and subsequent development, accurate insight into the risk status of water-gushing areas is like the key cornerstone of building a safety line. It is related to the success or failure of the entire project. A dual evaluation system is adopted to divide the risk levels of water-gushing areas.

[0089] First, the ratio of the hydraulic gradient in the water-gushing area to the critical hydraulic gradient of the formation is calculated. This ratio is a pressure ratio that measures the potential danger of the water-gushing area. The hydraulic gradient reflects the rate of change of energy of groundwater during the flow process, and the critical hydraulic gradient of the formation is the limit hydraulic condition that the formation can withstand. When the ratio is greater than 1, it means that the flow energy of groundwater has exceeded the tolerance threshold of the formation, and this place is defined as an active area, just like a tight bowstring, which may cause violent water-gushing at any time; when the ratio is less than or equal to 1, it indicates that the groundwater flow is still within the controllable range, and it is defined as an inactive area, which is relatively stable. At the same time, simulating the fault activity rate value is also an indispensable part. As an unstable factor in the formation, the activity rate of the fault is directly related to the risk of water-gushing. If the fault activity rate value is greater than 1cm / year, the crust moves frequently, the formation structure is easily destroyed, and the groundwater channel is disordered, which is defined as an active area; if the fault activity rate value is less than or equal to 1cm / year, the fault is relatively stable, has little impact on water-gushing, and is determined to be an inactive area.

[0090] Based on the above two evaluation dimensions, the risk level of the water-gushing area can be clearly defined. The water-gushing area where two active areas overlap is very likely to cause large-scale, sudden water-gushing disasters, posing a fatal threat to mine workers, equipment and project progress. The water-gushing area where the active area and the inactive area overlap is a medium-risk area. Although it is not as dangerous as the high-risk area, the unstable factors of groundwater and geological structure are intertwined, and we still need to remain vigilant at all times to prevent possible medium-scale water-gushing. The water-gushing area where two inactive areas overlap is a low-risk area, where the groundwater flows smoothly and the geological structure is stable, and only routine monitoring is required to ensure safety.

[0091] In order to make these risk areas clear at a glance, different colors are used to mark the dynamic changes of high-risk areas, medium-risk areas and low-risk areas in the stratigraphic structure model. For example, the eye-catching red represents high-risk areas, warning of extreme danger; yellow marks medium-risk areas; and green marks low-risk areas. In this way, whether it is geological prospectors conducting field surveys underground or engineering decision makers formulating mining plans on the ground, they can quickly grasp the risk dynamics of water-gushing areas through intuitive color markings, plan response strategies in advance, escort coal and rock geological exploration and development and utilization, and ensure that the project is steadily advancing on a safe track.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for surveying coal rock strata structure under water, characterized in that: The following steps are involved: S1: Divide the survey area into array grids, construct a three-dimensional coordinate system with the center of the array grid as the origin, define the X-axis and Y-axis in the vertical direction of the horizontal plane where the origin is located, define the Z-axis in the vertical direction where the origin is located, and determine the drilling point at the center point of each grid; S2: Use drilling equipment to perform drilling operations along the drilling points in the Z-axis direction, and after drilling a hole of a preset depth, sample the rock layer in the hole, and bring the sample back to the ground to test the data of its physical and mechanical parameters; S3: placing the acoustic wave transmitting transducer and the acoustic wave receiving transducer in two symmetrical drilling points respectively, the two symmetrical drilling points are symmetrical about the origin center, and within the same height range, detecting the stratum between the two symmetrical drilling points and generating acoustic wave spectrum data; S4: Considering the stratum as a continuous medium, the gravity stress values ​​of the stratum at different depths are calculated by integration. , the integral formula is ,in, is the function of formation density changing with depth, is the acceleration due to gravity; Discretize the deformation process of the stratum and analyze the strain values ​​at different time steps and spatial positions , the difference formula is ,in is the change in formation depth, and is the total depth of formation L; S5: Physical and mechanical parameter data of multiple samples, data of multiple acoustic wave spectra, and gravity stress value data And strain value data All were input into 3D geological modeling software to construct stratigraphic structural models; S6: Measure the hydraulic head and water storage rate of groundwater in the survey area, simulate the flow characteristics of groundwater in strata at different depths, and predict the possible water-gushing areas of groundwater in cracks and fault structures in combination with the pore structure parameters and structural characteristics in the stratigraphic structure model. In the stratigraphic structure model, determine the changing positions of cracks and faults in the strata using the time axis to form a changing interval with dynamic water-gushing areas.

