ABSTRACT: Stagecoach Draw Field: Gas Production from the Westernmost Marine Influenced Deposits of the Lewis Seaway Transgression into Southwestern Wyoming

Abstract

An exploration effort by Texaco E & P, targeting Upper Cretaceous marine influenced sandstones of the Almond Formation, resulted in a gas discovery in an under-explored area of the Green River Basin in southwestern Wyoming. The Stagecoach Draw Field, which encloses a structural-stratigraphic trap, is located on the Sandy Bend Arch in the basinal area between the Moxa Arch and the Rock Springs Uplift in Sweetwater County. Discovered in 1993, the field represents the first commercial discovery in this area of the basin. The initial play was conceptualized on the basis of regional stratigraphic correlation and paleogeographic reconstruction of individual upper Almond Formation marginal marine sandstones. The nearest Almond Formation production is located 50 miles to the east of the Stagecoach Draw Unit at the Patrick Draw and Desert Springs fields where individual parasequences prograded eastward during relative stillstands of the overall Lewis Seaway transgression. These productive upper Almond sandstone bodies were recognized in the subsurface to the west of the Almond outcrops on the Rock Springs Uplift. Integration of local structure and stratigraphy, by careful analysis of existing well penetrations, demonstrated the possibility an updip pinchout along the normally faulted, southeasterly plunge of the Sandy Bend Arch in the Stagecoach Draw area. An extensive coring program was undertaken to examine reservoir parameters and enable detailed reservoir characterization studies. A depositional model was assembled based on facies assemblages recognized in the cores. The model shows that the facies at Stagecoach Draw Field represent various subenvironments of a marginal marine setting, including tidal channel, lagoonal, tidal delta, and marsh/swamp facies. Development, consisting of 32 wells to date, has proven that several reservoir compartments exist in the field due to both structural and stratigraphic segmentation. Economics are highly affected by reservoir compartmentalization, hydrocarbon content, and permeability. Estimated ultimate recovery from the gas productive compartments may approach 50 BCFG of gas equivalent.