The temperature data available from the well bores are of different types and measured for different purposes. A fixed procedure for estimating the temperature at final TD is therefore not practically possible, but for most wells the estimation is done using a second order polynomial fit to the available measured temperatures from a well. Both Horner corrected wire line bht's and DST temperatures are used, but where DST data are available these are preferred. Grossly deviating data and data indicated in the well reports to be dubious are not used. If no data are available from the lower 500 m in a well, no TD temperature estimate is given for that well.
The diagram below illustrates standard procedure for a well. The uppermost data point, at sea floor, is usually set to 5°C. The data point at (15.6°C, 165 m bsfl) is from the Peon Discovery re-entry 35/2-1 R, a very shallow well temperature measurement. This data point has been used ever since the Peon data became available in 2006. In water depths exceeding 600 m the sea floor temperature is set to -0.5 °C and the Peon data point is not used. The thick dashed line shows final TD in the well, and the intersection between the polynomial fit (solid curve) and TD give the estimated "bottom hole temperature".