摘要
针对普通稠油油藏的特点,提出了混气表面活性剂驱提高采收率技术。为满足混气驱用表面活性剂乳化性能好、起泡能力高的要求,设计了双子型非离子-阴离子表面活性剂。首先优化了合成双子型非离子-阴离子表面活性剂所需中间体——双子二醇的条件,在此基础上合成了硫酸盐双子型非离子-阴离子表面活性剂。评价表明,分子中含有5个氧丙烯链节的硫酸盐非离子-阴离子双子表面活性剂9BS-5-0起泡能力与常用表面活性剂AOS相当;9BS-5-0使用质量分数为0.3%时可将油水界面张力降至0.028mN/m,优于胜利石油磺酸盐和重烷基本磺酸盐(高于0.05mN/m);其乳化能力则远好于胜利石油磺酸盐、重烷基本磺酸盐和AOS等表面活性剂。以新型表面活性剂9BS-5-0为主剂,通过与碱、甜菜碱复配,界面张力可达超低,乳化效果好(低于250转/min),起泡能力强(泡沫半衰期长达6min、起泡体积高于500ml)的有碱复合体系、无碱复合体系,可分别作为氮气混气驱、二氧化碳混气驱用表面活性剂复合体系。
以9BS-5-0构建的驱油体系为基础,进行了混气驱岩心封堵试验。结果发现,相同气液比时,泡沫对渗透率为2.409μm2、3.340μm2的亲油岩心具有较好的封堵效果,而对于渗透率为0.286μm2的亲油岩心封堵效果较差;与此相反,对于亲水岩心,渗透率越低,泡沫封堵性能越好。通过对比岩心中聚丙烯酰胺溶液的封堵能力发现,气液比分别为0.1、0.125的泡沫在渗透率为2.409μm2、3.340μm2的亲油岩心中所生产的阻力系数与粘度为40mPa·s的聚丙烯酰胺所产生的阻力系数相当,气液比为0.156的泡沫在渗透率为1.627μm2的亲水岩心所生产的阻力系数与粘度为20mPa·s的聚丙烯酰胺所产生的阻力系数相当,说明低气液比的泡沫对一定渗透率的岩心可具有好的封堵效果,为低气液比泡沫驱提供了支持。以50℃下粘度为327mPa·s的桩西稠油为对象,对混气表面活性剂驱进行物理模拟,研究表明气液比采用0.15~0.2时的混气驱即可取得较好的采油效果。微观驱油试验表明,混气驱通过乳化机理提高了驱油剂的洗油效率,通过贾敏效应提高了驱油体系的波及系数,通过泡沫的挤压携带作用将盲孔和管壁中的残余油驱替出来。
在室内试验的基础上,在桩106区块3个井组进行了混气表面活性剂驱矿场试验,到2009年9月底,不考虑递减累计净增油14128t,井组综合含水最高下降5.11%,取得了较好的经济效益。
Gas-surfactant flooding technology was proposed for conventional heavy oil reservoirs. The surfactants must have good emulsifying power and foaming ability, hence the molecular sructure of a nonionic-anionic Gemini surfactant was designed. A series of sulfate nonionic-anionic Gemini surfactants were synthesized after optimizing the synthetic conditions of their intermediate—Gemini diol. Then the foaming ability and the capacity to reduce IFT of these Gemini surfactants were evaluated. The results show that the Gemini surfactant of 9BS-5-0 which contains five oxypropylene groups has equivalent foaming ability with the common surfactant AOS; 9BS-5-0 with the mass fraction of 0.3% can lower IFT to 0.01mN/m, exibiting better performance than Shengli petroleum sulfonate and heavy alkylbenzene sulfonate ( more than 0.05mN/m ); Furthermore, its emulsifying capacity is much higher than these common surfactants too. Alkali and alkali-free compound systems can be obtained by combining 9BS-5-0 respectively with alkaline and betaine. The two systems have goog ability to reduce interfacial tension and emulisify crude oil ( minimum rotation rate is lower than 250r/min ), and good foaming ability ( foaming volume is larger than 500ml). So they can be used in N2-surfactant and CO2-surfactant flooding.
Gas-surfactant core plugging tests were carried out with the displacing systems developed from 9BS-5-0. The results indicated that the foams generated under the same gas/liquid ratio have better plugging effect on the oil-wet cores with permeability of 2.409μm2 and 3.340μm2, but worse plugging effecton the one with permeability of 0.286μm2. While for the water-wet cores, the lower permeability, the better plugging effect. The comparison and analysis of the plugging ability difference between foam and HPAM indicate that foams with GLR 0.1, 0.125 obtain the same resistance coefficient as HPAM solution with viscocity of 40mPa·s in oil-wet cores whose permeabilities are 2.409μm2 and 3.340μm2, and for the water wet core with permeability of 1.627μm2, the resistance coeifficent generated by foam with gas and liqulid ratio of 0.156 is as large as that generated by HPAM solutuin with viscocity of 20mPa·s. So it can be improved that low gas/liquid ratio foam has good plugging effect on the core with a certain permeability and provides support for the foam flooding with low gas and liqulid ratio. Gas-surfactant core flooding tests for Zhuangxi heavy oil (327mPa·s at 50℃) suggest that gas-surfactant systems with gas-liquid ratio ranging from 0.15 to 2.0 can achieve relatively high oil recovery. Micromodel flood tests show that the gas-surfactants can improve displacement efficency by emulsifying and sweep efficiency by Jamin effect, and drive residual oil in blind ends and on pore walls by compression and entrainment of foam.
Based on lab tests, gas-surfactant flooding pilot tests were carried out in three well groups of Zhuang106 block. The cumulative net oil increment amounted to 14128t regardless of production decline, and composite water cut was reduced by a maxium of 5.11% by the end of September, 2009.
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