大牛地气田污水回注井回注压力过高原因及对策研究

RESEARCH ON THE REASONS OF HIGH PRESSURE OF SEWAGE REINJECTION WELL AND SOLUTION IN DANIUDI GAS FIELD

针对大牛地气田W-4污水回注井回注压力急剧升高的问题,通过岩心环境扫描电镜(ESEM)和储层岩心敏感性评价实验对其进行分析研究。结果表明,该储层岩心内部含有绿泥石、绿/蒙混层和其他一些易引起储层岩心敏感性的黏土矿物;储层岩心具有弱速敏、强水敏,而且随着回注水累积孔隙体积倍数的增大,岩心渗透率不断下降。为此,提出在现场回注作业中,优化回注水水质,特别是水中悬浮固体含量小于1.0mg/L,防止回注水中悬浮固体含量过高,堵塞地层岩心微小裂缝孔隙和喉道,损害储层。要控制污水回注速度在临界流量之下。若是回注速度过大,岩心内部的黏土矿物或非黏土矿物在较大速度的回注流体冲刷之下,会发生松散、运移,最后堵塞储层岩心微小孔隙喉道,造成渗透率下降,回注压力升高。

According to the problem of injection pressure increase sharply in the W-4 sewage reinjection well in Daniudi gas field,the core of environmental scanning electron microscopy(ESEM) and reservoir core sensitivity were evaluated by experimental analysis.The results showed that:the reservoir core interior contained chlorite,green /Montmorillonite mixed layer and some other clay minerals which causes reservoir core sensitivity,the reservoir cores had weak velocity sensitivity and water sensitivity,and with the return water cumulative pore volume increases,the core permeability decreased gradually.Thus,some suggestions were put forward.First,the water quality was optimized in injection operation,especially,the suspended solids in water were less than 1 mg /L,preventing suspended solids block the formation core minute pore and throat.Second,sewage reinjection rate was controlled lower than critical flow rate.If the injection speed was too high,the clay minerals in the core inside or other matters under injection fluid scouring,would come loose,migration,finally block reservoir core minute pore and throat,causing reduction of permeability,and injection pressure becoming high.