In order to clarify the danger of water breakout in the bottom plate of extra-thick coal seam mining, 2202 working face of a mine in the west is taken as the research object, and it is proposed to use the on-site moni...In order to clarify the danger of water breakout in the bottom plate of extra-thick coal seam mining, 2202 working face of a mine in the west is taken as the research object, and it is proposed to use the on-site monitoring means combining borehole peeping and microseismic monitoring, combined with the theoretical analysis to analyze the danger of water breakout in the bottom plate. The results show that: 1) the theoretically calculated maximum damage depth of the bottom plate is 27.5 m, and its layer is located above the Austrian ash aquifer, which has the danger of water breakout;2) the drill hole peeping at the bottom plate of the working face shows that the depth of the bottom plate fissure development reaches 26 m, and the integrity of the water barrier layer has been damaged, so there is the risk of water breakout;3) for the microseismic monitoring of the anomalous area, the bottom plate of the return air downstream channel occurs in the field with a one-week lag, which shows that microseismic monitoring events may reflect the water breakout of the underground. This shows that the microseismic monitoring events can reflect the changes of the underground flow field, which can provide a reference basis for the early warning of water breakout. The research results can provide reference for the prediction of sudden water hazard.展开更多
In order to solve the problems of top-coal inadequate destruction and large amounts of gas emission in mining extra thick and hard coal seam,this study investigated the pre-splitting for deep borehole blasting and gas...In order to solve the problems of top-coal inadequate destruction and large amounts of gas emission in mining extra thick and hard coal seam,this study investigated the pre-splitting for deep borehole blasting and gas pre-draining technologies on top coal.The mechanism of the technologies was systematically expounded based on hard top-coal cracks development obtained by numerical simulation and theoretical analysis.The results show that explosive blasting in the hard rock results in a large number of cracks and large displacement in the rock mass due to the effect of explosion stress.Meanwhile,the thick top-coal caves,and desorbing gas flows along the cracks improve gas extraction.Finally,the pre-splitting for deep borehole blasting and gas pre-draining technologies was applied in No.3802 working face of Shui Liandong Coal Mine,which increases monthly output in the face to 67.34 kt and the drained gas concentration to 86.2%.The drained gas average concentration from each borehole reaches 40%,and the effect is remarkable.展开更多
This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content...This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content coals Staszic-Wujek Hard Coal Mine in the Upper Silesia Coal Basin(Poland).Five LRDD Boreholes(TM1a-TM5)with a length of 300 and 400 m were located over coal seam 501 in the fractured zone and monitored over six months of longwall face operations.LRDD Boreholes were combined with Cross-Measured Boreholes.Reservoir characterization and geological modeling supported the results obtained from gas drainage.The drainage efficiency of LRDD Boreholes was the approxi-mately 70%level,while conventional Cross-Measured Boreholes were only 30%.The highest goaf gas quality(94%methane concentration)was reported for TM4,placed at an average elevation of 41 m above coal seam 501.The highest goaf gas production(average 6.2 m^(3)/min)was reported for LRDD Borehole TM3.This borehole was placed within the fracture zone(average elevation of 24.4 m)and drilled through the sandstone lithotype with the best reservoir properties,enhancing drainage performance.LRDD Boreholes TM2 and TM4 achieved similar performance.These three LRDD Boreholes were drilled close to the maximum principal horizontal stress direction,providing borehole stability during under-mining.The lowest goaf gas production was reported for LRDD Boreholes TM1a and TM5.Both Boreholes were placed in the rubble zone.展开更多
When an extremely thick rock bed exists above a protected coal seam in the bending zone given the condition of a mining protective seam, this extremely thick rock bed controls the movement of the entire overlying stra...When an extremely thick rock bed exists above a protected coal seam in the bending zone given the condition of a mining protective seam, this extremely thick rock bed controls the movement of the entire overlying stratum. This extremely thick rock bed, called a ＂main key stratum＂, will not subside nor break for a long time, causing lower fractures and bed separations not to close and gas can migrate to the bed separation areas along the fractures. These bed separations become gas enrichment areas. By analyzing the rule of fracture evolution and gas migration under the main key stratum after the deep protective coal seam has been mined, we propose a new gas drainage method which uses bore holes, drilled through rock and coal seams at great depths for draining pressure relief gas. In this method, the bores are located at a high level suction roadway （we can also drill them in the drilling field located high in an air gateway）. Given the practice in the Haizi mine, the gas drainage rate can reach 73% in the middie coal group, with a gas drainage radius over 100 m.展开更多
Drainage influence radius is the basic parameter for borehole arrangement, while the effect of high pressure water jet slotting technology on borehole drainage influence radius has not been studied systematically. In ...Drainage influence radius is the basic parameter for borehole arrangement, while the effect of high pressure water jet slotting technology on borehole drainage influence radius has not been studied systematically. In this paper, a fully thermo-hydro-mechanical(THM) coupled model which represents the non-linear responses of gas extraction was implemented to demonstrate the reliability of this model through history data matching. Based on this model, the susceptibilities of gas extraction with single slotted borehole, including the permeability, the gas pressure, the temperature, the coal adsorption characteristics and the radius of slot, were quantified through a series of simulations. The simulation results revealed that increasing the permeability, initial gas pressure and temperature could develop the influence radius of single slotted borehole. This finite element model and its simulation results can improve the understanding of the coal-gas interactions of underground gas drainage and provide a scientific basis for the optimization of drainage systems.展开更多
Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound 'three soft' roof and the trouble-somesafety situation encountered in deep le...Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound 'three soft' roof and the trouble-somesafety situation encountered in deep level coal exploitation,proposed a new idea ofgob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The followingwere discovered:the dynamic evolution law of the crannies in the roof is influenced bymining,the formative rule of 'the vertical cranny-abundant area' along the gob-side,thedistribution of air pressure field in the gob,and the flowing rule of pressure-relieved gas ina Y-style ventilation system.The study also established a theoretic basis for a new miningmethod of coal mining and gas extraction which is used to extract the pressure-relievedgas by roadway retaining boreholes instead of roadway boreholes.Studied and resolvedmany difficult key problems,such as,fast roadway retaining at the gob-side without a coalpillar,Y-style ventilation and extraction of pressure-relieved gas by roadway retainingboreholes,and so on.The study innovated and integrated a whole set of technical systemsfor coal and pressure relief gas extraction.The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas.The research can provide a scientific and reliabletechnical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability.展开更多
Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts.The E_(9-10)coal seam is the main coal-producing seam but has poor quality ventilation,thus making it relatively difficult for gas extraction.The F...Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts.The E_(9-10)coal seam is the main coal-producing seam but has poor quality ventilation,thus making it relatively difficult for gas extraction.The F_(15)coal seam,at its lower section,is not prone to coal and gas outbursts.The average seam separation distance of 150 m is greater than the upper limit for underside protective seam mining.Based on borehole imaging technology for field exploration of coal and rock fracture characteristics and discrete element numerical simulation,we have studied the evolution laws and distribution characteristics of the coal and rock fissure field between these two coal seams.By analysis of the influential effect of group F coal mining on the E_(9-10)coal seam,we have shown that a number of small fissures also develop in the area some 150 m above the overlying strata.The width and number of the fissures also increase with the extent of mining activity.Most of the fissures develop at a low angle or even parallel to the strata.The results show that the mining of the F_(15)coal seam has the effect of improving the permeability of the E_(9-10)coal seam.展开更多
