New Mexico Geological Society Annual Spring Meeting — Abstracts

Geothermal reservoirs in a rift setting can be static or dynamic. Static geothermal systems represent deep-seated and confined reservoirs with temperatures that correspond to the temperature gradients associated with background upper crust heat flow. On the other hand, dynamic reservoirs or systems have active upflow and associated outflow plumes that convectively and/or advectively transfer deep-seated heat closer to the surface. The upflows and outflow plumes represent the flow paths and shallow storage or reservoirs for geothermal fluids. Because of the arid nature of Rio Grande rift region, many, if not most, geothermal systems are "blind" to surface hydrology and lack hot springs. This presents an opportunity to estimate total system thermal output by summation of conductive heat flow above the water table across the area of the upflow and outflow plume for a particular system. Six to eight geothermal systems in the southern Rio Grande rift region are of sufficient exploration maturity to assess natural conductive thermal output, estimate reservoir volume, and assess probable base or highest reservoir temperatures. There is an apparent inverse size scaling of thermal output in relation to base reservoir temperature. The largest thermal outputs correspond to very large reservoir volumes and low temperature (100o C) are associated with much smaller total heat flux and apparent reservoir volumes. Hydrogeology appears to play an important role. The largest systems may have more broadly distributed zones of upflow with large outflow plumes at shallow and intermediate depths (<1 km) in Paleozoic carbonate reservoirs. The smaller systems are intensely focused by a variety of bedrock structures that feed shallow outflow plumes of less extent in mostly Cenozoic basin fill deposits.