A method for determining reasonable negative pressure of gas extraction drilling holes in coal mines

Abstract

The present invention relates to a method for determining a reasonable negative pressure of gas extraction drilling holes in underground coal mines, and belongs to the field of coal mine gas extraction. The present invention selects an extraction area to carry out a gas extraction drilling hole to investigate the extraction effect, and constructs a spatiotemporal prediction model of different extraction negative pressures of regional boreholes, and then performs negative pressure extraction through regional boreholes and performs extraction effect inspection according to real-time extraction data, so as to optimize and adjust the mine extraction and digging succession plan, the extraction drilling hole engineering or the prediction model, realize the determination of the reasonable extraction negative pressure of the regional borehole and dynamically adjust and optimize it according to the spatiotemporal coupling relationship, and provide a basis for targeted intelligent extraction and control, thereby effectively improving the utilization efficiency of the extraction boreholes and the level of refined management technology, and ensuring the smooth connection between the coal mine gas extraction effect and the mine extraction and digging.

Description

Technical Field

[0001] The invention belongs to the field of coal mine gas extraction, and relates to a method for determining a reasonable extraction negative pressure of a gas extraction borehole in an underground coal mine. Background Art

[0002] At present, high-gas and protruding mines have generally built gas extraction systems, but they have been in a state of high safety risk, low efficiency and high energy consumption for a long time. The reduced gas extraction efficiency has led to the failure to solve the mine gas problem within the expected time, affecting the safe and efficient production of the mine; one of the main signs of reduced extraction efficiency is a significant drop in extraction concentration, and large concentration fluctuations further increase the difficulty of utilization, limiting the improvement of gas utilization and a large amount of greenhouse gas emissions; in addition, the gas concentration in some extraction pipelines is within the explosion limit, which is very easy to detonate the gas in the pipe; the single pump of the extraction system has a large operating power, resulting in high energy consumption in the operation of the extraction pump station.

[0003] The operating status of the gas extraction system directly affects the effect of gas control. The root cause of the above problems is the widespread mismatch between the extraction negative pressure and the extraction effect. Gas extraction drilling is the main way to extract gas in coal mines and the source of gas extraction in coal mines. In recent years, large-diameter drilling and kilometer-long drilling have been widely promoted and applied in coal mines. According to the current "Interim Provisions on Coal Mine Gas Extraction Standards": the orifice negative pressure of the pre-extraction gas drilling shall not be less than 13kPa, and the orifice negative pressure of the pressure-relief gas extraction drilling shall not be less than 5kPa. It can no longer meet the development needs of efficient extraction in coal mines, and there is a lack of dynamic adjustment standards for negative pressure in the extraction cycle of gas extraction drilling and investigation methods for the law of evolution over time and space. Therefore, determining the reasonable extraction negative pressure of gas extraction drilling holes in coal mines and the law of evolution over time and space can improve the safety and efficiency of the extraction system, promote the development of coal mine gas extraction from centralized control to intelligent control, and support the construction of intelligent coal mines. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for determining a reasonable extraction negative pressure of gas extraction boreholes in coal mines. By selecting boreholes in the extraction area to carry out an investigation on the influence of negative pressure on the extraction effect, a spatiotemporal prediction model of different extraction negative pressures of regional boreholes is constructed and the effect is tested, thereby obtaining a reasonable extraction negative pressure of the gas extraction boreholes, solving the problem of matching the extraction negative pressure and extraction effect of gas extraction boreholes in coal mines, thereby determining the dynamic adjustment of the negative pressure during the extraction cycle of the extraction boreholes and its evolution over time and space, in order to improve the safety and efficiency of the extraction system and support the construction of intelligent extraction in coal mines.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine, the method comprising the following steps:

[0007] S11: Drill holes in the selected extraction area to investigate the effect of negative pressure on extraction;

[0008] S12: Based on coal-rock gas geological conditions, extraction drilling engineering parameters and coal-bed gas extraction theory, a spatiotemporal prediction model for extraction drilling with different negative pressures was constructed;

[0009] S13: Carry out borehole gas extraction and data monitoring, determine the negative pressure of the extraction borehole and conduct extraction effect inspection and verification;

[0010] S14: Based on the S12 and S13 models and survey and monitoring results, optimize and adjust the models, engineering parameters or extraction and excavation plans, determine the reasonable extraction negative pressure, and guide the determination of extraction negative pressure in other areas.

[0011] Optionally, in S11, S101 is to conduct a study on the effect of negative pressure on extraction by drilling in the selected extraction area, which is divided into two parts: the distribution law of negative pressure along the axial direction of the borehole with the hole depth and the change law of negative pressure along the radial direction of the borehole with time, including the following steps:

[0012] S102: By examining the distribution and influence of negative pressure along the borehole axial direction with the depth of the borehole, including the negative pressure loss in the process of variable mass flow of borehole gas and the negative pressure loss in borehole leakage, the distribution and attenuation law of negative pressure along the depth of the borehole are obtained;

[0013] S103: The variation law of the negative pressure along the borehole radial direction over time, classification of extraction holes and observation holes, extraction of extraction holes after completion of construction by kilometer or ordinary directional drilling rigs and real-time monitoring of the negative pressure distribution in the hole, ordinary drilling of observation holes according to the design parameters of directional drilling construction and group arrangement, installation of pressure gauges outside the hole to monitor gas pressure or gas content and other parameters;

[0014] Optionally, in S102, the axial negative pressure distribution characteristics and attenuation law of the gas extraction borehole in the coal mine include the following steps:

[0015] S1021: Negative pressure loss during borehole gas variable mass flow. Because the borehole gas extraction process is a variable mass flow, its flow process is relatively complex. Its negative pressure loss is mainly divided into two parts: along-the-way and local negative pressure loss and variable mass mixed negative pressure loss.