According to the specific geological condition, analyzed the stress distribution of the overlying strata, the displacement of pressure released seam, thickness variation and the distribution of plastic zones by FLAG3D...According to the specific geological condition, analyzed the stress distribution of the overlying strata, the displacement of pressure released seam, thickness variation and the distribution of plastic zones by FLAG3D software to simulate mining of the long-distance lower protective seam. The research results show that the distribution of vertical stress appears as a ＂Double-hump＂ within the pressure-relief range of the protected coal seam and the swelling deformation curve of coal bodies takes an ＂M＂ shape. The swelling is divided into initial swelling, swelling increase and swelling compression stability. The maximum swelling ratio of the pressure released seam is 1.84%, protection angle of the lower protective coal seam along the strike direction is about 55°, protection angle below the dip direction is about 50°, protection angle above the dip direction is about 55°, and the coal seam compression zone resembles a ＂U＂ shape.展开更多
The pre-crack blast technology has been used to control the induction caving area in the roof. The key is to form the pre-crack seam and predict the effect of the seam. The H-J-C blast model was built in the roof. Bas...The pre-crack blast technology has been used to control the induction caving area in the roof. The key is to form the pre-crack seam and predict the effect of the seam. The H-J-C blast model was built in the roof. Based on the theories of dynamic strength and failure criterion of dynamic rock, the rock dynamic damage and the evolution of pre-crack seam were simulated by the tensile damage and shear failure of the model. According to the actual situation of No. 92 ore body test stope at Tongkeng Mine, the formation process of the pre-crack blast seam was simulated by Ansys/Ls-dyna software, the pre-crack seam was inspected by a system of digital panoramic borehole camera. The pre-crack seam was inspected by the system of digital panoramic borehole in the roof. The results of the numerical simulation and inspection show that in the line of centers of pre-hole, the minimum of the tensile stress reaches 20 MPa, which is much larger than 13.7 MPa of the dynamic tensile strength of rock. The minimum particle vibration velocity reaches 50 cm/s, which is greater than 30-40 cm/s of the allowable vibration velocity. It is demonstrated that the rock is destroyed near the center line and the pre-crack is successfully formed by the large diameters and large distances pre-crack holes in the roof.展开更多
Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a pot...Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a potential solution for enhancing borehole stability while considering gas production.In this work,we improved and implemented a dual-porosity,fully coupled geomechanical-hydraulic numerical model into COMSOL Multiphysics to investigate into this factor.The sophisticated numerical model incorporates various critical factors,including desorption-induced matrix shrinkage,stress-dependent anisotropic fracture permeability,and the interactions of gas flow and reservoir deformation in matrices and fractures.A suite of simulation scenarios(e.g.,varying coal strength)was carried out to quantify the impact of drilling azimuth on coal permeability evolution,cumulative gas production,and the borehole break-out width for Goonyella Middle Seam of Bowen Basin,Australia.The model was calibrated against both theoretical permeability values and field gas production data.Due to the lack of directly measured matrix permeability data,the actual gas production was used to back calculate the best-matched matrix permeability,which is 0.65μD for this particular work.Moreover,based on the breakout shape and induced volumetric strains around the borehole,drilling along the maximum horizontal stress does not necessarily lead to the best stability of the borehole,as generally believed.A drilling azimuth between 0and 60results in similar breakout width,whereas a drilling azimuth between 60and 90achieves the most efficient gas production.By considering both gas production efficiency and borehole stability,for this particular reservoir condition,the optimum drilling azimuth is determined to be between 45and 60.This study presents a practical approach for determining the optimum drilling azimuth in coal seam gas extraction through in seam boreholes.展开更多
The Kunlunshan Mountain Ms8.1 earthquake, occurred in Nov.14, 2001, is the first event with magnitude more than 8 in the China earthquake monitoring history, specifically at the beginning of digital techniques in prec...The Kunlunshan Mountain Ms8.1 earthquake, occurred in Nov.14, 2001, is the first event with magnitude more than 8 in the China earthquake monitoring history, specifically at the beginning of digital techniques in precursor monitoring networks. Any investigation of recorded data on this earthquake is very important for testing the operation of the digital monitoring networks and understanding the preparation, occurrence, and adjustment of stress/strain of strong continental earthquakes. In this paper we investigated the coseismic response changes of well water level of groundwater and volume strain meter of bore hole in digital earthquake monitoring network of Capital area and its vicinity, due to the Nov.14, 2001 Ms8.1 Kunlun Mountain earthquake. The responding time, shapes or manners, amplitudes, and lasting time of well water level and strain-meters to seismic wave are studied in comparison. Then we discussed the possibility that the response changes of groundwater to strong distant earthquakes can be understood as one kind of observing evidence of stress/strain changes induced by distant earthquake.展开更多
