Drunkard's Wash Project: Coalbed Methane Production From Ferron Coals in East-Central Utah
Robert A. Lamarre and Terry D. Burns
The Drunkard's Wash Project produces dry, coalbed methane gas from coals within the Ferron Sandstone Member of the Mancos Shale. The project covers 120,000 acres on the western flank of the San Rafael Uplift in east-central Utah. Gas was first produced into the sales line in January 1993. The field is being developed on 160 acre spacing with 73 wells currently producing 32.2 MMCFD for an average of 437 MCFD/well. Thirty three of those wells have been producing for 32 months and now average 637 MCFD/well. Most of the wells show a classic coalbed methane negative decline curve with increasing gas rates as the reservoir pressure declines due to production of water. Daily water production is 14,500 BPD, for an average of 199 BWPD/well.
Total coal thickness ranges from 7 ft to 48 ft, with an average of 24 ft. The coals occur in 3 to 6 seams at depths of 1350 to 2450 ft. The coal rank is high volatile A&B& bituminous. We can not yet see a correlation between total coal thickness and current production. All wells are cased and hydraulically stimulated and most require pumping units to handle the large volumes of water. However, 22 wells do not require pumps and flow unassisted to the surface.
The structure consists of monoclinal westward dip. A thin tonstein layer in the bottom coal seam serves as an excellent datum for mapping. Enhanced production is encountered along a southwest-plunging nose that probably formed additional fracture permeability within the coals. Northeast-trending reverse faults with small displacement appear to compartmentalize the reservoir.
The Ferron coals were deposited in a river-dominated deltaic system that prograded to the east and southeast during Turonian-Coniacian (Upper cretaceous) time. The Ferron Sandstone Member represents an eastward-thinning clastic wedge that was deposited during regression of the Western Interior Cretaceous seaway.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California