Micro-storage State and Mechanism of Shale Gas

Shale gas has attracted increasing attention as a new potential source of natural gas in recent years. Accurate micro-storage and mechanism of shale gas is important for defining and describing the adsorption characteristics, gas-in-place estimates. Organic-rich shale gas reservoirs were usually deposited under water environment which has great impact on shale gas adsorption. Different from the widely used solid-gas interface adsorption theory, the pore system in original shale reservoir is divided into solid-gas system and solid-liquid-gas system. In same statement, shale pores have stronger interaction with water molecules than CH4 molecules, especially in solid-gas system. Water molecules mainly formed as competitive adsorption with shale gas on solid surface (solid-gas system) and liquid water surface (solid-liquid-gas system). Maxim gravitational potential energy, Psi(max), the distance where Psi(max) occurs, z(m) and limited pore side, D-L are given. When pore size D < D-L, no matter in what position the adsorbed molecules is, it force by both sides of the pore silts. When D > D-L, the ratio of unaffected area increases to approximately 100% with pore side. When D < 10 nm, the ratio increases rapidly this means that the ratio of free gas increases quickly. When D > 50 nm, the ratio of unaffected area almost reaches 100%, which means that the content of free gas is far greater than the adsorbed gas. This study not only provides a new classification of shale pore system, but also can act as a reference to better understanding the adsorption mechanism of shale reservoir.