Estimation of Gas Storage Capacity Estimate in Coals and Shales

Over the past decade, extensive research efforts have been directed towards the exploration of unconventional natural gas reservoirs, with a particular focus on coalbed methane and shale gas. The distribution of gas content within these reservoirs is highly anisotropic and influenced by various factors. This chapter offers a thorough overview of the gas adsorption mechanism, various adsorption models, and the techniques employed in laboratory studies for both high-pressure and low-pressure gas adsorption. The impact of particle crush size, degassing conditions (including time and temperature), and the pore structural framework on low-pressure gas adsorption in shales and coal is thoroughly examined. Studies have found that diverse particle crush sizes play a important role in shaping pore characteristics and gas adsorption behavior in shales. Furthermore, distinct responses in adsorption isotherms and pore characteristics are evident under different degassing conditions, highlighting substantial alterations in pore structure. The chapter also delves into the evaluation of the fractal dimension of organic-rich shales, emphasizing its correlation with gas adsorption parameters. Correlations between fractal dimensions and thermal maturity, specific surface area, pore volume, and average pore radius, are pivotal for understanding fluid flow patterns and resource volume characteristics in unconventional reservoirs. Further, critical factors influencing gas adsorption in unconventional reservoirs is presented and provides valuable insights into the complex interplay of variables that dictate the behavior of these essential energy resources.