Molecular simulation of enhanced oil recovery in shale

Enhanced oil recovery (EOR) techniques (miscible/near miscible gas injection, chemical flooding and thermal) aim at increasing oil recovery factor, over which that would be achieved from natural depletion and pressure maintenance methods. As we embark on more complex EOR processes (e.g. miscible hydrocarbon/non-hydrocarbon, surfactant/polymer, smart water and combination of the three), complex phase equilibria, complicated rock/fluid interaction, and sophisticated transport through porous media will create a number of key technical challenges that must be addressed. The issue is significantly increased in unconventional resources as the physics behind the process is not very well understood. For these resources, effective enhanced oil recovery (EOR) techniques are required to displace oil from nanoscale shale matrix. Due to small permeability, it is difficult to conduct water and chemical flooding in these resources. Maintaining a stable flood front in immiscible gas flooding due to the severe fingering phenomenon in fractured shale formations. Gas huff-n-puff becomes the most suitable EOR method in shale reservoir development. For decades, CO2 (EOR) techniques that have been successfully applied in conventional reservoirs to improve oil production. In this work, we will investigate the physics behind CO2 injection into organic nanopores of shale using molecular dynamics simulations. A 3D kerogen structure is used with dodecane to study the huff-n-puff process at a molecular level. Results show that there is an optimal soaking time after which the recovery factor is not affected by soaking time anymore. Furthermore, carbon dioxide has high affinity to be adsorbed to kerogen walls and therefore desorbing the hydrocarbon molecules.