Methods for Petrological and Petrophysical Characterization of Gas Shales

The increasing significance of shale gas resources to the global energy supply has resulted in an increasing need to understand shales as gas reservoirs. Shales commonly have complex organic and inorganic compositions and ultrafine pore structures. Fluid flow and transport in shale gas reservoirs (SGRs) are scale-dependent processes, including adsorption/desorption and diffusion of gas, water imbibition, and other non-Darcy flows, which is in contrast with conventional natural gas reservoirs, such as sandstones. In recent years, the transferring of the opinion from the prior efforts on studying the source and seal potential to the purpose of the function as the gas reservoir is creating some new challenges to the conventional analysis methods for SGRs. There has been a much larger number of publications relating to "shale and method" in the last 5 years compared to previously. On the basis of a review of these publications, this review summarizes both progresses made to improve or modify conventional methods as well as the application of new, emerging methods for a description of the complex shale petrology, rock physics, and flow mechanisms. The main part of this review is divided into six sections: organic geochemical evaluation, pore properties, such as pore type, porosity, specific surface area, and pore size distribution, wettability assessment, quantification of imbibition, gas adsorption and diffusion, and permeability evaluation. In each section, the advantages and disadvantages of conventional and emerging methods are reviewed. The goal of this review is to provide a guide for the reader to help them choose appropriate methods for future work in SGRs.