Tectonic, Sedimentary, and Seismic Models for D Sandstone, Zenith Field Area, Denver Basin, Colorado

Abstract

Cretaceous D and J sandstones are oil and gas productive throughout a large area in the Denver basin. The Zenith field is a recently developed area that contains significant reserves in the D sandstone, with minor production from the J sandstone. Trapping of petroleum within these sandstones appears to be mainly stratigraphic with structure playing a minor role. The productive D sandstone in the Zenith field has previously been interpreted as a distributary channel deposit. I propose a new depositional environment for the D sandstone based on detailed mapping that suggests the D productive sandstones are of channel origin within a valley-fill complex. Analyses of seven stratigraphic intervals clearly show that paleostructure influenced D depositional patterns. Structurally low areas formed during D sandstone deposition and controlled the location of the D valley-fill deposits. The existence of a present-day structural low at the J sandstone level (stratigraphically older than the D sandstone) in the same area where the D valley-fill deposit occurs confirms the paleostructural interpretation. Seismic models were constructed and seismic data were examined in the Zenith field area to determine if thick D valley-fill deposits are detectable. An analysis of the Dakota interval on the model and seismic data shows an amplitude anomaly present in the position of the D valley-fill deposits.