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Pennsylvanian Morrow sandstones are oil and gas productive throughout a large area in southeast Colorado. The Sorrento field is a recent Morrow discovery with recoverable reserves estimated at more than 10 million bbl of oil in an area of 3,200 acres (1,280 ha.) at depths of 5,400 to 5,600 ft (1,646 to 1,707 m). Minor production also occurs from the Mississippian Spergen, Mississippian Saint Louis, and Pennsylvanian Marmaton.
Productive Morrow sandstones are interpreted on the basis of subsurface mapping as fluvial valley-fill deposits, mainly channel sandstone. These deposits are encased in marine shale and range in thickness from 5 to 55 ft (1.5 to 16.7 m). Net pay ranges from 5 to 30 ft (1.5 to 9.1 m). Porosities average 19% and permeabilities range from 1 to 4,000 md.
Analyses of Morrow stratigraphic intervals indicates that paleostructure influenced Morrow depositional patterns. Morrow channel sandstones accumulated in paleostructural low areas created by movement on basement fault blocks. Structural nosing is present in the same location and trend as the Morrow channels, indicating structural inversion. The field is regarded as a combination structural-stratigraphic trap.
Knowledge of paleostructural control on reservoir facies provides a new idea for exploration for Morrow reservoirs in southeast Colorado.
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