Successful Application of Foamed Viscoelastic Surfactant-Based Acid

摘要

A vertical well in a carbonate reservoir was damaged due torninvasion of large volumes of water from an upper formation.rnDiagnostic work (temperature survey and chemical analysis ofrnbailer samples) confirmed the communication between thernupper formation and the reservoir. Obviously, invasion ofrnlarge volumes of water can damage the well due to waterrnblockage and the formation of viscous emulsions inside thernformation. As a result of water invasion, the well ceased tornflow. A workover was conducted on this well to eliminate therndownhole communication, but still the well did not flow.rnTherefore, there was a need for an acid treatment to removernthe damage and restore well productivityrnThe well was perforated after the workover in 112 ftrnperforated intervals. In addition, the carbonate reservoir isrnheterogeneous with several high permeability zones. For thesernreasons, acid placement and diversion were important. Arnviscoelastic-based acid system was selected to combinerndiversion and dissolving capabilities in one system.rnMoreover, the viscoelastic-based acid was foamed to enhancerndiversion and improve lifting of the spent acid following therntreatment. Mutual solvent was added to the pre and postrnflushes to break the gel formed by the viscoelastic surfactantrnand help in removing the water blockage.rnThe treatment was applied using coiled tubing for betterrndiversion in the wellbore. The treatment was very successfulrnand resulted in major increases in oil production (more thanrn6,000 bbl/day). The well is still flowing at high rates ninernmonths after the treatment. No significant change in water-cutrnwas noted after the treatment.rnThis paper describes problem identification, fluidrnselection, and diversion. It will also discuss the first fieldrnapplication of foamed viscoelastic based-acid system.