Can East African rift basalts sequester CO2? Case study of the Kenya rift

Abstract

Basalts have shown greater potential for faster and permanent sequestration of anthropogenic CO2 than sedimentary formations. Sequestration occurs through mineral carbonation due to the abundance in divalent minerals making them efficient geological hosts where they occur. Rapid population and industrial growth in developing countries leads to an exponential increase in their CO2 emissions, from stationary sources hence there is an imminent need for solutions to limit the amount of CO2 released into the atmosphere. Carbon Capture and storage (CCS) projects globally are at various stages of development majority are located in America and Europe. However, the suitability of continental basalts occurring in the East African Rift for CCS has not been assessed. Their characteristics and occurrence close to stationary CO2 sources thus limiting the high cost of transportation to far-flung locations make them ideal. Our review identified about 19 basalt groups of Miocene to Recent age (23.02 to 0.01 Ma) with thickness ranging from a few meters to 1500 m in the Kenya rift. We assessed four key parameters to determine potential CO2 sequestration sites: water availability; subsurface temperature; permeability and porosity of target formation; and accessibility to geothermal systems. Minerals such as calcic plagioclase, iron oxides and clinopyroxenes in the basalts offer the divalent elements required for carbonation. The basalts have varying porosity values ranging between 1-30%. We assessed the viability and ranked the suitability of the regions in the Kenyan rift as central Kenya rift >northern Kenya rift > southern Kenya rift. The environmental and financial challenges and their mitigation options of CO2 sequestration in the Kenya rift basalts have also been discussed. The challenges that CCS projects in the Kenya rift have to deal with include the impact of toxic and corrosive gases from geothermal systems, leakages through faults and fractures, induced seismicity, and economic costs. This knowledge is required for identifying areas where more site-specific assessment and modelling can be done for CCS projects in identifying carbon sequestration areas that can help slow down climate change.