超临界二氧化碳压裂液降阻剂体系优选

Optimization of friction reducer systems for SC-CO_(2)fracturing fluids

SC-CO_(2)(超临界二氧化碳)压裂技术不仅具有油气增产与CO_(2)利用的双重作用,而且还能有效避免水力压裂导致的地层伤害、环境污染等问题,但SC-CO_(2)压裂液在压裂施工过程中存在摩阻过高的问题,从而制约了压裂工艺参数的设计与优化。为了改善SCCO_(2)压裂液该项性能的不足来提高压裂效果,通过分子模拟和实验相结合的方式对SC-CO_(2)压裂液的降阻机理和影响规律进行了分析;最后根据多种降阻剂的降阻和增黏功能,得到了混合种类降阻剂的优化比例并验证了其优化后的效果。研究结果表明:①CO_(2)管流摩阻内部阻力和外部阻力产生的根本原因是流体的黏性和惯性,宏观影响因素为流速、流道性质和流体性质,微观上由分子间作用力、分子热运动、界面黏附力控制;②SC-CO_(2)压裂液降阻剂的降阻机理有2大类,癸基聚氟酯与聚烯酸月桂酯通过控制CO_(2)分子运动降低SC-CO_(2)压裂液体系流动摩阻,二甲基聚硅氧烷通过降低管壁的相对粗糙度实现降阻;③室内测试表明,癸基聚氟酯、二甲基聚硅氧烷、聚烯酸月桂酯在SC-CO_(2)压裂液中的可溶性和降阻性显著,含有这三种降阻剂的降阻剂体系对SC-CO_(2)压裂液体系的降阻率大于65%。结论认为,经降阻剂优化后的SC-CO_(2)压裂液降阻效果显著,有望代替滑溜水压裂液对页岩气储层进行高效增产技术改造,该认识对SC-CO_(2)体系优化具有重要的现实和参考意义。

Supercritical carbon dioxide(SC-CO_(2))fracturing technology has dual functions of oil and gas stimulation and CO_(2)utilization,and can effectively avoid formation damage and environmental pollution caused by hydraulic fracturing.In the process of fracturing construction,however,SC-CO_(2)fracturing fluids have the problem of high friction,which restricts the design optimization of fracturing technological parameters.To overcome the high friction of SC-CO_(2)fracturing fluids and improve its fracturing performance,this paper analyzes the friction reduction mechanism of SC-CO_(2)fracturing fluids and their influential law by combining molecular simulation and experimental study.In addition,the optimal ratio of mixed friction reducers is optimized based on the friction reduction and viscosity increasing functions of several friction reducers,and the optimization effect is verified.And the following research results are obtained.First,the root cause of the formation of the internal and external friction of CO_(2)pipe flow is fluid viscosity and inertia.Macroscopically,it is influenced by flow velocity,flow channel property and fluid property,and microscopically,it is controlled by intermolecular force,molecular thermal motion,and interfacial adhesion.Second,the friction reducers for SC-CO_(2)fracturing fluids have two kinds of friction reduction mechanism.One is that decylpolyfluoroester and polylaurylacrylate reduce the flow friction of SC-CO_(2)fracturing fluid system by controlling CO_(2)molecular motion,and the other is that dimethylpolysiloxane reduces the friction by reducing the relative roughness of pipe wall.Third,laboratory tests show that decylpolyfluoroester,dimethylpolysiloxane,and polylaurylacrylate have good solubility and friction reducing efficiency in SC-CO_(2)fracturing fluids.The friction reducer system containing decylpolyfluoroester,dimethylpolysiloxane,and polylaurylacrylate provides a friction reducing rate of over 65%for SC-CO_(2)fracturing fluid system.In conclusion,the SC-CO_(2)fracturing fluid with the optimized friction reducers has significantly less friction and is very promising in replacing slickwater fracturing fluid to stimulate shale gas reservoirs for efficient production.The research results are of important practical and reference significance to the optimization of SC-CO_(2)systems.