Reservoir Characteristics and Exploitation-Related Processes at the CP IV Sector of the Cerro Prieto (México) Geothermal Field

Abstract

The CP IV sector (100 MWe) is located at the NE part of the Cerro Prieto geothermal field and started commercial exploitation in 2000. In this work the main characteristics of the CP IV reservoir, initial conditions and response to exploitation (2000-2005), were estimated. Well-bottom thermodynamic conditions were obtained by using the WELLSIM simulator and production data as input. The interpretation of the chemical and isotopic behavior of fluids together with well-bottom thermodynamic conditions allowed a reservoir conceptual model to be obtained. Results suggested the existence of two zones with different characteristics (southern and northern blocks), separated each other by the Fault H. At the southern block, located towards the E-SE, wells with high enthalpy (&#8805; 2000 kJ/kg), low chloride (&#8804; 7000 mg/kg), high CO2 (&#8805; 6‰ mol) and relatively &#948;D depleted (&#8804; -94‰) fluids were found. In contrast, in the northern block, located towards the W-NW, the wells produce lower enthalpy (<1800 kJ/kg), higher chloride (~12,000 mg/kg), lower CO2 (< 6‰ mol) and higher &#948;D (>-94‰) fluids compared to southern wells. The main reservoir processes were related to exploitation and included: boiling and steam condensation in wells at the NW and in the periphery of CP IV and the entry of lower temperature waters in the central part of CP IV.