Development of the Wyodak Coalbed Methane Resource in the Powder River Basin

Abstract

Abstract Just over ten years ago, coal bed methane production from Wyoming's Powder River Basin was virtually non-existent. Today, total gas production from Powder River Basin coals is almost 1 Bcf per day from nearly 10,000 wells. This tremendous resource is unique compared to other commercial coalbed methane plays with gas content an order of magnitude lower, and reservoir permeability values several orders of magnitude higher than other producing coal bed plays. This paper documents the results of an ongoing evaluation of the reservoir and production characteristics of the Wyodak coals located in the fairway of the Powder River Basin activity. Most of the drilling and production to date has focused on the Wyodak and equivalent coal horizons. A reservoir simulation model has been constructed covering 136 sections and including over 1300 wells. A detailed geological description and a large data base of core data and test results were used in the construction of the model. Historical gas production, water production, and reservoir pressure data were successfully matched from 1993 to the present during the calibration of the simulation model. The calibrated model was then used to evaluate optimum development strategies for this shallow, high permeability coal resource. This paper discusses the production characteristics of the Wyodak coal, the impact of well spacing and well timing on the recovery factor, and the influence of outside factors such as recharge from the regional aquifer. Our results contradict conclusions reported in prior studies concerning the influx of water from adjacent sand horizons. In addition, the effects of multiple well interference and depletion of undrilled portions of the coal by existing wells are documented and discussed.