Combination characteristics and favorable intervals of Early Carboniferous coal measure gas of Lianyuan sag, Hunan province

The Carboniferous coal measures in Lianyuan sag of Hunan province are characterized by vertical superposition of coal seams, shale and sandstones, horizontal wide distribution and mutual superposition, which has a good prospect of exploration and production of coal measures gas.However, there is still a lack of research on the geological characteristics of unconventional natural gas from an overall perspective.Taking the Early Carboniferous Ceshui formation as the research object, based on the lithofacies assemblage and experimental analysis of physical properties and gas bearing properties of typical wells in the study area, this paper discusses the symbiotic combination mode of coal measure gas and potential favorable coal measure gas intervals in Lianyuan sag.The results show that there are five types of lithofacies assemblage corresponding to the depositional environments of offshore shelf, barrier-tidal flat, barrier-swamp, lagoon-swamp and tidal flat-swamp and three types of coal measure gas assemblage models corresponding to the “single source and two reservoirs” and “two source and two reservoirs” and “two source and three reservoirs” in the Ceshui formation of Lianyuan sag.Based on the hierarchical weighting method, the upper part of the lower member of the Ceshui formation is considered as a favorable exploration interval.The coal seam as the main source rock and sandstone as the main reservoir is the most favorable, which concentrated in the central area of Lianyuan sag.The cumulative thickness of coal seam and its gas bearing property play a key role in coal measures gas reservoir in Lianyuan sag.