Wamsutter, the Keys to Unlocking This Giant Tight Gas Field

G. Earl Norris and Tony McClain
BP America Production Company, Houston, TX

Wamsutter is quickly becoming a giant gas field in the Eastern Greater Green River Basin (GGRB), Wyoming, USA. The Almond Formation is the main producing intervals in the Wamsutter Development Area (WDA) and it contains a complex 400'+ thick sequence of paralic, low permeability, over-pressured stratigraphic traps. One of the keys to unlocking these complex reservoirs is the use of Gross Depositional Environment (GDE) maps. These GDE maps can help predict reservoir sandstones in the upper, middle and lower Almond. The upper Almond marine section contains the largest reservoirs in areal extent in the GGRB. These large reservoirs have widely varying permeabilities, and fluid saturations leading to heterogeneous fluid distributions, as well as structural and stratigraphic traps, many of these in the same sand body. The middle Almond is mainly coastal plain deposits with an internal marine transgressive sequence on the eastern side of the field. Both of these facies contain significant reservoirs in tidal channels, fluvial channels, bay head deltas, and tidal deltas. The lower Almond is an alluvial plain to coastal plain deposit which contains reservoirs mainly in fluvial channels. The fluvial channels become less numerous from west to east across the WDA. Detailed GDE maps show very prominent and predictable reservoir trends in the upper, middle, and lower Almond Formation. Economic wells can generally be drilled where the GDE maps indicate stacked reservoirs.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005