The origin and distribution of a sandstone reservoir for petroleum are controlled primarily by the processes by which the sand was deposited. Studies of modern environments of deposition and associated Holocene deposits provide a basis for understanding petroleum fields and predicting reservoir distribution and behavior.
The Rocky Mountain province of the United States contains structural and stratigraphic traps from which petroleum is produced from all types of sandstone reservoirs ranging in age from Cambrian to the Eocene. Three large typical stratigraphic traps, where reservoirs are of Cretaceous age, are described. The Cut Bank field, Montana produces from alluvial point bar sandstones; Patrick Draw field, Wyoming produces from marine shoreline sandstones; and, Hartzog Draw field, Wyoming produces from marine shelf sandstones.