EXPERIMENTAL SIMULATION OF CO2-WATER-ROCK INTERACTIONS FOR CARBON SEQUESTRATION AND ENHANCED OIL RECOVERY IN NORTH DAKOTA WILLISTON BASIN

Carbon dioxide (CO₂) is injected to deep geological formations mainly for two purposes: CO₂ enhanced oil recovery (EOR) and CO₂ sequestration. The injection of into carbonate reservoirs and aquifers causes pore water to change pH. The lowering of pore water pH causes a reaction between the carbonic acid and carbonate rocks, which can change porosity, permeability, fluid chemistry, seismic velocity, and mechanical properties. With the increase in consideration for CO₂ enhanced oil recovery and CO₂ geologic sequestration within the basin, laboratory testing is necessary to limit reservoir damage and maximize oil production and/or CO₂ storage. The University of North Dakota Petroleum Engineering Laboratory developed a testing system that can be used to simulate the CO₂-water-rock interaction under deep reservoir conditions. Because much of the North Dakota Williston Basin hydrocarbon production comes from carbonate reservoirs, and there are only limited reservoir core samples available for extensive laboratory testing, Indiana Limestone is used as a standard for the tests, due to its uniform composition, texture, and structure. Different combinations of fluid injection scheme (CO₂-water ratio, injection rate, total injection volume, and pressure, etc) have been tested. Changes of rock porosity, permeability, seismic velocity, and geomechanical properties, as well as effluent geochemistry (pH, total dissolved solids, conductivity, etc) have been observed. This paper presents some of our initial analysis, and their impact on CO₂ sequestration and enhanced oil recovery.