Powder River Basin Coalbed Methane Wells—Reserves and Rates

Abstract

Abstract Coalbed methane has become a significant source of U.S. natural gas production, contributing 9% of the country's supply and 10% of its proved reserves. The most active coalbed methane area is the Powder River basin of eastern Wyoming, with more than 20,000 wells completed in the last 10 years with annual additions of greater than 2,000 wells. This study analyzed the projected ultimate recovery, flow rates and dewatering time of 6,600 wells producing from the Wyodak and Big George coal zones – the source of 58% of the basin's cumulative production, 61% of the current production and 45% of the CBM wells. For the Big George and Wyodak wells, the estimated ultimate recovery (EUR) averages 223 million cubic feet (MMcf) per well (median 168 MMcf). An average peak gas rate of 319 thousand cubic feet per day (Mcf/D) (median 236 Mcf/D) occurred an average of 1.2 years after the well was placed on production. The average well declined at a rate of 45% per year after entering the decline phase with very little hyperbolic behavior (average b = .09). Distributions of EUR and peak rates were strongly log-normal. The EUR and peak gas rates both show a slight overall deterioration over time, although the "spread" is larger with more high rate wells in later years. But the time to reach peak gas rate is shortening as more areas are dewatered. There seems to be only a slight correlation between total depth and EUR and little correlation between gross perforated interval and estimated ultimate recovery or peak rate, although the perforated interval information is very incomplete. Development of Powder River basin coalbed methane has an average finding cost of $.71/Mcf, and the mean well has a return-on-investment of 4.70:1 and a net present value index of 3.74, assuming a base gas price of $6.50/Mcf minus $1.50/Mcf for market differential and transportation.