[0016] S1022: Negative pressure loss caused by leakage in the borehole is mainly due to leakage in the shallow sealing section of the borehole and leakage in the deep fracture zone and string holes in the borehole. Among them, leakage in the shallow sealing section of the borehole is the main part of the negative pressure loss caused by leakage in the borehole.

[0017] Optionally, in S1021, the negative pressure loss during the mass flow of the borehole gas comprises the following steps:

[0018] S10211: Along-the-hole and local negative pressure loss. During the flow of gas in the borehole along the direction of the borehole, it needs to overcome the friction resistance of the borehole wall, which causes the loss of friction resistance along the way. It mainly includes the loss along the way of normal extraction of the extraction borehole, the loss of local collapse and blockage of the borehole, and the loss of local water accumulation in the borehole. This is also the main law and influencing factor of the distribution of negative pressure along the borehole axis with depth;

[0019] Optionally, the normal drainage negative pressure loss of the extraction borehole is mainly affected by the roughness of the through-layer borehole and the roughness of the in-layer borehole. That is, when there is no obvious instability, damage or blockage in the extraction borehole, the main factor affecting the loss of the borehole negative pressure in the hole is the roughness of the hole. The through-layer borehole is much different from the in-layer borehole. The through-layer hole is relatively smooth and the negative pressure loss is small; while the in-layer borehole is relatively rough, so the negative pressure loss is large.

[0020] Optionally, the local collapse loss of the borehole is mainly caused by the accumulation of coal slag in the borehole / collapse around the borehole and hydration expansion of coal and rock around the borehole. At this time, according to the collapse inside the borehole, the negative pressure loss may be large, and it may even be unable to be transmitted to the bottom of the hole. Therefore, it is impossible to achieve extraction of the entire hole section, resulting in failure of the local or entire hole section;

[0021] Optionally, the negative pressure loss due to local water accumulation in the borehole is mainly aimed at the downward borehole, which is divided into two types: downward borehole water accumulation blockage and local water accumulation blockage. In coal rock formations rich in water systems, there is generally more water accumulation in downward boreholes or horizontal boreholes, or water accumulation will still occur in local low-lying areas of kilometer-long boreholes. At this time, the negative pressure loss in the water-accumulated section is so large that the negative pressure will not be able to be transmitted to the bottom of the hole.

[0022] S10212: Variable mass flow mixed negative pressure loss, mainly gas flow acceleration negative pressure loss and variable mass flow mixed negative pressure loss. The gas flow in the extraction borehole belongs to variable mass flow, which will converge closer to the orifice. Therefore, the greater the orifice flow velocity, the increase in velocity will lead to a certain negative pressure loss.

[0023] S1022: Negative pressure loss caused by leakage in the borehole is mainly due to leakage in the shallow sealing section of the borehole and leakage in the deep fracture zone and string holes in the borehole. Among them, leakage in the shallow sealing section of the borehole is the main part of the negative pressure loss caused by leakage in the borehole.

[0024] Optionally, in S1021, the negative pressure loss caused by leakage in the borehole includes the following steps:

[0025] S10221: The shallow sealing section of the borehole is the main part of the negative pressure loss caused by air leakage in the borehole. The main reasons include insufficient sealing depth of the sealing section and loose sealing of the sealing section. The insufficient sealing depth of the sealing section is mainly because the sealing section cannot effectively seal the shallow fracture zone of the borehole, and the sealing depth does not reach the stress concentration zone or the original rock stress zone; the leakage caused by loose sealing of the sealing section may be due to damage of the sealing device, extraction pipe, etc., or the sealing material cannot effectively fill the space of the sealing section, and as time goes by, the cracks in the sealing section further develop, resulting in leakage.

[0026] S10222: Air leakage in deep boreholes is mainly caused by fracture zones in coal and rock strata and other serial holes, which can also lead to negative pressure loss inside the borehole.

[0027] Optionally, in S103, the variation law of the influence range of the negative pressure along the borehole radial direction over time includes the steps of:

[0028] S1031 determines the drainage of the observation hole and the negative pressure distribution in the hole to ensure normal drainage of the drainage hole. At the same time, a negative pressure monitoring device is arranged in the borehole to obtain the negative pressure distribution in the borehole in real time, mainly including the drainage hole engineering parameters, the drainage hole trajectory parameters and the negative pressure distribution along the hole depth;

[0029] Optionally, the extraction hole engineering parameters mainly include the extraction hole diameter, hole size, opening height, sealing process and parameters, among which the sealing process and parameters must meet the requirements of no air leakage or no obvious air leakage, otherwise it will be regarded as a sealing failure and normal inspection and analysis cannot be carried out;

[0030] Optionally, the extraction hole trajectory parameters mainly include drilling depth, inclination, azimuth, tool face angle, left and right deviation, up and down deviation, etc. A directional drilling rig can be used to construct and record the drilling trajectory. After determining the trajectory parameters of the extraction hole, an accurate positioning basis can be provided for the layout parameters of the observation hole.

