Borehole temperature estimation based on various data acquired at IODP 337.

Precise estimation of underground temperature by using drill holes is a challenging issue, since drilling operation disturbs the original underground temperature. A common procedure to estimate the undisturbed in-situ temperature in a borehole is to use the 'build-up' method, based on the measured values and their measured time after circulation of drill fluid, to estimate the equilibrium temperature. We acquired several datasets of borehole temperature at an IODP well, off northern Japan, and found that the temperature gradient is almost perfectly linear and the local undulations observed at the well were due to the thermal conductivity of the surrounding rocks.