Structural and Stratigraphic Compartmentalization of the Terry Sandstone and Effects on Reservoir Fluid Distributions in Hambert-Aristocrat Fields, Denver Basin, Colorado

Dwaine E. Edington, Roger M. Slatt, Hugo Araujo

Hambert-Aristocrat Fields are mature gas and oil producing fields in the Denver Basin of Colorado. Based on core analyses, the following facies occur within the productive Upper Cretaceous Terry Sandstone, each with characteristic average permeability and sand content: bioturbated mudstone (0.4 md, 7% sand); burrowed to bioturbated sandy mudstone (0.71 md, 37% sand); burrowed to bioturbated muddy sandstone (0.87md, 62% sand); fine-very fine grained planar to low angle cross-bedded sandstone (1.3 md, 94% sand); fine-very fine grained ripple cross-bedded sandstone (2.3 md, 93% sand).

In the western part of the area, the facies are arranged in a fining-upward or blocky sequence, but in the eastern part of the area, they are arranged in a coarsening-upward sequence. This complex character is due to the presence of three separate shingled, westward-backsteping sandstones. The boundary zone between the fining-and coarsening-upward trends is generally marked by relatively lower resistivity (<8 ohm-m) sandstones, unlike those on either side of the zone (>8 ohm-m).

Detailed analysis of >1100 wells indicates numerous northeast-trending, steeply-dipping faults occur with vertical offset of 30-100 ft. (9-30 m). Within individual fault blocks, initial GOR values vary among the different fault blocks, 30 that in some blocks, higher GOR's occur at structurally lower elevations than lower GOR's in other blocks.

These results suggest that faults in the Hambert-Aristocrat Fields are sealing to the migration of reservoir fluids and compartmentalize the Terry Sandstone. The presence of shingled sandstones also provides opportunity for stratigraphic compartmentalization. In this complex geologic setting, reservoir fluids can be distributed in a complex manner, including gas structurally beneath oil.

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