Unconformity-related oil entrapment in Muddy Sandstone: comparison of Kitty and Amos Draw fields, Powder River basin, Wyoming

Conference · Fri Aug 01 04:00:00 EDT 1986 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:7042080

Odland, S K; Gardner, M H; Gustason, E R

It has long been known that an unconformity plays a critical role in trapping oil in the Muddy Sandstone in the Powder River basin, but opinions have varied as to exactly where in the section that unconformity is located. Their work indicates that there are, in fact, two unconformities associated with the Muddy in the northern part of the basin. The older of these occurs on top of the Skull Creek Shale, whereas the younger is largely intraformational. In places, the younger unconformity has truncated the older one. It is the younger unconformity that is responsible for creating favorable settings for stratigraphic entrapment of oil. Two types of unconformity-related oil traps result from fluvial downcutting into and through the strand-plain sandstones of the oldest member of the Muddy during a major sea level drop. In cases where the unconformity cuts through the Muddy into the underlying Skull Creek Shale, permeable valley-fill sediments, deposited during the Muddy transgression, are juxtaposed against the impermeable Skull Creek Shale along the valley walls. Where valleys are oriented roughly perpendicular to regional structure, as at Kitty field, the updip portion of the valley wall can form a permeability barrier to the fluvial reservoir sandstones of the adjacent valley fill. In cases where the unconformity is intraformational, such as at Amos Draw field, early diagenetic clay, associated with the weathered horizon directly beneath the unconformity, can create a seal on top of the strand-plain sandstones of the oldest member of the Muddy.

• Research Organization: RPI Colorado, Inc., Boulder
• OSTI ID: 7042080
• Report Number(s): CONF-8609129-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 70:8
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
FEDERAL REGION VIII
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC TRAPS
MINERAL RESOURCES
MONTANA
NORTH AMERICA
OIL FIELDS
PETROLEUM DEPOSITS
POWDER RIVER BASIN
RESERVOIR ROCK
RESOURCES
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
USA
WYOMING