Abstract

The Greater Natural Buttes producing area (T. 8-11S., R. 19-24E.) produces from over 450 wells completed in the Tertiary Wasatch Formation and the Upper Cretaceous Mesaverde Group. Multiple zone completions are the rule, with variations in individual reservoir thickness, porosity, permeability and water saturation. Potentially productive sandstones can be isolated by several industry rules of thumb. Drilling shows and simplistic log analysis can be helpful for quick looks for these units.

Estimated Ultimate Recovery (EUR) by individual well can be performed by volumetric calculations from well logs, but several key parameters must be assumed, often leading to potentially erroneous conclusions. Decline curve analysis (DCA) and other material-balance techniques are considered to be more reliable. Using DCA for over 50 wells in the southwest portion of the producing area T. 10S., R. 19 and 20E., allows for a comparison of EUR and cumulative/annualized production rates. A comparison of this heuristic method to DCA-EUR provides a reasonable relationship.

Using the heuristic method from the study area over the Greater Natural Buttes producing area reveals a relationship between the EUR and the thermal maturity of the possible source rocks.