Abstract Previous analysis of production curves, from tight gas sand wells in the Uinta Basin of Utah, identified three types of performance - linear, intermediate and near radial. Six wells were performance - linear, intermediate and near radial. Six wells were selected, covering this distribution, and an attempt was made to determine dynamic reservoir gas volumes, and to compare these "production" volumes with volumes calculated from several different lenticular sand models.
Volumes of the 29 tight gas sandstones present in these six wells were approximated by using long term pressure buildups to calculate present pressures (and permeabilities). Then reservoir volumes were calculated using p/z vs cumulative production plots extrapolated to zero pressure. The average reservoir volume is interpreted to be about 240,000 cubic feet per foot of net pay.
The "production" volumes are compared with the equivalent calculated volumes using four different modeling techniques.
Reservoir Volume, 10(6) cu ft. Sum of All Wells Well C Production Production Volume 75.3 10.8
Knutson Model Volume 60.7 -
Knutson/Ward Model Volume 86.0 -
Baker Model Volume 10.6
Gidley et al Model Volume 136.1 -
The Knutson/Ward and Baker models seem to provide the best approximation of the "production" data. This approximation may have been better if a more sophisticated pressure buildup analysis had been used.
Apparent reservoir permeabilities, assuming radial flow, range from .009 to .052 millidarcies and actual sandstone matrix permeabilities are interpreted to range from .06 to .21 permeabilities are interpreted to range from .06 to .21 millidarcies.
Introduction This study encompasses an analysis of gas production, well log, and pressure buildup data obtained from gas wells in the Uinta Basin, Utah. The objectives were 1) to assess lenticular reservoir volumes and permeabilities, and 2) to test the ability of four tight gas sand reservoir models to predict reservoir volumes. Three of the four models were based on outcrop study data, the other model was based on an evaluation of production data in several western basins containing tight gas sand reservoirs.
Six tight Wasatch gas wells were made available for pressure buildup testing and analysis. They are designated simply as Wells "A, B, C…." to protect the confidentiality of the data.
All six wells have been somewhat continuously on production for 16 to 18 years. The number of months per year each well has been on production and the respective annual production volumes are presented in Table 1. As of June, 1979, cumulative production per presented in Table 1. As of June, 1979, cumulative production per well ranged from 447,000 to 1,587,000 MSCF, with an average of about 1,000,000 MSCF.
GEOLOGY OF THE WAS ATCH FORMATION IN THE UINTA BASIN The Wasatch Formation has been assigned to the Paleocene-Eocene of the Tertiary Period. It overlies the Cretaceous Mesaverde Formation and underlies the Tertiary Green River Formation of Eocene age.
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