Design and experimental testing of a high pressure, high temperature flow-through rock core reactor using supercritical carbon dioxide

Abstract

Anthropogenic CO 2 emission is of concern due to its likely contribution to global climate change. Geologic storage of CO 2 in deep brine-bearing aquifers is currently viewed as an alternative to its release to the atmosphere. The effects of injecting CO 2 into these aquifers are poorly understood. An experimental apparatus was developed to reproduce subsurface conditions relevant to geologic sequestration to simulate CO 2 injection and assess CO 2-brine-rock interactions. Technology available for this type of experimental apparatus was advanced by enhancing monitoring capabilities to include in situ pH, EC, pressure, and temperature measurement and continuous logging of these variables. This thesis describes the experimental apparatus and its novel capabilities, demonstrates its accuracy and precision, and presents and discusses a suite of CO 2-brine and CO 2-brine-rock interaction studies relevant to geologic sequestration. Experiments were conducted by flowing brine and/or supercritical CO 2 through the apparatus, with and without rock cores in line. Rock samples were limestones/dolostones from the Madison Formation in the western Black Hills, South Dakota, which was selected based on its applicability as a primary large-scale geological CO 2 storage target. Outcrop blocks were machined to produce cores with minimal evidence of weathering to best simulate subsurface Madison Formation rock. Brines were prepared in the laboratory of a similar composition to reported literature values for in situ Madison formation fluids. Results from the experimental system show good agreement with bench pH and EC measurements when utilizing standardized fluids. Experimental data indicate that adding CO 2 to brine under all tested conditions significantly reduces brine pH, an important control on subsurface geochemistry. This effect is partially buffered by flowing the fluids through Madison rock cores, due to dissolution of carbonate minerals, predominantly dolomite. The experiments indicate that samples of the Madison Formation with in situ brines can be partially dissolved via exposure to supercritical CO 2. Similar processes would likely occur in the subsurface Madison Formation in response to addition of supercritical CO 2. The novel experimental system provided new data that could be utilized in refining geochemical models; however, further improvements can be made to the system to improve its capabilities in this regard.