Effect of Surface Wettability on the Miscible Behaviors Of Co2-Hydrocarbon in Shale Nanopores

Abstract

Abstract The minimum miscible pressure (Pm) of CO2-hydrocarbon mixtures in nanopores is a key parameter for CO2-enhanced shale oil recovery. Although the miscible behaviors of CO2-hydrocarbon mixtures in nanopores have been widely investigated through the simulations and calculations, the heterogeneity of shale components with different affinity to hydrocarbons results in the deviation of traditional predictions and motivates us to investigate how the surface properties influence the CO2-hydrocarbon miscible behaviors in nanopores. In this work, we established a model and framework to determine the wettability-dependent physical phenomena and its impact on the Pm of CO2-hydrocarbon in shale nanopores. First, a generalized scaling rule is established to clarify the potential correlation between critical properties shift and wettability based on the analysis of microscopic interactions (fluid-surface interactions and fluid-fluid interactions). Second, a wettability-dependent SKR EOS is structured and a generalized and practical framework for confined phase behavior with different surface wettability is constructed. Subsequently, the Pm of CO2-hydrocarbon mixtures in confined space with various wettability is evaluated with our model. The calculated results demonstrate that the nanoconfined effects on Pm not only relate to the pore dimension but also depend on the contact angle. In an intermediate-wet nanopore, the minimum miscible pressure approaches the bulk value. In an oil-wet nanopore with a width smaller than 100nm, the minimum miscible pressure is suppressed by the confined effects, and the reduction is further strengthened with a reduction in pore dimension and increase of wall-hydrocarbon affinity. Our work uses a macroscopically measurable parameter (contact angle) to characterize the shift of critical properties derived from the microscopic interactions, and further construct a generalized and practical framework for phase behavior and minimum miscible pressure determination in nanopores with different surface properties. The method and framework can make a significant contribution in the area of upscaling a molecular or nanoscale understanding to a reservoir scale simulation in shale gas/oil research.