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

Abstract

Geothermal resources in deep sedimentary basins are underdeveloped. The Raton Basin is an asymmetric basin, the central portion of which in Colorado has been drilled extensively since 1998 for coalbed methane. Over 1900 bottom-hole temperature (BHT) data from these wells have been compiled to study the geothermal potential of the basin. Insufficient information was available from the Raton Basin BHT data to calculate drilling disturbance corrections: standard corrections were therefore applied from other Midcontinent basins. The mean corrected geothermal gradient from the corrected BHT data is 49 ± 12°C km-1 (2.7 + 0.7°F/100 ft, n=1842). There is a negative correlation between geothermal gradient and elevation which is interpreted to indicate a very slow groundwater flow down-dip in the west and up-dip in the east, resulting in forced thermal convection. The subsurface flow is also north and south inward toward the Purgatoire River drainage, and the highest gradients are located on the east-central side of the basin beneath this feature. Using geothermal gradients based on corrected BHT data, temperatures of 150°C (~300°F) are predicted at depths of less than 1600 m (5200 ft) in the regions of highest gradients, and at a slightly greater depth using the uncorrected BHT data. Permeabilities may not be high enough for a hydrothermal system at this depth, but formations ideal for hydrofracing are predicted for the creation of a sedimentary EGS system feeding a binary power plant.