A study of the reservoir at the Matsukawa geothermal field

Abstract

The geothermal fluid reservoir, which is now under exploitation at the Matsukawa geothermal field, is below the Matsukawa andesite layer which is widely over the area. Hot water and steam can be obtained from at, and below, the lower part of dacite tuff layer which lies beneath Matsukawa andesite. In this report, the writers compile the data of wells, concerning the lost circulation during drilling, electric logging, and temperature logging. The lost circulation data during drilling often show the possible positions of a more permeable zone compared to the zone surrounding it. Electric logging data give the clue to deduce whether the strata are permeable or not. Temperature logs obtained before discharging geothermal fluids often indicate the existence of a localized predominant place to supply hot fluid into the well from the surrounding formation. Interesting conclusions can be obtained especially by comparing temperature logs measured at different standing times or conditions in the well respectively. Theoretical consideration is shown about the flow of geothermal fluid through porous media into the well. In accordance with the theory, some probable patterns of temperature and pressure near the well are shown, and their applications to the examples obtained at the wells of Matsukawa and its adjacent geothermal areas are discussed.