Case Histories Of Subsurface Log Data Exploration Patterns In Eastern Powder River Basin Wyoming

A brief history of log evaluation in subject area is presented through cretaceous Newcastle Formation production to the Dakota and Minnelusa Formation discoveries and development phases, emphasizing the important items of formation evaluation information available from well logs. Derivation and interpretation of formation water resistivities in this exploration region is discussed and demonstrated by the presentation of seven development areas, as they existed prior to discovery for production and as they appear following development. This discussion emphasizes the presence and importance of water resistivity gradients which were demonstrated in 1962 Rocky Mountain Division of Production Paper No. 875-16-G, American Petroleum Institute. Six of the production examples were chosen from a regional study which yielded 46 prospective exploration areas, 14 or 30.0 percent of which are now productive from one or more horizons. Although support data for mapping these examples was derived from Cretaceous Dakota Formation, several of the areas were found to be productive from horizons other than Dakota, particularly the Minnelusa sands of Permian and Pennsylvanian age. The region is thereby demonstrated to contain vertically anomalous conditions of formation entrapment.