In-Situ Displacement of Crude Oil by Fracturing Fluid in Chang-6 Reservoir in Xingzichuan
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摘要: 杏子川地区延长组长6储层具有含油饱和度低、油湿性强，非均质性强（渗透率为0.10～1.0 mD）等特征。常规压裂液体系润湿改性能力弱、渗吸置换效果差，亟需研究具有渗吸提采功能的压裂液。借助了核磁共振T2谱手段，测试了不同组成和配比的化学剂对长6储层岩心内微-纳孔径原油的动用能力，并探究了压裂液原位置换原油的影响因素及其渗吸机理。结果表明：带负电的阴离子试剂AX-2更适合动用长6低含油饱和度储层，0.10% AX-2渗吸采收率大于30%，纳米小孔与微米大孔动用程度分别为42.08%与22.62%；将表面活性剂AX-2复配成为10 nm尺寸的纳米乳液AX-1，抗吸附能力更强，动用效果更佳，纳米孔与微米孔动用程度可提升至58.26%与29.70%；界面张力为1.5 mN/m时AX-1最适合动用长6储层原油，此时液体具有较高的渗吸动力与原油剥离能力。优选体系复配后现场压裂稳定，试油效果良好，平均日产油量超过26 t。Abstract: The Chang-6 reservoir in the Yanchang formation in Xingzichuan area is characteristic of low oil saturation, strong oil wetting and strong heterogeneity (permeability = 0.10 – 1.0 mD). In fracturing operations in this area, it was found that the conventional fracturing fluids have weak wettability alteration ability and poor imbibition displacement effect. To efficiently develop this reservoir, it is imperative to use a fracturing fluid with the ability of production enhancement by imbibition. Using NMR T2 spectrum, chemicals of different compositions were tested for their ability to produce the crude oils stored in the micrometer-nanometer sized pores in the Chang-6 reservoir, and the factors affecting fracturing fluids’ in-situ displacement of crude oil as well as the imbibition mechanism of the in-situ displacement are investigated. The results of the study show that compared with other agents, AX-2, a negatively charged ionic surfactant agent, is more suitable for producing the low oil saturation Chang-6 reservoir. Using 0.10% of AX-2, the imbibition recovery of oil is greater than 30%, and the percent oil produced from the small nanometer-sized pores is 42.08%, while that from the large micrometer-sized pores is 22.62%. If AX-2 is used to formulate a 10-nanometer nanoemulsion AX-1, it has stronger anti-adsorption ability and better performance in producing the oil from the Chang-6 reservoir; the percent oil produced from the nanometer pores is increased to 58.26%, while that from the micrometer pores is increased to 29.7%. An AX-1 emulsion with surface tension of 1.5 mN/m is the best emulsion for producing the Chang-6 reservoir, since this emulsion has higher imbibition force and crude oil stripping capacity. The fracturing fluid optimized with the AX-1 emulsion is used in field fracturing operations, and good results were obtained, the average daily production rate of crude oil reached 26 tons.
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Key words:
- Low oil saturation /
- Nano emulsion /
- NMR T2 spectrum /
- Imbibition replacement /
- Chang 6 sandstone
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