Promising Morrow Sandstone Discoveries in Southeastern Colorado: ABSTRACT

Eight new Morrow oil and gas fields have been discovered in southeastern Colorado during the past two years. The latest discovery resulted in a well flowing oil from a Morrow sandstone at an initial rate of 700 bbl of oil per day and 750 Mcf of gas per day. The trapping mechanism in this well, as in most, is a stratigraphic and structural combination. The depositional history of Morrow sandstones in southeastern Colorado was strongly influenced by regional tilt into the Anadarko basin, established at the close of Mississippian time. Mississippian rocks were subject to truncation in the area of the Las Animas arch and development of karst topography on the erosion surface. Transgression of the sea from the southeast in Morrowan time resulted in the deposition of a sandstone and shale sequence. The Morrow series consists of a basal transgressive sandstone member (Keyes sandstone) overlain by at least three sandstone units deposited during regressive pulses in an overall transgressive sequence. These Morrow sandstones generally trend from northwest to southeast toward the Anadarko basin; their source is inferred to have been the ancestral Rocky Mountain End_Page 672------------------------------ uplift for the upper sequence and the Amarillo uplift for the basal Keyes member. The environment of deposition appears to have been fluvial delta plains and associated tidal channels which were alternately created and destroyed by regression and transgression of the Morrowan seas. Distribution of these elongate sandstones is generally erratic and meandering; individual sand bodies have an estimated width of up to 1 mi (1.6 km) and a maximum thickness of 42 ft (12.8 m). The nature and distribution of these sandstones leave many areas essentially unexplored. Southeastern Colorado has had substantial Morrow discoveries which justify a closer look at the area. End_of_Article - Last_Page 673------------