is similar to the representation of fig1 a and it shows the segmentation in four sections 4 7 for which the mean temperature of each section has been selected as the representative temperature for the section considered fig2 a is transformed into the representation of fig2 b where in each section the temperature is considered to be constant and equal to the mean temperature in this part division into sections can be done automatically it preferably is an even division as for the temperature but not for the length the thermal profile can be segmented every 3 u00b0 c for example or more precisely every 0 5 u00b0 c thus the temperature amplitude is the same in each section the user can select the segmentation interval according to circumstances the temperature and the pressure in each section allows determination of the corresponding rheology by means of the mud database by first approximation the mean hydrostatic pressure can be selected for each section determined by the temperature range selected the effect of the temperature is generally preponderant in relation to the pressure concerning the rheology variation of the drilling fluid the pressure drop is then calculated for each section with the rheology determined for each section prior to being summed up in order to obtain the total pressure drop in the.