Geological characteristics and accumulation mechanisms of the “continuous” tight gas reservoirs of the Xu2 Member in the middle-south transition region, Sichuan Basin, China

Abstract

“Continuous” tight gas reservoirs are those reservoirs which develop in widespread tight sandstones with a continuous distribution of natural gas. In this paper, we summarize the geological features of the source rocks and “continuous” tight gas reservoirs in the Xujiahe Formation of the middle-south transition region, Sichuan Basin. The source rocks of the Xul Member and reservoir rocks of the Xu2 Member are thick (Xul Member: 40 m, Xu2 Member: 120 m) and are distributed continuously in this study area. The results of drilled wells show that the widespread sandstone reservoirs of the Xu2 Member are charged with natural gas. Therefore, the natural gas reservoirs of the Xu2 Member in the middle-south transition region are “continuous” tight gas reservoirs. The accumulation of “continuous” tight gas reservoirs is controlled by an adequate driving force of the pressure differences between source rocks and reservoirs, which is demonstrated by a “one-dimensional” physical simulation experiment. In this simulation, the natural gas of “continuous” tight gas reservoirs moves forward with no preferential petroleum migration pathways (PPMP), and the natural gas saturation of “continuous” tight gas reservoirs is higher than that of conventional reservoirs.