Geologic analysis of coal beds and associated rocks, estimation of methane content and potential based on coal, oil, and gas drill holes in the San Juan River Coal Region, Southwestern Colorado. 56 pages. 14 figures. 1 table. 6 plates (1:125,000). Digital PDF download. OF-80-02D
Excerpted from the Abstract:
The deepest, highest ranking and probably gassiest coals in the San Juan River coal region of southwestern Colorado are found in the 100 mile (mi) wide San Juan Basin of Colorado and New Mexico. The thickest and most continuous coal beds in the basin are found in the Cretaceous Fruitland Formation.
Logs from 231 petroleum exploration drill holes were used to produce the following: a Fruitland Formation isopach, a Pictured Cliffs structure map, Fruitland Formation net coal and net sand isopachs, and Fruitland coal percentage and sand percentage maps. Of the 231 holes, 8 produced natural gas from sandstones in coal bearing zones, 5 were production tested in mixed sandstone and coal intervals (one well had an initial production of 1.6 MMCFGPD), and 5 were drill stem tested in coal bearing zones (one flowed 1 MMCFG in 35 min).
The authors calculate 19.7 billion tons of coal are present in the study area. The coals are ranked high-volatile B (hvB) and high-volatile A (hvA) with local upgrading to medium-volatile (mv). Comparing gas contents of Cretaceous Raton Mesa coals to San Juan Basin coals, a gas potential exists ranging from 72 to 514 cubic feet/ton. The authors estimate a gas resource in the study area ranging from 1.4 to 10.0 trillion cubic feet.