Multi-Stage Alternative Acid Fracturing Technique in Carbonate Reservoirs Stimulation

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.