Coalbed Natural Gas Resource Potential of the Wyodak-Anderson Coal Zone in the Powder River Basin
The Powder River Basin in northeastern Wyoming and southeastern Montana is the second most prolific coalbed natural gas producing play area in the United States. In 2004, coalbed natural gas production from this basin totaled 339.6 Bcf from 13,880 wells. At the end of 2004, the cumulative coalbed natural gas production from this basin totaled 1.57 Tcf. Annual coalbed natural gas production from the Powder River Basin reached a plateau in 2003. In terms of future gas production capacity, the major play area in eastern Campbell County, Wyoming is becoming mature. Increasing coalbed natural gas production capacity in this play will require drilling in the deeper areas of the basin. A detailed geologic evaluation was made of the coalbed natural gas resource potential of the Wyodak-Anderson coal zone, which is the major target for coalbed natural gas exploitation in the Powder River Basin. The analysis covered areas where the overburden thickness was 150 ft or greater and the net coal thickness was 10 ft or greater. The analysis results indicate that the Wyodak-Anderson coal zone contains an estimated 19.8 Tcf of coalbed natural gas resources. The gas-in-place resource ranges from 0.5 Bcf to as much as 15 Bcf per square mile. Based on an 85 percent recovery factor, the potentially recoverable coalbed natural gas resource in the Wyodak-Anderson coal zone totals 16.8 Tcf. Roughly 68 percent of this resource is found at reservoir depths greater than 1,000 ft, which, to date, represents a relatively unexplored reservoir interval.