Shale Gas Occurrence State

Shale gas is natural gas that is self-generated, self-stored, and self-sealed in organic-rich shale systems. Its occurrence state and accumulation mechanism in reservoirs is completely different from conventional natural gas reservoirs. Shale gas exists in various states in reservoirs, including free gas, adsorbed gas, and dissolved gas. Free gas and adsorbed gas are the main occurrence states. Free gas is mainly distributed in larger pores and fractures, and the proportion of these pores in the reservoir largely determines the occurrence of free gas. Adsorbed gas is not only affected by temperature and pressure, but also by organic carbon content, shale maturity, water content, and mineral composition.