Geochemical alteration of simulated wellbores of CO2 injection sites within the Illinois and Pasco Basins

Geologic carbon sequestration is being considered in target basalt and sandstone formations. The chemical effects of CO2 exposure on the interface between Class H Portland cement paste and Grande Ronde Columbia River basalt, or between cement paste and Mt. Simon sandstone, has been examined at a microstructural level. This bonding interface is a potential leakage pathway for CO2 along a wellbore. The salinities of the formation solutions, basaltic Pasco Basin formation water (0.013 M), whereas the sandstone Illinois Basin brine (1.28 M), play a large role in CO2 solubility and cement alteration. Experimental cement-rock-fluid charges were held at 35 °C and PCO2=10MPa for up to 84 days, conditions under which the fluids are CO2-saturated. The basalt-cement experiment had ∼1 mm alteration at the interface and high levels of alteration of the cement paste exterior. The sandstone sample displayed less alteration at the cement paste interface. Geochemical modeling conducted with CHIM-XPT calculated the pH of the Pasco brine solution (basalt only) to be 12.23 with 50 g of CO2 (104 bar) and 161 g (306 bar). The pH of the Pasco solution (cement + basalt) started with at 11.82 and ended at 4.52 after 136 g of CO2(g) dissolved in solution, resulting in the precipitation of magnesite, calcite, and siderite. The basalt has high capacity to convert CO2 into minerals. The Illinois Basin brine containing Mt. Simon sandstone and cement paste never exceeded a pH of 5.8, had an estimated 139 g of CO2 with high capacity to store aqueous and brine-saturated CO2 and a lower risk of alteration to hardened cement paste.