Coalbed Natural Gas Resource Potential of Lignite Deposits in the Williston Basin

Nelson, Charles R. ¹ (1) Energy & Environmental Research Center, University of North Dakota, Grand Forks, ND

The Williston Basin, located in western North Dakota, eastern Montana and northwestern South Dakota, contains the second largest deposit of coal resources of any basin in the continental United States. This basin is a frontier coalbed natural gas play area. Currently, there are no producing coalbed natural gas wells in this basin. However, observations of the presence of flammable gas in water wells completed in lignite bearing zones, mud log gas shows when drilling through lignite seams, and gas emission from lignite drill cutting samples suggest that a large natural gas resource base might be present in the Williston Basin’s lignite coals.

A geologic evaluation was made of the coalbed natural gas resource potential of the Harmon, Hanson, and Harmon (?) lignite beds in the southwestern North Dakota portion of the Williston Basin. These are the thickest and most aerially extensive lignite beds in southwestern North Dakota. The analysis results indicate that for areas were the overburden thickness is at least 150 ft, the three lignite beds contain an estimated 0.93 Tcf of coalbed natural gas resources. The gas-in-place resource is estimated to be as large as 0.8 Bcf per square mile, which is comparable to that of areas in the Powder River Basin where there are large numbers of commercial coalbed natural gas wells. Assuming a gas recovery factor value of 85%, the potentially recoverable coalbed natural gas resource base in the three lignite beds in southwestern North Dakota would total 0.79 Tcf.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana