Lin Renyi, Luo Pingya, Sun Yang, Pan Yi, Sun Lei
The State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China.
ACS Omega. 2021 Sep 7;6(37):24185-24195. doi: 10.1021/acsomega.1c03751. eCollection 2021 Sep 21.
Fracture-type buried-hill reservoirs refer to dual media which have a fast breakthrough speed and a low sweep efficiency in the process of gas injection displacement. In order to overcome this problem, in this paper, a new profile control and oil displacement technology of pre-slug deep plugging by injection of different levels of nano-microspheres and natural gas was proposed. The mercury intrusion experiments were used to compare the fractal characteristics of the pore structures of the matrix and artificial fractured cores in the buried-hill reservoir. The results show that the heterogeneous characteristics of pores and fractures are the main factors leading to excessive gas breakthrough. Three nano-microsphere systems (WJ1, WJ2, and WJ3) with good temperature resistance, salt resistance, swelling properties, and stability were prepared using the inverse emulsion method. Core plugging performance tests show that WJ3 has the best plugging effect among the three nano-microsphere systems, followed by WJ2 and WJ1. According to the scanning electron microscopy observations, it was found that the sealing mechanism of nano-microspheres includes direct sealing, bridging sealing, adhesive sealing, direct pass, deformed pass, and crushing pass. Finally, the displacement experiments with a composite fractured core showed that compared with pure natural gas injection, the breakthrough time of the combined displacement process of nano-microspheres and natural gas was greatly extended, and the final oil displacement efficiency was increased to greater than 80%.
裂缝型潜山油藏是双介质油藏，在注气驱替过程中存在气窜速度快、波及效率低的问题。为解决这一问题，本文提出了一种注入不同粒径纳米微球与天然气前置段塞深部封堵的调剖驱油新技术。通过压汞实验对比了潜山油藏基质岩心与人造裂缝岩心孔隙结构的分形特征。结果表明，孔隙与裂缝的非均质性特征是导致气窜严重的主要因素。采用反相乳液法制备了具有良好耐温、耐盐、膨胀性能及稳定性的3种纳米微球体系（WJ1、WJ2和WJ3）。岩心封堵性能测试表明，WJ3在3种纳米微球体系中封堵效果最佳，其次是WJ2和WJ1。通过扫描电子显微镜观察发现，纳米微球的封堵机理包括直接封堵、桥接封堵、黏附封堵、直接通过、变形通过和挤压通过。最后，复合裂缝岩心驱替实验表明，与单纯注天然气相比，纳米微球与天然气组合驱替过程的突破时间大幅延长，最终驱油效率提高至80%以上。
