Detailed sedimentological and petrophysical analyses of cores from producing Morrow Sandstone fields along the Colorado-Kansas Stateline Trend indicates that reservoir production properties vary greatly between the two major paleovalley-fill producing facies, fluvial and tidal (estuarine) sandstones. The suite of sedimentary structures observable in cores also differs greatly between fluvial and tidal deposits, in fields such as Moore-Johnson, Arapahoe and SW Stockholm. These fields are internally complex, contain geographically and vertically limited reservoirs and can only be effectively and economically drained if the detailed internal architecture of the reservoirs is understood. Where tidal sandstones interfinger with fluvial sandstones, vertical permeability is diminished and flow units are fragmented. Tidally deposited (estuarine) sandstones are finer grained and more clay prone than the sandstones deposited by fluvial processes, and as a result have poorer reservoir properties. Thin, mm thick, clay drapes, common in tidal channel accretion point bars, may significantly reduce vertical permeabilities.
Paleovalley-fill deposits in the Morrow Stateline Trend fields differ significantly from deltaic deposits with which they are commonly confused. They differ depositionally, geometrically and in the characteristics and distribution of flow units.