Langmuir Parameters Prediction: New Insights into the Porosity of the Nanoporous Media of Organic Media of Organic-Rich Shale

Abstract

Shale is a type of unconventional reservoir with a significant potential for storing natural gas attributed to its ability to host hydrocarbons as both free and sorbed phases. However, modeling this multi-physics storage capacity requires redefining some macroscopic parameters such as the porosity to capture the adsorption behavior and pore compressibility, which changes over the entire production life of the asset. Besides, a distinct confining stress phenomenon occurs in a reservoir with a different faulting system and degree of stress heterogeneity. Such mechanisms at nanoscale are complex and difficult to isolate through conventional experimental approaches. Alternatively, computational frameworks like molecular simulation can provide a proxy to accurately describe such intervening mechanisms. The study starts with recreating realistic organic matter structures from a given macromolecule kerogen unit using a molecular dynamics protocol. The created structures were subject to adsorption analysis and mechanical properties assessment while tracking the changes in porosity and pore size distribution. The analyses were used to redefine the porosity considering the adsorption behavior, mechanical properties, pore, and confining pressures. Furthermore, a correlation between stress-induced porosity and Langmuir quantities was developed to predict the Langmuir parameters. The logarithmic function-based model showed that a 33.3% change in stress-dependent kerogen porosity could result in a Langmuir amount, pressure and maximum adsorbed gas density variation of around 100%, 100%, and 50% respectively. Consequently, nanoporosity influence on Langmuir parameters should be critically understood as it plays a significant role in adsorbed gas storage and molecular transport processes in organic-rich shale.