Resumo

ARELLANO-GOMEZ, Víctor Manuel et al. Characteristics and main processes in the Cerro Prieto IV reservoir. Tecnol. cienc. agua [online]. 2010, vol.1, n.1, pp.121-136. ISSN 2007-2422.

A study of the Cerro Prieto IV reservoir, which is located in the NE of the Cerro Prieto geothermal field, was carried out in order to define the main characteristics at "baseline state" conditions (prior to commercial exploitation) and the initial response to exploitation for 2000-2005. The well-bottom thermodynamic conditions were obtained by simulation of heat and fluid flows in wells using the WellSim software with historical production data as input. Chemical and isotopic data of produced fluids were analyzed in order to define their behavior patterns over time. These patterns were then related to simulation results to obtain a conceptual model for the reservoir. The thermodynamic, chemical and isotopic characteristics for baseline state conditions indicated that there were two zones with different characteristics which are separated by the Fault H. From the boundary formed by the wells 429D, 420,409 and 410 to the E-SE, wells with high enthalpies (≥2,000 kJ/kg), low reservoir chloride (≤ 7,000 mg/kg), high CO2 (≥ 6‰ molar) and relatively depleted δD values for the total discharge (≤ -94‰ ) were found. This zone was called "southern block". The other zone was called "northern block" and is found from the location of the wells 419, 415 and 430 D to the W-NW, where wells exhibit lower enthalpies, (of between 1,400 and 1,800 kJ/kg), higher reservoir chlorides (up to 12,000 mg/kg), lower CO2 concentrations (< 6‰ molar) and more enriched δD values (≥ -94 ‰) compared to those characteristics found for the "southern block" wells. The main reservoir processes identified to occur due to exploitation were: boiling and steam condensation in wells located at the NW and in the periphery of CP IV and the entry of lower temperature waters in the central part of the CP IV area. It was also found that the fault system associated to this part of the Cerro Prieto geothermal field controls the reservoir hydrodynamics.0 At present, the CP IV area has an installed power capacity of 100 MWe.

Palavras-chave : Cerro Prieto IV; reservoir processes; thermodynamic conditions; chemical composition of fluids; reservoir exploitation.

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