An economic analysis of a geothermal field development has been performed using a Monte Carlo simulation model. The model is formulated much along the lines of that of conventional oil and gas development. However, since necessary data to carry out the analysis have not so much accumulated in the field of geothermal energy in Japan as in oil and gas, simplified formulation of input data has been obliged. This study has picked up a particular geothermal field in Japan where commercial operation of 50 MWe power generation has started and there fore physical and economical characteristics of geothermal resources in the area are fairly understood. The authors analyze the accompanying economic risk when another 50 MWe power plant is to be operated in an adjacent area. Input data are formulated deducing from the past experiences. Expected present worths as well as distributions of present worths are computed for several cases. Some important parameters are changed during the model study and their influences on the economics are studied.
It is well-known that the saturated water for an unit volume has a maximum enthalpy at 330°C. This fact by itself indicates that the highest-grade geothermal reservoir will be of 330°C because the “ore grade” of a reservoir is consideres to be proportional to the heat content stored in definite dimensions. On the other hand, the maximum reservoir temperatures of very active sysems in the world increase with increasing the depth of the reservoir nearly along the boiling curve of water in which the density of high temperature waters is taken into consideration (Hayashi et al., 1981). Consequently, the depth of the highest-grade geothermal reservoir can be predicted before deep drilling as follows: 1750 m for a field with an activity index of 100, 2700 m for one of 90, and below 3500 m for one of 80 . Since the enthalpy of the saturated water for a unit volume varies a little over a temperature range of 300 to 350°C, reservoirs almost equivalent to the highest-grade ones will be expected at depths ranging from 1100 to 2350 m for a field registering 100 in the activity index, below 1600 m for one of 90, and below 2550 m for one of 80.
In this paper we describe the results of self potential survey conducted over Onikobe geothermal area in Narugo-cho, Miyagi prefecture, and discuss the relationship of the measured self potential anomaly to the calculated potential profile and the geologic structure. We introduce two types of models to interpret the measured self potential variation. In this analysis, it is assumed that the sources of self-potential generation are roughly coincident in location and depth with known faults. The potential fields generated by the models are compared with the actual profiles . A new model consisting of dipolar current distribution (Corwin et al., 1981) is generally valid for the interpretation of the field data obtained by both B and D3 survey lines. The agreement appears to be reasonably well. This implies that the self potential anomalies seen in Onikobe geothermal area may be related to the faults.
A measurement was operated on 26 November 1978 for the wall temperature of the Jobu railway tunnel which is known as a hot tunnel penetrating the Kurobe Sennindani hot dry rock in the central Japan, by means of infrared radiation thermometers. Correction of the measured temperature is carried out for emissivity of the tunnel wall of rough granite surface, by solving the linear simultaneous equations. Signifi cant correction (6.2°C of its maximum) is due to large variation and irregular distribution of the temperature on the wall surface. Comparison of the corrected temperature with the thermistor thermometer-measuring temperature in the winter of 1975-76 is discussed. It was shown that the infrared radiation thermometer got an advantage over the thermistor thermometer in such severe condition of 41.5°C of the maximum air temperature and 88 to 97 % of relative humidity in the tunnel, because of its faster measurement of 6 hours than that of the latter of 19 days.
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