[0031] Optionally, the negative pressure distribution along the hole depth is to arrange a negative pressure monitoring device along the borehole depth in the extraction hole, so as to obtain the negative pressure values ​​at different depths in real time and the negative pressure attenuation law along the axial direction of the borehole. At the same time, observation holes are arranged in groups at different depths on both sides of the extraction hole, so that the negative pressure distribution law along the axial direction of the borehole and the radial influence range under different negative pressure values ​​can be realized in one borehole.

[0032] S1032 arranges observation holes in groups and monitors data, which can be specifically achieved by monitoring parameters such as pressure or flow in the holes, including observation hole engineering parameters, observation hole trajectory parameters, and observation hole distribution layout parameters.

[0033] Optionally, the observation hole engineering parameters mainly include the observation hole diameter, hole depth, opening height, sealing depth and sealing process, among which the observation hole sealing adopts different sealing processes according to the coal seam, through-layer drilling and drilling inclination, but the sealing depth must meet the monitoring parameter requirements to prevent air leakage in the sealing section and cause the survey failure.

[0034] Optionally, the observation hole trajectory parameters include drilling depth, inclination, azimuth, tool face angle, left and right deviation, up and down deviation, etc. A directional drilling rig can be used to construct and record the drilling trajectory to achieve precise spatial positioning of the extraction hole and the observation hole, which facilitates accurate measurement and investigation and analysis of the extraction data and monitoring data.

[0035] Optionally, the grouping arrangement of the observation holes includes the spacing between boreholes, the number of grouped boreholes, and the arrangement of borehole depths within and within the group, so as to examine the changes in monitoring parameters in the grouped observation holes under different extraction negative pressures along the borehole depths, thereby examining the radial extraction effect of reasonable negative pressure under the coupling of multiple factors at different depths of the extraction borehole.

[0036] Optionally, the 12 extraction boreholes with different negative pressure extraction spatiotemporal prediction models are established based on coal rock layer and gas storage conditions, extraction borehole engineering parameters, coal seam gas extraction theory, etc., and constructing a regional borehole extraction spatiotemporal prediction model with different negative pressure extraction includes the following steps:

[0037] The coal-rock layer and gas occurrence conditions, coal-rock geological parameters include tunnel surrounding rock stress distribution, mining stress distribution, soft coal rock firmness and coal-rock water content; coal-rock gas occurrence parameters include coal-rock gas pressure, coal-rock gas content pressure, coal-rock permeability, coal-rock density and coal-rock porosity and other basic parameters;

[0038] The extraction drilling engineering parameters include the hole opening position, drilling depth, hole diameter, spacing, inclination, orientation and sealing process and parameters, and the drilling construction parameters are recorded in detail;

[0039] The coal seam gas extraction theory mainly includes coal seam gas seepage and diffusion theory, mass conservation law and fluid mechanics theory, and is the theoretical basis for constructing a spatiotemporal prediction model for different extraction negative pressures of gas extraction boreholes.

[0040] Optionally, after constructing the spatiotemporal prediction model of different regional borehole extraction negative pressures in S12, proceed to step S13 to perform regional borehole extraction verification and ultimately determine a reasonable extraction negative pressure;

[0041] S301: Determine the regional borehole negative pressure for extraction, and conduct daily extraction data monitoring. During the extraction process, try to maintain the negative pressure according to the extraction effect investigation and prediction model of the negative pressure, or compare the offset of the negative pressure value to ensure the best extraction effect;

[0042] S302: During the regional borehole extraction process, the obtained extraction data is fitted and compared with the predicted values ​​of the constructed regional borehole different extraction negative pressure spatiotemporal prediction model. If the results are consistent, the process proceeds to S14, indicating that the predicted negative pressure value is consistent with the actual extraction effect, and the extraction can be achieved within the planned time. If the results are inconsistent, it is necessary to predict the extraction time under the existing extraction conditions, and then proceed to S303;

[0043] S303: After fitting and comparing the actual drainage effect with the predicted drainage target time, whether it will affect the mine drainage and excavation replacement plan, if yes, go to S304, otherwise go to S301 and continue normal drainage and drainage data monitoring;

[0044] S304: When affecting the mine extraction and excavation succession plan, according to whether to adjust the regional extraction target time, if yes, proceed to S306, if not, proceed to S305;

[0045] S305: In the case of not adjusting the time for reaching the target of regional coal seam extraction, the only way is to adjust the mine extraction and excavation replacement plan, that is, to extend the extraction target time accordingly, and then extend the mine excavation replacement time in sequence, and then enter S301 to continue to extract the regional boreholes;

[0046] S306: If it is necessary to adjust the regional coal seam extraction target time, that is, when the mine extraction and excavation succession plan remains unchanged, by adjusting the drilling parameters, extraction parameters or performing coal seam permeability enhancement, drilling repair and other operations, the regional coal seam extraction target time can be normal or advanced without affecting the mine extraction and excavation plan, and then enter S12.

