Reservoir Geometry of the Regressive Fox Hills Sandstone:
Control on Aquifer Quality
Marieke Dechesne and Robert G. Raynolds. Denver Museum of
Nature & Science, 2001 Colorado Boulevard, Denver, CO 80205, phone:
303-370-6047, [email protected]
In the Denver
Basin the littoral to
near-shore Fox Hills Sandstone was deposited during the early phase of the Laramide orogeny as the
Cretaceous Interior Seaway retreated to the northeast. This approximately 68 MY
regressive sandstone is composed of a series of shingles reflecting episodic
seaway retreat. We illustrate the detailed geometry of the sandstone elements
that make up the Fox Hills Sandstone. This unit is an important aquifer in the Denver Basin
and the distribution of porosity, permeability, and facies
tracts is important in predicting the performance of water wells.
A data base of thousands of oil and gas wells and thousands
of water wells is available for study. A subset of these wells has been
analyzed to create a three-dimensional model using ArcGIS
software. Seven shingles are mapped in detail. Our three dimensional model
permits the effective and efficient communication of critical reservoir
parameters to resource planners. Comparisons are made to other well-studied
regressive systems in the San Juan
and Greater Green River basins. We propose that non-uniform subsidence has
influenced the stacking pattern of this regressive succession, controlling both
the distribution of net sandstone and of coal-bearing strata. These parameters
are critical to predicting reservoir performance and quality. The patterns we
document are relevant to any effort to extract fluids from rocks of this facies association.