Avoiding Pitfalls in Thermal Profile Data Interpretation Makushin Volcano, Alaska

Abstract

During exploration of the Makushin Geothermal Area, Unalaska Island, Alaska, it was found that the deep water table and shallow high temperatures in the geothermal area resulted in misleading temperature gradients in two temperature gradient holes. The temperature profiles observed in these holes are characterized by long (250 to 600 foot) isothermal zones of 21 -212°F at intermediated depths. The base of the isothermal zone is interpreted as the depth of the water table, where boiling occurs in the completion tubing under atmospheric conditions. The top of the isothermal zone represents the depth at which steam condensation occurs. It is recommended that turn temperature gradients in such isothermal zones be interpreted symmetrical interpolation between upper and lower temperature measurements.