[0047] Optionally, after determining the negative pressure of the extraction borehole in S13 and verifying the extraction effect, proceed to step S14;

[0048] In S14, after determining the negative pressure of the gas extraction borehole and verifying the extraction effect, the prediction model, extraction drilling engineering parameters or the mine extraction excavation plan are optimized and adjusted accordingly, and finally a reasonable extraction negative pressure is determined, which is used as a guide to determine the borehole negative pressure in other areas;

[0049] Adjusting the mine excavation plan is to extend the time to reach the extraction target by adjusting the mine excavation plan without adjusting the extraction negative pressure;

[0050] Adjusting the extraction drilling project parameters is to modify the extraction drilling project parameters, such as borehole diameter, borehole depth, borehole spacing, layout method, etc., without adjusting the extraction negative pressure and the extraction plan. After completing the above measures, re-conduct borehole gas extraction and revise the borehole gas extraction prediction model. According to the extraction effect inspection cycle or regularly, conduct preliminary evaluation of extraction effect and extraction compliance.

[0051] The beneficial effects of the present invention are as follows: the present invention selects a gas extraction area to carry out gas extraction drilling to investigate the extraction effect, and constructs a spatiotemporal prediction model for different extraction negative pressures in regional boreholes, and then performs negative pressure extraction through regional boreholes and verifies the extraction effect based on real-time extraction data, thereby optimizing and adjusting the mine extraction and digging succession plan, the extraction drilling project or the prediction model, and realizing the determination of a reasonable extraction negative pressure for the regional boreholes and dynamically adjusting and optimizing it based on the spatiotemporal coupling relationship, providing a basis for targeted intelligent extraction and control, thereby effectively improving the utilization efficiency of extraction boreholes and the level of refined management technology, and ensuring the smooth connection between the coal mine gas extraction effect and mine extraction and digging.

[0052] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0054] Figure 1 A schematic diagram of a method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine;

[0055] Figure 2 A flow chart for determining a reasonable negative pressure for gas extraction drilling provided by the present invention;

[0056] Figure 3 It is a schematic diagram of the distribution characteristics of the extraction negative pressure along the axial direction of the borehole with the depth of the borehole according to the present invention;

[0057] Figure 4 It is a schematic diagram of the spatial and temporal evolution characteristics of the extraction negative pressure along the borehole radial direction according to the present invention. DETAILED DESCRIPTION

[0058] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0059] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0060] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0061] like Figure 1 As shown, the method for determining the reasonable negative pressure of gas extraction drilling holes in coal mines in this embodiment of the present invention includes the following steps:

[0062] Step S11: drilling holes in the selected extraction area to investigate the effect of negative pressure on extraction;

[0063] Step S12: constructing a spatiotemporal prediction model for extraction of different negative pressures in extraction boreholes;

[0064] Step S13: determining the negative pressure of the extraction borehole and performing extraction effect inspection and verification;

[0065] Step S14: Integrate the borehole negative pressure action mechanism, prediction model and drainage monitoring data obtained in steps S11, S12 and S13, and then optimize and adjust the model, engineering parameters or drainage excavation plan, determine a reasonable drainage negative pressure, and guide other areas to determine a reasonable drainage negative pressure;

[0066] like Figure 2 The figure shows the flow chart for determining the reasonable negative pressure of gas extraction boreholes. The process includes the following steps:

[0067] Step S11: First, the effect of negative pressure on extraction is investigated in the selected area, mainly including the variation of negative pressure along the axial and radial directions of the borehole over time, which mainly includes the following steps:

[0068] Step S102: By examining the distribution and influence of negative pressure along the borehole axial direction with the depth of the borehole, including the negative pressure loss in the process of variable mass flow of borehole gas and the negative pressure loss in the borehole leakage, the distribution and attenuation law of negative pressure along the depth direction of the borehole are obtained;

[0069] Step S103: The influence range of negative pressure along the borehole radial direction over time is classified into extraction holes and observation holes. After the extraction holes are constructed by a kilometer or ordinary directional drilling rig, extraction is carried out and the negative pressure distribution in the hole is monitored in real time. The observation holes are drilled by ordinary directional drilling according to the design parameters and arranged in groups. A pressure gauge is installed outside the hole to monitor parameters such as gas pressure or gas content.

[0070] In this embodiment, step S12 is based on the on-site investigation of the influence of the extraction negative pressure on the extraction effect in step S11, and combines the regional drilling parameters and theoretical basis to build a spatiotemporal prediction model of different extraction negative pressures in the regional drilling, which mainly includes the following steps:

[0071] Step S201: construct a spatiotemporal prediction model for different negative pressures of regional borehole extraction, which is mainly based on coal rock layer and gas storage conditions, extraction drilling engineering parameters, coal seam gas extraction theory, etc., wherein the geological parameters of the coal rock layer include the stress distribution of the tunnel surrounding rock, the mining stress distribution, the firmness of the soft coal rock and the water content of the coal rock layer, and the coal seam gas storage parameters include the basic parameters such as coal seam gas pressure, coal seam gas content pressure, coal seam permeability, coal seam density and coal seam porosity; the extraction drilling engineering parameters include the opening position, drilling depth, hole diameter, spacing, inclination, orientation and sealing process and parameters, and the drilling construction parameters are recorded in detail; the coal seam gas extraction theory mainly includes the coal seam gas seepage diffusion theory, the law of conservation of mass and fluid mechanics, etc., which are the theoretical basis for constructing the spatiotemporal prediction model for different negative pressures of gas extraction boreholes;

