Microbially enhanced geologic containment of sequestered supercritical CO2

Geologic sequestration of CO2 involves injection into underground formations including oil beds, deep un-minable coal seams, and deep saline aquifers with temperature and pressure conditions such that CO2 will likely be in the supercritical state. It is important that the receiving aquifer have sufficient porosity and permeability and be overlain by a suitable low-permeability cap rock formation. Supercritical CO2 injected into the receiving formation is only slightly soluble in water (approximately 4%) and therefore two fluid phases develop. Also, supercritical CO2 is less dense and much less viscous than the initially resident brine resulting in the potential for upward leakage of CO2 through fractures, disturbed rock, or cement lining near injection wells. This paper summarizes recent research on microbially-based strategies for controlling leakage of CO2 during geologic sequestration. We examine the concept of using engineered microbial biofilms which are capable of precipitating crystalline calcium carbonate using the process of ureolysis. The resulting combination of biofilm plus mineral deposits, if targeted near points of CO2 injection, may result in the long-term sealing of preferential leakage pathways. Successful development of these biologically-based concepts could result in a CO2 leakage mitigation technology which can be applied either before CO2 injection or as a remedial measure.