Abstract
Numerous acid stimulation techniques have been employed in water injectors to achieve uniform distribution across the injection interval. Mechanical and chemical diversion techniques were utilized separately and jointly to eliminate high permeability zones or thief zones where most of the injection water is flowing into a thin layer of the injection profile. The choice of placement techniques and chemical diversions plays an important role in the treatment success.
This paper presents case histories of acid treatments performance evaluation based on placement and diversion techniques. Based on the calculated time-lapsed injectivity index model and flow-meter surveys, the effectiveness of various mechanical and diversion techniques were evaluated. Placement techniques were either using bullheading or coiled tubing technique. The study covered 49 treatments using bullheading technique and 33 treatments using coiled tubing technique. The chemical diversions included polymer and surfactant-based in-situ gelled acids and foam diversion.
Flow meter survey conducted on several seawater injectors indicated that polymer-based acids damaged some zones of the injection interval. This resulted in poor distribution of the injected water. Foam diversion using bullheading technique did not improve the injection profile in the presence of thief zones. Wells treated by placing the acid using CT showed better performance than those wells treated by placing the acid by bullheading. Combinations of mechanical (CT) and chemical diversion (foam) showed better results than using chemical or chemical diversion alone. Viscoelastic surfactant-based acid showed significant increase in the injectivity index.
