EXPERIMENTAL STUDIES USING SUPERCRITICAL CO₂ TO CHALLENGE BRINE AQUIFER ROCKS

Geologic storage of CO₂ by injection into deep brine aquifers is currently viewed as a promising avenue for sequestering CO₂ due to large potential storage space, general proximity to significant point sources of CO₂, and mean porosities and permeabilities favorable to injection. However, commonly utilized geochemical models may not accurately represent the relevant subsurface conditions and rock-water -supercritical CO₂ reactions. Experimental testing of reservoir rock cores to supercritical CO₂ challenge under controlled laboratory conditions provides baseline data for determining likely subsurface geochemical reactions and reaction rates.

In this study, we analyze the effects of injecting supercritical CO₂ into rock cores prepared from Madison Formation outcrop. The Madison Formation represents a deep brine aquifer system in the Powder River Basin, WY, that has been suggested as an important target for CO₂ sequestration. We have developed a flow-through core reactor in which rock cores from the Madison Formation are flooded with supercritical CO₂ and reproduced formation water under typical reservoir conditions to simulate the near-well effects of CO₂ injection. We report on the physical effects, including changes in crush strength, porosity, and permeability, as well as brine chemistry evolution as a result of injecting CO₂ into Madison Formation cores. Preliminary data demonstrate that supercritical CO₂ injection can cause significant changes in Madison Formation core permeability and compressional fracture strength without comparable change in porosity.