Feasibility of Re-injecting the Production Effluent from Alkali–Surfactant–Polymer Flooding Systems Back into a Reservoir to Further Improve Oil Recovery

Abstract

Alkali–surfactant–polymer (ASP)-produced effluent contains polymer, alkali and surfactant, and it has higher content of suspended oil droplets and suspended solids than ordinary effluent. To decrease environmental pollution caused by the discharge of produced effluent, the feasibility of re-injecting a new ASP flooding system prepared with ASP-produced effluent was studied and discussed in this paper. The results of the experiments reveal that three main factors affect the performance of the new ASP system: the polymer concentration, the suspended oil droplet and suspended solids content and the salinity of the ASP-produced effluent. It is recommended that the average content of suspended oil droplets and suspended solids does not exceed 500 mg/l and that the salinity does not exceed 8000 mg/l when the produced effluent is introduced into a new ASP system. Subsequently, a laboratory displacement experiment on ASP flooding was performed. The experimental results reveal that the oil recovery of the new ASP flooding system was improved by 20.38%, and the ultimate oil recovery was 65.46%, which is 0.65% higher than that of an ASP flooding system prepared with ordinary effluent. ASP-produced effluent and ordinary effluent achieve nearly the same oil recovery. However, ASP-produced effluent is more environmentally friendly. An oil displacement test of ASP flooding with a new ASP flooding system was conducted in block A of W oil field, and good development results were achieved: The 25 production wells in the pilot test area were all effectively improved, with the minimum water cut reduced by 14.40% and the average daily oil production increased by 51.28 tons.