Influence of confinement effect on recovery mechanisms of CO2-enhanced tight-oil recovery process considering critical properties shift, capillarity and adsorption

Abstract

The primary focus of this study is to develop an understanding of the role of confinement effect during CO2 injection by proposing a new phase equilibrium calculation model, which also accounts for critical properties shift, capillarity and adsorption behavior. An iterative algorithm based on updating of the compositions of components in the bulk phases has been developed to calculate phase equilibrium properties. This new and improved model has been validated by experiment results. Results show that the adsorption behavior would increase the interfacial tension and capillary pressure, and the state of phase equilibrium is greatly affected by pore size. Using findings from our model, relationships between the confinement effect and important recovery mechanisms in CO2 injection, such as, extraction of light hydrocarbons, minimum miscible pressure with oil, diffusivity and mass transfer, oil solubility and viscosity reduction have been investigated. We note that the confinement effect contributes to a decrease in CO2 extraction capability of lighter hydrocarbons, and, to a lower minimum miscible pressure with the oil. On the other hand, the confinement effect could cause an increase in the CO2 diffusion coefficient in the liquid phase with a reduction in the pore size. The mass transfer seems to be enhanced with confinement effect. The CO2 solubility in tigth oil increases and the viscosity of dissolved oil phase could be higher. In general, the confinement effect appears to have a positive impact on the recovery mechanisms of CO2 injection in tight reservoirs.