Mitigating Silicate Scale in Production Wells in an Oilfield in Alberta

Abstract

Abstract Alkaline surfactant polymer (ASP) floods in sandstone reservoirs are associated with silicate scaling of production wells. Many wells require numerous workovers and some must be abandoned. Mineral scale inhibitors are generally ineffective at treating silicate scale in these wells. An oilfield in southern Alberta was placed under an ASP flood for enhanced oil recovery and subsequently experienced severe silicate scaling of production wells. The wells were under artificial lift with submersible progressing cavity pumps (PCPs). The silicate scaling resulted in numerous well workovers to replace the pumps and associated rods. Two new silicate scale inhibitors were developed and applied down hole to production wells via continuous injection. The dose of chemical applied was approximately 250-500 ppm per well. The inhibitors decreased silicate scaling as evidenced by significantly increased run life of most wells. One well that required consecutive workovers after three and four months, respectively, was treated with inhibitor at 500 ppm and has subsequently produced without problems for more than 12 months. Similar results were seen with other wells. PCP torque has generally not increased, and, in some cases, has actually decreased with the scale treatment. In addition, coupons of treated wells have generally been clean, indicating that silicate scale is not depositing on metal surfaces. Even though the inhibitors must be applied at several hundred ppm to mitigate silicate scaling, significant cost savings have been realized because of the reductions in well workovers and associated lost production. This paper will discuss the issues encountered at this oilfield and the resultant solutions and successful outcome.