A drilling cuttings-based coal reservoir geological information prediction method

Abstract

This invention discloses a method for predicting coal reservoir geological information based on drill cuttings. It fully utilizes the directional drilling process in coal mines to obtain the pore structure characteristics of coal seams at different depths in different boreholes. Simultaneously, it predicts the amount of gas emitted from drill cuttings during drilling. Data integration yields the pore structure and gas occurrence information of the target coal seam along the entire drilling path. This method not only achieves full coverage testing along the drilling path but also reduces errors caused by the anisotropy of coal seam occurrence, enabling refined detection of coal reservoir information. Furthermore, this invention uses interpolation methods to obtain the porosity and permeability distribution of different layers within the detection range. Combined with an established mathematical model, it calculates and analyzes the gas occurrence and flow patterns of the coal seam within the detection range, ultimately predicting the gas content and distribution within the entire coal seam structure. This facilitates timely guidance for subsequent coalbed methane resource exploration and development.

Description

Technical Field

[0001] This invention relates to a method for predicting geological information of coal reservoirs based on drill cuttings, which is mainly applicable to the technical fields of coal seam geophysical exploration and transparent mine construction. Background Technology

[0002] Chinese coal seams generally exhibit characteristics of "high content, high ground stress, high gas pressure, and low permeability." Therefore, it is necessary to conduct advanced exploration of their geological characteristics before coal resource mining. Existing advanced exploration methods generally employ geophysical exploration and drilling. Geophysical exploration is based on the differences in the physical properties of coal and rock, such as density, magnetization, conductivity, and radioactivity. Specialized equipment is used to detect the distribution and variation characteristics of the physical fields of different geological bodies. Combined with known geological data, analysis can determine the geological structure, hydrogeological conditions, and adverse geological bodies in the area. This method has the advantages of lightweight equipment and high efficiency, but it is easily affected by external environmental interference and has limitations in the accuracy of measuring instruments. Drilling, on the other hand, uses drilling rigs to drill into the coal seam and extract samples. By monitoring various parameters during the drilling process and analyzing the samples, the distribution patterns of the coal seam's occurrence state can be determined. It has advantages such as high accuracy, strong intuitiveness, and wide applicability.

[0003] Existing methods for determining pore structure and gas occurrence information typically rely on conventional laboratory experiments. However, from field sampling to the completion of laboratory testing, these conventional methods are not only costly but also often lag behind coalbed methane resource exploration and development practices due to their long testing cycles (generally 1-2 months), preventing them from providing timely guidance for exploration and development. During drilling, a large amount of drill cuttings is generated as the drilling depth increases. These cuttings contain rich information on pore structure and gas occurrence, which is closely related to coal seam gas content, coal seam gas pressure, coal seam permeability coefficient, coal seam fractures, and geological structures.

[0004] Currently, there is limited research on in-situ testing information in coal mines. Therefore, there is an urgent need for a new method that can quickly and accurately predict coal seam pore structure and gas occurrence information by obtaining drill cuttings in situ underground and testing them. This is the research direction required by this invention. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for predicting coal reservoir geological information based on drill cuttings. By obtaining drill cuttings in situ underground and testing them using low-field nuclear magnetic resonance (NMR) detection technology, the pore structure and gas occurrence information of the coal seam can be predicted quickly and accurately.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a method for predicting coal reservoir geological information based on drill cuttings, the specific steps of which are as follows:

[0007] Step 1: Determine the parameters and layout scheme of cross-layer boreholes based on the occurrence conditions of coal and rock strata and the spatial stratigraphic relationship between the roadway and the coal seam.

[0008] Step 2: Drill the first cross-layer borehole from the roadway into the target coal seam according to the cross-layer borehole parameters and layout plan determined in Step 1. Stop drilling when the drill bit reaches the critical point between the target coal seam and the rock strata. Use clean water to clean the cross-layer borehole and remove the rock cuttings.

[0009] Step 3: Install a T-joint at the opening of the first cross-layer borehole. Start the drilling rig and pass the drill bit through the T-joint to continue drilling towards the target coal seam from the first cross-layer borehole in Step 2. At the same time, connect the remaining end of the T-joint to the blowout preventer (BOP). Stop drilling when the first cross-layer borehole has completed the length of one drill rod in the target coal seam and a second drill rod needs to be added. During the drilling process, coal dust, water, and gas generated are discharged to the BOP. The coal dust and water are separated in the BOP under the action of gravity. The coal dust falls into the collector for collection. The gas generated in the borehole enters the gas parameter test tube through the BOP. The gas concentration sensor and gas flow meter monitor the gas concentration data and gas flow data in the gas parameter test tube in real time. The data is uploaded to the PLC controller once per second, and finally the gas is transported to the underground gas extraction pipeline.

[0010] Step 4: The collected coal dust is subjected to multi-stage sieving. Then, coal dust conforming to the target particle size range is piled up. The T2 relaxation distribution of the coal dust pile is obtained using a portable nuclear magnetic resonance (NMR) spectrometer. A surface relaxation rate characterization model for the coal dust pile is constructed, and combined with the obtained T2 relaxation distribution, the surface relaxation rate range is calculated. Next, the T2 relaxation spectrum is quantized into an absolute pore size distribution curve to obtain the basic occurrence parameters of the first through-layer borehole within the length of the first drill rod in the target coal seam. These parameters include the mean pore size distribution r1 and the NMR porosity. and nuclear magnetic permeability k1;

[0011] Step 5: The drill bit continues drilling deeper into the target coal seam along the direction of the first cross-layer borehole until the length of the second drill rod is completed. Drilling stops when this point is reached. Steps 3 and 4 are repeated to monitor gas data during the drilling of the second drill rod and to process coal cuttings. The basic occurrence parameters of the first cross-layer borehole within the target coal seam within the length of the second drill rod are obtained, including the average pore size distribution r² and nuclear magnetic resonance porosity. And nuclear magnetic permeability k2; after completion, continue drilling the first cross-layer borehole, and then complete the third, fourth and so on, and obtain the basic storage parameters and gas monitoring data within the drilling range of each drill rod; until the designed length of the first cross-layer borehole in the target coal seam is reached, the construction and data acquisition process of the first cross-layer borehole is completed;

[0012] Step 6: Construct each cross-layer borehole in the order of the layout plan determined in Step 1. Repeat Steps 2 to 5 for each cross-layer borehole until the construction of all cross-layer boreholes and the data acquisition process are completed.

[0013] Step 7: Based on the gas concentration data and gas flow data corresponding to each of the cross-layer drilling processes obtained in Step 6, establish a mathematical separation model, use the mathematical separation model to calculate the data of each cross-layer drilling, and obtain the gas occurrence law and gas flow law in the region according to the construction sequence of each cross-layer drilling.

[0014] Step 8: Based on the data of all cross-layer boreholes obtained in Step 6 (including gas concentration data, gas flow rate data, average pore size distribution, NMR porosity and NMR permeability), arrange them according to the construction sequence of each cross-layer borehole and the construction sequence of each drill rod in the same cross-layer borehole. Then, use the interpolation method to iteratively calculate the arranged data to obtain the pore-permeability space distribution within the coal seam structure.

[0015] Step 9: Based on the gas occurrence and flow patterns obtained in Step 7, and the pore-permeability space distribution within the coal seam structure obtained in Step 8, predict the gas content and occurrence distribution within the coal seam structure, thereby providing a basis for optimizing intelligent gas extraction.

[0016] Furthermore, the specific parameters for the cross-layer drilling in step one are as follows: the diameter of the cross-layer drilling is 75-90 mm, and the designed length of the cross-layer drilling within the target coal seam is L.

[0017] Furthermore, the arrangement scheme for the cross-layer drilling in step one is as follows: determine the number of cross-layer drilling holes and determine the construction sequence of each cross-layer drilling hole.

[0018] Furthermore, all the drilling holes are constructed using water drilling, and multiple water filter holes are arranged on the bottom and surrounding walls of the blowout preventer to separate coal dust and water.