[0072] In this embodiment, step S11 and step S12 are combined, and then step S13 is entered to determine the negative pressure of the extraction borehole and perform extraction effect inspection and verification, which mainly includes the following steps:

[0073] Step S301: Determine the regional borehole negative pressure for extraction, and conduct daily extraction data monitoring. Try to maintain the negative pressure during the extraction process according to the negative pressure extraction effect investigation and prediction model, or compare the offset of the negative pressure value to ensure the best extraction effect;

[0074] Step 302: During the regional borehole extraction process, the obtained extraction data is fitted and compared with the predicted values ​​of the constructed regional borehole different extraction negative pressure spatiotemporal prediction model. If the results are consistent, the process proceeds to step S14, indicating that the predicted negative pressure value is consistent with the actual extraction effect, and the extraction can be achieved within the planned time. If the results are inconsistent, it is necessary to predict the extraction time under the existing extraction conditions, and then proceed to step S303;

[0075] Step S303: after fitting and comparing the actual extraction effect with the predicted extraction target time, whether it will affect the extraction and excavation replacement plan of the mine, if yes, proceed to step S304, otherwise proceed to step S301, and continue normal extraction and extraction data monitoring;

[0076] Step S304: When affecting the mine extraction and excavation succession plan, according to whether to adjust the regional extraction target time, if yes, proceed to step S306, if not, proceed to step S305;

[0077] Step S305: In the case where the time for reaching the target extraction target of the regional coal seam is not adjusted, the only way is to adjust the mine extraction and digging replacement plan, that is, to extend the extraction target extraction time accordingly, and then extend the mine digging replacement time in sequence, and then enter step S301 to continue to extract the regional boreholes;

[0078] Step S306: if it is necessary to adjust the regional extraction target time, that is, when the mine extraction and excavation succession plan remains unchanged, by adjusting the drilling parameters, extraction parameters or performing coal seam permeability enhancement, drilling repair and other operations, the regional coal seam extraction target time is normal or advanced without affecting the mine extraction and excavation plan, and then enter step S12;

[0079] In this embodiment, after the regional borehole negative pressure extraction in step S13, the results are compared with the spatiotemporal prediction results, and the mine extraction excavation is carried out in a targeted manner, and then step S14 is entered;

[0080] In this embodiment, in step S14, after the regional borehole negative pressure extraction is determined, a comparative analysis is performed according to different extraction negative pressure spatiotemporal prediction models, so as to determine the regional borehole negative pressure for extraction, and to evaluate the extraction compliance, and to optimize and adjust the model, drilling engineering parameters or mine extraction excavation plan accordingly according to the comparison results of step S13, and finally determine the reasonable extraction negative pressure, and guide the determination of reasonable extraction negative pressure in other regions;

[0081] like Figure 3 The figure shows the distribution characteristics of the negative pressure along the borehole axis with the depth of the borehole, which includes the following steps:

[0082] Step 1021: negative pressure loss in the variable mass flow process of borehole gas, mainly including two parts: along-the-way and local negative pressure loss, and variable mass flow mixed negative pressure loss. This is the negative pressure loss in the variable mass flow during the gas confluence process at the borehole wall;

[0083] Step 10211: along-the-way and local negative pressure loss. In the process of gas flowing in the borehole along the direction of the borehole, it is necessary to overcome the friction resistance of the borehole wall, which causes along-the-way friction resistance loss, mainly including normal extraction negative pressure loss of the extraction borehole, local collapse and blockage negative pressure loss of the borehole, and local water accumulation negative pressure loss of the borehole; the normal extraction negative pressure loss is mainly affected by the roughness of the through-layer borehole and the roughness of the in-layer borehole. The main factor affecting the loss of borehole negative pressure in the hole is the roughness of the hole. The negative pressure loss of the through-layer borehole is relatively small, and the negative pressure loss of the in-layer borehole is relatively large; the local collapse and blockage loss of the borehole is mainly caused by the accumulation of coal slag in the borehole, the collapse and blockage around the borehole, and the hydration and expansion of the coal rock around the hole, which will lead to a large negative pressure loss and even fail to be transmitted to the bottom of the hole; the local water accumulation negative pressure loss of the borehole is mainly aimed at the downward borehole, which is divided into downward borehole water accumulation blockage and local water accumulation blockage. At this time, the negative pressure loss of the water accumulation section is relatively large, and the extraction negative pressure will also be unable to be transmitted to the bottom of the hole.

[0084] Step 10212: variable mass flow mixed negative pressure loss, mainly including flow acceleration negative pressure loss and variable mass flow mixed negative pressure loss. The gas flow in the extraction borehole belongs to variable mass flow, which will be gathered closer to the orifice. Therefore, the greater the orifice flow velocity, the increase in velocity will lead to a certain negative pressure loss.

