DETECTION OF HYDROTHERMAL ALTERATION IN A SEDIMENTARY TYPE GEOTHERMAL SYSTEM USING WELL LOGS.

A study was conducted to examine well log responses in the hydrothermally altered zones of a sedimentary type geothermal reservoir. The logs were run under precooled borehole conditions. In spite of uncertainties about the borehole temperature at the time of logging and lack of calibration data for quantitative estimation, qualitative interpretation of the logs indicate that the zones with extensive hydrothermal alteration are detectable on conventional logs such as conductivity surveys, S. P. , compensated density and neutron logs. These observations confirm the worthiness of wireline logs in geothermal exploration.