[0019] Furthermore, in step four, the multi-stage screening specifically involves transferring coal dust onto a screening device for three-stage screening. The mesh sizes for the first, second, and third stages of screening are 4–6 mm, 3–5 mm, and 1–3 mm, respectively. The sample container used for accumulating the coal dust has the following dimensions: The cylinder body is made of hydrogen-free PEEK material.

[0020] Furthermore, the establishment of the mathematical separation model in step seven specifically involves:

[0021] ①The average total gas emission during the drilling of the i-th drill pipe is: the overall gas occurrence characteristics of the coal body traversed from the borehole opening to the drill bit when the borehole reaches the i-th drill pipe, including the sum of coal cuttings, the amount of gas desorbed from the coal body, and the amount of free gas transported from fractures. The calculation formula is:

[0022]

[0023] In the formula, C represents the average total gas emission during the drilling process of the i-th drill pipe; ij Let Q be the borehole gas concentration at time j, in %; ij Let m be the gas flow rate at time j. 3 / min; n is the number of data samples taken during the period from the start to the end of drilling the i-th drill pipe;

[0024] ② The average gas emission from the coal wall of the i-th drill pipe (i.e., the average gas emission during the period of drilling stoppage after removing coal cuttings and adding drill pipes) is calculated as follows: When drilling reaches the i-th drill pipe, the amount of gas desorbed from the coal body and the amount of free gas transported from the fractures along the path from the borehole opening to the drill bit are calculated using the following formula:

[0025]

[0026] In the formula, C represents the average gas emission from the borehole wall during the drilling process of the i-th drill pipe; ik Q represents the methane concentration in the borehole at time k, in %; ik Let m be the gas flow rate at time k. 3 / min; m is the number of data samples taken during the i-th drill pipe's downtime;

[0027] ③ The average gas emission from drill cuttings in the coal seam where the i-th drill rod is located is: the amount of gas desorption from drill cuttings generated during the drilling process from the i-th drill rod to the (i-1)-th drill rod when the borehole reaches the i-th drill rod. It reflects the gas content of the coal seam in that local area, and the calculation formula is:

[0028]

[0029] In the formula, The average gas emission rate of drill cuttings in the coal seam where the i-th drill pipe is located; The average comprehensive gas emission intensity of the borehole during the drilling process of the i-th drill pipe; It represents the average gas emission from the borehole coal wall during the drilling process of the (i-1)th drill rod.

[0030] Furthermore, the relaxation rate characterization model for the coal dust accumulation surface constructed in step four is specifically as follows:

[0031]

[0032] In the formula, T2 is the nuclear magnetic resonance relaxation value, in milliseconds; T 2b For volume relaxation, ms; w p The effective average size of the coal dust is in mm; Nuclear magnetic resonance porosity;

[0033] The surface relaxation rate range was calculated using a surface relaxation rate characterization model for coal dust accumulations combined with the T2 relaxation distribution of coal dust accumulations. Then, based on... The obtained NMR relaxation values ​​are converted into absolute pore size r, and Fs is the pore shape factor; thus forming an absolute pore size distribution curve.

[0034] Furthermore, the specific process of arranging and obtaining the spatial distribution of pore seepage in step six is ​​as follows: The sequence number of the first through-layer borehole is set as b1, and the borehole is assigned numbers 1, 2…k according to the construction sequence of each drill rod, thereby obtaining the spatial coordinates of the construction sections of each drill rod as (x1, y1, z…k). 1k According to this borehole location definition rule, the spatial coordinates of the drill rod sections of the i-th borehole, following the construction sequence of cross-layer drilling, are (x...). i ,y i ,z ik The data of each section of coal cuttings in each cross-layer borehole after arrangement are iteratively calculated using the variation function and Kriging estimation method to obtain the porosity distribution within the coal seam structure.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] (1) This invention makes full use of the directional drilling process in coal mines. It takes the coal cuttings generated by each drill rod during the drilling process of each cross-layer borehole as the research object. It uses nuclear magnetic resonance technology to test the coal cuttings accumulation, which can obtain the pore structure characteristics of coal seams at different drilling depths in different boreholes. At the same time, gas flow meters and methane sensors are used to monitor the gas flow during the drilling process of each cross-layer borehole, and the amount of gas emitted from the drill cuttings during the drilling process is predicted. By integrating the data with the length of each drill rod during the drilling process, the pore structure and gas occurrence information of the target coal seam along the entire drilling process can be obtained. This not only achieves full coverage testing along the drilling process, but also reduces the error caused by the anisotropy of coal seam occurrence, and achieves refined detection of coal reservoir information.

