Research on Factors Influencing Weak Alkali Surfactant Polymer Flooding System

After 43 years of water drive development, the DG oilfield reached the stage of high recovery and ultrahigh watercut. At present, the efficiency of enhanced oil recovery (EOR) technologies, namely waterflooding, in the DG oilfield and the stable production are low. To develop and evaluate a new EOR mode, we have performed pilot tests comparing the waterflooding technique and the weak-alkali alkali/surfactant/polymer (ASP) flooding. Based on the laboratory tests, the formulation of the weak-alkali ASP flooding system has been developed. The objective of the new EOR method is to maintain the stability of the system under reservoir conditions. In this paper, we focus on the factors influencing the effectiveness of the proposed weak-alkali ASP system, including sodium and potassium ion concentrations, calcium and magnesium ion concentrations, water quality, and the shear viscosity of the solution. The results show that, depending on water quality and the ion concentrations, the interfacial tension of the developed weak-alkali ASP system can be maintained at an ultralow level below 10–3 mN/m. The influence of sodium and magnesium ion concentrations is slightly higher than that of potassium and calcium ion concentrations, respectively. Considering the cost-effectiveness of the new system, it is recommended that the solution be diluted with clean water mixed with oilfield sewage, and the calcium and magnesium ions be removed from the solution before preparation. When the core permeability is 95·10–3 μm2, the pore throat size has little effect on the molecular weight and viscosity of the system after shearing.