CARBON DIOXIDE SEQUESTRATION IN THE ORISKANY SANDSTONE AQUIFER

The current study addresses the potential of the Oriskany sandstone aquifer in New York, Ohio, Pennsylvania and West Virginia to serve as a trapping reservoir for carbon dioxide. The Oriskany sandstone aquifer was selected for this study because it meets many of the criteria required of a potential sequestration horizon: sufficient subsurface extent to provide for the potential sequestration of significant volumes of carbon dioxide, adequate porosity and permeability, and depths greater than 800 meters permitting carbon dioxide to be injected as a supercritical fluid.

To determine the capacity of the Oriskany sandstone aquifer to trap carbon dioxide as a soluble component, a series of experiments were conducted in natural Oriskany brine solutions. The experiments were conducted at a temperature range of 21-75 degrees Celsius and pressures from 1 to 400 bars. At these temperatures, the carbon dioxide pressure is essentially equivalent to the total pressure. The solubility experiments were conducted in a Dickson-type flexible-cell system. The Dickson-type reaction cell allows gas-saturated fluid samples to be taken into gas-tight syringes without changing in-situ conditions during sampling. Experimental results indicate an increase in carbon dioxide solubility as carbon dioxide pressure increases. The experiments also indicate a decrease in carbon dioxide solubility as temperature increases. The experimental results are in good agreement with theoretical predictions.

The calculation of the capacity of an aquifer to trap carbon dioxide as a soluble component requires the determination of the density of the carbon dioxide saturated solution at all locations within the aquifer. The capacity of the aquifer can be determined by combining the solubility of carbon dioxide along with the density, the extent of the formation, and porosity. The density of carbon dioxide saturated Oriskany brine was estimated as a function of temperature and pressure over the full range of conditions studied. The variation in density between brine with and without carbon dioxide increases as pressure increases but does not differ by more than 0.5 percent over the full range of conditions considered.