[0037] (2) The method of the present invention can realize the in-situ testing of the pore structure and gas occurrence information of coal seams underground, reducing the cumbersome and time-consuming process of sampling on site and testing indoors. Compared with existing testing methods, the present invention not only shortens the testing time, but also eliminates the need for additional construction through coal dust testing. It can be achieved by using the underground cross-layer drilling process, thus not only shortening the testing time but also reducing the testing cost, making it easy to promote and use underground.

[0038] (3) This invention uses interpolation to obtain the porosity and permeability distribution of different layers of coal seam within the detection range, and combines the established mathematical model to calculate and analyze the gas occurrence law and gas flow law of coal seam within the detection range. Finally, it realizes the prediction of gas content and occurrence distribution in the entire coal seam structure, which facilitates timely guidance for subsequent coalbed methane resource exploration and development.

[0039] (4) This invention utilizes a portable nuclear magnetic resonance spectrometer to perform in-situ testing of coal dust information, which can promptly obtain coal seam occurrence information and save a lot of manpower and material resources. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the layout of the drilling holes for construction according to the present invention.

[0041] In the diagram: 1-Drill bit, 2-Drill rod, 3-Sealing section, 4-Tunnel sidewall, 5-Tee connector, 6-Drilling rig, 7-Blowout preventer, 8-Valve, 9-Gas flow meter, 10-Gas concentration sensor, 11-Downhole gas extraction pipeline, 12-PLC controller, 13-Drill cuttings collection port, 14-Gas parameter testing pipe. Detailed Implementation

[0042] The present invention will be further described below.

[0043] like Figure 1 As shown, the specific steps of the present invention are as follows:

[0044] Step 1: Based on the occurrence conditions of the coal and rock strata and the spatial relationship between the roadway and the coal seam, determine the parameters and layout scheme of the cross-strata boreholes; the specific parameters of the cross-strata boreholes are: the borehole diameter is 75-90mm, and the designed length of the cross-strata borehole within the target coal seam is L; the specific layout scheme of the cross-strata boreholes is: determine the number of cross-strata boreholes and determine the construction sequence of each cross-strata borehole; all cross-strata boreholes are drilled using the water drilling method.

[0045] Step 2: Drill the first cross-layer borehole from the sidewall 4 of the roadway to the target coal seam according to the cross-layer borehole parameters and layout scheme determined in Step 1. Stop drilling when the drill bit 1 reaches the critical point between the target coal seam and the rock strata. Clean the cross-layer borehole with clean water and remove the rock cuttings.

