碳酸盐岩储层多级交替酸压技术研究

Multi-Stage Alternative Acid Fracturing Technique in Carbonate Reservoirs Stimulation

为扩大酸液在碳酸盐岩储层压裂裂缝中的波及范围及作用距离,实现酸液对裂缝中岩面的非均匀刻蚀,提高酸蚀导流能力,提出了碳酸盐岩多级交替酸压技术。在分析多级交替酸压机理的基础上,采用压裂裂缝模拟软件,对前置液造缝阶段裂缝参数变化规律、造缝液体类型及交替注酸阶段交替注入参数进行了模拟优化,并进行了流态模拟与酸液腐蚀试验,优化了交替注入液体体系。模拟及试验结果表明:设计压裂缝长的70%是在裂缝快速增加阶段形成的,裂缝快速增加阶段可作为最佳的前置液造缝阶段,该阶段结束后即是多级交替注入酸液的最佳时机。多级交替泵注胶凝酸+压裂液及胶凝酸+交联酸段塞过程中,每级顶替液排量以阶梯递增方式注入、每级顶替液液量按递减方式注入、提高顶替液黏度和增加交替注入级数都有利于提高酸液在裂缝中的波及范围及均匀分布。研究结果可为碳酸盐岩储层的高效酸压提供理论依据。

This paper proposes a technique to increase the sweeping volume and penetration of acidizing fluid in the fracturing of carbonate reservoirs,to realize non-uniform acid etching on rock surface in fractures,and to improve the conductivity of acid etchings,multi-stage alternative acid fracturing technique in carbonate reservoirs.After the mechanisms of multi-stage alternative acid fracturing were investigated,fracture propagation rates in pad pumping,the type of prepad and the injection parameters in the alternative acid injection stage were simulated and optimized using the hydraulic fracturing simulation software.Fluid flow simulation and acid corrosion experiment were carried out,and alternative injected fluid systems were optimized.Simulation and experimental results showed that 70% of designed fracture length is created at the high-speed fracture increasing stage.This stage could be taken as the optimal fracture creation stage of the prepad followed by multi-stage alternative acid injection.During the multi-stage alternative injection of gelling acid,fracturing fluid,gelling acid and crosslinked acid plug,the sweeping area and uniform distribution of acidizing fluid in fracture could be improved by increasing the injection rate and the viscosity of displacement fluid in each stage and alternative plugs,while decreasing the injected volume of displacement fluid in each stage gradually.The research results would provide a theoretical basis for the efficient acid fracturing of carbonate reservoirs.