Evaluation of New Innovative Cement Blend for Enhanced CO2 and H2S Resistance
Abstract Achieving zonal isolation is incumbent upon preventing undesirable flow of hydrocarbons, carbon dioxide, and hydrogen sulfide, as well as other fluids. The risks associated with zonal isolation being compromised come from different mechanisms, such as insufficient displacement efficiency, tubular corrosion, cement cracking, micro-annuli from hydration shrinkage or pressure changes as well as erosion. It is therefore important to understand how CO2, H2S and other factors interact with cement under downhole conditions. The cementing materials are important to the short- and long-term integrity of the well and helping to ensure that no unwanted flow paths are formed that can threaten the safety, health and environment, and also the impact on the profitable life of the well. Thus, pathways for CO2 and H2S as well as other fluids should be avoided and blocked if they occur. Described herein is the evaluation of a novel cement admixture developed for improving the resistance of the cement matrix to chemical attack from CO2 and H2S, and its incorporation in a tailored cement design. The development of this design focused on applications in wells in the Norwegian Waters where CO2 and H2S are present. A comprehensive test program using customized equipment provided the necessary information to evaluate the performance. Further discussed are methods developed to test and evaluate the performance of this new design as effectively as possible by using available test equipment in new ways and new combinations. Test results support the novel cement admixture combined with ordinary Portland cement (OPC) in terms of pumpability, curing time, permeability and mechanical properties is technically and financially viable given that necessary blend optimization is done. Hence, the cement blend can be used without changing the existing cement infrastructure, methods, vetting and procedures that exist for well cementing today. Finally, the outcome of the first field test on an offshore permanent abandonment plug as part of a mature field plug and abandonment campaign is briefly referenced.