A review of phase behavior simulation of hydrocarbons in confined space: Implications for shale oil and shale gas

In oil field development, phase behavior would influence fluid components and mobility, thus affecting production. As a fine-grained sedimentary rock, shale brings difficulties to observing and modelling fluid behavior in similar ways to conventional reservoir experiments and simulations due to the abundance of nanometer-sized pores. Confined in nanopores, hydrocarbons exhibit largely different phase behavior in shale reservoirs. Limited experiments showed the shifts of phase envelopes, heterogeneous density profiles, and decreasing fluid viscosity. There exist controversies concerning bubblepoint deviation and critical density shift. Based on experimental observations, various computational methods are proposed to simulate phase behavior in confined spaces. These methods can be classified as either molecular simulation methods or varieties of equation of state. This article presents a review of the deviated phase behaviors of hydrocarbons in confined space and approaches to modelling them. Comparisons are made among different models. This article also proposes some promising research directions for future simulation models of shale oil and shale gas reservoirs. • Deviated critical properties of confined fluid based on molecular simulations are summarized. • Modelling methods of deviated phase behavior in nanopores are compared. • Future development directions of field-scale numerical simulation of shale reservoirs are discussed.