In order to determine the coal bed methane potential of the Raton basin, Colorado Geological Survey potential of the Raton basin, Colorado Geological Survey personnel studied the geography, the geology, the personnel studied the geography, the geology, the history of oil and gas exploration, and the coal resources and past production in the Raton coal region. Data gathered during study of the above disciplines, along with direct measurements of the coals' gas content, can be used to estimate the methane potential of the Raton basin.
Introduction
Coal has been mined commercially in the Colorado portion of the Raton basin since 18701; reports of portion of the Raton basin since 18701; reports of methane gas occurrences in the coal mines date back to the same period. Oil and gas exploration in the region began late in the last century. Explorationists encountered methane gas as they drilled through coal zones; they even tested some coal beds. Today coal mines, coal core holes, and oil and gas tests are still encountering large amounts of coal-derived methane. If the amount and source of this gas could be better defined, possible coal mining hazards could be predicted and an untapped gas source utilized.
In 1975, the U.S. Bureau of Mines provided the Colorado Geological Survey with a grant to gather data on the methane potential of the coal beds of Colorado. During this grant, Survey geologists located 32 historically gassy mines and recorded methane emission rates from operating mines. In addition, Survey geologists began using the U.S. Bureau of Mines "direct method" of desorbing (or measuring the gas emitted by) fresh coal core samples to determine the total gas content of a coal.
Today, this research continuous under two grants a U.S. Department of Energy Grant entitled "Evaluation of the Methane Potential of Unmined/Unminable Coalbeds in Colorado" and a Colorado Oil and Gas Conservation Commission grant entitled "Conservation of Methane from Mined/Minable Gaseous Coal Beds". Forty one coal core samples from the Raton coal region alone, have or are being desorbed. In addition, the geography, geology, oil and gas resources, and coal resources of the region are being studied to provide a framework for the methane data.
GEOGRAPHY
The Raton basin is a 241 × 193 Rm (150 × 120 mi.) north-south trending structural basin in southeastern Colorado and northeastern New Mexico (Fig. 1). The area of the Colorado portion of the basin is approximately 12,950 km2 (5000 mi.2). The basin is bounded by the Sangre de Cristo Mountains to the west, the Wet Mountains and the Apishapa uplift to the north and northeast, and the Sierra Grande-Las Animas arch to the east and southeast.
The coal bearing region in Colorado is a 2850 km2 (1100 mi.2) area in Las Animas and Huerfano Counties. The region is a plateau within the basin edged by the cliff-forming outcrop of the Trinidad sandstone. The elevation of the coal region ranges from 2130 m (7000 ft) in the east to 2740 m (9000 ft) in the west; the highest point is West Spanish Peak at 4152.29 m (13,623 ft). The plateau is dissected by the Purgatoire, Huerfano, Cuchara, and Apishapa Rivers (all Purgatoire, Huerfano, Cuchara, and Apishapa Rivers (all eastward draining tributaries of the Arkansas River) (Fig. 1).
The largest towns of the region occur where these rivers flow onto the plains: Trinidad (population 9901) on the Purgatoire, Walsenburg (population 4329) on the Cuchara, and Aquilar (population 699) on the Apishapa. Important land uses include grazing cattle and sheep, dry farming (at intermediate elevations), irrigation farming (along larger streams), lumbering (in the mountains), and coal mining.
The climate of the coal region is dependent on the elevation and ranges from semiarid in the plains to subhumid in the mountains. Most precipatation occurs as thundershowers from April through September; there is a dry spell in June.
Vegetation is also elevation dependent. Eighty percent of the area is in the foothills vegetation percent of the area is in the foothills vegetation zone of open coniferous forests and grasslands.
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