Shale gas in the Sichuan Basin features in multi-domain

multi-layer and multi-types.The main controlling factors for shale gas accumulation are favorable sedimentary facies

thermal maturity and preservation condition.High quality marine shale of deep shelf facies is high in hydrocarbon source quality

reservoir quality and fracturability

thus is the most favorable sedimentary facies.Sequences of carbonate lake slope storm beach facies consist of interbedded shale and limestone.The close combination of shale with high hydrocarbon source quality and limestone with high reservoir quality and high fracturability provides favorable conditions for shale gas accumulation.Shale with moderate thermal maturity(2%-3%) for peak gas generation has the most developed gas-saturated organic pores

thus the best storage capacity.Shale gas content generally increases with increasing buried depth under burial conditions.The adsorbed gas content decreases slowly

while the free gas content increase rapidly.Overpressure zone is favorable to free gas preservation.On this basis

gas shales in the Sichuan Basin can be divided into three layer series and five types.The thick shale of deep shelf facies with ultrahigh pressure within the Late Silurian basin and that with overpressure at the inner edge of the basin are the most favorable for shale gas enrichment.Favorable areas of shale gas in different layer series were predicted according to the criteria of favorable sedimentary facies zones

moderate thermal maturity (R

o

=1.3%-3.5%)

pressure coefficient over 1.2 and buried depth less than 4 500 m.