Study on Continuous Sealing Law of Different Viscoelastic Diverting Acids in Dengying Formation of Sichuan Basin

Abstract

Dengying Formation carbonate reservoir in Gaomo area of Sichuan Basin has strong heterogeneity, and reservoirs I, II and III with permeability ranging from 0.05 to 3.02 mD. The use of diverting acid has played an important role in reservoir stimulation, but the rule of continuous plugging about diverting acid is unclear. In this paper, different fractures are simulated by slotted outcrop cores. Under the same confining pressure, different constant injection pressure modes are adopted to seal reservoirs I, II and III with diverting acid. The different types of viscoelastic diverting acid lasting sealing time and core etching shape are analyzed. The results show that the viscoelastic diverting acid with low acid concentration has different plugging regularity compared with viscoelastic diverting acid with high acid concentration. The viscoelastic diverting acid with low acid concentration has better plugging ability for type I reservoirs, and can be continuously plugged for more than 30 min within 4 MPa, while the viscoelastic diverting acid with high acid concentration has better plugging ability for type II and III reservoirs. For reservoirs II, plugging time is as long as 30 min under 10 MPa; for reservoirs III, more than 30 min within 13 MPa was obtained. Two field tests have been carried out, and the results show that the two types of diverting acid have the same continuous plugging performance as the laboratory study. Through the study of plugging performance, the rules of different plugging of low acid concentration viscoelastic diverting acid and high acid concentration viscoelastic diverting acid for reservoirs I, II and III are clarified, which provides a strong basis for efficient diverting acidification of strong heterogeneous reservoirs.