Chapter 12 - High-Pressure Methane Adsorption in Shale

Abstract

Accurately determining the adsorbed methane content is critical for the assessment of shale gas reserves and the design of effective production strategies. Methane adsorption in shale has been extensively studied by volumetric and gravimetric isothermal adsorption experiments, but the maximum pressure in most of the previous experiments is far below the actual formation pressure. In this chapter, high-pressure methane adsorption experiments on Lower Silurian Longmaxi shale samples were conducted. The experimental isotherms increased to its maximum value and then decreased with further increasing pressures, and this abnormal behavior was described by some classical models. A novel model by combining the micropore filling and monolayer coverage theories was established to describe the methane adsorption process in shale. The adsorption isotherms and the capacities for micropores and mesopores can be calculated using this new model separately, showing that 77%–97% of methane molecules are adsorbed in micropores. The methane adsorption mechanism in shale is summarized as follows: the majority of methane molecules filled micropores, and the remainder were monolayer-adsorbed in mesopores.