Poncho Field--Cretaceous J"Sandstone Stratigraphic Traps--Denver Basin, Colorado: ABSTRACT"

Abstract

Distributary channel and delta destructional sandstones of Early Cretaceous age are important reservoirs for stratigraphic traps in the J sandstone at Poncho field, Adams and Arapahoe Counties, Colorado. Cores and logs from the field area reveal a lowermost, nonproductive, northeast-trending delta front sandstoe (J-3); a middle complex of southeast- and east-trending, productive distributary channel sandstones (J-2) that grade into tightly cemented delta fringe marine sediments to the southeast and northeast; and an upper, northeast trending, productive delta destructional sandstone (J-1). Vertical and lateral sequences of sedimentary structures, textures, trace fossil assemblages, and geometry and trend of sandstone bodies suggest that these units were part of a wave-dominated delta complex that prograded to the east and southeast from the area of Lonetree field. Thin section and SEM analyses reveal that the principal cements in both reservoir sandstones are quartz overgrowths, kaolinite, and chlorite, and that the bulk of the porosity is secondary and related to dissolution of carbonate cement and feldspar grains. Porosities and permeabilities are most variable and lowest in the nonproductive delta front sandstones, averaging 15% and 7 md; variable and intermediate in the productive distributary channel sandstones, averaging 16% and 28 md; and most uniform and highest inmore » the overlying delta destructional sandstones, averaging 21% and 88 md.« less