Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface struc...Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface structures.A coal mine in Shanxi,China,utilizes a split-level longwall layout(SLL)for a sub-horizontal No.8 coal seam to improve the cavability of mudstone interlayer and top coal.This layout,however,also produced unexpectedly favorable surface subsidence.Subsidence of No.6 and No.8 longwall panels was monitored while mining was conducted.Field instrumentation and numerical simulation were carried out.It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other.Due to elimination of conventional parallelepiped gate pillar,No.6 and No.8 gobs were connected.Extraction of two SLL panels acted as one supercritical panel.The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed.Therefore,SLL is more favorable for postmining land reuse as gobs are more consolidated underground.展开更多
As the ultra-heavy oil reservoirs developed by steam assisted gravity drainage(SAGD)in the Fengcheng oilfield,Xinjiang have problems such as huge steam usage,long preheating period,low production,and inaccessible rese...As the ultra-heavy oil reservoirs developed by steam assisted gravity drainage(SAGD)in the Fengcheng oilfield,Xinjiang have problems such as huge steam usage,long preheating period,low production,and inaccessible reserve in local parts.Based on the rock mechanics and porosity/permeability characteristics of heavy oil reservoir and interlayer,a series of true triaxial experiments and CT tests considering the fracturing fluid injection rate,viscosity,perforation density and location of fracture initiation were conducted to disclose the propagation behavior of micro-and macro-fractures in the reservoirs and mudstone interlayers.These experiments show that fracturing in the heavy oil reservoirs only generates microfractures that cannot break the interlayer.In contrast,when fracturing in the interlayer,the higher the injection rate(greater than 0.6 m^3/min),the lower the viscosity,the easier it is to form macro-fractures in the interlayers,and the further the fractures will propagate into the reservoirs.Also,increasing perforation density tends to create complex macro-fracture network in the interbedded reservoirs and mudstone interlayers.The findings of this study can provide scientific guidance for the selection of fracturing layer and the optimization of parameters in the interlayer fracturing of heavy oil reservoirs.展开更多
基金This study was funded by the General Program of the National Natural Science Foundation of China(52274092)Hu-Bao-E National Independent Innovation Demonstration Zone Construction Science and Technology Support Project(2023XM08)Funds for Talents Supported by the China Association for Science and Technol-0gy(YESS20200211).
文摘Ground subsidence caused by extraction of longwall panels has always been a great concern all over the world.Conventional longwall mining system(CLMS)gives rise to wavy subsidence causing great damage to surface structures.A coal mine in Shanxi,China,utilizes a split-level longwall layout(SLL)for a sub-horizontal No.8 coal seam to improve the cavability of mudstone interlayer and top coal.This layout,however,also produced unexpectedly favorable surface subsidence.Subsidence of No.6 and No.8 longwall panels was monitored while mining was conducted.Field instrumentation and numerical simulation were carried out.It is demonstrated that an asymmetric subsidence profile with stepped subsidence and cracks occurred on the tailgate side but relatively mild and smooth deformation on the other.Due to elimination of conventional parallelepiped gate pillar,No.6 and No.8 gobs were connected.Extraction of two SLL panels acted as one supercritical panel.The maximum possible subsidence was reached which lowers the likelihood of potential future secondary subsidence as underground gob fractures and voids have closed.Therefore,SLL is more favorable for postmining land reuse as gobs are more consolidated underground.
基金Supported by the National Natural Science Foundation of China(51404281)
文摘As the ultra-heavy oil reservoirs developed by steam assisted gravity drainage(SAGD)in the Fengcheng oilfield,Xinjiang have problems such as huge steam usage,long preheating period,low production,and inaccessible reserve in local parts.Based on the rock mechanics and porosity/permeability characteristics of heavy oil reservoir and interlayer,a series of true triaxial experiments and CT tests considering the fracturing fluid injection rate,viscosity,perforation density and location of fracture initiation were conducted to disclose the propagation behavior of micro-and macro-fractures in the reservoirs and mudstone interlayers.These experiments show that fracturing in the heavy oil reservoirs only generates microfractures that cannot break the interlayer.In contrast,when fracturing in the interlayer,the higher the injection rate(greater than 0.6 m^3/min),the lower the viscosity,the easier it is to form macro-fractures in the interlayers,and the further the fractures will propagate into the reservoirs.Also,increasing perforation density tends to create complex macro-fracture network in the interbedded reservoirs and mudstone interlayers.The findings of this study can provide scientific guidance for the selection of fracturing layer and the optimization of parameters in the interlayer fracturing of heavy oil reservoirs.
