A resurgence of industry interest in Denver basin oil and gas prospects has been reflected by a 30 per cent increase in the number of wells completed in western Nebraska during 1965. Eastern Colorado drilling activity has shown decline of less than 10 per cent compared with 1964. Any significant increase in the number of wells drilled ultimately will reverse the continuing decline of oil and gas production.

Exploratory drilling to the shallow. Cretaceous "D" and "J" Sandstone objectives was well dispersed throughout the basin and resulted in the discovery of many commercial, though no truly significant, fields. The 11-well Stage Hill field on the Scotts Bluff-Banner County line is representative, both geologically and economically, of the better structural-stratigraphic type oil accumulations discovered in western Nebraska. The Moccasin field of eastern Adams County is typical of the small, though profitable, structural-stratigraphic "J" Sandstone oil accumulations discovered in eastern Colorado.

Several exploratory tests to pre-Cretaceous objectives on the western flank of the Chadron arch and in extreme northwestern Nebraska were unsuccessful. Encouragement in searching for pre-Cretaceous oil and gas production on the fringes of the Denver basin in Colorado was afforded by a gas discovery in the Pennsylvanian Morrow Sandstone, Kit Carson County, and an oil discovery in the Mississippian Osage, northern Prowers County. The gas discovery is high on the eastern flank of the basin and appears to be a stratigraphic accumulation trapped in lenticular Morrow sandstones. A unique feature of this Morrow gas is its high helium content--more than 4 per cent.

The Comanche field discovery of oil in Mississippian Osage carbonates is the first indication of commercial oil production in the Mississippian in eastern Colorado. This discovery, even though it is located in the Hugoton embayment of the Anadarko basin, suggests that Mississippian carbonates may be prospective for oil and gas throughout much of the eastern flank of the Denver basin. The Comanche field appears to be primarily a structural accumulation on the western, or upthrown, side of a major northeast-trending fault zone.

Seismic activity and exploratory drilling to the Permian Lyons Sandstone and Big Blue carbonate objectives in the deeper part of the basin have increased during 1965. The increased interest in pre-Cretaceous objectives, combined with a continuing search for new Cretaceous "D" and "J" Sandstone fields, should maintain a relatively high level of exploratory activity during the coming year.

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