Numerical Assessments of Key Aspects Influencing Supercritical CO_2 Foam Performances when Using CO_2-Soluble Surfactants

摘要

Experimentally, supercritical CO2-soluble surfactant foams have displayed significant superiorities over conventional aqueous soluble one in promoting foam strength, accelerating surfactant/foam propagation, and enhancing oil recovery. It was observed that the eventual foam performances could be the counterbalance results of faster foam propagation and reduced local pressure gradient characterized by the magnitudes of partition coefficients between CO2/aqueous, which was designated as spreading effect. This paper aims to numerically investigate the key aspects influencing supercritical CO2-soluble surfactant foam performances in a homogeneous analogue system, with respect to injection periods, critical foaming concentration and surfactant adsorption determined by the surfactant structure, and injection foam quality. It is found that stepwise oil production consists of three stages in sequence attributed to the distinct recovery mechanisms. The optimal partition coefficient for a studied system cannot be derived directly by the absolute value of the surfactant partition coefficient but is affected by the employed rock, fluids, and injection conditions. The less EO group endues higher partition capacity and adsorption on the rock surface simultaneously. The tradeoff results in the least adverse impact for high partition capacity surfactants even though the optimal value shifts to the lower end. The impacts of injection foam quality are the combination of the total injection rate, amount of injection fluids, miscibility between Gas/Oil, and surfactant spreading. Surfactant partition coefficient values determine the eventual impacts of promoted or suppressed spreading effects. The studies in this article promote the understandings of this novel technology to maximize the oil recovery as well as CO2 utilization.