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A Preliminary Analysis of Geothermal Resources in the Central Raton Basin, Colorado, from Bottom-Hole Temperature Data

Morgan, Paul 1
1 Colorado Geological Survey, Denver, CO.

The Raton Basin is the southernmost classical Laramide basin in the Rocky Mountain region and straddles the New Mexico-Colorado state line. An asymmetric basin, deeper to the west, its central portion lies at the western end of Las Animas County, Colorado. Over 1900 bottom-hole temperatures (BHTs) were compiled from the logs of 1886 wells in Las Animas County, most of which were drilled over the past fifteen years, and are associated with the extraction of coalbed methane, primarily from Upper Cretaceous and Paleocene formations. Most of the wells from which the BHT data were collected were drilled in about a day using air percussion rotary rigs, and to depths of less than 1100 m (3600 ft). The exclusive use of air in drilling many of the shallower holes and short drilling times deviates from conditions for which general temperature corrections for the effects of drilling were derived. However, even before correction, the data show significant coherent trends, with higher gradients, in general, in the western portions of the study area. BHT data from 54 wells in the depth range of 1128 to 2253 m (3700 to 7400 ft) were corrected by standard correction techniques. These corrections were checked and found to be consistent with extrapolated equilibrium temperatures at two depths in a deep well in which temperature data were available at four different times. Data from these deeper wells, and tentative data from the shallower wells, allow general conclusions to be made concerning geothermal resources in Las Animas County and in particular in the central Raton Basin. Geothermal gradients in Las Animas county west of the Raton Basin are typically <40°C km-1 (22°F/1000 ft) and do not indicate significant geothermal resources. Much of the Raton Basin has gradients in the range of 40-60°C km-1 (22-33°F/1000 ft), and locally gradients exceed 60°C km-1 (33°F/1000 ft) and continue to depths of at least 2000 m (6550 ft). The corrected BHT temperature at this depth is 113°C (235°F), which is hot enough for electricity generation using binary power-plant technology. Water is abundant at shallower depths in the basin. If sufficient natural or stimulated permeability exists, or can be made at a depth of 2000-2500 m (6500-8200 ft) for hot water production and reinjection, the central Raton Basin is a good candidate for binary power-plant electricity generation.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009