致密油藏不同类型渗吸剂提高采收率机制

EOR Mechanisms of Different Imbibition Agents in Tight Oil Reservoirs

晏 翔 戴彩丽 刘 合 孟思炜 金 旭 吴一宁

YAN Xiang DAI Caili LIU He MENG Siwei JIN Xu WU Yining

渗吸作用被认为是一种提高致密油藏采收率的重要方式。压裂后会采取闷井措施以通过渗吸作用置换原油，通常使用表面活性剂和纳米材料等化学剂，以提高渗吸置换效率，但不同类型渗吸剂的提高采收率机制还有待区分并阐释。文章对比了4种渗吸剂体系的渗吸提采效果，分别为高界面张力（?30 mN/m）体系：二氧化硅纳米流体和纯水；中等界面张力（1～10 mN/m）体系：单种表面活性剂体系；超低界面张力（＜10-3 mN/m）体系：表面活性剂复配体系。结果表明，二氧化硅纳米流体及单种表面活性剂体系主要依靠润湿反转效应，在油湿储层提高渗吸采收率，此外单种表面活性剂体系可降低界面张力，提高油滴通过孔喉时的可形变性，缓解贾敏效应，减少油滴被夹断并滞留于孔隙内的可能性，从而提升原油动用程度，然而采收率结果显示利用降低界面张力方式提采幅度有限，润湿性的改善对提高渗吸采收率的重要性高于界面张力的降低。但在强油湿性孔隙，当润湿性改善效果不佳，毛管力驱动效应难以充分发挥时，表面活性剂复配体系表现出最优的渗吸提采性能，其具有的超低油水界面张力促使油水自发乳化现象的发生，并将渗吸模式由毛管力驱动转变为重力驱动，自发形成的乳化油滴在重力作用下被排出孔隙。依靠超低界面张力使原油自发乳化的重力驱动渗吸模式，为提高渗吸采收率提供了新的途径。

Imbibition is a crucial approach for improving oil recovery in tight reservoirs. A shut-in strategy is usually adopted to enhance oil recovery by imbibition after fracturing，and chemical agents such as surfactant and nanomaterials are used to improve imbibition efficiency. However，the enhanced oil recovery（EOR）mechanisms of different types of imbibition agents need be distinguished and explained. In this study，four types of imbibition agent systems were employed to conduct imbibition experiments，including silica nanofluid and pure water with high interfacial tension（IFT）（?30 mN/m），pure surfactant solution with medium IFT（1—10 mN/m）and surfactants compound system with ultra-low IFT（＜10-3 mN/m）. The results showed that，as for the silica nanofluid and pure surfactant solution，the wettability alteration was the main EOR mechanism to improve the imbibition recovery in oil-wet reservoirs. Furthermore，the pure surfactant system could reduce the IFT and increased the deformability of oil droplets when the droplets passed through the pore throat. Therefore，the Jamin effect was alleviated，and the possibility of the oil droplets being snapped off and retained in the pore space is reduced，thereby improving the utilization degree of unrecovered oil. Nevertheless，the recovery results indicated that IFT reduction had a limited impact on the recovery enhancement，and that wettability improvement was more significant for improving recovery than IFT reduction. However，in the strong oil-wet pores，when the improvement of wettability was not effective and capillary force could not work ，the surfactant compound system exhibited the best imbibition performance. The ultra-low IFT between oil and water favored the spontaneous emulsification of oil，and changed the imbibition pattern from capillary force-driven imbibition to gravity-driven imbibition，and the emulsions formed spontaneously were drained out from the pore under the effect of gravity. The gravity-driven imbibition， which relies on the ultra-low IFT to promote the spontaneous emulsification of crude oil，provides a novel approach for enhancing imbibition recovery.

10.19346/j.cnki.1000-4092.2024.04.008