Geological Controls On The Accumulation Of Coalbed Methane In The Hancheng Demonstration Area

In this paper,the study area is the demonstration area of Hancheng coalbed methane exploration and development.Based on the analysis of geological exploration,drilling data,mine geology and other available information,combining basin evolution,tectonic features,sequence stratigraphy,sedimentary facies analysis and hydrogeological conditions,I have preliminarily identified the control action of Methane enrichment.Understanding as follows:Analyzed the data of carbon isotope in methane and research and divided the CBM genetic types of the study area,I reached that the CBM genetic types of the study area is thermogenic gas,and the coalbed methane in some areas has experienced fractionation significantly,such as diffusive and transport,etc.That resulted in low gas saturation.Tectonic directly controls the formation of coal-bearing strata and the whole process of coal-bed methane production,gathering,so it is the important factor of controlling factor of the CBM.After the formation of the study area coal,there are two main hydrocarbon phase,corresponding to late Hercynian to Indosinian when the coal seams reached the maximum depth and Late Jurassic to Early Cretaceous when tectonic events occurred.Different types ofgeological tectonic would affect gas-bearing reservoirs of coal.Four major tectonic effects have been found in the area.It is easier to form an enclosed space for syncline and reverse faults to make the gas content increases.The anticline is easier to form the tensile fractured to make the gas escape.normal faults may form an open interval,so that the gas content is reduced.Sequence stratigraphy control plane development and distribution of coal.sedimentary environment differences lead to form the different cover and storage types and accumulation mode in the study area.By drilling data of 8 coalbed methane wells of the area,I analyzed the single well phase of Shanxi Formation and Taiyuan Formation stratum,and on its basis,I also analyzed well tie sedimentary facies and flat sedimentary facies.Compare distribution law of sedimentary microfacies of Shanxi Formation and Taiyuan Formation and in the longitudinal direction.Combined with single-well,well tie-phase and flat sedimentary facies analysis,I got that the seam thickness and roof and floor work together to influence the coalbed methane reservoir.By analyzing the aquifer,impermeable layer in the area,I studied the filling,runoff and discharge conditions of the main aquifer,then analyzed the hydrodynamics impactforthe gas content and obtained that coalbed methane was flowing from southwest to northeast along with groundwater migration.The coal thermal maturity value is not consistent with high values of coalbed gas content in this area,that reflects the migration of groundwater in the area has some influence on the gas content.