A conventional method of zonal isolation utilizes setting casing in the wellbore using cement. Then, the casing is perforated and a screen is installed. Finally, gravel is placed to control solids production. The shortcoming of this method is that it reduces the inner diameter of the completion, which limits the productivity of the treated well. The best current isolation method is to use either expandable casing or swelling packers. Swelling packers undergo dynamic swelling when in contact with water or oil. The swelling rubbers are bounded to any size of pipe where the thickness of the rubber controls the pressure difference developed across the pipe.1
In this study, water swelling packers from three different vendors were examined at 190ºF using different brines and 15 wt% HCl acid. The effects of 15 wt% HCl acid on the swelled elastomers and exposure to low salinity aquifer water after the acid were examined in detail.
Water swelling packers were able to hold differential pressures of more than 2,000 psi. Coupons obtained from vendors I&II showed acceptable results for 5 and 20 wt% NaCl. Packers soaked in fluids of high pH values (potassium formate with pH 9.5) or low pH values (15 wt% HCl acid with pH nearly 0) did not swell. Water swelling packers obtained from one vendor failed to seal in 20 wt% NaCl. Hydrochloric acid resulted in a significant reduction in the volume of the swelled coupons even after soaking for 15 minutes only. Immersing the coupons after acid exposure in field injection water did not regain their volume prior to soaking in HCl acid solutions.
Based on the above results, it is strongly recommended to perform quality testing for the elastomers before field application. Every effort should be made not to expose water swelled packers with concentrated HCl acids during matrix acidizing.