Depositional Environments and Diagenesis of D Sandstone, Wild Horse Field, Weld County, Colorado: ABSTRACT

Abstract

Wild Horse field is located on the gentle east flank of the Denver basin, northwest of Fort Morgan, Colorado. Production was established during 1981 from a 12-ft (3.7 m) thick porous sandstone in the lower part of the D sandstone of Cenomanian age. To date, 10 producing wells have been completed. Proven productive area is 1,800 ac and estimated reserves are 1.2 million bbl oil equivalent. D sandstone facies form complex reservoirs associated with regressive deltaic and marine sandstone deposited during a regional sea level drop 95 Ma. Traps are primarily stratigraphic in nature although fracturing has enhanced production. The D sandstones in the Wild Horse field area are interpreted to be the product of an episodic northwestward progradation of a lobate river-dominated delta system. On the basis of differences of the internal structure, textures, mineral composition, and trace-fossil content, the D sandstone is divided into five lithofacies: shoreface, prodelta platform, delta front, delta plain, and transgressive marker sandstone. The producing sandstones occur in overlapping bars proximal and lateral to principal channels in a bay-filled sequence. Calibration of well logs using cores allows detailed subsurface mapping of producing facies for more efficient development of the field. Original porosity has been reduced mainly by quartz overgrowth cementation. Porosity interconnection is present due to dissolution of framework grains and of the early diagenetic calcite cement. Pore-filling cements such as chlorite, kaolinite, and pyrite may produce formation damage if not treated during completion operations. End_of_Article - Last_Page 871------------