Influence of Salt Solution Collapse on Hydrocarbon Production and Potential, Denver Basin, Colorado, Nebraska, and Wyoming

David W. Oldham

Regional structural mapping of Cretaceous hydrocarbon reservoirs (including the D Sandstone and Niobrara Chalk) in the Denver basin reveals a number of localized structural lows situated immediately to the east (regionally updip) of several oil and gas fields. Structural relief across the anomalies, which exceeds 250 feet in places, is interpreted to be due to collapse in response to subsurface dissolution of Permian salt. Seismic data and models support a salt-dissolution hypothesis.

Correlations of Guadalupian and Leonardian strata across the basin have identified ten stratigraphic intervals that, in places, are salt-bearing. Areal distribution of individual salt beds is controlled by: (1) the configuration of evaporite basins during precipitation, (2) truncation at a pre-Jurassic unconformity, and (3) subsurface dissolution.

Studies across producing areas indicate that the influence of structure on trap development is greater where salt dissolution and resultant collapse occurred during or after Late Cretaceous - Early Tertiary time, possibly due to introduction of fluids along Laramide-activated basement faults. there collapse appears to have occurred during Jurassic or Early Cretaceous time (prior to deposition of major reservoirs), structure is relatively simple at the level of the productive or prospective formations, and traps are primarily of the stratigraphic type.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995