[0085] Step 1022: Negative pressure loss due to borehole leakage, which mainly includes two types of negative pressure loss caused by leakage in the shallow sealing section of the borehole and leakage in the middle depth of the borehole;

[0086] Step 10221: The shallow sealing section of the borehole is the main part of the negative pressure loss caused by air leakage in the borehole. The main reasons include insufficient sealing depth of the sealing section and loose sealing of the sealing section. The insufficient sealing depth of the sealing section is mainly because the sealing section cannot effectively seal the shallow fracture zone of the borehole, and the sealing depth does not reach the stress concentration zone or the original rock stress zone; the leakage caused by loose sealing of the sealing section may be due to damage of the sealing device, the extraction pipe, etc., or the sealing material cannot effectively fill the space of the sealing section, and as time goes by, the cracks in the sealing section further develop, resulting in leakage.

[0087] Step 10222: In the deep part of the borehole, there are mainly two situations: gas leakage in the coal rock layer fracture zone and gas leakage in other boreholes, which will aggravate the negative pressure loss in the borehole;

[0088] like Figure 4 The figure shows a schematic diagram of the investigation of the influence range of the negative pressure of extraction along the borehole radial direction over time, which includes the following steps:

[0089] Step S1031: extraction of the extraction hole and negative pressure distribution in the hole. The extraction hole is constructed by kilometer or ordinary directional drilling to seal the hole and connect the extraction, which mainly includes the extraction hole engineering parameters, extraction hole trajectory parameters, and negative pressure distribution along the hole depth. The extraction hole engineering parameters mainly include the extraction hole diameter, hole diameter, hole opening height, sealing process and parameters. The extraction hole trajectory parameters mainly include drilling depth, inclination, azimuth, tool face angle, left and right deviation, up and down deviation, etc. The negative pressure distribution along the hole depth is to arrange a negative pressure monitoring device along the depth of the borehole in the extraction hole, which can obtain the negative pressure values ​​at different depths in real time, and obtain the negative pressure attenuation law along the axial direction of the borehole. At the same time, observation holes are arranged in groups at different depths on both sides of the extraction hole, which can realize the negative pressure distribution law along the axial direction of the borehole and the radial influence range investigation under different negative pressure values ​​in one borehole;

[0090] Step S1032: Arrange observation holes in groups and monitor data. The observation holes are constructed with ordinary drilling rigs and are precisely constructed according to the extraction hole parameters and design parameters. The observation hole engineering parameters mainly include the observation hole diameter, hole depth, opening height, sealing depth and sealing process, etc. The observation hole trajectory parameters include drilling depth, inclination, azimuth, tool face angle, left and right deviation, up and down deviation, etc. The grouping arrangement of observation holes includes drilling hole spacing, group drilling number, and intra-group and group drilling depth arrangement.

