Prospects for Electricity Generation in the San Luis Basin, Colorado, USA

Abstract

The San Luis basin is the largest and deepest basin in the Neogene Rio Grande rift, and has many similarities to the basins of the US Basin and Range Province. It is asymmetric with a displacement of as much as 9 km on its eastern margin, and approximately 6.4 km of sedimentary rocks of late Oligocene or younger age in the deepest portion of the basin. Temperature measurements in shallow wells in the northern basin have an average geothermal gradient of 59.0 ± 11.8°C km-1 (± standard deviation). The average gradient calculated from corrected bottom-hole temperatures from 24 wells drilled for hydrocarbon exploration is 36.7 ± 5.6°C km-1 at a mean depth of 2,460 ± 857 m. A single well drilled in the southern part of the City of Alamosa had a geothermal gradient of 49.9°C km-1 and a bottom-hole temperature of 106°C at 2,170 m (7,118 ft). Although some scatter in the geothermal gradients in the basin is considered to be data scatter, some of the variations are considered to be real lateral variations, at least part of which correlates with subsurface structure. High gradients are associated with ascending ground water where the water rises up and over buried basement structures, driven by variations in the ground water potentiometric surface. Two hot springs have been correlated with the eastern boundary fault system of the basin: these features are believed to be associated with the ascent of buoyant thermal waters along increased permeability associated with the fault system. Temperatures in the geothermal systems are estimated to be about 150°C at a depth of 2 km (6,550 ft) or less, sufficient for electricity generation with binary power plant technology.