Abstract: T3x2 gas reservoir is a typical “tight sandstone gas” reservoir, which features in low porosity and ultra-low permeability. The basin modeling results shows that T3x2 gas reservoir has gone through four processes: burial, uplift, re-burial and re-uplift. T3x2 was compacted and became tight sandstone before the Cretaceous. T3x1, which lies beneath T3x2, started to generate gas in late Jurassic. The peak of gas generation started in late Cretaceous and ended in Paleocene. The critical moment of gas migration and accumulation was in late Cretaceous, that is early than the age when T3x2 became tight sandstone. Based on the geological models and the characteristics that the buoyancy of gas in water is not the main drive of gas flow in tight sandstone, this paper proposes the method of modeling gas migration and accumulation, and then uses it to predict the gas distribution in T3x2. As a result, the modeling is consistent 88 percent with the actual data of the discovered resources at Hechuan1 Block and Tongnan2 Block. It confirms the predicting model is rational. Furthermore, the modeling results show there are half of natural gas undiscovered in the Hechuan area, located at the northeast of Hechuan, and north and southeast of Tongnan.

Key words: tight sandstone gas, resource assessment, unconventional resource, basin modeling, predicting model, Hechuan Area, Sichuan Basin