Effect of HCl Acid and Brines on Water-Swelling Packers

Abstract

Achieving successful zonal isolation during well completion is critical to minimize early water production. Currently, cementing is the only method used in Saudi fields to provide zonal isolation. However, in horizontal sections, cementing becomes a challenge and excessive water production can occur because of channeling. Another method for zonal isolation is to use a rubber elastomer bonded onto a base pipe. The rubber swells in water and provides a seal between the base pipe and the open hole. This paper will outline the step-by-step qualification testing that was carried out in Saudi Aramco facilities in an attempt to improve zonal isolation in horizontal and multilaterals wells.In this study, we present laboratory evaluation of elastomers at 190ºF using brines of different ionic strengths and pH values. The evaluation involved examining the effect of salinity and pH on elastomer swelling rate. Also, the study investigated the effect of 15 wt% hydrochloric acid (HCl) on swollen elastomers and whether the exposure to water after acid would restore their sizes. To the best of the authors' knowledge, no previous work has been performed to examine the impact of these factors on the swollen packers.The elastomer bonded onto pipes was tested in autoclaves. The pressure drop across the pipes was measured as a function of time. The influences of pH and divalent cations on water-swelling packers were investigated using elastomer samples. Swelling was related to fluid characteristics.Some water-swelling packers withstood pressures up to 5,000 psi at 190ºF after placing the elastomers in brines with salinities up to 200,000 mg/L. However, the swollen elastomers shrank in 15 wt% HCl. A calcium chloride (CaCl 2 ) completion fluid, a common fluid used in Saudi Aramco fields, at 72 lb/ft 3 (pcf) failed to swell the elastomers. Re-exposure of shrunken coupons to water did not restore their initial swollen volume before acid soaking. This paper discusses the advantages and limitations of water-swelling elastomers and gives recommendations for successful field applications.

Performance evaluation of water-swelling and oil-swelling elastomers

“…Swelling results in changes in volume, thickness, density, hardness, and other material properties of these elastomers. [7][8][9] A necessary input for each of the above tasks is the knowledge of the effect of swelling on material behavior of the elastomer under specific well conditions.…”