Advances on the Mechanism of Reservoir Forming and Gas Accumulation of the Longmaxi Formation Shale in Sichuan Basin, China

Shale gas has become one of the most important natural gas resources. The Sichuan Basin in China is one of the main shale gas production areas and has entered large-scale commercial development. The mechanism of shale gas accumulation is an important scientific problem in shale gas exploration. This work systematically summarizes the understanding of shale gas accumulation in terms of shale gas generation mechanisms, pore evolution mechanisms, gas migration mechanisms, and gas accumulation models. This work reviews the formation process of methane in shale and clarifies that the causes of methane formation vary according to the evolutionary stage. The formation and evolution of organic pores and mineral pores in shale are analyzed using a thermal simulation; the organic pore content is found to vary significantly with evolutionary stage. In addition, this work focuses on an analysis of the migration mechanism of shale gas, discussing the impacts of shale anisotropy, self-sealing, porosity and permeability, various forces, and pathway availability on shale gas migration. In addition to the actual gas content of the shale gas reservoir, shale gas accumulation is analyzed using mathematical and evolutionary models, and the accumulation process is revealed. This work provides important guidelines for shale gas exploration in the Sichuan Basin, which has undergone complex tectonic evolution.