Abstract:

This article is dedicated to two shale gas intervals such as Longmaxi Formation and Daanzhai Section of Ziliujing Formation in the Sichuan Basin. In this study we analyzed and examined the basic conditions concerning the formation of marine and lacustrine shale gas, accumulation mechanisms and potential intervals, based on systematic experimental analysis of Longmaxi Formation in the Fuling Shale Gas Field and Daanzhai Section of Ziliujing Formation in Yuanba and Fuling areas and also based on the comparisons between six properties of shale reservoirs such as lithologies, geophysical properties, electric properties, shale gas contents, geochemical properties and brittle properties. It is considered that the differences between organic pores developed in marine and lacustrine shales are the main reasons for great differences in gas contents. Both marine and lacustrine shales have remarkable exploration prospects. Due to the differences among TOC, Ro and organic matter type, the organic pores develop better in marine shales. The intervals of organicrich mudstones or shales with streak or stripe limestones developed in shallowsemideep lacutrine are favorable facies belts for shale gas exploration. The lithofacies of grapholite shales with spicules and radiolarians deposited in deep shelf at the bottom of Longmaxi Formation are the most favorable for shale gas exploration. Furthermore, organicrich mudstones or shales are developed in shallow shelf, though the protecting conditions are destructed to a certain degree, the areas with high adsorbed gas still have potentials for shale gas exploration.

Key words: shale gas, accumulation mechanism, organic pores, Longmaxi Formation, Daanzhai Section, Sichuan Basin