Shale Gas Reservoir Characterization: Understanding the Shale Types and Storage Mechanisms for Effective Exploration and Production

Shale gas refers to the natural gas trapped within shale formations, which are fine-grained sedimentary rocks rich in petroleum and natural gas resources. It exists in shale rocks as either free gas or adsorbed gas, resulting from the thermal alteration of kerogen, an insoluble organic matter. Shale acts as both the source and reservoir rock for shale gas. When the hydrocarbon generated inside the shale cannot be expelled to the reservoir rock, the shale itself becomes the reservoir. Various factors influence the gas generation and accumulation processes, including the extent and thickness of the shale layer, total organic carbon content, kerogen type, maturity, permeability, mineralogy, and brittleness versus ductility. Although shale rocks serve as both the source and reservoir, the extraction of shale gas requires hydraulic fracturing techniques such as acidization, propane injection, CO2 fracturing, and other methods. The exploration of shale reservoirs involves assessing total organic content, porosity, micro-fractures, and the geometry of porous spaces. Therefore, integrated studies encompassing geological, geochemical, petro-physical, geophysical, geomechanical, and technical aspects are necessary to identify optimal areas for shale gas exploration, exploitation, and recovery.