Microbial-induced risks associated with CO₂ storage

Most subsurface environments host a variety of microorganisms regardless of their harsh conditions [1]. Many microorganisms can use CO₂ for catabolism and/or anabolism [2]. As such, microbial growth fuelled by CO₂ injection can have various side effects such as reduction of injectivity, decrease in storage capacity, and microbial-induced corrosion [3]. The microbial corrosion induced by microbial reduction of CO₂ depends on CO₂ metabolism, as well as, different mechanisms used by microbes to uptake electrons from Fe(0). Besides the corrosion induced by microbial reduction of CO₂, CO₂ can also activate other corrosive metabolisms by dissolving the mineral matrix and imposing other electron acceptors that were not accessible otherwise. These minerals can either act as an electron acceptor for electrons donated from iron and therefore trigger corrosion directly, or they can cause corrosion indirectly by producing corrosive products such as H2S [4]. In this paper, we thoroughly review various metabolisms that can be activated by CO₂ injection. We then assess the induced risk associated with each metabolism in terms of corrosion and injectivity impairment for several hydrocarbon fields in the Danish North Sea. Further, we evaluate the impact of impurities (in the CO₂ injection stream) on both methanogenic and sulfate-reducing bacteria. Considering various parameters such as mineral type (e.g., carbonate or sandstone) and CO₂ injection scenarios, we discuss the optimum scenario and reservoir conditions for which microbial risks are minimal.