Coupling Control of Tectonic Dynamical Conditions to Coalbed Methane Reservoir Formation in the Qinshui Basin,Shanxi,China

Tectonic dynamical conditions include many factors,and it is the basic to understand the CBM(coalbed methane)-reservoir-controlling effect of tectonic dynamical conditions that the correlations between the factors and the CBM-reservoir formation are analyzed comprehensively.Thus,based on some methods such as basin analysis,tectonic stress field simulation,vitrinite optical fabric and structural curvature,the paper analyzed the correlations of the basin evolvement,tectonic stress field,structure differentiation and tectonic coalbed alteration corresponding to CBM reservoir formation effect,and discussed the tectonic dynamical characteristics affording the favorable occurrence of CBM enrichment and high permeability districts.The results indicate that the Yanshanian movement was a key stage to control the CBM reservoir formation,during which the general pattern of the CBM occurrence in the basin was established under the control of the secondary folds and high angle normal faults derived from the tectonic stress field with the main compressive stress of approximately horizontal NW-SE orientation,that is to say,the NNE-NE secondary folds are major CBM-controlled structure in the basin.The control of the tectonic dynamics to the coal reservoir permeability is not only materialized by the occurrence of the vitrinite optical indicating faces,but also might be why the middle structural-main-curvature value and high main-stress-difference are most be propitious to the occurrence of the CBM-reservoirs with high permeability.The CBM-pooling effect in the Qinshui basin depended on the reasonable matching among the above mentioned tectonic dynamical factors,by which it is predicted that there might exist the tectonic dynamical conditions that favor the CBM reservoir formation in four districts including the northern Yangcheng,Anze-Qinshui,Qinyuan and Wuxiang.