Few attempts have been made to investigate EOR methods in unconventional plays. However, it is evident that to improve oil recovery, one should first have access to the trapped oil inside the matrix media. Extremely heterogeneous rock and ultra-low matrix permeability present significant challenges for application of conventional displacement methods. In these formations, capillary imbibition or gravity are not effective production mechanisms because of oil-wet or mixed-wet nature of rock fabric as well as the low permeability of the matrix. Resistance to liquid flow is much higher compared to gas because of existing capillary pressure in microfractures and higher viscosity. The combination of these factors highlights the potentials of gas injection as a feasible oil recovery practice compared to other EOR scenarios.

The primary objective of this paper is to study the recovery potential of fractured low permeable Bakken formations under gas injection by focusing on hydrocarbon transport mechanisms from fractures into the matrix and vice versa. The numerical study was performed using field-scale matrix/fracture model. Our computational results indicated that the recovery mechanism in the ultra-low permeable formation with high capillary pressure is dominated by gas diffusion. Conceptually, we have described the mechanism of oil component vaporization and effect of injected gas composition on this process. The utility of this study is a qualitative and quantitative evaluation of basic recovery mechanisms in a fracture/matrix model that have a direct application in the prediction, designing, and analysis of hydrocarbon recovery in Bakken formation.

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