The Anschutz Ranch East field is the largest hydrocarbon accumulation discovered to date in the Western Overthrust Belt. Analyses of reservoir fluid samples from the discovery well indicated that the fluid is a rich gas condensate with liquid dropout under reservoir conditions as high as 40 percent of the hydrocarbon pore volume. The proximity of the fluid dew point pressure to the original reservoir pressure dictated that a plan-of-depletion be established very early in the life of the field to avoid reservoir damage and the potential loss of significant liquid reserves. This requirement was further amplified by the fact that some of the depletion alternatives involved major front-end monetary commitments and long lead times for implementation.
Using preliminary reservoir data together with compositional simulators, various depletion alternatives ranging from primary depletion to full pressure maintenance were evaluated. Variables examined in the study included such factors as type of injection fluid and injection-production well configuration. Full pressure maintenance using nitrogen preceded by a hydrocarbon-nitrogen gas buffer in an inverted nine-spot pattern was selected as the most attractive depletion method. This plan was approved by the working interest owners and state regulatory agencies and is currently being implemented.
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