Coalbed Methane System And Its Developmental Mechanism In Tucheng Syncline,Guizhou,China

There are multiple sets of CBM systems in the vertical direction of the Upper Permian Longtan Formation in Tucheng syncline.Difference among fluid pressure systems are the important restrictive factors for CBM co-mining production.Therefore,coalbed methane geological information is extracted from coalbed methane exploration and development data in this article.Combining with coalbed methane development test results and sample test data,characteristics of sequence stratigraphic framework of Longtan Formation in Tucheng syncline was studied.The regional distribution characteristics of superposed relationship among CBM systems and geological controls were analyzed.There are apparent internal structural differentiation in Tucheng syncline,most of the coal reservoirs in the syncline are over pressue and the pressure coefficient of coal reservoirs is fluctuating in the vertical direction.Meceral composition and quality of coals has a cyclic distribution under framework of sequence structure.It was found that the gas content?the porosity and the permeability of the coal seam near surface of maximum flooding are lower.The superposed relationship among CBM systems was significant.Logging response is analyzed,identifying the key horizons of water-blocking gas barrier with siderite.Combining the change rule of the physical property of reservoir,the Longtan formation was divided into four CBM systems.It is found that the hydrodynamic connection between the three-level sequence stratigraphic units is weak,it constitutes the hydrogeological foundation of the superposition of CBM systems.The variation range of gas content gradient and fluid pressure coefficient of coal seam declaring that the superposed relationship among CBM systems is stronger in the areas with weak structural deformation?low degree of fracture development and inactive hydrodynamic condition.Studies suggest that the Late Permian Longtan period is mainly a shallow water delta sedimentary environment in Tucheng.syncline.This is an important geological reason for the development of mudstone with siderite.In the NW-SE direction,the thickness and stability of coal seam are gradually improved,the development of key horizons is gradually increasing,the superposed relationship among CBM systems gradually increasing.There are 65 figures,25 tables and 161 references in this article.