Geothermometry At Long Valley Caldera Geothermal Area (Sorey, Et Al., 1991)
Exploration Activity: Geothermometry At Long Valley Caldera Geothermal Area (Sorey, Et Al., 1991)
|Exploration Activity Details|
|Location||Long Valley Caldera Geothermal Area|
|Activity Date||1985 - 1988|
Sorey et al. (1991) integrated information from previous scientific and private industry investigations with new data obtained from fluid sampling, test drilling, and geological and geophysical studies conducted between 1985-1988 into a comprehensive conceptual model of the present-day hydrothermal flow system at Long Valley caldera. Lithology and temperature gradient data from wells drilled prior to 1988 are summarized in detail in the compilation, which includes information from numerous wells described in previous studies, and data from many of the wells are available online through the U.S. Geological Survey (Farrar et al., 2010). Thermal conductivity, XRD, and isotopic analyses of core cuttings from several of the wells discussed have been completed in several studies, and seem to prove useful in most cases (Flexser, 1991; Goff et al., 1991; Smith and Suemnicht, 1991). Results from these studies are also summarized in Sorey et al. (1991). Relevant data from chemical and isotopic studies published during the same year are also considered in the review.
Estimated temperatures for the Long Valley geothermal reservoir were calculated for the RDO-8 and Casa Diablo (MBP-1 and MBP-3) well samples using five different geothermometers, which produced a range of temperatures from 181-248°C. The Na/K and Na/K/Ca geothermometers yielded an average temperature of 218°C, in good agreement with the maximum temperature of 214°C measured in the reservoir at that time. Silica-geothermometer temperature estimates for the well samples ranged from 196-202°C. This temperature range is lower than the cation-geothermometer temperature estimates for the same samples, indicating loss of silica in association with declining reservoir temperatures or with dilution by waters of comparatively lower silica content. Sulfate-water isotope geothermometer temperature estimates for the two Casa Diablo wells were 222° and 232°C, whereas the anhydrite-solubility geothermometer temperature estimates for the RDO-8 and Casa Diablo MBP-3 wells were 231° and 248°C, respectively. Given the lack of information on the existence of anhydrite in the reservoir rock, the sulfate-water isotope temperature estimate is considered the more reliable of the estimates provided by the two sulfate-dependent geothermometers.
- Michael L. Sorey, Gene A. Suemnicht, Neil C. Sturchio, Gregg A. Nordquist (December 1991) New Evidence On The Hydrothermal System In Long Valley Caldera, California, From Wells, Fluid Sampling, Electrical Geophysics, And Age Determinations Of Hot-Spring Deposits