update on drilling, page-2

re: update on drilling--some history here Methane from coal represents an emerging energy resource that has considerable long-term potential for discovery and development. Within the coterminous United States, this resource has been estimated at 675 tcf, distributed among more than two dozen basins (Scott, 1993; Tyler et al., 1995). No less than 79% of this total is identified in basin provinces of the Rocky Mountain region, where extensive deposits of Late Cretaceous and early Tertiary coals are found at shallow depths of 500-5000 ft (150-1500 m). Several new and ongoing plays in Rocky Mountain basins have exhibited considerable success, beginning in the 1990s, owing in large part to advances in the ability to characterize and produce the relevant coalbed methane (CBM) reservoirs. Among these plays are the Fort Union Formation (Paleocene) of the Powder River basin, the Vermejo Formation (Late Cretaceous) of the Raton basin, and the Ferron Sandstone Member of the Mancos Shale of central Utah. In particular, the Ferron play is unique in terms of high gas content and production and may well represent one of the most prospective CBM areas in North America.

The Ferron Sandstone play is located along the western margin of the San Rafael Swell, a prominent Laramide (Late Cretaceous-Eocene) uplift in central Utah (Figure 1). The play fairway is estimated to be 6-10 mi (10-16 km) wide and 20-60 mi (32-96 km) long, corresponding to shallow coal occurrence in the Ferron Sandstone, a sequence of interbedded fluvial-deltaic sandstone, shale, and coal in the lower part of the Cretaceous Mancos Shale (Figure 2). To date, drilling activity has been concentrated along the northeastern part of the fairway, where three fields have been opened (see Figure 1). The largest of these is Drunkards Wash unit, consisting of more than 230 wells on 160 ac (64 ha) spacing. The CBM reservoirs in this field average 24 ft (7.2 m) in net thickness and occur at depths of 1100-3400 ft (330-1030 m). Productive coal beds consist of high-volatile B bituminous coal that commonly exhibit uncommonly high gas contents. Production from Drunkards Wash unit began in 1992 and has been impressive. Average daily flow rates have increased steadily from less than 300 mcf to more than 620 mcf, in part as a result of increased dewatering due to rapid growth in the number of producers. Negative gas declines have typified most wells along with decreases in water production. By November 1999, cumulative production for the unit exceeded 125.9 bcf for a total of 259 wells. Analyses of well performance suggest a productive life of 20 yr or more for individual wells, and ultimate recoverable reserves are in the range of 2-4 bcf. This translates into a minimum of 1-2 tcf recoverable for the field itself and as much as 4-9 tcf for the entire fairway.