[0091] The method for determining the reasonable extraction negative pressure of underground gas extraction boreholes in coal mines described in the present invention first selects regional boreholes to conduct an investigation on the effect of negative pressure on extraction, and then constructs a spatiotemporal prediction model for different extraction negative pressures of regional boreholes. Then, regional drilling is carried out for extraction and extraction data monitoring is performed. By comparing and analyzing the actual extraction effect with the predicted value, a basis is provided for optimizing and adjusting the drilling engineering parameters, the prediction model, or adjusting the mine extraction and digging plan, and a reference is provided for guiding the determination of extraction negative pressure in other areas, so as to improve the utilization efficiency of extraction boreholes and the level of refined management technology in a targeted manner, and ensure the smooth connection between coal seam gas extraction effect and mine extraction and digging.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine, characterized in that: The method comprises the following steps: S11: Drill holes in the selected extraction area to investigate the effect of negative pressure on extraction; S12: Based on coal-rock gas geological conditions, extraction drilling engineering parameters and coal-bed gas extraction theory, a spatiotemporal prediction model for extraction drilling with different negative pressures was constructed; S13: Carry out borehole gas extraction and data monitoring, determine the negative pressure of the extraction borehole and conduct extraction effect inspection and verification; S14: Based on the S12 and S13 models and the inspection and monitoring results, optimize and adjust the models, engineering parameters or extraction and excavation plans, determine the reasonable extraction negative pressure, and guide the determination of the extraction negative pressure in other areas; In the above S11, S101 is to select a drilling area to carry out a study on the effect of negative pressure on extraction, which is divided into two parts: the distribution law of negative pressure along the axial direction of the drilling hole with the hole depth and the change law of negative pressure along the radial direction of the drilling hole with time, including the following steps: S102: By examining the distribution and influence of negative pressure along the borehole axial direction with the depth of the borehole, including the negative pressure loss in the process of variable mass flow of borehole gas and the negative pressure loss in borehole leakage, the distribution and attenuation law of negative pressure along the depth of the borehole are obtained; S103: The variation law of negative pressure along the borehole radial direction over time, classification of extraction holes and observation holes, extraction of extraction holes after completion of construction by kilometer or ordinary directional drilling rigs and real-time monitoring of negative pressure distribution in the hole, ordinary drilling of observation holes according to design parameters, directional drilling construction and group arrangement, installation of pressure gauges outside the holes to monitor gas pressure or gas content parameters; In S102, the axial negative pressure distribution characteristics and attenuation law of the gas extraction borehole in the coal mine include the following steps: S1021: Negative pressure loss during borehole gas variable mass flow. The borehole gas extraction process belongs to variable mass flow, and its negative pressure loss is divided into two parts: along-the-way and local negative pressure loss and variable mass mixed negative pressure loss; S1022: Negative pressure loss caused by leakage in the borehole, which includes leakage in the shallow sealing section of the borehole and leakage in the fracture zone and string holes at a medium depth in the borehole. Leakage in the shallow sealing section of the borehole is part of the negative pressure loss caused by leakage in the borehole; In S1021, the negative pressure loss during the mass flow of borehole gas includes the following steps: S10211: Along-the-hole and local negative pressure loss. During the process of gas flowing along the borehole, it needs to overcome the friction resistance of the borehole wall, resulting in the loss of friction resistance along the way. This includes the loss along the way of normal extraction of the extraction borehole, the loss of local collapse and blockage of the borehole, and the loss of local water accumulation in the borehole. This is the law and influencing factor of the distribution of negative pressure along the borehole axis with depth. The normal negative pressure loss of the extraction borehole is affected by the roughness of the through-layer borehole and the roughness of the in-layer borehole. That is, when there is no obvious instability, damage or blockage in the extraction borehole, the roughness of the hole affects the loss of the negative pressure in the borehole. The through-layer borehole is more different than the in-layer borehole. The through-layer hole is relatively smooth and the negative pressure loss is small; the in-layer borehole is relatively rough and the negative pressure loss is large. The local blockage loss of the borehole includes the blockage caused by the accumulation of coal slag in the borehole / blockage around the borehole and the blockage caused by the hydration and expansion of coal rock around the borehole. The local water accumulation negative pressure loss of the borehole is for the downward borehole, which is divided into two types: downward water accumulation blockage and local water accumulation blockage. In the coal and rock layer rich in water system, the negative pressure loss of the water accumulation section in the downward borehole or horizontal borehole is large, so that the negative pressure cannot be transmitted to the bottom of the hole; S10212: Variable mass flow mixed negative pressure loss, which includes gas flow acceleration negative pressure loss and variable mass flow mixed negative pressure loss. The gas flow in the extraction borehole belongs to variable mass flow, which will converge closer to the orifice position. Therefore, the greater the orifice flow velocity, the increase in velocity will lead to a certain negative pressure loss.

2. A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine according to claim 1, characterized in that: In S1021, the negative pressure loss caused by leakage in the borehole includes the following steps: S10221: Shallow sealing section of the borehole, which is the part where the negative pressure loss is caused by air leakage in the borehole. There are two types of air leakage caused by insufficient sealing depth of the sealing section and loose sealing of the sealing section. The insufficient sealing depth of the sealing section means that the sealing section cannot effectively seal the shallow fracture zone of the borehole, and the sealing depth does not reach the stress concentration zone or the original rock stress zone; the air leakage caused by loose sealing of the sealing section is caused by the sealing device, the extraction pipe is damaged, or the sealing material cannot effectively fill the sealing section space, and as time goes by, the fractures in the sealing section further develop, resulting in air leakage; S10222: Deep in the borehole, there is air leakage caused by fracture zones in the coal strata and cross-holes in other boreholes, which leads to negative pressure loss inside the borehole.

3. A method for determining a reasonable negative pressure of gas extraction drilling holes in coal mines according to claim 1, characterized in that: In S103, the variation law of the influence range of negative pressure along the borehole radial direction over time includes the following steps: S1031 determines the drainage of the observation hole and the negative pressure distribution in the hole to ensure that the drainage hole is drained normally. At the same time, a negative pressure monitoring device is arranged in the borehole to obtain the negative pressure distribution in the borehole in real time, including the drainage hole engineering parameters, the drainage hole trajectory parameters and the negative pressure distribution along the hole depth; The parameters of the extraction hole engineering shall include the extraction hole diameter, hole opening height, sealing process and parameters. The sealing process and parameters shall meet the requirements of no air leakage or no obvious air leakage, otherwise it will be regarded as sealing failure and normal inspection and analysis cannot be carried out; The trajectory parameters of the extraction hole include the drilling depth, inclination, azimuth, tool face angle, left-right deviation, and up-down deviation. A directional drilling rig is used for construction and the drilling trajectory is recorded. After the trajectory parameters of the extraction hole are determined, an accurate positioning basis is provided for the arrangement parameters of the observation hole. The negative pressure distribution along the borehole depth is to arrange the negative pressure monitoring device along the borehole depth in the extraction hole, obtain the negative pressure values ​​at different depths in real time, and obtain the negative pressure attenuation law along the borehole axis. At the same time, observation holes are arranged in groups at different depths on both sides of the extraction hole, so as to realize the negative pressure distribution law along the borehole axis and the radial influence range under different negative pressure values ​​in one borehole; S1032: arranging observation holes in groups and monitoring data, specifically by monitoring pressure or flow parameters in the holes, including observation hole engineering parameters, observation hole trajectory parameters, and observation hole distribution and arrangement parameters; The observation hole engineering parameters include the observation hole diameter, hole depth, hole opening height, hole sealing depth and hole sealing process. The observation hole sealing adopts different hole sealing processes according to the coal seam, through-layer drilling and drilling inclination. However, the hole sealing depth must meet the monitoring parameter requirements to prevent leakage in the sealing section and cause the survey failure. The observation hole trajectory parameters include drilling depth, inclination, azimuth, tool face angle, left-right deviation, and up-down deviation. A directional drilling rig is used for construction and the drilling trajectory is recorded to achieve precise spatial positioning of the extraction hole and the observation hole, which is convenient for accurate measurement, investigation and analysis of extraction data and monitoring data. The grouping arrangement of observation holes includes the spacing between boreholes, the number of grouped boreholes, and the arrangement of borehole depths within and within groups, so as to investigate the changes in monitoring parameters in the grouped observation holes under different extraction negative pressures along the borehole depths, and to investigate the extraction effect of reasonable negative pressure along the radial direction under the coupling of multiple factors at different depths of the extraction boreholes.

