Abstract: Geothermal Exploration in Central Colorado

John C. Romero, Donald W. Fawcett

Exploration is being conducted to define the relation between geothermal resources and associated groundwater resources of the San Luis and upper Arkansas Valleys of south-central Colorado, and to predict and evaluate the potential impact of geothermal-resource development on water resources and on vested water rights. This evaluation will allow maximum development of geothermal resources without causing material injury to vested groundwater rights.

The San Luis Valley and Upper Arkansas Valley, in association with the Rio Grande rift, exhibit several characteristics favorable for commercial geothermal-energy sources (youthful volcanic activity, thermal springs and wells, and above-normal heat flow). Several public and private entities have expressed interest in the rift and a small amount of local exploration has been initiated. More exploration is anticipated since the recent designation of Valley View, Mineral, Poncha, Mount Princeton, and Cottonwood Hot Springs as "Known Geothermal Resource Areas" (KGRA's). The current investigative program focused on these KGRA's.

Since June 4, 1975, approximately 1,350 sq mi (3,500 sq km) of the region has been investigated by a combination of office research and field reconnaissance. About 1,250 sq mi (3,240 sq km) has been expressed on composite geologic maps which are near the last stages of completion. Three test wells drilled to depths of 545,940, and 1,035 ft (166, 286, 315 m) were completed during fall and winter of 1975. Water samples collected from these wells and from the region's hot and warm springs were utilized to predict reservoir temperatures. Pump tests performed in the three wells yielded information on transmissivities and specific capacities of the perforated intervals. During 1976, a comprehensive geophysical program was completed. Water samples from several important streams in the upper rkansas Valley were obtained and analyzed; these will establish additional baseline data for streams in areas where geothermal energy may be developed in the future.

Geothermal reservoir temperatures, estimated from analyses of water from the three test wells and from hot and warm springs in the northern San Luis Valley, range from about 60°C to about 360°C. Reservoir temperatures estimated from analyses of water from hot and warm springs in the upper Arkansas Valley range between about 110 and 200°C.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado