Potential for CO2 Ehanced Oil Recovery in the Appalachian Basin

The Appalachian basin oil and gas producing region has a large amount of oil which will be left in the ground, or “stranded”, following the use of today’s oil recovery practices. A major portion of this “stranded oil” is in mature reservoirs that based on this study appear to be technically amenable to enhanced oil recovery (EOR) using carbon dioxide (CO2) injection. Beyond its potential to augment U.S. oil production, CO2 EOR has the potential for permanently storing CO2, while adding value by maximizing oil recovery. CO2 EOR effectively reduces the cost of capturing and storing CO2 by earning revenues for the CO2 emitter from sales of CO2 to oil producers.

CO2 EOR, a tertiary recovery method in which supercritical CO₂ is injected into depleted oil reservoirs and has been in use by the oil industry for over 45 years.  Utilizing CO2 EOR has a distinct advantage over waterflood-only recovery in that above a certain pressure the CO₂ becomes miscible with the in-situ oil (minimum miscibility pressure – MMP). This causes the oil to swell and become less viscous and more mobile allowing for production from the residual zones. The implementation of CO₂ EOR methods are limited to the reservoirs in which MMP can be achieved and have adequate sweep, but there are major economic limiting factors, especially if the injected CO₂ is procured from high-cost anthropogenic sources.

A focused study of the Jacksonburg-Stringtown field in north-central West Virginia demonstrates the potential in the region.  The field has been under waterflood for a number of years.  A minimum miscibility pressure analysis determined that the MMP of the oil within the Jacksonburg-Stringtown field was 941 psi at a reservoir temperature of 80 °F (25 °C). Using an average hydrostatic gradient of 0.465 psi/ft, the target reservoir must be at a minimum depth of 2,500 feet (800 m) in order for the injected CO₂ to reach MMP. The Lower Gordon Stray reservoir at the Jacksonburg-Stringtown field is at a depth of approximately 2800 to 3000 feet. In addition crude oils with API gravity greater than 22° are best suited for CO₂ EOR. The oil in the Jacksonburg-Stringtown field has an API value of 46.5° at reservoir conditions which satisfies this general requirement.