The Use of Molecular Simulations to Construct and Study Organic Pores and Fluids Present in Shale Reservoirs

In this work, we use molecular simulations to create molecular models of organic matter found in shales (the so-called kerogen) to study the spatial distribution and flow of fluids in unconventional reservoirs. The models account for the chemical functionality of kerogen with the corresponding degree of thermal maturity and the densities are consistent with reported experimental data. For overmature kerogen, the models serve as rigid frameworks for the study of adsorption of pure CH₄ and CO₂ using Monte Carlo simulations. For mature kerogen, we study the spatial distribution of a mixture of hydrocarbons (representative of a volatile oil), asphaltenes/resins, water, and carbon dioxide in organic pores using equilibrium molecular dynamics. We then employ these models as rigid frameworks for the investigation of flow of liquid dodecane through organic matter using nonequilibrium molecular dynamics. All the simulations are run at typical reservoir conditions.

With our approach we gain insights on molecular signatures of macroscopic phenomena that are still not well understood due the difficulties to isolate organic matter in the laboratory, the inconclusiveness and poor resolution of experiments. Molecular simulations offer an alternative way to investigate these systems.