Multi-factor productivity(MFP) in underground coal mining has been on the decline for the last decade.The mining industry requires a viable and sustainable approach to overcome the current downtrend. This is only poss...Multi-factor productivity(MFP) in underground coal mining has been on the decline for the last decade.The mining industry requires a viable and sustainable approach to overcome the current downtrend. This is only possible by concurrently focussing on productivity improvement and operating costs reduction,delivered through both incremental and step change technology development. Four technologies are presented in this paper: fibre optic borehole sensing has been demonstrated to reveal detailed information about gas flow influx, water level and borehole blockage events occurring along the length of a surfaceto-inseam lateral. Fibre optic gas sensing has also been investigated, and this technology promises a remote, intrinsically safe, distributed solution. Recent developments in continuous water jet drilling technology have demonstrated a step change increase in drilling rates and flexibility for coal seam degassing,applicable in both surface-to-inseam and underground in-seam applications. The application of water jet technology to the cable bolt drilling problem offers potential to address a serious health and safety and productivity issue in the roadway development process.展开更多
To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture devel...To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture development of floor coal-rock mass of the protective seam and migration rule of pressure-relief gas from a protected seam so as to obtain an effective pressure- relief gas extraction method.The results show that after the upper protective seam was mined,mining-induced fracturing floor coal-rock mas...展开更多
文摘In order to clarify the danger of water breakout in the bottom plate of extra-thick coal seam mining, 2202 working face of a mine in the west is taken as the research object, and it is proposed to use the on-site monitoring means combining borehole peeping and microseismic monitoring, combined with the theoretical analysis to analyze the danger of water breakout in the bottom plate. The results show that: 1) the theoretically calculated maximum damage depth of the bottom plate is 27.5 m, and its layer is located above the Austrian ash aquifer, which has the danger of water breakout;2) the drill hole peeping at the bottom plate of the working face shows that the depth of the bottom plate fissure development reaches 26 m, and the integrity of the water barrier layer has been damaged, so there is the risk of water breakout;3) for the microseismic monitoring of the anomalous area, the bottom plate of the return air downstream channel occurs in the field with a one-week lag, which shows that microseismic monitoring events may reflect the water breakout of the underground. This shows that the microseismic monitoring events can reflect the changes of the underground flow field, which can provide a reference basis for the early warning of water breakout. The research results can provide reference for the prediction of sudden water hazard.
基金financially supported by the National Natural Science Fund of China(Nos.51004003 and 51474009)Anhui Province Education Department Natural Science Fund Key Project of China(No.KJ2010A091)
文摘In order to solve the problems of top-coal inadequate destruction and large amounts of gas emission in mining extra thick and hard coal seam,this study investigated the pre-splitting for deep borehole blasting and gas pre-draining technologies on top coal.The mechanism of the technologies was systematically expounded based on hard top-coal cracks development obtained by numerical simulation and theoretical analysis.The results show that explosive blasting in the hard rock results in a large number of cracks and large displacement in the rock mass due to the effect of explosion stress.Meanwhile,the thick top-coal caves,and desorbing gas flows along the cracks improve gas extraction.Finally,the pre-splitting for deep borehole blasting and gas pre-draining technologies was applied in No.3802 working face of Shui Liandong Coal Mine,which increases monthly output in the face to 67.34 kt and the drained gas concentration to 86.2%.The drained gas average concentration from each borehole reaches 40%,and the effect is remarkable.
