Geology and Methane Content of the Book Cliffs Coal Field

Abstract

The Book Cliffs coal field contains as many as 14 coal zones, all within the Upper Cretaceous Blackhawk Formation. The Blackhawk Formation consists of deltaic and nearshore sediments deposited in a fluctuating, but overall regressive, setting along the western margin of a shallow seaway. Laramide deformation tilted strata in the Book Cliffs gently to the north toward the axis of the Uinta basin. One hundred and twenty-three drill-hole coal samples were collected and analyzed from the ten thickest and most continuous coal zones in the Book Cliffs field. Residual, desorbed, and total gas content were determined using the Bureau of Mines direct method. The resulting coal-bed methane content maps show areas of economic potential where 90% of the gas could be recovered. The 90% methane recovery level corresponds to a total methane content of 154 ft[sup 3]/ton. These results show that (1) methane contents increase with increasing depth, (2) methane content locally can exceed 3.5 billion ft[sup 3]/mi[sup 2] for a 10-ft-thick coal bed, and (3) methane gas resource of 4.4-5.0 tcf are conservatively estimated for the Book Cliffs coal field to a depth of 9000 ft.