To enhance gas drainage in the soft and hard interbedded(SHI)coal seam,it’s necessary to unload the insitu stress and improve its gas migration performance.In this research,a directional hydraulic flushing(DHF)techno...To enhance gas drainage in the soft and hard interbedded(SHI)coal seam,it’s necessary to unload the insitu stress and improve its gas migration performance.In this research,a directional hydraulic flushing(DHF)technology was carried out.The stress-unloading and gas migration improvement mechanism was analyzed through numerical simulation,and systematic engineering tests were conducted to verify the gas drainage effect.The results show that the improvement of gas migration performance in the SHI coal seam is caused by a combined effect of seepage-improving and diffusion-improving.After DHF,stress-unloading and plastic failure could be achieved both in the soft coal(SC)sublayer and in the hard coal(HC)sublayer.However,the gas diffusion capacity improves significantly in the SC sublayer,while the gas seepage capacity improves notably in the HC sublayer.Meanwhile,the stress-unloading and gas migration improvement effect improves with the flushing radius and the thickness of the SC sublayer.Besides,after adopting the DHF technology,the gas drainage effect improved markedly.The borehole number dropped by 49%,the gas drainage ratio increased from 26.0%to 48.2%,and the average coal roadway excavation speed increased from 2.4 to 5.6 m/d.展开更多
Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage perfor- mance. However, it frequently occurs that a large amount of slotting products （mainly the coal slurry and gas） i...Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage perfor- mance. However, it frequently occurs that a large amount of slotting products （mainly the coal slurry and gas） intensely spurt out of the borehole during the slotting, which adversely affects the slotting efficiency. Despite extensive previous investigations on the mechanism and prevention-device design of the spurt during ordinary borehole drilling, a very few studies has focused on the spurt in the s Ottlng pro ] ＂ _ cess. The slotting spurt is mainly caused by two reasons： the coal and gas outburst in the borehole and the borehole deslagging blockage. This paper focuses on the second reason, and investigates the hydraulic deslagging flow patterns in the annular space between the drill pipe and borehole wall Results show that there are six deslagging flow patterns when the drill pipe is still： pure slurry flow, pure gas flow, bubble flow, intermittent flow, layering flow and annular flow. When the drill pipe rotates, each of those six flow patterns changes due to the Taylor vortex effect. Outcomes of this study could help to better understand the slotting-spurt mechanism and provide guidance on the anti-spurt strategies through eliminating the borehole deslagging blockage.展开更多
Radial borehole fracturing that combines radial boreholes with hydraulic fracturing is anticipated to improve the output of tight oil and gas reservoirs.This paper aims to investigate fracture propagation and pressure...Radial borehole fracturing that combines radial boreholes with hydraulic fracturing is anticipated to improve the output of tight oil and gas reservoirs.This paper aims to investigate fracture propagation and pressure characteristics of radial borehole fracturing in multiple layers.A series of laboratory experiments with artificial rock samples(395 mm×395 mm×395 mm)was conducted using a true triaxial fracturing device.Three crucial factors corresponding to the vertical distance of adjacent radial borehole layers(vertical distance),the azimuth and diameter of the radial borehole are examined.Experimental results show that radial borehole fracturing in multiple layers generates diverse fracture geometries.Four types of fractures are identified based on the connectivity between hydraulic fractures and radial boreholes.The vertical distance significantly influences fracture propagation perpendicular to the radial borehole axis.An increase in the vertical distance impedes fracture connection across multiple radial borehole layers and reduces the fracture propagation distance along the radial borehole axis.The azimuth also influences fracture propagation along the radial borehole axis.Increasing the azimuth reduces the guiding ability of radial boreholes,which makes the fracture quickly curve to the maximum horizontal stress direction.The breakdown pressure correlates with diverse fracture geometries observed.When the fractures connect multi-layer radial boreholes,increasing the vertical distance decreases the breakdown pressure.Decreasing the azimuth and increasing the diameter also decrease the breakdown pressure.The extrusion force exists between the adjacent fractures generated in radial boreholes in multiple rows,which plays a crucial role in enhancing the guiding ability of radial boreholes and results in higher breakdown pressure.The research provides valuable theoretical insights for the field application of radial borehole fracturing technology in tight oil and gas reservoirs.展开更多
High concentration and large flow flux of gas drainage from underground coal seams is the precondition of reducing emission and large-scale use of gas.However,the layered occurrence of coal seams with tectonically def...High concentration and large flow flux of gas drainage from underground coal seams is the precondition of reducing emission and large-scale use of gas.However,the layered occurrence of coal seams with tectonically deformed sub-layers and intact sub-layers makes it difficult to effectively drain gas through commonly designed boreholes.In this study,the gas drainage performance in coal seams with different combinations of tectonically deformed sub-layers and intact sub-layers was numerically analyzed.The analysis results show that the gas drainage curve changes from a single-stage line to a dual-stage curve as the permeability ratios of Zone II(kII)and Zone I(kI)increase,raising the difficulty in gas drainage.Furthermore,a dual-system pressure decay model based on the first-order kinetic model was developed to describe the dual-stage characteristics of pressure decay curves with different permeability ratios.In the end,the simulation results were verified with reference to in-situ drainage data from literature.The research results are helpful for mines,especially those with layered coal seams comprising tectonically deformed sub-layers and intact sub-layers,to choose appropriate gas drainage methods and develop the original drainage designs for achieving better gas drainage performance.展开更多
Hydraulic fracturing technology is an important means of shale gas development,and microseismic monitoring is the key technology of fracturing effect evaluation.In this study,hydraulic fracturing and microseismic moni...Hydraulic fracturing technology is an important means of shale gas development,and microseismic monitoring is the key technology of fracturing effect evaluation.In this study,hydraulic fracturing and microseismic monitoring were simultaneously conducted in the Eyangye 2HF well(hereinafter referred to as EYY2HF well).The target stratum of this well is the second member of the Doushantuo Formation of the Sinian System,which is the oldest stratum of horizontal shale gas wells in the world.A total of 4341 microseismic fracturing events were identified,and 23 fracturing stages of the well were defined.The fluctuation of the number of events showed a repeating“high-low”pattern,and the average energy of these events showed minimal differences.These findings indicate that the water pressure required for the reconstruction of the EYY2HF well is appropriate.The main body of the fracture network extended from northwest to southeast,consistent with the interpretation of regional geological and seismic data.The stimulated rock volumes showed a linear increase with the increase of the fracturing stage.Some technological measures,such as quick lift displacement,quick lift sand ratio,and pump stop for secondary sand addition,were adopted during fracturing to increase the complexity of the fracture network.Microseismic fracture monitoring of the well achieved expected eff ects and guided real-time fracturing operations and fracturing eff ect evaluation.展开更多
基金the financial support from the National Natural Science Foundation of China(Nos.52104210,52174217,and 51874294)the Natural Science Foundation of Shanxi Province(No.20210302124350)Project Funded by China Postdoctoral Science Foundation(No.2022M710595).
文摘To enhance gas drainage in the soft and hard interbedded(SHI)coal seam,it’s necessary to unload the insitu stress and improve its gas migration performance.In this research,a directional hydraulic flushing(DHF)technology was carried out.The stress-unloading and gas migration improvement mechanism was analyzed through numerical simulation,and systematic engineering tests were conducted to verify the gas drainage effect.The results show that the improvement of gas migration performance in the SHI coal seam is caused by a combined effect of seepage-improving and diffusion-improving.After DHF,stress-unloading and plastic failure could be achieved both in the soft coal(SC)sublayer and in the hard coal(HC)sublayer.However,the gas diffusion capacity improves significantly in the SC sublayer,while the gas seepage capacity improves notably in the HC sublayer.Meanwhile,the stress-unloading and gas migration improvement effect improves with the flushing radius and the thickness of the SC sublayer.Besides,after adopting the DHF technology,the gas drainage effect improved markedly.The borehole number dropped by 49%,the gas drainage ratio increased from 26.0%to 48.2%,and the average coal roadway excavation speed increased from 2.4 to 5.6 m/d.
文摘Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage perfor- mance. However, it frequently occurs that a large amount of slotting products （mainly the coal slurry and gas） intensely spurt out of the borehole during the slotting, which adversely affects the slotting efficiency. Despite extensive previous investigations on the mechanism and prevention-device design of the spurt during ordinary borehole drilling, a very few studies has focused on the spurt in the s Ottlng pro ] ＂ _ cess. The slotting spurt is mainly caused by two reasons： the coal and gas outburst in the borehole and the borehole deslagging blockage. This paper focuses on the second reason, and investigates the hydraulic deslagging flow patterns in the annular space between the drill pipe and borehole wall Results show that there are six deslagging flow patterns when the drill pipe is still： pure slurry flow, pure gas flow, bubble flow, intermittent flow, layering flow and annular flow. When the drill pipe rotates, each of those six flow patterns changes due to the Taylor vortex effect. Outcomes of this study could help to better understand the slotting-spurt mechanism and provide guidance on the anti-spurt strategies through eliminating the borehole deslagging blockage.
