二氧化碳黏弹性泡沫驱体系的优化

Optimization on Carbon Dioxide Viscoelasticity Foam System

针对延长油田低渗透高矿化度油藏采用常规泡沫注入性和耐盐性差而导致的提高采收率难度大的实际问题,基于表面活性剂分子的自组装特性,以自创的改进泡沫复合指数为指标,在无聚合物、无碱条件下,通过考察起泡剂、助起泡剂、稳定剂和络合剂用量对泡沫性能的影响,确定了具有高耐盐性的黏弹性CO_(2)泡沫驱体系。通过金相显微镜观察所形成泡沫的微观形貌,并考察了泡沫的黏弹性。配方为0.20%UCAB+0.20%SDS+0.09%三乙醇胺+0.08%EDTA的泡沫溶液黏度为15.2 mPa∙s,起泡体积达560 mL,半衰期为58 min,改进泡沫复合指数为370272 mL∙min∙mPa∙s。所形成的黏弹性CO_(2)泡沫呈不规则的五边形或六边形,具有一般泡沫特征。黏弹性测试表明小分子自组装形成了蠕虫状胶束,胶束相互缠结和缔合,宏观上体现出了聚合物的黏弹性。该泡沫驱油体系既满足注入性又发挥了聚合物的黏性驱油和弹性驱油特征,有效提高采收率。

In view of the practical problems of low permeability and high salinity reservoirs in Yanchang oilfield,such as poor salt tolerance of conventional foam injection and bad oil displacement efficiency,a viscoelastic carbon dioxide foam flooding system was studied in this paper.Based on the self-assembly characteristics of surfactants,the main foaming agent,auxiliary foaming agent,stabilizer and complexing agents were screened out in formation water without alkali and polymer.The formulation of 0.20%UCAB+0.20%SDS+0.09%triethanolamine+0.08%EDTA was determined by single factor method.Under the optimized condition,the viscosity of the foam flooding system was 15.2 mPa·s,the foaming volume was 560 mL,the half-life was 58 min,and the improved foam composite index(I_(PCV))was 370272 mL·min·mPa·s.Metallographic microscope showed that the bubbles were irregular polygons such as pentagonal or hexagonal,indicating that the viscoelastic carbon dioxide foam had the general bubble characteristics.The viscoelasticity test showed that the small molecules formed wormlike micelles by self-assembling,and wormlike micelles entangled and associated with each other,macroscopically reflecting the viscoelasticity of polymer.Therefore,the foam flooding system not only met the injectivity,but also displayed the viscous and elastic oil displacement characteristics of polymer,which could enhance oil recovery effectively.