Borehole Experiments of Synthetic Fluid Inclusion Logging at WD-1 in the Kakkonda Geothermal Field, Northeastern Japan

Abstract

Synthetic fluid inclusion logging is a new method of temperature measurement and direct fluid sampling in hightemperature geothermal wells. The method has been developed by the Geological Survey of Japan and the New Energy and Industrial Technology Development Organization (NEDO). The first borehole experiment was carried out in the fall of 1994 at a deep research hole (WD-1) drilled by NEDO in the Kakkonda geothermal field, northeastern Japan, and several experiments were conducted in 1995 and 1996. In the experiments, cracked crystals (quartz and calcite) soaked in solutions in gold or platinum capsules were mounted on containers for temperature measurement. The containers were placed in the borehole for one hour to three months. Trapping temperatures of fluid inclusions were determined by microthermometric measurement. Within short (one hour, one, two and three days), middle (one month) and long (three months) term experiments, fluid inclusions were synthesized in all quartz crystals soaked in alkaline solution, in some quartz crystals in NaCl solutions, and in all calcite crystals. Homogenization temperatures of the fluid inclusions were mostly concordant with borehole temperatures which were measured by other conventional logging tools. For fluid sampling, cracked quartz crystals without sealing are mounted in containers through which borehole fluid flows. A small number of fluid inclusions were synthesized under the short and middle term experiments, and many inclusions were synthesized enough for chemical analyses under the long term experiment. These results indicate that the synthetic fluid inclusion logging system is available to temperature measurement and fluid sampling in high-temperature geothermal wells.