[0046] Step 3: Install a T-joint 5 at the opening of the first cross-layer borehole. Start the drilling rig 6 and pass the drill bit through the T-joint 5 to continue drilling towards the target coal seam from the first cross-layer borehole in Step 2. At the same time, connect the remaining end of the T-joint 5 to the blowout preventer (BOP). Drilling continues until the first cross-layer borehole has completed the drilling of one drill rod length within the target coal seam and a second drill rod is needed. Drilling is stopped when this is done. Coal dust, water, and gas generated during drilling are discharged to the BOP. The coal dust and water are separated within the BOP under gravity, and the coal dust falls into a collector for collection. Gas generated in the borehole enters the gas parameter testing tube 14 through the BOP. The gas concentration sensor 10 and the gas flow meter 9 monitor the gas concentration and gas flow data in the gas parameter testing tube 14 in real time. The data is uploaded to the PLC controller 12 once per second, and finally the gas is transported to the underground gas extraction pipeline 11. The above-mentioned BOP is an existing structure. Figure 1 As shown, it includes a blowout preventer (BOP) chamber 7, a gas parameter testing tube 14, and a PLC controller 12. The BOP chamber 7 has an inlet at the upper end, a drill cuttings collection port 13 at the lower end, and a gas outlet on the side. The inlet is connected to the remaining port of a tee connector 5 and is equipped with a valve 8 to control the connection between the BOP and the borehole. A collector is provided at the lower part of the drill cuttings collection port 13 to collect coal cuttings after they enter the BOP chamber 7. The gas outlet is connected to one end of the gas parameter testing tube 14, and the other end of the gas parameter testing tube 14 is connected to the underground gas extraction pipeline 11. The gas parameter testing tube 14 is equipped with gas... The concentration sensor 10 and the gas flow meter 9 are used to obtain the gas concentration data and gas flow rate in the gas parameter test tube 14 when the gas generated by drilling and coal dust enters the gas parameter test tube 14 through the blowout preventer 7. The PLC controller 12 is connected to the gas concentration sensor 10 and the gas flow meter 9 to obtain the data monitored by both for subsequent analysis and processing. Multiple water filter holes are arranged on the four walls near the bottom of the blowout preventer 7 to discharge the water discharged from the drilling through the water filter holes, thereby achieving effective separation of coal dust and water.

[0047] Step 4: Perform multi-stage sieving on the collected coal dust. Specifically, transfer the coal dust to a sieve for three-stage sieving. The mesh sizes for the first, second, and third stages are 4–6 mm, 3–5 mm, and 1–3 mm, respectively. Then, select coal dust that meets the target particle size range (i.e., 0.5–5 mm) for stockpiling. The sample container used for stockpiling the coal dust has the following dimensions: The cylinder is made of hydrogen-free PEEK material; the T2 relaxation distribution of the coal dust accumulation was obtained using a portable nuclear magnetic resonance spectrometer; a surface relaxation rate characterization model for the coal dust accumulation was constructed, specifically as follows:

[0048]

[0049] In the formula, T2 is the nuclear magnetic resonance relaxation value, in milliseconds; T 2b For volume relaxation, ms; w p The effective average size of the coal dust is in mm; Nuclear magnetic resonance porosity;

[0050] The surface relaxation rate range was calculated using a surface relaxation rate characterization model for coal dust accumulations combined with the T2 relaxation distribution of coal dust accumulations. Then, based on... The obtained nuclear magnetic resonance relaxation values ​​are converted into absolute pore size r, and Fs is the pore shape factor; thus, an absolute pore size distribution curve is formed, and the basic occurrence parameters of the first cross-layer borehole within the length of the first drill rod in the target coal seam are obtained, including the mean pore size distribution r1 and nuclear magnetic resonance porosity. and nuclear magnetic permeability k1;

[0051] The aforementioned portable nuclear magnetic resonance spectrometer employs low-field nuclear magnetic resonance detection technology, which is an emerging detection technology. It inverts full-scale pore information by utilizing the relaxation behavior of 1H protons within the pore structure. Using this nuclear magnetic resonance detection technology, important coal seam parameters such as porosity, permeability, percentage of movable fluid, and pore size distribution can be obtained rapidly, in situ, and non-destructively.

[0052] Step 5: The drill bit continues drilling deeper into the target coal seam along the direction of the first cross-layer borehole until the length of the second drill rod is completed. Drilling stops when this point is reached. Steps 3 and 4 are repeated to monitor gas data during the drilling of the second drill rod and to process coal cuttings. The basic occurrence parameters of the first cross-layer borehole within the target coal seam within the length of the second drill rod are obtained, including the average pore size distribution r² and nuclear magnetic resonance porosity. And nuclear magnetic permeability k2; after completion, continue drilling the first cross-layer borehole, and then complete the third, fourth and so on, and obtain the basic storage parameters and gas monitoring data within the drilling range of each drill rod 2; until the designed length of the first cross-layer borehole in the target coal seam is reached, the construction and data acquisition process of the first cross-layer borehole is completed;

[0053] Step 6: Construct each cross-layer borehole in the order of the layout plan determined in Step 1. Repeat Steps 2 to 5 for each cross-layer borehole until the construction of all cross-layer boreholes and the data acquisition process are completed.