文摘This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content coals Staszic-Wujek Hard Coal Mine in the Upper Silesia Coal Basin(Poland).Five LRDD Boreholes(TM1a-TM5)with a length of 300 and 400 m were located over coal seam 501 in the fractured zone and monitored over six months of longwall face operations.LRDD Boreholes were combined with Cross-Measured Boreholes.Reservoir characterization and geological modeling supported the results obtained from gas drainage.The drainage efficiency of LRDD Boreholes was the approxi-mately 70%level,while conventional Cross-Measured Boreholes were only 30%.The highest goaf gas quality(94%methane concentration)was reported for TM4,placed at an average elevation of 41 m above coal seam 501.The highest goaf gas production(average 6.2 m^(3)/min)was reported for LRDD Borehole TM3.This borehole was placed within the fracture zone(average elevation of 24.4 m)and drilled through the sandstone lithotype with the best reservoir properties,enhancing drainage performance.LRDD Boreholes TM2 and TM4 achieved similar performance.These three LRDD Boreholes were drilled close to the maximum principal horizontal stress direction,providing borehole stability during under-mining.The lowest goaf gas production was reported for LRDD Boreholes TM1a and TM5.Both Boreholes were placed in the rubble zone.
基金Projects 2005CB221503 supported by the National Basic Research Program of China70533050 and 50674089 by the National Natural Science Foundation of China2005BA813B-3-06 by the National Tenth 5-Year Key Scientific and Technological Project
文摘When an extremely thick rock bed exists above a protected coal seam in the bending zone given the condition of a mining protective seam, this extremely thick rock bed controls the movement of the entire overlying stratum. This extremely thick rock bed, called a ＂main key stratum＂, will not subside nor break for a long time, causing lower fractures and bed separations not to close and gas can migrate to the bed separation areas along the fractures. These bed separations become gas enrichment areas. By analyzing the rule of fracture evolution and gas migration under the main key stratum after the deep protective coal seam has been mined, we propose a new gas drainage method which uses bore holes, drilled through rock and coal seams at great depths for draining pressure relief gas. In this method, the bores are located at a high level suction roadway （we can also drill them in the drilling field located high in an air gateway）. Given the practice in the Haizi mine, the gas drainage rate can reach 73% in the middie coal group, with a gas drainage radius over 100 m.
基金financial support from the National Natural Science Foundation of China (No.51404250)the Fundamental Research Funds for the Central Universities (No.2013QNB19)+2 种基金the Natural Science Foundation of Jiangsu,China (No.BK20140189)the China Postdoctoral Science Foundation (Nos.2014M550315,2014M550316,2016T90526)the College Graduate Research and Innovation Program of Jiangsu Province (No.KYLX15_1408)
文摘Drainage influence radius is the basic parameter for borehole arrangement, while the effect of high pressure water jet slotting technology on borehole drainage influence radius has not been studied systematically. In this paper, a fully thermo-hydro-mechanical(THM) coupled model which represents the non-linear responses of gas extraction was implemented to demonstrate the reliability of this model through history data matching. Based on this model, the susceptibilities of gas extraction with single slotted borehole, including the permeability, the gas pressure, the temperature, the coal adsorption characteristics and the radius of slot, were quantified through a series of simulations. The simulation results revealed that increasing the permeability, initial gas pressure and temperature could develop the influence radius of single slotted borehole. This finite element model and its simulation results can improve the understanding of the coal-gas interactions of underground gas drainage and provide a scientific basis for the optimization of drainage systems.