2. A method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S1, in a three-dimensional coordinate system, a plurality of radial construction lines are defined in a horizontal plane where the origin is located, and the plurality of radial construction lines are arranged radially with the origin as the intersection point, and each radial construction line passes through at least four drilling points, and the four drilling points are grouped in pairs, and each group of drilling points is arranged symmetrically with the origin as the center; The distance between two adjacent drilling points in the same quadrant on the same radial structural line is 10 to 30 meters, and the distance between two drilling points in the same quadrant on the same radial structural line is 30 to 50 meters.

3. The method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S2, during the drilling operation, the drilling parameters are monitored in real time, and the vertical deviation of the drilling does not exceed ±0.5°, and the depth error does not exceed ±0.5m; When the drilling equipment reaches the predetermined depth, the hole wall is processed to remove loose materials and impurities on the hole wall surface so that the hole wall surface roughness is less than ±1cm.

4. The method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S2, the drilling equipment uses a core barrel drill bit, the single drilling depth of the drilling equipment is no more than 30m, coal and rock samples are collected at different depth intervals, and no less than 5 samples are collected from each hole, and the length of the sample is 2 to 2.5m; After the collected samples reach the ground, they are sealed and transported to the laboratory for physical and mechanical experiments: a. Weigh and measure the sample and calculate the density of the sample, with the error controlled within ±0.5%; b. Use a compressive strength testing machine and a tensile strength testing machine to test the uniaxial compressive strength and tensile strength of the sample. The loading rate is controlled at 0.05-0.5 mm / min and the test accuracy is within ±1%; c. Use ultrasonic pulse method to measure the elastic modulus and Poisson's ratio of the sample. The measurement frequency range is 50-500kHz and the measurement accuracy is within ±3%; d. The pore distribution of the sample is measured by mercury injection test. The mercury injection pressure range is 10-100MPa. The porosity measurement accuracy is within ±0.1%, and the pore size distribution measurement accuracy is within ±0.01mm. e. Use the steady-state method or pulse decay method to measure the permeability of the sample. Nitrogen or helium is used as the gas. The permeability measurement range is 5 to 100 mD, and the test accuracy is within ±5%.

5. The method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S3, the acoustic wave transmitting transducer and the acoustic wave receiving transducer are respectively placed in two symmetrical boreholes and synchronously lowered to multiple sampling areas in sequence to perform acoustic wave detection respectively; The acoustic wave transmitting transducer and the acoustic wave receiving transducer are both located in the middle of the sampling area, and the acoustic wave transmitting transducer and the acoustic wave receiving transducer synchronously transmit and receive acoustic waves to generate a horizontal acoustic wave spectrum; The acoustic wave transmitting transducer and the acoustic wave receiving transducer are respectively located at the top and the bottom of the sampling area, and the acoustic wave transmitting transducer and the acoustic wave receiving transducer synchronously transmit and receive acoustic waves to generate two inclined acoustic wave spectra respectively; The propagation time, amplitude attenuation and phase change parameters of a horizontal acoustic wave spectrum and two inclined acoustic wave spectrums in the same symmetrical boreholes are measured. The propagation time measurement accuracy reaches ±0.05ms, the amplitude attenuation measurement accuracy reaches ±0.05dB, and the phase change measurement accuracy reaches ±0.1°. The parameters of propagation time, amplitude attenuation and phase change are used to construct the acoustic wave velocity image of the stratum where the sampling area is located through tomography technology. The tomography algorithm uses an iterative reconstruction algorithm to perform fine imaging of the stratum, and the image resolution reaches ±0.5m. According to the acoustic wave velocity image, the structural interface and distribution characteristics of the abnormal body in the stratum are identified, and the spatial morphology and extension direction of the structural stratum within the height of the sampling area are analyzed.

