A 50-MW½ geothermal power plant is being considered for the Baca site in the Vailes Caldera, New Mexico, as a joint venture of the Department of Energy (DOE) and Union Oil Company of California. To date, over 20 wells have been drilled on the prospect, and the data from these wells indicate the presence of a high-temperature, liquid-dominated reservoir. In this paper, data from the open literature on the physical characteristics of the field are used to estimate the amount of hot water in place (reservoir capacity) and the length of time the reservoir can supply steam for a 50-MW½ power plant (reservoir longevity). The reservoir capacity is estimated to be 10 •2 kg of hot fluid by volumetric calculations using existing geological, geophysical, and well data. The criteria used are described and the sensitivity of the results discussed. The longevity of the field is studied using a two-phase numerical simulator (SHAFT79). A number of cases are simulated based upon different boundary conditions and upon injection and production criteria. The results obtained from the simulation studies indicate that it is questionable that the Baca field can supply enough steam for a 50-MWe power plant for 30 years. Although the estimated reservoir reserves greatly exceed those needed for a 50-MW½ power plant, the low transmissivity of the reservoir would cause localized boiling and rapid pressure decline during exploitation. It is therefore apparent that the conventional zero-dimensional (lumped parameter models) cannot be used to evaluate the generating capacities of low-permeability fields such as the Baca field.
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A 50 MW geothermal power plant is currently under development at the Baca site in the Valles Caldera, Ne Mexico, as a joint venture of the Department of Energy (DOE), Union Oil Company of California and the Public Service Company of New Mexico (PNH). To date, over 20 wells have been drilled on the prospect, and the data from these wells indicate the presence of a high-temperature liquid dominated reservoir. In this paper, data from open literature on the field are used paper, data from open literature on the field are used to estimate the amount of hot water in place (reservoir capacity) and the length of time the reservoir can supply steam for a 50 MW power plant (reservoir longevity). The reservoir capacity is estimated by volumetric calculations using existing geological, geophysical and well data. The criteria used are described and the sensitivity of the results discussed. The longevity of the field is studied using two-phase numerical Simulator (SHAFT 79). A number of cases are studied based upon different boundary conditions, and injection and production criteria. Constant or variable mass production is employed in the simulations with closed, semi-infinite or infinite reservoir boundaries. In one of the cases, a fault zone feeding the production region is modeled. The injection strategy depends on the available waste water. The results of these simulations are discussed and the sensitivity of the results, with respect to mesh size and the relative permeability curves used, are briefly studied. Introduction The Baca geothermal field is located in the Valles Caldera, New Mexico, about 55 miles north of Albuquerque. The field is being developed by the Union Oil Company of California and the Public Service Company of New Mexico. To date, over 20 geothermal wells have been drilled in the Valles Caldera, varying in depth from 2000 to over 9000 feet (1). Six of the wells have been drilled in the Sulfur Creek area, the remainder along Redondo Creek (Fig. 1). The wells in the Sulfur Creek area have penetrated a high-temperature but low-productivity formation. In the Redondo Creek area, the wells have encountered a high-temperature (>550 deg. F) liquid-dominated reservoir. Interpretation of the well data by Union Oil (1) indicates the presence of a liquid dominated reservoir and a separate steam reservoir, which are not in hydraulic communication. However, a recent study by Grant (2) suggests that there is actually only one liquid-dominated reservoir, with an overlying two-phase zone. It is extremely important to make reliable estimates of the mass of hot water in place (reservoir capacity) and the length of time the reservoir can supply steam for a 50 MW power plant (reservoir longevity). The reservoir longevity depends both on the reservoir capacity and on the overall development plan for the field (flow rates, injection, etc.) This paper represents the first in a series of studies of the reservoir capacity and longevity of the Baca field. In this first study the reservoir capacity is estimated by volumetric calculations, using existing geological, well, and geophysical data. An initial study of the reservoir longevity is also made using the two-phase numerical simulator SHAFT 79, developed at LBL. Because of the lack of available data, we made a number of assumptions during the course of the study. Therefore, the results presented here are preliminary. New estimates will be made as more data are accumulated; GEOLOGY The topographically high Valles Caldera is a subcircular volcanic depression, 12 to 15 miles in diameter, formed 1.1 million years ago. This resurgent caldera is characterized by a ring fracture zone where a number of rhyolitic volcanic domes are found (1). A broad structural dome, with a summit at Redondo Peak, is located near the center of the caldera and is bisected by a large northeast trending central graben (Redondo Creek). A detailed geological description of the Valles Caldera region can be found in references 3, 4 and 5. Geologic cross-sections of the Valles Caldera region are shown in Figure 2.
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