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Waples et al. 2004 have developed a method for correcting log-derived temperatures in deep wells (3500-6500 m) by comparing log temperatures from the Gulf of Campeche (Mexican Gulf of Mexico) with DST temperatures in the same wells. The equations developed in this study are modified slightly from those of Waples & Mahadir Ramly (2001), which were calibrated using data from depths <3500 m in Malaysia. The correction depends strongly on time since end of mud circulation (TSC) and, to a much lesser degree, on depth. The corrected subsurface temperature (Celsius) is given by

T_{true} = T_{surf} + f · (T_{meas}-T_{surf}) - 0.001391(Z-4498)

The following figure (Fig. 3 from Waples et al, 2004) shows the amount of correction strongly depends on time since end of mud circulation (TSC). The scatter is typical of BHT data and gives a good sense of the error bars associated with such a correction.
Where T_{meas} is the measured log temperature in Celsius, Z is depth below sea floor in meters and T_{surf} is the sea floor or land surface temperature. The correction factor, f, is a function of TSC.

A similar correction developed using a larger data set from various geographical areas is available here

** References:**

- Waples, Douglas W., J. Pacheco and A. Vera, A method for correcting log-derived temperatures in deep wells, calibrated in the Gulf of Mexico, Petroleum Geoscience, Vol 10 2004, pp.239-245
- Waples, D.W. & Mahadir Ramly 2001. A statistical method for correcting log-derived temperatures. Petroleum Geoscience, 7, 231-240.

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