Selection and Application of BaSO4 Scale Inhibitors for a CO2 Flood, Rangely Weber Sand Unit, Colorado

Abstract

Summary The objective of this study was to develop a cost-effective scale-control program for the Rangely field CO2 project. The primary challenge was to identify scale inhibitors to control an existing barium sulfate (BaSO4) problem at the new, low-pH conditions caused by CO2 injection. A secondary concern was the change in produced-water composition and increased calcium carbonate (CaCO3) scaling tendency caused by the dissolution of carbonate minerals in the reservoir rock by the low-pH CO2 injection water. Laboratory evaluation identified several polymer-based and phosphonate scale inhibitors for the low pH (estimated 4.5) at CO2 production wells and near-neutral pH conditions in the surface facilities. Field tests show a good correlation to laboratory results. Suitable phosphonate products are preferred to polymer inhibitors because their residual concentrations may be determined accurately, they are generally cheaper, and they have a longer squeeze treatment life.