Geologic Model and Coalbed Methane Potential of the Coalmont Formation, North Park Basin, Colorado

Martin, Christopher B.
Consultant - Colorado Geological Survey, Denver, CO

North Park Basin contains abundant coals in outcrop and at shallow depths. However, very little is known about the coalbed methane resource potential of this basin. As part of a project between the Bureau of Land Management and the Colorado Geological Survey, a study to assess the methane production potential of the coal-bearing formations of North Park Basin was recently completed. A geologic model for coal deposition as well as resource potential maps are presented for the basin.

North Park Basin is an intermontane basin located in northwestern Colorado. It is bounded on the west by the Park Range and to the east by the Front Range. It is enclosed to the north by Independence Mountain and to the south by the Rabbit Ears Range.

The sedimentary sequence in North Park Basin ranges from Late Permian to Quaternary with pre-Quaternary rocks having a maximum thickness of approximately 17,000 feet. The most abundant coal-bearing formation in the basin is the Tertiary Coalmont Formation, where coal thickness reaches 50 feet at subsurface depths less than 200 feet.

Outcrop studies aided in developing a geologic model for the Coalmont Formation. Exploratory drill hole and oil and gas well logs were used to correlate the stratigraphy. Cross-sections are presented to illustrate the geologic model for the Coalmont Formation. Net coal thickness maps show the distribution of coal throughout the basin. Coalbed methane potential maps are also presented showing the variation in coal rank, heating value, mudlog gas shows, and drill-depth to coal zones.