Prediction Model Of Coal-Body Structure And High Quality CBM Reservoirs In Xishan-gujiao Block,Shanxi,China

Investigation and prediction on coal structure and its controlling factors is a basis for formulating the scheme of coalbed mechane?CBM?exploration and exploitation.The controls of tectonic evolution,style combination and surrounding rock strength on coal deformation in the Gujiao Block,Shanxi Province was studied,and the mathematical models of identification for coal seams and fractural permeability were established.The study area was zoned according to coalbody strucuture,and favorable CBM production districts were predictd.It was founded that there exsita large amount of the brittle joints in the coal seams,but rare kneaded and wrinked deformation.The primary structure and cataclastic coals develop predominantly,with a small proportion of mylonitic coal.Based on the logging responses of five calibration boreholes,the mathematical model of identification for the coalbody structure of No.8 coal seam was established,was apllied to indentify the coalbody structures in 31 boreholes,and the coal seam reconstruction was zoned in the block.The controlling factors of coalbody structure were characterized quantitatively.The mechanical parameters of coals for influencing coalbody structure were screened using grey correlation method,and the stress was characterized quantitatively using structural curvature method.It is suggested that the coal seam thickness,structure and local structure controlled the coalbody structure as key geological factors.Using FLAC^3D software,the influence of the folds and faults on the coal deformation was simulated and studied,which revealed the mechanical mechanism was for the deformation.Based on the structural curvature,coal seam thickness as well as the mathematical model of the fracture openness of coal seam,the fractural permeability of No.8 coal seam was predicted,taking the well-testing results as a constraint.The prediction model of the acoustic logging response to the poisson ratio,elasticity modulus,compressive strength and other geological parameters was established according to the measured data of mechanical properties.Then,the controls of the mechanical properties of the roof and floor rocks on the hydraulic fracturing fractures of coal seams were discussed.Using grey fuzzy method,the types of the favorable CBM production districts for the No.8 coal seam was distinguised,and the geological controls were discussed.