Abstract:

The paper primarily studied geological background of organicrich shale and its distribution characteristics, reservoirforming conditions of shale gas and potential favorable areas of shale gas reservoir development. The study started from basic data such as the field surface outcrops, underground core and typical profile, and by the analysis of the reservoirforming conditions of shale gas in the lower Paleozoic of Chongqing and its adjacent, and using comprehensive information method, the favorable areas for shale gas reservoirs were predicted. The results indicate that the Qiongzhusi Formation of Lower Cambrian system organicrich shale, Wufeng Formation of Upper Ordovician system and Longmaxi Formation of Lower Silurian system organicrich shale in the study area were characterized by wide distribution, great thickness, buried moderately, good organic type, high organic content, high organic thermal evolution degree and high hydrocarbon potentials. The shale is rich in brittle minerals, with great quantity of matrix micropore and cracks, and good reservoir conditions, which offered sufficient accumulated space and migration pathway for shale gas. The result of isothermal adsorption simulate test and well site desorption test showed that the two sets of black shale all have strong ability and high performance of gas adsorption. The widespread multistage gas shows of many wells drilled in the black shale strata in this area indicated the great potential of shale gas. In a word, the tectonic evolution characteristics and geological conditions in this area are similar to the typical shale gas basins in Eastern America, and the study area is a favorable and prospective place for shale gas exploration, having lots of advantages for forming shale gas reservoir.

Key words: Lower Paleozoic, Chongqing and its adjacent areas, shale gas, organicrich shale, conditions of accumulation, favorable area