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Defining the Supercritical Phase Window for CO 2 in Coalbed Methane Reservoirs of the Black Warrior Basin : Implications for CO 2 Sequestration and Enhanced Coalbed Methane Recovery
| Content Provider | Semantic Scholar |
|---|---|
| Author | Pashin, Jack C. McIntyre, Marcella R. |
| Copyright Year | 2003 |
| Abstract | Sorption of gas onto coal is sensitive to pressure and temperature, and CO2 can be a supercritical fluid in coalbed methane reservoirs. More than 5,000 coalbed methane wells have been drilled in the Black Warrior basin in west-central Alabama, and the hydrologic and geothermic information from these wells provides a robust database that can be used to assess the potential for CO2 sequestration in coalbearing strata. Reservoir temperature within the coalbed methane target zone generally ranges from 80 to 125°F, and geothermal gradient ranges from 6.0 to 19.9°F/1,000 ft. Hydrostatic pressure gradients range from normal (0.43 psi/ft) to extremely underpressured (< 0.05 psi/ft) and have a bimodal distribution. Reservoirs have potential for supercritical fluid conditions beyond a depth of 2,480 ft under a normal pressure gradient. All target coal beds are subcritically pressured in the northeastern half of the coalbed methane exploration fairway, whereas those same beds were in the supercritical phase window prior to gas production in the southwestern half of the fairway. Although mature reservoirs are in the CO2 gas window, supercritical conditions may develop as reservoirs equilibrate toward normal pressure after abandonment. Coal can hold large quantities of CO2 under supercritical conditions, but the mobility and reactivity of supercritical fluid in coal has not been determined in the field. CO2 sequestration and enhanced coalbed methane recovery show great promise in subcritical reservoirs, and additional research is required to assess the behavior of CO2 in coal under supercritical conditions, where additional sequestration capacity may exist. Introduction Coalbed methane has been produced commercially from the Black Warrior basin of Alabama since 1980, and more than 3,400 wells are currently producing. Many of these wells are reaching maturity, and ECBM (enhanced coalbed methane recovery) through injection of CO2 has potential to reduce greenhouse gas emissions from coal-fired power plants while increasing reserves significantly (Pashin et al., 2001, 2003) (Fig. 1). The volume of gas that coal can adsorb is sensitive to temperature and pressure (Jüntgen and Karweil, 1966; Kim, 1977; Yang and Saunders, 1985), and these variables can vary greatly in coalbed methane reservoirs (Pashin et al., 1991; Scott et al., 1994; Ayers and Kaiser, 1994). Importantly, the critical point for CO2 is within the range of known reservoir conditions (Fig. 2). Coal can hold a large volume of CO2 under supercritical conditions (Kroos et al., 2001), but little is known about the long-term stability of supercritical CO2 in coal. Supercritical CO2 is commonly used as an organic solvent, so identifying areas where supercritical reservoir conditions may exist or develop is important when screening areas for CO2 sequestration and ECBM. SUPERCRITICAL CO2 WINDOW IN BLACK WARRIOR BASIN 2 Fig. 1. Index map of the eastern Black Warrior basin in Alabama showing locations of coalbed methane fields, underground coal mines, coal-fired power plants, and Appalachian folds and thrust faults (after Pashin et al., 2001). Fig. 2. Phase diagram for CO2 showing relationship of the critical point to temperature-pressure conditions in coalbed methane reservoirs of the Black Warrior basin. 0 5 10 mi 5 5 0 5 10 15 km FAYETTE WALKER JEFFERSON |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www2.gsa.state.al.us/CO2/CO2page/Pashin%200316.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
