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An Overview of Production Performance for Selected Rocky Mountain Unconventional Gas Reservoirs

Stark, Pete
IHS Energy Group, Englewood, CO

Unconventional gas reservoirs are commanding increasing attention from U.S. producers. Interest is driven by several factors including increased gas prices, improved completion technologies and lack of conventional reservoir targets.. Many such plays were established more than a decade ago when Section 29 tax credits were applied to designated tight sand, Devonian shale and coalbed methane reservoirs. Gas productivity patterns provide a framework to compare and contrast unconventional reservoir performance in proven and emerging unconventional gas reservoirs. Over the past decade, several general production performance patterns have been observed for established coalbed and tight sand reservoirs in the Rocky Mountain region: 1)Average peak gas well production rates have tended to decrease, 2) First year production decline rates have tended to increase, and 3) Average cumulative production over the first 24 months has varied from year to year in most basins.

Tight sand production in the Jonah Field and Pinedale Anticline is an exception. There, average peak well production and average 24 month cumulative production increased markedly after 1995 when improved frac methods were introduced. No such consistent improvements are observed in other unconventional reservoirs assessed in this study. This paper presents gas productivity trends for selected coalbed methane plays in the Raton, San Juan, Uinta and Powder River Basins and for selected tight sand plays in the Green river, Piceance and Uinta Basins, the Pinedale Anticline and Jonah Field. The objective is to provide benchmarks to guide investments into future unconventional gas plays.