Modeling the CO2-Water-Rock Interactions Aimed for Carbon Dioxide Storage in the Hygiene Formation, Denver Basin (Co) and Ericson/Rock Springs Formations, Rock Springs Uplift (Wy)
Geological storage of carbon dioxide is one of the most promising solutions for climate change mitigation. CO2 captured from large stationary sources such as coal fired power plants and refineries can be safely injected and stored in appropriate geological formations, which include mature and depleted oil fields, unmineable coal deposits and saline aquifers.
The Hygiene Formation (Upper Cretaceous Pierre Shales Group) and the Rock Springs and Ericson Formations (Late Cretaceous Mesaverde Group) are both good candidate reservoirs for carbon dioxide storage. The Hygiene Formation consists of paralic, medium sized quartzarenitic sandstones with average-low porosity, while Rock Springs and Ericson Formations consist of shallow marine and fluvial lithic sandstones, respectively.
Geochemical modeling of the interactions between these reservoirs with supercritical CO2 was carried out using the Geochemist's Workbench suite (v.7.0). Mineralogical composition was obtained from petrographic analysis of samples collected from outcrops of both formations. Two representative brines from each formation were selected, with depths and salinities suitable for CO2 storage projects (less than 5000 ft and higher than 10 g/L, respectively). A temperature of 60 degrees C was assumed (geothermal gradient). Injected CO2 pressure was set at 100 bar. (Both conditions ensure a supercritical state for carbon dioxide.)
Kinetic modeling of the system including secondary minerals (determined by equilibrium state calculation) was carried out, with a time span of 100,000 years. Carbonate minerals were assumed to be in local equilibrium. Rate constants were taken from the literature. Mineral specific surface areas (SSA) were calculated assuming 0.2 mm spherical grains, with no roughness.
Modeling results show that formation of carbonates starts after ca. 10000 years of simulation. In the Hygiene Formation, precipitation starts earlier (less than 5000 years), with predominance of ordered dolomite. In the Ericson and Rock Springs formations, siderite is formed preferentially. Calcite and magnesite are not formed in any of the reservoirs. Other common alterations observed are: dissolution of feldspars, complete dissolution of smectite in the first 10000 years, and precipitation of kaolinite.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009