基金The authors gratefully acknowledge the financial support received from the Strategic Cooperation Technology Projects of CNPC and CUPB(No.ZLZX2020-01)the National Key Scientific Research Instrument Research Project of NSFC(No.51827804).
文摘Radial borehole fracturing that combines radial boreholes with hydraulic fracturing is anticipated to improve the output of tight oil and gas reservoirs.This paper aims to investigate fracture propagation and pressure characteristics of radial borehole fracturing in multiple layers.A series of laboratory experiments with artificial rock samples(395 mm×395 mm×395 mm)was conducted using a true triaxial fracturing device.Three crucial factors corresponding to the vertical distance of adjacent radial borehole layers(vertical distance),the azimuth and diameter of the radial borehole are examined.Experimental results show that radial borehole fracturing in multiple layers generates diverse fracture geometries.Four types of fractures are identified based on the connectivity between hydraulic fractures and radial boreholes.The vertical distance significantly influences fracture propagation perpendicular to the radial borehole axis.An increase in the vertical distance impedes fracture connection across multiple radial borehole layers and reduces the fracture propagation distance along the radial borehole axis.The azimuth also influences fracture propagation along the radial borehole axis.Increasing the azimuth reduces the guiding ability of radial boreholes,which makes the fracture quickly curve to the maximum horizontal stress direction.The breakdown pressure correlates with diverse fracture geometries observed.When the fractures connect multi-layer radial boreholes,increasing the vertical distance decreases the breakdown pressure.Decreasing the azimuth and increasing the diameter also decrease the breakdown pressure.The extrusion force exists between the adjacent fractures generated in radial boreholes in multiple rows,which plays a crucial role in enhancing the guiding ability of radial boreholes and results in higher breakdown pressure.The research provides valuable theoretical insights for the field application of radial borehole fracturing technology in tight oil and gas reservoirs.
基金National Science Foundation of China(Nos.51904311,51874314)Beijing Municipal Natural Science Foundation(8194072)+1 种基金Fundamental Research Funds for the Central Universities(2019QY02)State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University)(WS2019A04).
文摘High concentration and large flow flux of gas drainage from underground coal seams is the precondition of reducing emission and large-scale use of gas.However,the layered occurrence of coal seams with tectonically deformed sub-layers and intact sub-layers makes it difficult to effectively drain gas through commonly designed boreholes.In this study,the gas drainage performance in coal seams with different combinations of tectonically deformed sub-layers and intact sub-layers was numerically analyzed.The analysis results show that the gas drainage curve changes from a single-stage line to a dual-stage curve as the permeability ratios of Zone II(kII)and Zone I(kI)increase,raising the difficulty in gas drainage.Furthermore,a dual-system pressure decay model based on the first-order kinetic model was developed to describe the dual-stage characteristics of pressure decay curves with different permeability ratios.In the end,the simulation results were verified with reference to in-situ drainage data from literature.The research results are helpful for mines,especially those with layered coal seams comprising tectonically deformed sub-layers and intact sub-layers,to choose appropriate gas drainage methods and develop the original drainage designs for achieving better gas drainage performance.
基金National key R&D plan(2016YFC060110605)National major projects(2016ZX05034004-005)。
文摘Hydraulic fracturing technology is an important means of shale gas development,and microseismic monitoring is the key technology of fracturing effect evaluation.In this study,hydraulic fracturing and microseismic monitoring were simultaneously conducted in the Eyangye 2HF well(hereinafter referred to as EYY2HF well).The target stratum of this well is the second member of the Doushantuo Formation of the Sinian System,which is the oldest stratum of horizontal shale gas wells in the world.A total of 4341 microseismic fracturing events were identified,and 23 fracturing stages of the well were defined.The fluctuation of the number of events showed a repeating“high-low”pattern,and the average energy of these events showed minimal differences.These findings indicate that the water pressure required for the reconstruction of the EYY2HF well is appropriate.The main body of the fracture network extended from northwest to southeast,consistent with the interpretation of regional geological and seismic data.The stimulated rock volumes showed a linear increase with the increase of the fracturing stage.Some technological measures,such as quick lift displacement,quick lift sand ratio,and pump stop for secondary sand addition,were adopted during fracturing to increase the complexity of the fracture network.Microseismic fracture monitoring of the well achieved expected eff ects and guided real-time fracturing operations and fracturing eff ect evaluation.
