海上油田酸液预解堵体系筛选及评价

某海上油田属于砂岩油藏,完井采用砾石充填。钠土矿物中主要含蒙脱石,其次为石英、斜长石等。针对海上砂岩油藏伤害的特点以及对无机絮凝剂稳定化钠土的成分分析,研究了酸化预解堵体系。经过酸液类型及浓度的确定、添加剂的筛选以及物理模拟实验,确定了酸液预解堵体系配方。初步筛选出的前置酸和后置酸体系为7%盐酸(HCl),主体酸体系为5%HCl+5%氟硼酸(HBF4)+1%醋酸(HAc),其对稳定化钠土的溶蚀率分别为2.78%、21.77%,其对砾石的溶蚀率分别为0.38%、1.04%。缓蚀剂BJ最佳加量0.5%,缓蚀率大于95%;黏土稳定剂WS-1最佳加量为3%,防膨率为85.96%。优选出的酸化解堵配方为:前置酸和后置酸为7%HCl+0.5%BJ+3%WS-1,主体酸为5%HBF4+5%HCl+1%HAc+0.5%BJ+3%WS-1。酸液体系配伍性良好。酸液体系解堵效果较好,提高渗透率倍数达7倍以上。该酸液体系能溶解絮凝物,产生较大孔隙,可在一定程度上提高岩心渗透率,达到解堵的目的。

Screening and Evaluation on Acidification Plug Pre-Removal System in Offshore Reservoir

Considering an offshore oilfield was a sandstone reservoir and its completion had characteristic of gravel pack, this paper studied the acidification plug pre-removal system. After the determination of type and concentration of acid, screening of additives and physical simulation experiment, acidification plug pre-removal system was determined. Ahead acid and overflush acid were preliminarily confirmed as hydrochloric acid with mass fraction of 7%. The formula of primary acid was preliminarily established: 5% hydrochloric acid, 5% fluoboric acid, 1% acetic acid. The corrosion rate to stabilized na-bentonite of ahead acid and overflush acid was only 2.78% and that of the primary acid was up to 21.77%, while the corrosion rate to gravel of that was 0.38% and 1.04%, respectively. The optimum dosage of corrosion inhibitor BJ was 0.5% and the rate of corrosion inhibition was more than 95%. While the optimum dosage of clay stabilizer WS-1 was 3% and the rate of anti-swelling was 85.96%. The best formula of acidification plug pre-removal system was obtained as follows: ahead acid and overflush acid consisting of 7% hydrochloric acid, 0.5% BJ and 3% WS-1, main acid consisting of 5% fluoboric acid, 5% hydrochloric acid, 1% acetic acid, 0.5% BJ and 3% WS-1. The system had good compatibility. The effect of plug removal was satisfying while the permeability recovery ratio was improved more than 7 times. The acid fluid system could dissolve the flocculation, produce larger pores, and improve the permeability to achieve the purpose of plug removal.