During August 1983, Golden Buckeye Petroleum completed the Dinner 15-1 well, 4 mi (6.4 km) northeast of Greeley, Colorado, pumping 107 BOPD and 30 BWPD through untreated perforations in the "Parkman sandstone" at a depth of approximately 3,650 ft (1,112 m). This completion established the first reported "Parkman" production in Colorado. The Dinner 15-1 has produced over 13,000 bbl of oil and 9,500 bbl of water in 16 months, and has ultimate oil reserves estimated to be 60,000 bbl. Since August 1983, six more "Parkman" wells have been completed by St. Michael Exploration, Coors Energy, and Golden Buckeye.

The productive facies is a permeable, highly glauconitic, shaly, fine to medium-grained quartz sandstone. "Parkman" is the drillers' informal name for the Larimer and Rocky Ridge Sandstone Members of the Pierre Shale. The Larimer and Rocky Ridge Members correlate to younger rocks than the Parkman Sandstone of the Powder River basin. Environments of deposition are being studied at an outcrop area approximately 25 mi (40 km) northwest of the Larimer and Rocky Ridge productive area.

Hydrocarbon trapping in the fields discovered to date is due to a combination of structural and stratigraphic factors. The permeable "Parkman" facies must be present and the permeable sand must be sealed by structural closure, fault closure and/or updip pinch-out. High-angle listric normal faults, which create local horst and graben systems, account for the "Parkman" structural traps. Relief on these faults is on the order of 20-60 ft (6-18 m). Productive areas probably average 80-160 ac per field.

Well-cost payout can be achieved within 1 year and undiscounted returns in excess of five to one are forecast for many completions.

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