Symbiotic combination of coal measure gas and its geological origin in typical blocks of Eastern Yunnan and Western Guizhou

Coal-measure gas is an important natural gas resource.In order to understand the type and geological origin of the coal-measure gas symbiosis combination, based on the logging data of 13 coal-bed methane exploration and development wells in eastern Yunnan and western Guizhou, the Permian coal measures in the study area are analyzed.The characteristics of sandstone and shale gas surveys show that the coal seams in the study area are distributed in groups, the total thickness of the coal seams is relatively large, the coal ranks are mainly middle-high rank, the metamorphism is high, and the gas content is good.The gas survey in coal measure sandstone and mud shale shows that the abnormality is frequent, the total thickness of the abnormal horizon is large, and the plane and vertical distribution are significantly different.The co-existence combination of coalbed methane, sandstone gas, and shale gas is diversified, and the coal measures are vertically stacked with multiple sets of different types of coal measure gas reservoirs, and there are also large differences between regions.Five types of gas reservoirs are classified including separate independent sandstone gas reservoirs, independent shale gas reservoirs, shale-sandstone interbedded gas reservoirs, single-coal-shale-sandstone interbedded gas reservoirs, and multi-coal coal-shale-shale-sandstone interbedded gas reservoirs.Longtan Formation coal seams, sandstone, and shale are thinly interbedded, causing different gas reservoirs to form alternately.Among them, single coalbed methane reservoirs are distributed throughout the entire interval of Longtan Formation in western Guizhou and mainly developed in the upper coal measures, while single-coal interbedded gas reservoirs of Longtan Formation in eastern Yunnan mainly exist in the middle section of coal measures.Multi-coal interbedded gas reservoirs exist in the whole section of Longtan Formation, and mainly exist in the middle section of Longtan Formation in western Guizhou and the lower section of Longtan Formation in eastern Yunnan.The geological genesis of coal-measure gas reservoirs is studied, and it is found that coal-measure gas reservoirs are affected by the coupling of depositional environment, tectonic effect, thermal evolution and hydrological conditions.The relative stable depositional environment(such as delta),good preservation conditions, and relative closed hydrological characteristics and a high degree of thermal evolution are favorable conditions for the enrichment of three gases in coal measures.