文摘Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound 'three soft' roof and the trouble-somesafety situation encountered in deep level coal exploitation,proposed a new idea ofgob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The followingwere discovered:the dynamic evolution law of the crannies in the roof is influenced bymining,the formative rule of 'the vertical cranny-abundant area' along the gob-side,thedistribution of air pressure field in the gob,and the flowing rule of pressure-relieved gas ina Y-style ventilation system.The study also established a theoretic basis for a new miningmethod of coal mining and gas extraction which is used to extract the pressure-relievedgas by roadway retaining boreholes instead of roadway boreholes.Studied and resolvedmany difficult key problems,such as,fast roadway retaining at the gob-side without a coalpillar,Y-style ventilation and extraction of pressure-relieved gas by roadway retainingboreholes,and so on.The study innovated and integrated a whole set of technical systemsfor coal and pressure relief gas extraction.The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas.The research can provide a scientific and reliabletechnical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability.
基金financially supported by the State Key Basic Research Program of China(No.2011CB201203)the State Key Special Program of China(No.2011ZX05040-001-005)the National Natural Science Foundation of China(No.51374256)
文摘Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts.The E_(9-10)coal seam is the main coal-producing seam but has poor quality ventilation,thus making it relatively difficult for gas extraction.The F_(15)coal seam,at its lower section,is not prone to coal and gas outbursts.The average seam separation distance of 150 m is greater than the upper limit for underside protective seam mining.Based on borehole imaging technology for field exploration of coal and rock fracture characteristics and discrete element numerical simulation,we have studied the evolution laws and distribution characteristics of the coal and rock fissure field between these two coal seams.By analysis of the influential effect of group F coal mining on the E_(9-10)coal seam,we have shown that a number of small fissures also develop in the area some 150 m above the overlying strata.The width and number of the fissures also increase with the extent of mining activity.Most of the fissures develop at a low angle or even parallel to the strata.The results show that the mining of the F_(15)coal seam has the effect of improving the permeability of the E_(9-10)coal seam.
基金Supported by the Basic Research Program of National Natural Science Foundation of China(50834005)
文摘According to the specific geological condition, analyzed the stress distribution of the overlying strata, the displacement of pressure released seam, thickness variation and the distribution of plastic zones by FLAG3D software to simulate mining of the long-distance lower protective seam. The research results show that the distribution of vertical stress appears as a ＂Double-hump＂ within the pressure-relief range of the protected coal seam and the swelling deformation curve of coal bodies takes an ＂M＂ shape. The swelling is divided into initial swelling, swelling increase and swelling compression stability. The maximum swelling ratio of the pressure released seam is 1.84%, protection angle of the lower protective coal seam along the strike direction is about 55°, protection angle below the dip direction is about 50°, protection angle above the dip direction is about 55°, and the coal seam compression zone resembles a ＂U＂ shape.
基金Project(2006BAB02A02)supported by the National Key Technology R&D Program for the 11th Five-year Plan of ChinaProject(09JJ4025)supported by the National Natural Science Foundation of Hunan Province,ChinaProject(51074178)supported by the National Natural Science Foundation of China
文摘The pre-crack blast technology has been used to control the induction caving area in the roof. The key is to form the pre-crack seam and predict the effect of the seam. The H-J-C blast model was built in the roof. Based on the theories of dynamic strength and failure criterion of dynamic rock, the rock dynamic damage and the evolution of pre-crack seam were simulated by the tensile damage and shear failure of the model. According to the actual situation of No. 92 ore body test stope at Tongkeng Mine, the formation process of the pre-crack blast seam was simulated by Ansys/Ls-dyna software, the pre-crack seam was inspected by a system of digital panoramic borehole camera. The pre-crack seam was inspected by the system of digital panoramic borehole in the roof. The results of the numerical simulation and inspection show that in the line of centers of pre-hole, the minimum of the tensile stress reaches 20 MPa, which is much larger than 13.7 MPa of the dynamic tensile strength of rock. The minimum particle vibration velocity reaches 50 cm/s, which is greater than 30-40 cm/s of the allowable vibration velocity. It is demonstrated that the rock is destroyed near the center line and the pre-crack is successfully formed by the large diameters and large distances pre-crack holes in the roof.
