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Comparing FRACHEM and TOUGHREACT for reactive transport modelingof brine-rock interactions in enhanced geothermal systems (EGS)

Description: Coupled modelling of fluid flow and reactive transport ingeothermal systems is challenging because of reservoir conditions such ashigh temperatures, elevated pressures and sometimes high salinities ofthe formation fluids. Thermal hydrological-chemical (THC) codes, such asFRACHEM and TOUGHREACT, have been developed to evaluate the long-termhydrothermal and chemical evolution of exploited reservoirs. In thisstudy, the two codes were applied to model the same geothermal reservoir,to forecast reservoir evolution using respective thermodynamic andkinetic input data. A recent (unreleased) TOUGHREACT version allows theuse of either an extended Debye-Hu?ckel or Pitzer activity model forcalculating activity coefficients, while FRACHEM was designed to use thePitzer formalism. Comparison of models results indicate that differencesin thermodynamic equilibrium constants, activity coefficients andkinetics models can result in significant differences in predictedmineral precipitation behaviour and reservoir-porosity evolution.Differences in the calculation schemes typically produce less differencein model outputs than differences in input thermodynamic and kineticdata, with model results being particularly sensitive to differences inion-interaction parameters for highsalinity systems.
Date: November 15, 2005
Creator: Andre, L.; Spycher, N.; Xu, T.; Pruess, K. & Vuataz, F.-D.
Partner: UNT Libraries Government Documents Department

Geology, resistivity, and hydrochemistry of the Ojo Caliente hot springs area, northern New Mexico

Description: Geothermal fluids of the Ojo Caliente area discharge from a northeast trending normal fault that juxtaposes Precambrian metarhyolite and Tertiary sediments. An electrical resistivity survey shows that the fluids emerge from the fault and flow as a plume of thermal water into cold aquifers east of the fault. Geochemistry of fluids indicates a maximum reservoir temperature at depth of 80/sup 0/C with no suggestion of high temperature isotopic exchange between water and reservoir rocks. From this data, it is believed that the Ojo Caliente system is suitable only for small-scale direct use geothermal applications.
Date: January 1, 1982
Creator: Stix, J.; Pearson, C.; Vuataz, F.; Goff, F.; East, J. & Hoffers, B.
Partner: UNT Libraries Government Documents Department

Roosevelt Hot Springs/hot-dry-rock prospect and evaluation of the Acord 1-26 well

Description: Previous hot, dry rock (HDR) geothermal resource evaluation efforts have identified the Roosevelt Hot Springs KGRA as a prime HDR target. The size of the HDR resource is estimated to be at least eight times larger than the adjacent hydrothermal resource. Further research activities to evaluate this HDR resource have involved review of data from the Acord hot dry well, the seismic structure of the area, fluid geochemistry, and hydrology of a shallow aquifer. These recent results are summarized and the most likely HDR prospect area is identified.
Date: January 1, 1983
Creator: Shannon, S.S. Jr.; Goff, F.; Rowley, J.C.; Pettitt, R.A. & Vuataz, F.D.
Partner: UNT Libraries Government Documents Department

Hydrogeochemistry of the Qualibou Caldera Geothermal System, St. Lucia, West Indies

Description: Interpretation of hydrogeochemical data and supporting geologic and electric resistivity data have been used to define the basic structure of the Qualibou Caldera geothermal system and propose a model of hydrologic flow. The geothermal system at Sulphur Springs consists of three layers: (1) an upper steam condensate zone; (2) an intermediate vapor zone, which may be restricted to the Sulphur Springs area only; and (3) a lower brine zone. Four lines of evidence suggest that temperatures of the brine layer may exceed 230/sup 0/C at depths of perhaps 1 km. Outlying thermal springs along the northwest side of the caldera do not indicate derivation from underlying high-temperature sources. It is suggested that the main reservoir upflows in the Belfond-Sulphur Springs area and flows laterally in the subsurface toward the northwest caldera wall.
Date: January 1, 1984
Creator: Goff, F. & Vuataz, F.D.
Partner: UNT Libraries Government Documents Department