Abstract: The Wamsutter Sweetspot: A Continuing Enigma in Tight Formation Gas

Randal L. Billingsley, L. W. E. Reinert

The Wamsutter area earned the nickname "Sweetspot" for its anomalously high Mesa Verde Group productivity following its discovery in 1979. Located in Wyoming on the east flank of the Green River Basin near the crest of the Wamsutter Arch, the Wamsutter-Echo Springs-Standard Draw Units are expected to yield upwards of 1 TCF of sweet gas from the marine bar sands in the Upper Cretaceous upper Almond Formation. Nearly 100 wells have been drilled in and near this prolific area where the main pay occurs between the depths of -1700^prime and -3000^prime subsea and average well recovery is expected to be over 10 BCF/well based on 640 acre spacing. Low water productivity, lack of a well defined free water level, and pressure gradients in the .5-.58 psi/ft range make this field a potential ana og for basin-centered gas exploration.

Experience in this area indicates that there are anomalies between expected productivity based on gas-in-place calculations and reservoir engineering projections and actual production. Actual production can be difficult to reconcile with estimated in situ permeability, effective permeability, porosity, calculated saturations and projected drainage areas using established models. Models incorporating actual production data are most effective for projecting

future performance, leading to the conclusion that historical approaches depending on capillilarity concepts are inadequate to fully describe the reservoir in all cases. Work is continuing to develop a higher level reservoir model that more closely fits the performance history of the area.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994