[0054] Step 7: Based on the gas concentration and gas flow rate data corresponding to each of the cross-layer drilling processes obtained in Step 6, establish a mathematical separation model, specifically as follows:

[0055] ①The average total gas emission during the drilling of the i-th drill pipe is: the overall gas occurrence characteristics of the coal body traversed from the borehole opening to the drill bit when the borehole reaches the i-th drill pipe, including the sum of coal cuttings, the amount of gas desorbed from the coal body, and the amount of free gas transported from fractures. The calculation formula is:

[0056]

[0057] In the formula, C represents the average total gas emission during the drilling process of the i-th drill pipe; ij Let Q be the borehole gas concentration at time j, in %; ij Let m be the gas flow rate at time j. 3 / min; n is the number of data samples taken during the period from the start to the end of drilling the i-th drill pipe;

[0058] ② The average gas emission from the coal wall of the i-th drill pipe (i.e., the average gas emission during the period of drilling stoppage after removing coal cuttings and adding drill pipes) is calculated as follows: When drilling reaches the i-th drill pipe, the amount of gas desorbed from the coal body and the amount of free gas transported from the fractures along the path from the borehole opening to the drill bit are calculated using the following formula:

[0059]

[0060] In the formula, C represents the average gas emission from the borehole wall during the drilling process of the i-th drill pipe; ik Q represents the methane concentration in the borehole at time k, in %; ik Let m be the gas flow rate at time k. 3 / min; m is the number of data samples taken during the i-th drill pipe's downtime;

[0061] ③ The average gas emission from drill cuttings in the coal seam where the i-th drill rod is located is: the amount of gas desorption from drill cuttings generated during the drilling process from the i-th drill rod to the (i-1)-th drill rod when the borehole reaches the i-th drill rod. It reflects the gas content of the coal seam in that local area, and the calculation formula is:

[0062]

[0063] In the formula, The average gas emission rate of drill cuttings in the coal seam where the i-th drill pipe is located; The average comprehensive gas emission intensity of the borehole during the drilling process of the i-th drill pipe; The average gas emission from the borehole wall during the drilling process of the (i-1)th drill rod;

[0064] The data for each cross-layer borehole were calculated based on the above formulas, and the gas occurrence and flow patterns within the area were obtained according to the construction sequence of each cross-layer borehole.

[0065] Step 8: Based on the data of all cross-layer boreholes obtained in Step 6 (including gas concentration data, gas flow rate data, average pore size distribution, NMR porosity, and NMR permeability), arrange the data according to the construction sequence of each cross-layer borehole and the construction sequence of each drill rod in the same cross-layer borehole. Then, use interpolation to iteratively calculate the arranged data to obtain the spatial distribution of pores and permeability within the coal seam structure. Specifically, set the sequence number of the first cross-layer borehole as b1, and assign the numbers 1, 2, ..., k to each drill rod in the borehole according to their construction sequence, thus obtaining the spatial coordinates of the construction sections of each drill rod as (x1, y1, z). 1k According to this borehole location definition rule, the spatial coordinates of the drill rod sections of the i-th borehole, following the construction sequence of cross-layer drilling, are (x...). i ,y i ,z ik The data of each section of coal cuttings in each cross-layer borehole after arrangement are iteratively calculated using the variation function and Kriging estimation method to obtain the porosity distribution within the coal seam structure.