4. A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine according to claim 3, characterized in that: In S12, the spatiotemporal prediction model for extraction of different negative pressures in extraction boreholes is established based on coal-rock layer and gas storage conditions, extraction drilling engineering parameters, and coal seam gas extraction theory. The spatiotemporal prediction model for extraction of different negative pressures in regional boreholes is constructed, including the following steps: The coal-rock layer and gas occurrence conditions, coal-rock layer geological parameters include tunnel surrounding rock stress distribution, mining stress distribution, soft coal rock firmness and coal-rock layer water content; coal-seam gas occurrence parameters include coal-seam gas pressure, coal-seam gas content pressure, coal-seam permeability, coal-seam density and coal-seam porosity basic parameters; The extraction drilling engineering parameters include the hole opening position, drilling depth, hole diameter, spacing, inclination, orientation and sealing process and parameters, and the drilling construction parameters are recorded in detail; The coal seam gas extraction theory includes the coal seam gas seepage and diffusion theory, the law of conservation of mass and the fluid mechanics theory, and is the theoretical basis for constructing a spatiotemporal prediction model for different extraction negative pressures of gas extraction boreholes.

5. A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine according to claim 4, characterized in that: After constructing the spatiotemporal prediction model of different regional drilling extraction negative pressures in S12, proceed to step S13 to perform regional drilling extraction verification and ultimately determine a reasonable extraction negative pressure; S301: Determine the regional borehole negative pressure for extraction, and conduct daily extraction data monitoring. During the extraction process, try to maintain the negative pressure according to the extraction effect investigation and prediction model of the negative pressure, or compare the offset of the negative pressure value to ensure the best extraction effect; S302: During the regional borehole extraction process, the obtained extraction data is fitted and compared with the predicted values ​​of the constructed regional borehole different extraction negative pressure spatiotemporal prediction model. If the results are consistent, then enter S14, indicating that the predicted negative pressure value is consistent with the actual extraction effect, and the extraction is achieved within the planned time; if the results are inconsistent, it is necessary to predict the extraction time under the existing extraction conditions, then enter S303; S303: After fitting and comparing the actual drainage effect with the predicted drainage target time, whether it will affect the mine drainage and excavation replacement plan, if yes, go to S304, otherwise go to S301 and continue normal drainage and drainage data monitoring; S304: When affecting the mine extraction and excavation succession plan, according to whether to adjust the regional extraction target time, if yes, proceed to S306, if not, proceed to S305; S305: In the case of not adjusting the time for reaching the target of regional coal seam extraction, the only way is to adjust the mine extraction and excavation replacement plan, that is, to extend the extraction target time accordingly, and then extend the mine excavation replacement time in sequence, and then enter S301 to continue to extract the regional boreholes; S306: If it is necessary to adjust the regional coal seam extraction target time, that is, when the mine extraction and excavation succession plan remains unchanged, by adjusting the drilling parameters, extraction parameters or performing coal seam permeability enhancement and drilling repair operations, the regional coal seam extraction target time can be normal or advanced without affecting the mine extraction and excavation plan, and then enter S12.

6. A method for determining a reasonable negative pressure of a gas extraction borehole in a coal mine according to claim 5, characterized in that: After the negative pressure of the extraction borehole is determined in S13 and the extraction effect is verified, step S14 is entered; In S14, after determining the negative pressure of the gas extraction borehole and verifying the extraction effect, the prediction model, extraction drilling engineering parameters or the mine extraction excavation plan are optimized and adjusted accordingly, and finally a reasonable extraction negative pressure is determined, which is used as a guide to determine the borehole negative pressure in other areas; Adjusting the mine excavation plan is to extend the time to reach the extraction target by adjusting the mine excavation plan without adjusting the extraction negative pressure; Adjusting the extraction drilling engineering parameters is to modify the extraction drilling engineering parameters, including the borehole diameter, borehole depth, borehole spacing and layout, without adjusting the extraction negative pressure and the extraction plan. After completing the above measures, re-conduct borehole gas extraction and revise the borehole gas extraction prediction model. According to the extraction effect inspection cycle or regularly, conduct preliminary evaluation of the extraction effect and extraction compliance.

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