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

摘要

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 degrees C and PCO₂=10 MPa 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 CO_2(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.