Date of Award

Spring 1-1-2010

Document Type


Degree Name

Master of Science (MS)


Geological Sciences

First Advisor

Matthew J. Pranter

Second Advisor

Rex D. Cole

Third Advisor

Edmund R. Gustason


The reservoir architecture, reservoir quality, and associated sandstone-body connectivity of the Williams Fork Formation at Mamm Creek Field vary stratigraphically and with depositional setting. The fluvial and shallow-marine sandstones were deposited within alluvial-plain, coastal-plain, and shallow-marine settings. The stratigraphic interval consists of porous but low permeability (tight-gas) sandstones that form the main gas-producing reservoirs in the Piceance Basin.

Fluvial sandstones that are observed and interpreted in the Williams Fork Formation at Mamm Creek Field primarily include single-story channel bodies (e.g., channel bars; point bars) and crevasse splays. These deposits can be isolated bodies but also form amalgamated multistory channel bodies and channel complexes.

Stratigraphic analysis of the fluvial deposits shows a relatively low, but variable, net-to gross ratio (30-76%) for the lower Williams Fork Formation with numerous laterally continuous coal beds. The middle Williams Fork Formation exhibits a relatively higher net-to-gross ratio (50-80%), and the net-to-gross ratio of the upper Williams Fork Formation ranges from 15 to 60%. Horizontal variogram correlation lengths of the sandstones are relatively short (<800 ft; 244 m) with respect to the distances between wells (330 ft [100 m] in north-south direction, and 1,320 ft [402 m] in east-west direction) and do not vary significantly stratigraphically. Variogram polar plots of the sandstones and effective porosity values indicate preferential trends of continuity in the north northeast to south-southwest direction.

Three-dimensional reservoir models are used to explore how the fluvial sandstone bodies, effective porosity, and pay are distributed and interconnected. Static sandstone-body connectivity is greater than 52% for irregular 10-ac [660 ft; 201 m] well densities and decreases by as much as 25% with lower well densities (i.e., 40- and 160- ac). The middle Williams Fork Formation exhibits static connectivity values that are as much as 15% higher as compared to the lower Williams Fork Formation. Considering only reservoir-quality sandstones and calculated pay, results illustrate a decrease in static connectivity by as much as 57 to 74%, respectively, as compared to scenarios that include all sandstones. The static sandstone-body connectivity results provide a high estimate of connectivity, whereas the pay-based results provide a “base-case” or lower estimate of connectivity.

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