Analysis Of The Reservoir-Forming Conditions Of Shale Gas Potential In Sichuan Basin

In the paper, the reservoir-forming conditions and favorable exploration zones of Sichuan Basin have been systematically studied by geologic analogue methods, and preliminarily forecast the early Palaeozoic shale gas resources potential with analogy and volumetric methods. First, the reservoir-forming characteristics of shale gas in America were summarized. It is accounted that the thick shale deposited on a certain depth and hypoxic environment can provide source and reservoir for shale gas. The abundance, type and thermal evolutionary degree of organic matter are main geologic factors affecting shale gas generation. Shale gas reservoir is mainly correlated with surface area, pore and fracture. Dense shale itself can rely on their own ultra-low porosity and permeability as caprock to keep gases preserved in the reservoirs, which is called"continuous accumulation"play. Combined with the deposition, distribution, hydrocarbon generation, reservoir, cap rock and preservation features of Lower Palaeozoic shale in Sichuan Basin, the reservoir-forming conditions were systematically studied. Sichuan Basin have shale with the potential to produce gas. There are three shales present, Lower Cambrian Qiongzhusi Group, Upper Ordovician Wufeng Group and the Lower Silurian Longmaxi Group, which have rich organic matter, good organic type and high organic degree, generally in super maturation. After Cambrian formation deposited, the basin has experienced multiphase tectonic movements, which caused a great quantity of cracks, conformities and wrinkles, offering sufficient accumulated spaces for shale gas. The low porosity and permeability enable shale be good cap rock. Multiphase movements have not sharply damaged largely the marine bed. Through the comparison with American shale gas, it was found that their geologic features are similar. The shale gas resources potential in these shales calculated by analogy and volumetric methods is great. Gas shows are frequent found in the Lower Palaeozoic shale, it indicated the great potential of shale gas in this area. Finally, through the shale index of thickness distribution, organic carbon content, thermal evolution degree and gas generation level in Sichuan Basin, the favorable exploration zones were preliminarily forecast.