Characterization of CO2 Solubility in Brines for the Purpose of Carbon Sequestration: Focus on the Rose Run Formation in Eastern Ohio
Anthropogenic CO2 is one of the main causes of climate change, hence limiting CO2 release from major point sources should have a positive impact on the environment. Injecting CO2 into saline formations is one way to reduce these emissions. Knowing the solubility of CO2 in brines found in possible injection sites is imperative for the characterization of injection limits. CO2-saturated brine is denser than CO2-free brine; therefore, the denser brine will sink toward the bottom of the formation, making it unlikely to leak back to the surface. The pressure of an oversaturated brine could force CO2(g) to migrate upward into potable aquifers and even back to the surface. Only injecting the amount of CO2 that is able to dissolve into the brine will ensure that all of the CO2 can be trapped permanently. Dissolved CO2 reacts with the surrounding rock, initially dissolving the rock, but eventually precipitating minerals that could decrease the porosity of the formation, making leakage even less likely while increasing the integrity of the formation.
CO2 solubility was measured in 1-4 m NaCl, CaCl2, MgCl2 brines in pressures up to 15 MPa at room temperature (25±1°C). Solubility data for brine other than NaCl, including more complex brines, is not found in the literature at temperatures and pressures that are present in possible injection sites. Experimental results in de-ionized water and NaCl brines from the current data compare well to published data and to the Duan et al. (2006) model; it is assumed that the solubility data in the other brines is accurate as well. Solubility of CO2 increases directly with pressure until it reaches a critical point where solubility does not increase significantly with increasing pressure. Solubility is inversely proportional to salinity and dependent on the type of salt present in the brine. The Appalachian Basin, specifically the Rose Run Formation that spans most of eastern Ohio, is more saline than other basins that are currently proposed as injection sites. The main components of the Rose Run Formation brine include NaCl, CaCl2, MgCl2 and KCl and will be tested for CO2 solubility to evaluate the capacity of the formation.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012