[0066] Step 9: Based on the gas occurrence and flow patterns obtained in Step 7, and the pore-permeability space distribution within the coal seam structure obtained in Step 8, predict the gas content and occurrence distribution within the coal seam structure, thereby providing a basis for optimizing intelligent gas extraction.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for predicting coal reservoir geological information based on drill cuttings, characterized in that, The specific steps are as follows: Step 1: Determine the parameters and layout scheme of cross-layer boreholes based on the occurrence conditions of coal and rock strata and the spatial stratigraphic relationship between the roadway and the coal seam. Step 2: Drill the first cross-layer borehole from the roadway into the target coal seam according to the cross-layer borehole parameters and layout plan determined in Step 1. Stop drilling when the drill bit reaches the critical point between the target coal seam and the rock strata. Use clean water to clean the cross-layer borehole and remove the rock cuttings. Step 3: Install a T-joint at the opening of the first cross-layer borehole. Start the drilling rig and pass the drill bit through the T-joint to continue drilling towards the target coal seam from the first cross-layer borehole in Step 2. At the same time, connect the remaining end of the T-joint to the blowout preventer (BOP). Stop drilling when the first cross-layer borehole has completed the length of one drill rod in the target coal seam and a second drill rod needs to be added. During the drilling process, coal dust, water, and gas generated are discharged to the BOP. The coal dust and water are separated in the BOP under the action of gravity. The coal dust falls into the collector for collection. The gas generated in the borehole enters the gas parameter test tube through the BOP. The gas concentration sensor and gas flow meter monitor the gas concentration data and gas flow data in the gas parameter test tube in real time. The data is uploaded to the PLC controller once per second, and finally the gas is transported to the underground gas extraction pipeline. Step 4: The collected coal dust is subjected to multi-stage sieving. Then, coal dust conforming to the target particle size range is piled up. The T2 relaxation distribution of the coal dust pile is obtained using a portable nuclear magnetic resonance (NMR) spectrometer. A surface relaxation rate characterization model of the coal dust pile is constructed, and combined with the obtained T2 relaxation distribution, the surface relaxation rate range is calculated. Next, the T2 relaxation spectrum is quantized into an absolute pore size distribution curve to obtain the basic occurrence parameters of the first through-layer borehole within the length of the first drill rod in the target coal seam. These parameters include the mean pore size distribution r1 and the NMR porosity. and nuclear magnetic resonance permeability k1; Step 5: The drill bit continues drilling deeper into the target coal seam along the direction of the first cross-layer borehole until the length of the second drill rod is completed. Drilling stops when this point is reached. Steps 3 and 4 are repeated to monitor gas data during the drilling of the second drill rod and to process coal cuttings. The basic occurrence parameters of the first cross-layer borehole within the target coal seam within the length of the second drill rod are obtained, including the average pore size distribution r² and nuclear magnetic resonance porosity. And nuclear magnetic permeability k2; after completion, continue drilling the first cross-layer borehole, and then complete the third, fourth and so on, and obtain the basic storage parameters and gas monitoring data within the drilling range of each drill rod; until the designed length of the first cross-layer borehole in the target coal seam is reached, the construction and data acquisition process of the first cross-layer borehole is completed; Step 6: Construct each cross-layer borehole in the order of the layout plan determined in Step 1. Repeat Steps 2 to 5 for each cross-layer borehole until the construction of all cross-layer boreholes and the data acquisition process are completed. Step 7: Based on the gas concentration data and gas flow data corresponding to each of the cross-layer drilling processes obtained in Step 6, establish a mathematical separation model, use the mathematical separation model to calculate the data of each cross-layer drilling, and obtain the gas occurrence law and gas flow law in the region according to the construction sequence of each cross-layer drilling. Step 8: Based on the data of all cross-layer boreholes obtained in Step 6, arrange them according to the construction sequence of each cross-layer borehole and the construction sequence of each drill rod in the same cross-layer borehole. Then, use the interpolation method to iteratively calculate the arranged data to obtain the distribution of pore seepage space within the coal seam structure. Step 9: Based on the gas occurrence and flow patterns obtained in Step 7, and the pore-permeability space distribution within the coal seam structure obtained in Step 8, predict the gas content and occurrence distribution within the coal seam structure, thereby providing a basis for optimizing intelligent gas extraction.

2. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The specific parameters for the cross-layer drilling in step one are as follows: the diameter of the cross-layer drilling is 75-90mm, and the designed length of the cross-layer drilling within the target coal seam is L.

3. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The specific arrangement scheme for the cross-layer drilling in step one is as follows: determine the number of cross-layer drilling holes and the construction sequence of each cross-layer drilling hole.

4. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, All the drilling through the layers was carried out using water drilling.

5. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The multi-stage screening in step four specifically involves transferring coal dust onto a screening device for three-stage screening. The mesh sizes for the first, second, and third stages of screening are 4–6 mm, 3–5 mm, and 1–3 mm, respectively. The sample container used for stockpiling the coal dust has the following dimensions: The cylinder body is made of hydrogen-free PEEK material.

6. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The specific steps in step seven of establishing the mathematical separation model are as follows: ①The average total gas emission during the drilling of the i-th drill pipe is: the overall gas occurrence characteristics of the coal body traversed from the borehole opening to the drill bit when the borehole reaches the i-th drill pipe, including the sum of coal cuttings, the amount of gas desorbed from the coal body, and the amount of free gas transported from fractures. The calculation formula is: In the formula, C represents the average total gas emission during the drilling process of the i-th drill pipe; ij Let Q be the borehole gas concentration at time j, in %; ij Let m be the gas flow rate at time j. 3 / min; n is the number of data samples taken during the period from the start to the end of drilling the i-th drill pipe; ② The average gas emission from the coal wall of the i-th drill rod is: the amount of gas desorbed from the coal body and the amount of free gas transported from the borehole to the drill bit when drilling reaches the i-th drill rod. The calculation formula is: In the formula, C represents the average gas emission from the borehole wall during the drilling process of the i-th drill pipe; ik Q represents the methane concentration in the borehole at time k, in %; ik Let m be the gas flow rate at time k. 3 / min; m is the number of data samples taken during the i-th drill pipe's downtime; ③ The average gas emission from drill cuttings in the coal seam where the i-th drill rod is located is: the amount of gas desorption from drill cuttings generated during the drilling process from the i-th drill rod to the (i-1)-th drill rod when the borehole reaches the i-th drill rod. It reflects the gas content of the coal seam in that local area, and the calculation formula is: In the formula, The average gas emission rate of drill cuttings in the coal seam where the i-th drill pipe is located; The average comprehensive gas emission intensity of the borehole during the drilling process of the i-th drill pipe; It represents the average gas emission from the borehole coal wall during the drilling process of the (i-1)th drill rod.

7. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The surface relaxation rate characterization model of the coal scrap accumulation constructed in step four is as follows: In the formula, T2 is the nuclear magnetic resonance relaxation value, in milliseconds; T 2b For volume relaxation, ms; w p The effective average size of the coal dust is in mm; Nuclear magnetic resonance porosity; The surface relaxation rate range was calculated using a surface relaxation rate characterization model for coal dust accumulations combined with the T2 relaxation distribution of coal dust accumulations. Then, based on... The obtained nuclear magnetic relaxation values ​​are converted into absolute pore size r, and Fs is the pore shape factor; This results in the formation of an absolute aperture distribution curve.

8. The method for predicting coal reservoir geological information based on drill cuttings according to claim 1, characterized in that, The specific process of arranging and obtaining the spatial distribution of pore seepage in step six is ​​as follows: The sequence number of the first through-layer borehole is set as b1. Within this borehole, the drill rods are numbered 1, 2…k according to their construction sequence, thus obtaining the spatial coordinates of each drill rod's construction section as (x1, y1, z…k). 1k According to this borehole location definition rule, the spatial coordinates of the drill rod sections of the i-th borehole, following the construction sequence of cross-layer drilling, are (x...). i ,y i ,z ik The data of each section of coal cuttings in each cross-layer borehole after arrangement are iteratively calculated using the variation function and Kriging estimation method to obtain the porosity distribution within the coal seam structure.

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