Numerical Simulation Research Of The Stress Of Large Bore Roadway-type Horizontal Wells

Coalbed methane and coal are co-associated minerals with homologous and different phases,the development of coalbed methane and coal mining promote and restrict each other.It is of great practical significance for realizing coordinated mining of coal and coalbed methane and ensuring mine safety in production to use the impact of coal mining activities on the development of coalbed methane,increase the production of CBM wells in the affected area,promote the efficient drainage.This paper takes the north of Fanzhuang block in the southern Qinshui Basin where CBM exploration and development is relatively active in China as an example.Based on the collection of the Fanzhuang block and its adjacent mine-Hudi mine excavation data,and CBM well drainage data,this paper summarizes the temporal and spatial laws of mine mining and CBM well drainage.The calculation model of stress field under the coupling action of coal seam and roof and floor around the roadway-type horizontal wells during excavation is established by the numerical simulation software ABAQUS.The stress distribution characteristics around the wells under different conditions of wellbore shapes,sizes and excavation directions are discussed.The results show that:(1)Mine excavation has both positive and negative effects on CBM well drainage.The abnormal drainage of coalbed methane wells in Hudi mining area is mainly affected by mining activities,underground gas drainage and the decrease of reservoir fluid pressure.(2)The finite element method is used to analyze the distribution characteristics of the rock stress field around the well during the excavation of a large-diameter roadway-type horizontal well.Point out the range of severe stress release zone and stress influence zone,and then analyze the stress change characteristics of plastic zone,elastic zone and original rock stress zone.According to the relationship between effective stress and permeability,the change law of permeability in the "three zones" during the excavation process is analyzed.(3)The coupling effect of coal seam and roof and floor obviously changes the stress distribution around the roadway-type horizontal wells,especially in the vertical direction,which presents discontinuity and incompatibility,and increases the stress concentration at the lithological mutation interface.Conducive to the release of rock stress around the well.The circular roadway-type horizontal well is more conducive to stress release and well diameter expansion to a certain extent.(4)Rectangular and circular roadway-type horizontal wells have basically the same range of stress influence zone around the well,which is about 80 m.the stress release in the influence range of circular roadway-type horizontal wells is more severe.Stress concentration occurs in the severe stress release zone of rectangular roadway-type horizontal wells,which is not conducive to the release of ground stress.The range of the severe stress release zone and stress influence zone of the surrounding rock of the roadway-type horizontal well increases with the increase of the borehole size,and the influence of the borehole size on the range of the stress influence zone around the well is greater than that of the severe stress release zone.(5)After a roadway-type horizontal well is excavated along the maximum or minimum horizontal principal stress,stress concentration occurs in the vertical principal stress,and stress release occurs in the maximum and minimum horizontal principal stress.Surrounding rock stress release produces a certain range of severe stress release zone and stress influence zone.Excavating roadway horizontal wells in the direction of the minimum horizontal principal stress is more conducive to stress release.This paper contains 36 figures,6 tables and 107 references.