Oil Recovery Enhancement by Composite Flooding Technology for Gasi N1–N21 Ultra-High-Salinity Reservoir in Qinghai Oilfield
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摘要: 青海油田尕斯N1–N21油藏的地层水矿化度和钙镁离子含量超高,进行凝胶与表面活性剂复合驱,常规凝胶易脱水破胶,长期稳定性差,同时常规表面活性剂易与地层水中的钙镁离子发生反应产生沉淀。针对前一问题,合成了适用于尕斯N1–N21油藏的抗高盐有机凝胶,配方为0.3%~0.4%聚合物+0.2%~0.3%交联剂+0.1%~0.2%稳定剂,该体系在68 ℃条件下初凝时间大于70 h,成胶后凝胶黏度大于1.0×104 mPa∙s;优选了抗高盐表面活性剂QH-1,评价了界面张力和驱油效果,发现质量分数0.4%的QH-1溶液可提高采收率18.72%。室内试验结果表明,交替注入抗高盐有机凝胶和QH-1能有效遏制水的无效循环,提高中低渗区域的驱油效率,优化的“凝胶+QH-1”复合驱可提高采收率27.6%以上。该复合驱在尕斯N1–N21油藏9口注水井进行了应用,应用后对应油井的平均含水率由80%降至70%,增产油量2.41×104 t。研究结果表明,“凝胶+QH-1”复合驱提高采收率技术对青海油田尕斯N1–N21超高盐油藏增油降水具有很好的效果,具有推广价值。Abstract: The salinity and the content of calcium and magnesium ions are ultra-high in the formation water of Gasi N1–N21 reservoir in Qinghai Oilfield. While using gel and surfactant composite flooding, conventional gels are prone to dehydrate and break, showing poor long-term stability. Meanwhile, conventional surfactants are easy to react with the calcium and magnesium ions in formation water to cause precipitation. In view of this, a high-salinity-resistant organogel suitable for Gasi N1–N21 reservoir was developed, which consisted of polymer (0.3%–0.4%) + crosslinking agent (0.2%–0.3%) + stabilizer (0.1%–0.2%). The initial setting time of the system was longer than 70 h at 68 ℃, and the viscosity after gelling was greater than 1.0×104 mPa·s. What's more, a high-salinity-resistant surfactant QH-1 was optimized, and the interfacial tension and oil displacement effect were evaluated, witha finding that the QH-1 solution with a mass fraction of 0.4% could enhance the oil recovery by 18.72%. The laboratory test results indicated that alternate injection of the high-salinity-resistant organogel and QH-1 could effectively curb the ineffective water circulation and improve the oil displacement efficiency in the low and medium permeability areas. Notably, the optimized “gel + QH-1” composite flooding was capable of enhancing oil recovery by more than 27.6%. The composite flooding was applied to 9 water-injection wells in Gasi N1–N21 reservoir. As a result, the average water cut of these oil wells decreased from 80% to 70%, and the oil production increased by 2.41 × 104 t. The research results show that the oil recovery enhancement by “gel + QH-1” composite flooding is effective in enhancing oil production and decreasing water cut in Gasi N1–N21 ultra-high-salinity reservoir, so it is worthy of promotion and application.
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表 1 抗高盐有机凝胶68 ℃下的性能
Table 1 Performance of high-salinity-resistant organogels at 68 ℃
聚合物
质量分数,%交联剂
质量分数,%稳定剂
质量分数,%表观黏度/
(mPa∙s)初凝时间/h 0.2 0.1 0.05 1 500 180 0.2 0.10 2 500 150 0.3 0.20 3 200 130 0.3 0.1 0.05 4 000 125 0.2 0.10 8 200 100 0.3 0.20 10 300 80 0.4 0.1 0.05 8 400 105 0.2 0.10 11 200 90 0.3 0.20 13 000 75 表 2 抗高盐有机凝胶封堵性能试验结果
Table 2 Test results of plugging performance of high-salinity-resistant organogels
凝胶 渗透率/mD 压力梯度/(MPa∙m–1) 注入凝胶 水驱 1 391 3.20 3.84 1 050 0.68 2.86 5 103 0.30 4.14 2 420 4.48 5.02 1 120 1.20 6.67 5 260 0.48 8.31 表 3 抗高盐有机凝胶转向效果试验结果
Table 3 Test results of steering effect of high-salinity-resistant organogels
凝胶 渗透率/mD 含油饱和度,% 采收率,% 水驱 注凝胶 1 356 62.8 5.6 21.7 987 66.5 32.2 57.0 4 981 71.2 45.1 55.7 2 398 63.6 6.1 23.0 1 056 67.1 33.1 59.4 5 138 73.4 48.3 59.6 表 4 耐高盐表面活性剂QH-1岩心驱油的试验结果
Table 4 Core displacement test results of high-salinity-resistant surfactant QH-1
岩心渗透率/
mDQH-1质量
分数,%水驱采收
率,%QH-1驱采
收率,%365 0.1 25.50 6.12 342 0.2 27.68 12.47 381 0.3 26.72 15.11 357 0.4 25.55 18.72 表 5 “凝胶+QH-1”复合驱岩心驱替试验结果
Table 5 Core displacement test results of "Gel +QH-1" composite flooding
凝胶与QH-1组合形式 渗透率/mD 含油饱和度,% 采收率,% 水驱 “凝胶+ QH-1”复合驱 0.10 PV凝胶+0.20 PV表面活性剂 463 64.3 30.5 58.1 1 635 67.5 36.5 66.8 0.10 PV凝胶0.25 PV表面活性剂 568 62.1 29.7 59.2 1 890 70.4 37.5 68.7 0.10 PV凝胶+0.30 PV表面活性剂 324 61.3 28.5 61.2 1 500 72.1 35.2 69.5 注:1)凝胶配方为0.4%耐高盐聚合物+0.2%交联剂+0.1%稳定剂;表面活性剂为0.3%QH-1。 -
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