Research on Enrichment and Accumulation Mechanism of Shale Gas and Its Formation Conditions in China

For finding out the favorable enrichment zone, it is significant to study the mechanism and conditions of shale gas enrichment at the early stage of explo ration and development.The mechanisms and conditions controlling shale gas enrichment were summarized in this paper.The results show that the accumulation proces s of the shale gas possesses the comprehensive characteristics of typical coalbed methane, source-contracting gas and entrapped gas enrichments.The shale gas enri chment is influenced by multiple geologic factors including total organic carbon (TOC) content, maturity of organic matter, mineral composition, pore-fracture and crack, thickness, burial depth and reservoir pressure and others, among which the former four factors are the main shale gas reservoir-forming conditions.Higher TOC content in shale is much favorable for gas enrichment due to the larger hydrocarbon-generating potential and storage capacity for shale.Thermogenic gas content will increase with the increasing thermal maturity (R 0) of shale, particular in the range of 1. 1%3.0%, while it is unfavorable for the accumulation of shale gas as R 0 increase for biog enic gas reservoir.Mineral matters reflect the depositional environment of shale, which affects the gas enrichment resulting from affecting the organic carbon content.Mi cropores affect adsorbed gas content, and intergranular pores and fractures influence free gas content.Cracks have destructive effects on shale gas reservoir.