Abstract Carbon dioxide (CO 2 ) sequestration in coal seams represents one (of only two) geological sequestration option that has the potential to yield a value-adding byproduct (enhanced coalbed methane [ECBM] recovery) to mitigate sequestration costs (the other being enhanced oil recovery [EOR]). Although the global pervasiveness of coal seams and their substantial adsorption capacity for CO 2 would suggest they represent a significant sequestration opportunity, the infancy of the technology as well as concerns over future coal minability has tempered sequestration capacity estimates. These two issues, an incomplete understanding of the interactions between CO 2 and coal (and the implications that derive therefrom, such as knowing what are the most appropriate geological environments for sequestration, what are the best well development strategies, how should wells be operated, etc.) and the potential future minability of coal (i.e., what exactly is a deep, unminable coal that will not be developed at some future date), represent the major obstacles to widespread acceptance of coal seams as a viable carbon sequestration option. The largest CO 2 -ECBM field test was performed by Burlington Resources (now ConocoPhillips) at the Allison unit in the San Juan Basin from 1995 to 2001. In this pilot test, approximately 336,000 t of CO 2 was injected into four wells completed in the Fruitland coal. Improvement in ECBM recovery was predicted, and the ability of the coal to adsorb and retain CO 2 was demonstrated. Smaller two-well and single-well tests have also been performed in Poland, Japan, Canada, and China. These are primarily government-funded demonstration projects with the primary objective of testing carbon sequestration technology. Additional field tests with similar objectives are also currently (as of this writing) in the planning stages as part of the U.S. Department of Energy’s (DOE) Regional Carbon Sequestration Partnership program. Economic analysis suggests that the CO 2 -ECBM process can be profitable in some cases. Besides the obvious importance of infrastructure costs and energy prices to economic performance, a key technical factor is the ability to maintain high CO 2 injection rates into the coal seams, which is a challenge because CO 2 tends to swell coal, thus reducing permeability and injectivity. Overcoming this challenge, via the identification of the most favorable reservoir environments, the best project development strategies, appropriate operating practices, etc., represents a critical milestone toward the widespread acceptance of the technology.

Abstract Exposed at Allison are the Ordovician St. Peter Sandstone, Joachim Dolomite, Plattin, Kimmswick, and Fernvale Limestones, and Cason Shale, as well as the Mississippian Boone Formation. A geologic map of the vicinity of Allison is in McFarland and others (1979). The Allison section, along with related exposures, is included in Craig and others (1984). The outcrop consists of two obvious, closely spaced roadcuts, referred to by local geologists as Allison South and Allison West (Fig. 1). Allison South is on Arkansas 9, approximately 4 mi (6 km) north of Mountain View. Allison West is on Arkansas 14, approximately 0.5 mi (0.8 km) west of its junction with Arkansas 9, between the small community of Allison and the entrance to Blanchard Spring Caverns. The roadcuts are in Sec. 14 and 10, T.15N., R.11W. of the Sylamore and Fifty Six 7½-minute Quadrangles, respectively. Both Allison localities are easily accessible. Neither Arkansas 9 nor 14 is heavily traveled. Ample shoulder space makes these locations ideal for relatively large groups. Parking at Allison South is better on the shoulder west of the highway. A turnout opposite Allison West allows convenient parking there. Allison South provides a nearly complete exposure from uppermost St. Peter Sandstone through Plattin Limestone. Higher rocks are better viewed at Allison West, which exhibits a complete section from uppermost Plattin into the lower part of the Boone Formation.