文摘Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a potential solution for enhancing borehole stability while considering gas production.In this work,we improved and implemented a dual-porosity,fully coupled geomechanical-hydraulic numerical model into COMSOL Multiphysics to investigate into this factor.The sophisticated numerical model incorporates various critical factors,including desorption-induced matrix shrinkage,stress-dependent anisotropic fracture permeability,and the interactions of gas flow and reservoir deformation in matrices and fractures.A suite of simulation scenarios(e.g.,varying coal strength)was carried out to quantify the impact of drilling azimuth on coal permeability evolution,cumulative gas production,and the borehole break-out width for Goonyella Middle Seam of Bowen Basin,Australia.The model was calibrated against both theoretical permeability values and field gas production data.Due to the lack of directly measured matrix permeability data,the actual gas production was used to back calculate the best-matched matrix permeability,which is 0.65μD for this particular work.Moreover,based on the breakout shape and induced volumetric strains around the borehole,drilling along the maximum horizontal stress does not necessarily lead to the best stability of the borehole,as generally believed.A drilling azimuth between 0and 60results in similar breakout width,whereas a drilling azimuth between 60and 90achieves the most efficient gas production.By considering both gas production efficiency and borehole stability,for this particular reservoir condition,the optimum drilling azimuth is determined to be between 45and 60.This study presents a practical approach for determining the optimum drilling azimuth in coal seam gas extraction through in seam boreholes.
基金supported by Natural Science Foundation of China(41274061 and 40374019)
文摘The Kunlunshan Mountain Ms8.1 earthquake, occurred in Nov.14, 2001, is the first event with magnitude more than 8 in the China earthquake monitoring history, specifically at the beginning of digital techniques in precursor monitoring networks. Any investigation of recorded data on this earthquake is very important for testing the operation of the digital monitoring networks and understanding the preparation, occurrence, and adjustment of stress/strain of strong continental earthquakes. In this paper we investigated the coseismic response changes of well water level of groundwater and volume strain meter of bore hole in digital earthquake monitoring network of Capital area and its vicinity, due to the Nov.14, 2001 Ms8.1 Kunlun Mountain earthquake. The responding time, shapes or manners, amplitudes, and lasting time of well water level and strain-meters to seismic wave are studied in comparison. Then we discussed the possibility that the response changes of groundwater to strong distant earthquakes can be understood as one kind of observing evidence of stress/strain changes induced by distant earthquake.
基金Australian Coal Association Research Program (ACARP)CRCMining’s Coal Technologies and Fugitive Emissions Research programThe University of Queensland
文摘Multi-factor productivity(MFP) in underground coal mining has been on the decline for the last decade.The mining industry requires a viable and sustainable approach to overcome the current downtrend. This is only possible by concurrently focussing on productivity improvement and operating costs reduction,delivered through both incremental and step change technology development. Four technologies are presented in this paper: fibre optic borehole sensing has been demonstrated to reveal detailed information about gas flow influx, water level and borehole blockage events occurring along the length of a surfaceto-inseam lateral. Fibre optic gas sensing has also been investigated, and this technology promises a remote, intrinsically safe, distributed solution. Recent developments in continuous water jet drilling technology have demonstrated a step change increase in drilling rates and flexibility for coal seam degassing,applicable in both surface-to-inseam and underground in-seam applications. The application of water jet technology to the cable bolt drilling problem offers potential to address a serious health and safety and productivity issue in the roadway development process.
基金Funded by the Major State Basic Research Development Program of China(No.2005CB221503)the Key Program of the Natural Science Foundation of China(No.70533050,50904068 and 50674089)
文摘To ensure the mining safety of working face in the protective seam and meanwhile extract pressure-relief gas of the lower protected seam and eliminate its outburst risk,the present study researched into fracture development of floor coal-rock mass of the protective seam and migration rule of pressure-relief gas from a protected seam so as to obtain an effective pressure- relief gas extraction method.The results show that after the upper protective seam was mined,mining-induced fracturing floor coal-rock mas...
