--> ABSTRACT: Undrilled Muddy Formation (Lower Cretaceous) Paleodrainage Basin, Southwestern Wyoming and Northwestern Colorado, by John Dolson and Van Leighton; #91022 (1989)

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Undrilled Muddy Formation (Lower Cretaceous) Paleodrainage Basin, Southwestern Wyoming and Northwestern Colorado

John Dolson, Van Leighton

The Muddy formation (Lower Cretaceous) of the central and northern Rocky Mountains has produced over 1.5 billion bbl of oil equivalent hydrocarbons. Traps are developed in buried hills, valley fills, and onlapping marine sands associated with subaerial unconformities formed during a sea level drop.

At least 10 paleodrainage basins developed at maximum lowstand. Of these, production has been established in seven. One such paleodrainage, herein designated the Washakie/Sand Wash basin (WSW) drainage, is only drilled peripherally and remains essentially untested over nearly 20,000 km2.

The WSW paleodrainage is productive in Wyoming from local tributary sandstones at Sugar Creek field (Sierra Madre uplift) and Lost Soldier field (Sweetwater uplift). A major through-going trunk drainage network is productive at Brady field (Rock Springs uplift) and in numerous pools on the Axial and Douglas Creek arches of northwestern Colorado.

A recent deep wildcat in northwestern Colorado has confirmed subsurface existence of additional valley networks. Ten to fourteen percent porosity at 5,800 m and recent deep Muddy equivalent valley fill discoveries on the southern Moxa arch (Wyoming) demonstrate reservoir potential throughout this trend.

Future drilling successes will require 3,400 to 6,000-m deep tests but should result in significant deep gas and condensate production.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.