Abstract

The Lower-Upper Cretaceous Cedar Mountain and Dakota formations are easy to distinguish in outcrop due to lithological and color variations but they are difficult to correlate in the subsurface. Cedar Mountain and Dakota (CMD) sandstones are important gas reservoirs in the southern Uinta Basin, yet their subsurface distribution is poorly constrained due to difficulties in distinguishing the two units in the subsurface, as well as differentiating the interval from the underlying Upper Jurassic Morrison Formation. The first step in understanding the distribution of these intervals and the respective contributions of these sandstones to gas production is to develop a correlation model for them.

Outcrop gamma-ray logs through the CMD were obtained at six locations on the southern rim of the Uinta Basin. An additional outcrop gamma-ray log was acquired from the east flank on the San Rafael Swell to characterize the log signature of the Buckhorn Conglomerate, the lowermost member of the Cedar Mountain Formation. The outcrop logs showed consistent signatures at the stratigraphic contacts between the Morrison, Cedar Mountain and Dakota formations, and the overlying Upper Cretaceous Mancos Shale. There were no identifiable patterns to partition these intervals further. These gamma-ray profiles were used to construct a correlation envelope for the CMD interval in the southeastern Uinta Basin.