Organic nanopores in source rocks such as kerogen and bitumen significantly contribute to hydrocarbon storage due to their hydrophobic surfaces and nanoscale sizes. The nano-confinement effects make it challenging to predict the fluid behavior with conventional theoretical frames. Consideration of multi-component fluids is also considered as an added complexity in the analysis. Most of previous studies have been limited in scope to simple pure fluids confined in nanopores for unconventional gas reservoirs. In this study we investigate fluid behavior of multicomponent oil fluids is investigated under nano-confinement. At pore scale, we study lean gas (C2H6 and CO2) injection for oil production in unconventional resources. Monte Carlo simulation is carried out to restore in-situ molecular configuration inside model kerogen. Injecting agents are introduced in stages, and the enhanced recovery is systematically analyzed. Also, mechanical properties of the fluid mixtures and injecting agents in kerogen are investigated using simulation of Molecular Dynamics. The results show that fluids in smaller nanopores have relatively higher density with greater amounts of heavy components compared to bulk fluids in microcracks. The compositional variance in nanopores limits the thermodynamic recovery below 15 % and makes pressure depletion ineffective for oil production from shale oil reservoirs. C2H6 injection drives significant improvement in recovery, up to 90 %, and the enhancement is 5 – 20 % higher than that with CO2 agent. In addition, injected C2H6 reduces viscosity of hydrocarbons 10 to 30 % and enhances mobility especially in small nanopores. Diffusion of injecting agents is further analyzed. This investigation provides a new insight into C2H6 injection as an alternative-injecting agent for unconventional resources.

Molecular simulation of kerogen oil recovery using lean gas injection

2019 Spring National Meeting

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