Hu Haohan, Hu Youlin, Weng Xuejing
College of Petroleum Engineering, Yangtze University, Wuhan 430100, China.
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum at Beijing, Beijing 102249, China.
Gels. 2025 May 8;11(5):347. doi: 10.3390/gels11050347.
EZFLOW weak gel drilling fluid, a drilling fluid system with distinctive internal architecture, has been extensively implemented in horizontal well drilling operations at the Western South China Sea oilfields. Its unique internal structure causes specific functional mechanisms. The rheological mechanism was investigated through microstructural characterization, revealing that the microstructure comprises a reversible network structure with sol particles either encapsulated within the network or embedded at nodal points. This distinctive spatial network configuration endows the system with exceptional rheological properties. The plugging mechanism was elucidated via pre- and post-PPA test characterization of sand disc surface morphology. Experimental results demonstrate that the rheology modifier EZVIS forms deformable aggregates and films through intermolecular or intramolecular association in aqueous solutions, effectively plugging micro-nano pores/throats and microfractures to inhibit drilling fluid filtrate invasion. Concurrently, the rigid plugging material EZCARB establishes physical barriers at micro-nano pores/throats through bridging mechanisms. Notably, the dense filter cake formed by EZFLOW weak gel drilling fluid exhibits poor flowback characteristics, potentially inducing reservoir damage. Based on mechanistic analyses of rheological behavior, plugging performance, and filter cake composition, a filter cake removal fluid formulation was developed through: (1) creation of retarded acid HWCP to degrade polymer EZVIS and dissolve temporary plugging agent EZCARB; (2) development of corrosion inhibitor HWCI to mitigate corrosion rates. Laboratory evaluations demonstrated effective filter cake elimination and reservoir protection capabilities. Post-treatment analysis of EZFLOW-contaminated reservoir cores showed complete filter cake removal at core end faces with permeability recovery values exceeding 95%, indicating superior filter cake dissolution capacity and reservoir protection performance that significantly reduces formation damage.
EZFLOW弱凝胶钻井液是一种具有独特内部结构的钻井液体系，已在南海西部油田的水平井钻井作业中得到广泛应用。其独特的内部结构导致了特定的功能机制。通过微观结构表征研究了流变机制，结果表明微观结构由一种可逆网络结构组成，溶胶颗粒要么包裹在网络内，要么嵌入节点处。这种独特的空间网络构型赋予了该体系优异的流变性能。通过对砂盘表面形貌的PPA前后测试表征阐明了封堵机制。实验结果表明，流变改性剂EZVIS在水溶液中通过分子间或分子内缔合形成可变形的聚集体和薄膜，有效地封堵微纳米孔隙/喉道和微裂缝，抑制钻井液滤液侵入。同时，刚性封堵材料EZCARB通过桥接机制在微纳米孔隙/喉道处建立物理屏障。值得注意的是，EZFLOW弱凝胶钻井液形成的致密滤饼具有较差的返排特性，可能会导致储层损害。基于对流变行为、封堵性能和滤饼组成的机理分析，通过以下方式开发了一种滤饼清除液配方：（1）制备缓速酸HWCP以降解聚合物EZVIS并溶解临时封堵剂EZCARB；（2）开发缓蚀剂HWCI以降低腐蚀速率。室内评价表明其具有有效的滤饼清除和储层保护能力。对受EZFLOW污染的储层岩心进行处理后的分析表明，岩心端面的滤饼完全清除，渗透率恢复值超过95%，表明其具有优异的滤饼溶解能力和储层保护性能，可显著减少地层损害。
