He Zhijun, Wang Jintang, Liao Bo, Bai Yujing, Shao Zihua, Huang Xianbin, Wang Qi, Li Yiyao
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China.
Gels. 2022 Jul 15;8(7):442. doi: 10.3390/gels8070442.
China has abundant shale gas resources with great potential, which may serve as a significant support for the development of a "low-carbon economy". Domestic shale gas resources are buried deeply and difficult to exploit due to some prevalent issues, such as long horizontal sections, severe development of reservoir fractures, strong sensitivity to water, borehole instability, etc. Compared to water-based drilling fluids, oil-based drilling fluid exhibits better inhibition and good lubricity and is thus broadly used in shale gas drilling, but it is confronted with the challenge of removing the harmful solid phase. Selective chemical flocculation is one of the most effective methods of removing the harmful solid phase in oil-based drilling fluid. In this study, interactions between the flocculation gel for oil-based drilling fluid and clay minerals were investigated by molecular simulation, which revealed the molecular-scale selectivity of the flocculation gel for rock cuttings with negative charges. Calculations showed that the flocculation gel is highly effective for the flocculation of negatively charged cuttings, but it is ineffective for flocculating neutral cuttings. The flocculation gel is not very effective for cuttings with high hydrophilicity, and it is totally ineffective for flocculating cuttings with poor hydrophilicity. Within a limited concentration range, the flocculation effect can be enhanced by increasing the flocculation gel concentration. The performance of the flocculation gel declined at elevated temperatures.
中国拥有丰富的页岩气资源，潜力巨大，可为“低碳经济”发展提供重要支撑。国内页岩气资源埋藏深，因水平段长、储层裂缝发育严重、水敏性强、井壁不稳定等普遍问题而难以开采。与水基钻井液相比，油基钻井液抑制性更好、润滑性良好，因此在页岩气钻井中广泛应用，但面临着去除有害固相的挑战。选择性化学絮凝是去除油基钻井液中有害固相最有效的方法之一。本研究通过分子模拟研究了油基钻井液絮凝凝胶与黏土矿物之间的相互作用，揭示了絮凝凝胶对带负电荷岩屑的分子尺度选择性。计算表明，絮凝凝胶对带负电荷岩屑的絮凝效果很好，但对中性岩屑絮凝无效。絮凝凝胶对亲水性高的岩屑效果不太好，对亲水性差的岩屑完全无效。在有限的浓度范围内，增加絮凝凝胶浓度可增强絮凝效果。絮凝凝胶在高温下性能下降。
