Stop-go temperature logging for precision applications

We describe a new field procedure for stop-go temperature logging of boreholes that attains millikelvin precision. Temperature is recorded continuously throughout the entire log, but the logging probe is held stationary for a fixed time at discrete depth intervals. Equilibrium temperatures at the discrete depths are based on extrapolations of time series using the heat-diffusion theory for an infinitely long cylinder. For a Fenwahl K212E thermistor probe having a time constant of about 7s, temperatures are still 6mK away from equilibrium after a wait time of 30s; but temperatures extrapolated from the time series are within 2mK of equilibrium. A time series over a duration of seven time constants of the probe allows the user to reproduce temperature estimates within millikelvins. The technique was applied at GC-1, a borehole in northwestern Utah.