STRATIGRAPHY AND HYDROCARBON POTENTIAL OF THE MUDDY SANDSTONE, WIND RIVER BASIN, FREMONT COUNTY, WYOMING 

Lisa Costanzo, Colorado School of Mines Geology Department, Golden, Colorado, [email protected]

The Muddy Sandstone in Fremont County, Wyoming represents a potential hydrocarbon exploration opportunity on the Wind River Indian Reservation.  The Muddy has been extensively explored in the eastern and southern regions of the Wind River Basin, but is relatively under-explored on the reservation. Production trends to the east of the reservation occur in northwest trending paleovalleys and it is likely these paleovalley trends may repeat on the reservation.

The lower Cretaceous Muddy Sandstone consists of a complex series of marine and nonmarine coastal/valley-fill facies whose distribution is controlled by paleotopography and sea-level fluctuations of the Cretaceous Western Interior Seaway. Previous interpretations have described the lower facies as a shoreline/estuarine deposited during relative sea level lowstands. The upper facies is described as incised valley fill deposited during transgressive and highstand periods.  The Muddy is unconformably underlain by the Albian age marine Thermopolis Shale and is overlain conformably by the Cenomanian age marine Mowry Shale. 

The goal of the study is to explore the hydrocarbon potential of reservoir quality Muddy Sandstone and determine the extents of these deposits on the Wind River Indian Reservation. Application of a sequence stratigraphic framework to well log correlation, core and thin section study, outcrop observations, geologic mapping, production mapping will aid in defining the facies distribution and placement of sandstone bodies.