Cement Designs for High-Rate Acid Gas Injection Wells

Abstract

Abstract High rate acid gas injection wells pose a significant challenge for the design of cementing systems. CO2 conversion of Portland cement to calcium carbonate is a significant problem. This paper describes the design and use of two cement systems for high rate acid gas injection wells. The paper compares risks and benefits of a high alumina cement slurry to those of a specialty Portland based system. Case history reviews of the application of both systems on liner cement jobs are detailed. The systems were used on wells designed for a 65% H2S, 35% CO2 injection stream at a rate of 65 million scf/day. High alumina cement is used in many applications to address the problem of CO2 conversion of Portland cement. The cement is resistant to CO2, but high temperature fluid loss control was not available, preventing its application on long liners. Lack of an effective high temperature fluid loss additive required the development of an alternate Portland based system. Later development of an effective high temperature fluid loss additive ultimately allowed use of the high alumina cement system. A CO2 resistant Portland system was developed by limiting the cement concentration and reducing total system permeability by use of specialty sized particles. This paper discusses the development and testing of a Portland based cement system and the associated risks with the use of this specialty system. Quality control steps to address the complex blending process and steps taken to improve system reliability are presented. Background Two acid gas injection wells (AGI 3–14 and 2–18) were drilled in the western United States as part of an overall gas plant de-bottlenecking. Plant throughput capacity was being increased by converting the plant to acid gas disposal by injection. The anticipated waste gas stream was 65% H2S and 35% CO2, with the design volume for the wells being based on the capacity of the plant plus adequate backup.