Permian-Pennsylvanian Reservoirs, Northern Denver Basin

Frank Maio

During the past three years the attention of Rocky Mountain operators has been focused on Permian-Pennsylvanian reservoirs in the Nebraska Panhandle. Relatively inexpensive drilling, a good wildcat success ratio, and impressive oil production have made the Northern Denver one of the most active areas in the Rockies during the current drilling slump.

In early 1986 Celsius Energy and Sun Exploration and Production Company opened Bird field in Cheyenne County with the Livingston 1-33 pumping 180 bbl of oil/day from Missouri (Pennsylvanian) pay intervals. Celsius, as field operator, has offset the discovery with three additional producers. The best production has come from the McMillan 3-1 which has totaled 141,000 bbl of oil of 24° API crude in the first nine months of pumping oil from intervals at 6,839 to 6,857 ft. The major Missouri reservoir at Bird field is a peloid skeletal lime packstone/grainstone with moldic and vugular dissolution porosity created by meteoric waters during subaerial exposure. All four wells at Bird field have an ooid/peloid lime grainstone Virgil (Pennsylvanian) reservoir behind production casing from 6,650 to 6,750 ft.

Farther west in Kimball County, Exxon is producing Wolfcampian (Permian) oil at Kleinholtz field. Six miles to the south, Sun has put its Prairie State 1 on pump, producing Wolfcampian oil and gas between 8,300 and 8,400 ft at an initial rate of 160 bbl of oil and 56 bbl of water. The Wolfcampian pay zones in Kimball County are anhydritic peloid skeletal dolomitic wackestone/packstones.

The Kimball and Cheyenne County Paleozoic fields are structures upon the flanks of the Kimball-Morrill high, defined by thinning of Permian and Pennsylvanian beds and by subcrops of Mississippian and Ordovician carbonates. These Paleozoic structures are often coincident with upthrown Precambrian fault blocks that are controlled by recurrent movement along basement faults.

In the northern half of the Nebraska Panhandle, Bird Oil and True Oil have completed wells in Des Moinesian (Pennsylvanian) dolomites. In this area, restricted conditions prevailed during most of Permian-Pennsylvanian time as interpreted from the presence of salt beds in Wolfcampian strata and supratidal anhydrites capping Pennsylvanian cycles.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.