COMPARISON OF CHEMICAL AND HYSTERESIS CO2 TRAPPING IN THE NUGGET FORMATION

The Moxa Arch Anticline is a regional‑scale northwest‑trending uplift in western Wyoming and it has been chosen for CO2 capture and storage. The Nugget Sandstone is a deep saline aquifer that has been a candidate for CO2 storage. In this paper we compare the amount of mineral and solution trapping in comparison with dynamic hysteresis trapping based on compositional simulation. To the best of our knowledge this is the first paper to computationally assess the chemical trapping in the Nugget formation and to compare these three trapping mechanisms against each other. Reaction‑path and kinetic modeling of CO2C_‑brineC_‑mineral reactions in the Nugget formation was investigated to probe the factors that affect capacity for CO2 chemical trapping. The solution and precipitation trapping of CO2 are functions of temperature, pressure, CO2 fugacity and brine composition. The geochemical simulation of this system was explored in order to assess how mineralogy might change and the relative importance of mineral and solution trapping phenomena through time. After 30 years, 0.06 g of CO2 per kg of reacted rock is sequestered as mineral phases and solution trapping amounts to 3.1 g/kg rock. In comparison, a recent computational study of the Rose Run sandstone, Ohio indicates a much higher (30 times higher) mineral trapping capacity, mainly because of the presence of glauconite as an iron source for siderite formation. The total hysteresis trapping in our study is 4.5g/kg rock based on compositional simulation for the same period of time. These results reveal that mineral trapping in the Nugget formation is not significant but that total chemical trapping might be as high as 70% of hysteresis trapping. Therefore, the contribution and importance of chemical trapping in CO2 sequestration should be taken into account for assessment of CO2 sequestration.