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Abstract: Exploration Strategies for D Sandstone Reservoirs in Basin-Center Area, Denver Basin


Cretaceous D sandstones are oil and gas productive throughout a large area in the Denver basin. The D was derived from the east during a regressive event between two marine transgressions. Trapping within the D is mainly stratigraphic with structure playing a secondary role. Conventional types of traps and a basin-center accumulation are both present in the basin.

The basin-center accumulation area is characterized by widespread occurrence of hydrocarbons and the lack of free water zones downdip from oil and gas accumulations. The basin-center accumulation appears to be related to an area of high geothermal gradients referred to as the "Wattenberg thermal anomaly." Exploration strategies in the basin-center accumulation include: 1) mapping of basin center limits; 2) sequence stratigraphic analysis of reservoir rocks; 3) detailed structural mapping to determine areas of fracturing and faulting; 4) seismic modeling of reservoirs; and 5) seismic acquisition (2-D or 3-D) in areas pinpointed by subsurface geology.

Drilling statistics indicate variable recoveries from D fields located within Morgan and Weld Counties, Colorado. Average per well recoveries for this study area are low which has discouraged exploration and development. The best or highest recovery areas (sweet spots) can be determined by integrated subsurface and seismic mapping. The sweet spot areas are related to distributary channel and valley fill depositional environment of the reservoir sandstone and fracturing. Fracturing is caused by faulting and folding of reservoir rocks.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado