胜利油区配注污水水质对化学驱效果的影响

Influence of injection water quality on performance of chemical flooding in Shengli oilfield

胜利油区化学驱单元大多采用污水配注化学剂,配注污水水质对化学驱效果影响较大。在统计胜利油区化学驱历年配注污水水质的基础上,分析了水质对聚合物溶液粘度、表面活性剂油水界面张力的影响。结果表明,化学驱配注污水矿化度和钙、镁离子质量浓度逐年升高,Fe2+质量浓度最高达6.6 mg/L,S2-质量浓度最高达5.5 mg/L。配注污水水质不达标会导致聚合物溶液粘度降低,钙离子质量浓度为300 mg/L就会导致聚合物溶液粘度下降50%,钙离子质量浓度达到400 mg/L,表面活性剂油水界面张力升高一个数量级;当Fe2+质量浓度增大至1 mg/L时,聚合物溶液粘度保留率仅为55%;当S2-质量浓度为2 mg/L时,聚合物溶液粘度保留率仅为47.4%。对比2001—2011年胜利油区化学驱矿场应用聚合物溶液粘度与质量浓度发现,配注污水矿化度、钙、镁离子质量浓度逐年升高,水质不合格导致化学剂用量逐年增加。为了保证化学驱效果,必须通过改善配注污水水质减缓聚合物溶液粘度损失、增加表面活性剂界面活性,从而减少化学驱中化学剂用量,降低投资成本。

The oilfield sewage is usually re-injected in chemical flooding units and the water quality has a significant influence on theperformance of chemical flooding. In this paper, the variation of injection water over years in Shengli oilfield is statistically analyzed.Our results show that the total salinity and divalent-cation(Ca2+and Mg2+) content keep increasing, meanwhile, the impurities such asFe2+, S2-and COD are contained in the injection water. The influence of water quality on the viscosity and interfacial tension is investi-gated. Experimental results show that the viscosity of polymer decreases due to the interaction between ions and polymer. The interfa-cial tension increases because the Shengli petroleum sulfonate(SLPS) precipitates with divalent cations. Furthermore, the viscosity atwellhead is much lower than that of measured in laboratory, implying that the chemical concentration used in the field has to be consid-erablyincreased in order to reach the same viscosity.