Use of 2-D Seismic for Coalbed Methane (Cbm) Development in the Powder River Basin, Wyoming
Devon Energy purchased and reprocessed carefully selected 2-D seismic lines located throughout its Tertiary CBM play in the Powder River Basin in Campbell and Johnson Counties, Wyoming. Shot in the 1970’s and 1980’s and designed for deeper targets, these lines nonetheless revealed interesting shallow data at the CBM level which led to the acquisition of 80 miles of 2-D lines in 2005. The new lines were planned for target depths of 1000-2000 feet and have proven useful for delineating features which impact CBM field development of Big George coals in the Juniper Draw and Pine Tree fields. These features include faults, the merging/splitting of coal seams, and zones of limited or missing coal.
In the Juniper Draw Field, a “want”, or zone of no coal, is the dominant feature that has been identified through seismic and has impacted surrounding coal thicknesses and structure. The “want” contains no Lower Big George coal, while the Middle Big George coal is positioned structurally higher with consistent thickness. The seismic expression of this feature has been interpreted as either a fault-bound, up-thrown block, or a result of preferential compaction around channel-fill, both resulting in increased accommodation space adjacent to the “want”. Just to the west of the “want”, some of the thickest coals in the basin have been encountered (one well contains 228 feet of Lower Big George coal).
In the Pine Tree Field, fluvial channel-fill forms “partial wants”, or zones of limited coal, with Big George coal having been compacted on top of and around them. Different from the “want” in Juniper Draw, these features have resulted in thinner coals (less than 50% thickness) than the structurally lower coals encountered away from the channels. Also identified in the seismic are high amplitude reflectors shown above these channel features, which possibly indicate gas charged sands. Some of these locations are being logged during the current drilling program.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009