Laboratory evaluation and numerical simulation of the alkali–surfactant–polymer synergistic mechanism in chemical flooding

Alkali–surfactant–polymer (ASP) flooding, which can reduce interfacial tension (IFT) and the mobility ratio between oil and water phases, has been proven to be effective for enhancing oil recovery in laboratory experiments and field pilots. However, the study of interactions within alkali–surfactant–polymers for chemical flooding is neither comprehensive nor complete until now. Laboratory experiments were conducted and a corresponding numerical simulation model was established to characterize multiple component interactions during the ASP flooding process. Synergistic effects of multiple component interactions on viscosity variation, IFT reduction, and multicomponent adsorption were studied separately. ASP solution viscosity shows non-linear variation behavior with an increasing polymer concentration. Alkali decreases the molecular hydraulic radius of a polymer, and then limits its contribution to viscosity. Oil–water interfacial tension decreases with the join in of polymer which can act as an alternative effect to replace surfactant adsorbed on a mineral surface. Petroleum acid will react with alkali and produce petroleum soap to perform a synergetic action with the surfactant on IFT reduction. Adsorption fraction and diffusion rate of a surfactant will diminish due to rheology improvements caused by a polymer. Alkali can protect a surfactant from adsorption consumption by competitive adsorption. A viscosity non-linear logarithm mixing method, IFT reduction–relative permeability curve interpolation method, and a multicomponent adsorption isotherm model were developed to characterize and simulate the synergistic effects obtained by experiments. A novel ASP flooding numerical simulation model was constructed which coupled the synergistic effects simulation methods of viscosity variation, IFT reduction, and multicomponent adsorption. The numerical simulation result based on the proposed model has better agreement with experiment results compared with that of the traditional model. Validation results proved the effectiveness of the proposed model which can be used to enhance a synergistic mechanism study and field application of ASP flooding.