Study Explores Potential of Subsurface Biomineralization in CO2 Injection, Storage

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 231806, “Exploring the Potential of Subsurface Biomineralization During CO2 Injection and Storage,” by Stephen Heath, SPE, Creative Chemical Solutions; Khosro Jarrahian, Petronas and Heriot-Watt University; and Eric MacKay, SPE, Heriot-Watt University. The paper has not been peer-reviewed. _ This study reviews subsurface microbial activity, biomineralization reactions, and the mechanisms prevalent for bioremediation of wells, stabilization of cements, and increase in CO2 trapping and leakage reduction during CO2 injection and storage. Laboratory studies have revealed that microbial growth under supercritical CO2 conditions is challenged by acidic brine pH and elevated CO2 partial pressures. However, the presence of minerals such as calcite, dolomite, feldspars, and clay minerals can buffer these stresses and sustain microbial communities to enable biofilm formation and bioprecipitation of carbonate minerals to increase CO2 trapping in the reservoir. Biogeochemical Effect of CO2 Injection Subsurface formations naturally host diverse microbial communities that can respond to CO2 injection. Microbial processes can influence storage performance by contributing to injectivity reduction, mineral precipitation, and microbially influenced corrosion (MIC). Microorganisms can affect CO2 injection and storage in the four following ways: - Biofilm formation can alter flow and storage - Microbially enhanced geochemical reactions can promote biomineralization - Carbonate minerals can be dissolved through acid production - Metals can be mobilized through redox reactions Laboratory studies show that high CO2 pressures generally decrease microbial viability. However, this effect is moderated by reservoir characteristics such as mineral buffering, rock porosity, and biofilm formation, which can protect microorganisms in CO2-rich environments. Sandstone systems typically provide more-favorable conditions for microbial persistence than carbonate formations. Despite the fact that CO2 has negative effects on cell number and activity, some laboratory investigations replicating subsurface conditions have demonstrated the survival of microorganisms even after injection of supercritical CO2. Multiple metabolic pathways may be activated following CO2 injection, including sulphate reduction, nitrate reduction, methanogenesis, and acetogenesis, depending on reservoir properties. Further microbial metabolisms may become activated within or at the wellbore under CO2 storage conditions. At the well surfaces, sulfate-reducing bacteria (SRB) can use metallic iron directly as an electron donor. This drives a process known as electrical MIC. One study devoted to the effect of CO2 on bacterial growth investigated the evolution of microbial communities in a deep saline aquifer during geological CO2 storage at the Ketzin pilot site in Germany, with emphasis on microbiological monitoring. The Ketzin pilot trial revealed significant effects of CO2 on microbial communities and demonstrated the ability of these microbes to adapt to geochemical conditions resulting from CO2 injection. This has important implications for carbon capture and storage (CCS) operations because SRB-mediated reactions and biofilm formation can influence mineral precipitation and dissolution, alter porosity and permeability, and affect near-well injectivity.