Model-Dependence of Size and Position of Heat Source in a Geothermal Reservoir

This paper describes effects of boundary conditions on a geothermal reservoir analysis, using a porous model and data from Takenoyu geothermal field, in Kumamoto prefecture, Japan. The conclusions are as follows: (1) Under the assumption that the vertical length is 1.0km and there is a horizontal heat source on the bottom, the estimation error of temperature distribution in a case of the horizontal length of 2.5km almost agrees with the case of 5.0km. In the both cases, the heat source length of 1.0km gives the minimum estimation error between the calculation and the observation data. (2) When the heat source is assumed to be on the bottom or the center axis, the calculation agrees with the temperature data in the range from ground surface to 400m depth level. However, the latter calculation disagrees with the data in the range deeper than 400m. (3) Performance index evaluating differences between field data and model calculations should be defined not only by temperature, but also mass and heat discharges at the surface, in order to identify the size and position of the heat source. (1982) 4, 143-158. Bödvarsson, G. S. and C. F. Tsang(1982) Injection and Thermal Breakthrough in Fractured Geothermal Reservoirs, J. Geophy. Res., 87, 1031-1048. Bödvarsson, G. S., K. Pruess, V. Stefansson and E-T. Eliasson(1984)The Krafla Geothermal Field, Iceland: 2 The Natural State of the System, Water Resource Res., 20, 1531-1544. Cheng, P. and K. Lau(1973) Numerical Modelling of Hawaiian Geothermal Resources, Geothermics, 2,90-93. Goyal,K.P. and D. K. Kassoy(1981) A Plausible Two-Dimensional Vertical Model of the East Meas Geothermal Field, California, J. Geophysical Res., 86, 10719-10733. Mercer, J. W. and C. R. Faust(1979)Geothermal Reservoir Simulation: 3 Application of Liquid and Vapor-Dominated Hydrothermal Modeling Techniques to Wairakei, New Zealand, Water Resource Res. 15, 653-671. Morris, C.W. and D. A. Cambell(1981)Geothermal Reservoir Energy Recovery-A ThreeDimensional Simulation Study of the East Meas Field, JPT. 33, 735-742. (1984), 6, 263-277. Pruess K. (1983)Heat Transfer in Fractured Geothermal Reservoirs with Boiling, Water Resources Res., 19,201-208. (1987), 8, 243-259. Tsang, C. F., D. C. Mangold, C. Doughty and M. J. Lippmann(1984) Prediction of Reinjection Effects in the Cerro Prieto Geothermal System, Geothermic, 13, 141-162. (1983), p.117-118. Yamaguchi, S. and S. Hirakawa(1984) Proposal of a Numerical for a Naturally Fractured Geothermal Reservoir, J. Geothermal Res.Soc.Jpn, 6, 21-31. (1983), 5, 167-185.