Joint Meeting: University of Wyoming Department of Geology and Geophysics Wyoming Geological Association Geological Survey of Wyoming: April 2-4, 1982 Laramie, Wyoming: Subsurface Practices in Geology and Geophysics Abstracts of Papers - Compiled by James R. Steidtmann

Cretaceous sandstones are oil and gas productive throughout a large area in the Denver basin. The Lanyard field is a structural-stratigraphic trap which has produced in excess of 2,388,000 bbls of oil and 4.1 bcf of gas from the D Sandstone. Productive sandstones are interpreted to be channel deposits on the basis of subsurface mapping and core examination.

Seven Cretaceous stratigraphic intervals from the Lanyard field area were identified from well data. Areas of thickness variations on these isopach maps are caused by unconformities, convergence, and normal faulting. Thickness variations caused by unconformities and convergence may be related to paleostructure; variations caused py normal faulting are post depositional and related to Laramide (present) structure. Analyses of the seven stratigraphic intervals clearly shows that paleostructure influenced D depositional patterns. D channel sandstones accumulated in a northeast-trending paleostructural low area. Present-day structure is a southwest-plunging structural nose. The trend and location of the nose is identical to the trend and location of the D channel system. Thus, the palestructural low area has undergone structural inversion and is now a structural high.

Knowledge of paleostructural control on reservoir facies provides a new idea for petroleum exploration in the D Sandstone of the Denver basin.