6. A method for surveying coal and rock strata structure under water as claimed in claim 5, characterized in that: After completing the sonic wave detection of multiple sampling areas of two symmetrical boreholes in the same group, alternately perform sonic wave detection on two adjacent sampling areas of the two symmetrical boreholes in the same group; When performing acoustic wave detection in an alternating manner, the acoustic wave transmitting transducer and the acoustic wave receiving transducer are both located in the middle of the sampling area, forming a plurality of acoustic wave spectra at the first angle and a plurality of acoustic wave spectra at the second angle, respectively. The plurality of acoustic wave spectra at the first angle are coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in the two adjacent sampling areas, respectively, and the plurality of acoustic wave spectra at the second angle are coupled with the horizontal acoustic wave spectra and the inclined acoustic wave spectra in the two adjacent sampling areas, respectively. After taking a weighted average of the two, the structural interface and the distribution characteristics of the abnormal body in the stratum between the two adjacent sampling areas are simulated, and the spatial morphology and extension direction of the structural stratum are analyzed.

7. A method for surveying coal and rock strata structure under water as claimed in claim 1, characterized in that: In step S5, when constructing the stratigraphic structural model, the strata are divided into sequences of different levels, each sequence consisting of a relatively integrated set of strata, whose top and bottom interfaces are unconformities or comparable conformities, and the stratigraphic sequence boundaries of the strata are determined by identifying lithological changes and sedimentary cycle marks, and the location of the coal seam and the trend of the change in the thickness of the coal seam are used for comparative tracking to provide a basic framework for the stratigraphic structural model. Several three-dimensional grid units are divided within the basic framework, and a stratigraphic interface model is constructed in the three-dimensional grid unit using an interpolation method. For each stratigraphic interface model, the interface elevation value of each three-dimensional grid unit is obtained by interpolation calculation based on the depth information of the stratigraphic interface in the drilling and sampling areas.

8. A method for surveying coal and rock strata structure under water as claimed in claim 7, characterized in that: When dividing several three-dimensional grid units within the basic framework, the grid size is divided according to the importance and stability of the area where the stratum is located: In important and unstable areas of the formation, the grid size is (2-5) m × (2-5) m × (2-5) m; In non-important and stable areas of the stratum, the grid size is (5-20) m×(5-20) m×(5-20) m.

9. A method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S6, when simulating the flow characteristics of groundwater in strata at different depths, the flow equation of groundwater in coal and rock strata is established: ; in, and are the permeability coefficients in the X-axis and Y-axis directions respectively, h is the water head, S is the water storage rate, and t is the time. When solving the flow equation, the integral transformation and numerical calculation methods in calculus are used.

10. The method for surveying coal rock strata structure under water as claimed in claim 1, characterized in that: In step S6, the risk level is divided according to the water-gushing area, and the ratio of the hydraulic gradient of the water-gushing area to the critical hydraulic gradient of the formation is calculated. When the ratio is greater than 1, it is defined as an active area, and when the ratio is less than or equal to 1, it is defined as an inactive area; the fault activity rate value is simulated, and if the fault activity rate value is greater than 1 cm / year, it is defined as an active area, and if the fault activity rate value is less than or equal to 1 cm / year, it is defined as an inactive area; The water-gushing area where two active areas overlap is a high-risk area, the water-gushing area where an active area and an inactive area overlap is a medium-risk area, and the water-gushing area where two inactive areas overlap is a low-risk area. In the stratigraphic structure model, the dynamic change areas of high-risk areas, medium-risk areas and low-risk areas are marked with different colors.

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