Abstract: Donkey Creek North Minnelusa 3-D: Challenging Conventional Wisdom

FREDERICK, JOHN B., KAREN T. DEAN, STEVEN G. FRYBERGER, and TIM D. WILCOX

Three dimensional (3-D) seismic data acquired in 1992 over the Donkey Creek North Minnelusa Upper B sandstone oil field, Powder River Basin, Wyoming, significantly revised the existing reservoir interpretation. The 3-D survey not only provided a more accurate map of the reservoir distribution around the producing wells, but it also uncovered additional development locations. With porous Minnelusa sandstones (low velocity, low density) encased by tight carbonates (high velocity, high density) the large acoustic impedance contrasts yield high amplitude seismic events. Seismic amplitude mapping of interpreted Minnelusa sandstones correlates reasonably well with reservoir quality when the temporal resolution of the seismic data is sufficient to discriminate the individual sandstones. The 3-D seismic data volume allows a more accurate interpretation of the reservoir areal extent. Due to the small size of the survey (1.5 miles square) and a high effort dynamite source, the survey cost approximately $75,000 per square mile. In spite of this cost, the survey led to the drilling of two additional producing wells located in positions chosen to optimize secondary recovery efforts. These two new wells potentially doubled the fields recoverable reserves. It provided the ability to map the reservoir extent and structural position, thereby significantly reducing drilling risk. The 3-D mapping of the Upper B sandstone altered all previous interpretations and challenged conventional wisdom regarding the shape and lateral extents of Minnelusa reservoirs.

AAPG Search and Discovery Article #90944©1997 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma