Abstract: Long Distance Migration and the Morrow Formation of Southeast Colorado

Paul H. Wiemann, Jon S. Nelson, Daniel L. Pearson

Hydrocarbon migration out of the Denver and Anadarko basins to the Pennsylvanian Morrow Formation of the Las Animas Arch has been accepted prima facie because the Morrow has yet to be an accepted source rock. Problematically, neither basin meets all three requirements for long distance migration (gradient, migration pathway and source rock). Suggested migration along Morrow fluvial channel systems, requires migration up a dip of less than 0.67° prior to the formation of faults, fractures, and permeability barriers which would result in trapping or loss from the pathways.

While the Anadarko has source rocks for hydrocarbon generation, structural deformation occurred in both basins during and after the deposition of the Morrow and prior to hydrocarbon generation. Migration of oil out of the Denver Basin, into the Morrow, would require either generation from continental orogenic sediments (Fountain Formation) or migration from the Cretaceous units. The Cretaceous units are the only source rocks richer than the Morrow. Migration from the Cretaceous would require crossing 2300 stratigraphic feet of continental and evaporite sediments and the downward penetration of the Morrow cap rock.

The absence of a gradient, migration pathway, and in the case of the Denver basin, accessible source rocks, renders long distant migration implausible. Reexamination of published source rock data and previously unpublished Phillips Petroleum Company data, shows the Morrow to be thermally mature, with sufficient total organic carbon to be the hydrocarbon source for the Morrow in southeast Colorado.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994