ANALYSIS OF RECHARGE COOLDOWN AT THE WESTERN BOUNDARY OF CERRO PRIETO I GEOTHERMAL FIELD
Extensive study of the Cerro Prieto geothermal field has provided much geologic and thermodynamic data of its structurally-complex, liquid-dominated reservoir. Several of the studies investigated the resource characteristics of fluid and energy flow. An early report by Mercado (1975) showed that the heat source for the part of the reservoir under development, now called Cerro Prieto I (CPI), originated in the eastern part of the field. Subsequent studies confirmed the flow of hot water from the east. A summary of several experimental and numerical studies of fluid and energy transport in the field was given by Lippmann and Bodvarsson (1983). The hydrogeologic model of Halfman et al. (1982) shows hot-water flow from the east divided into a shallow (alpha) aquifer at about 120Om and a deeper (beta) aquifer at about 170Om depth. A cross section along an east-west direction shows a central upflow to the two aquifers and uncertain geology beyond the western border of the field near well M-9. It also shows a fault dividing the line of border wells at M-29 from the inner wells at M-25 to the east. The hydrogeology of the field was described by Sanchez and de la Pena (1981) as an alluvial unit from the surface to about 700 m over the production zone and a shale-sandstone unit comprising an upper, shallow (alpha) aquifer bounded below by a basement horst overlying a deeper (beta) aquifer. To date, much of the cumulative production at Cerro Prieto I has been from the alpha aquifer. Piezometric level measurements over the first 5 years of operation showed a decline in the western zone beyond the production wells. Over the 10-year period of continuous production, a significant temperature decline has been observed along the westernmost line of wells. Several investigations of the recharge characteristics of the field have been reported. Mercado (1975) and Elders et al. (1984) indicated a flow of cold groundwater from the east. Mercado also noted that cold water was entering the reservoir from the west. In studying the expectations of field deliverability, reservoir life, and ultimate recovery of the resource, Castaceda et al. (1983) from a reservoir simulation model indicated a major degree of cold-water recharge into CPI from the west and north sides of the field. From reported chemical and thermal changes with production, Grant and O'Sullivan (1982) considered the reservoir as a leaky aquifer rather than confined, and attributed one quarter to one half of the recharge to percolation of fresh water from cooler rocks above the reservoir. From the accumulated chemical and production database, Grant, Truesdell, and Macon (1984) suggested that the western part of the alpha aquifer was essentially unbounded and that mixing with colder water by dilution rather than by boiling is the reservoir's response to continued extraction. They suggested that local boiling occurs in most of the wells as pressure decreases but that no general vapor zone has developed.
- Research Organization:
- Stanford University, Stanford, California
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AS03-80SF11459
- OSTI ID:
- 892159
- Report Number(s):
- SGP-TR-84; CONF-850107-19; TRN: US200622%%744
- Resource Relation:
- Conference: 10. annual workshop on geothermal reservoir engineering, Stanford, CA (US), 01/22/1985
- Country of Publication:
- United States
- Language:
- English
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