It is important to know the temperature distribution in the wellbore during drilling to develop and evaluate the bit and/or mud for high temperature geothermal wells. But, normally only the inlet and outlet temperatures of drilling fluid can be measured during drilling in the field.
Authours proposed a method which estimates temperature distribution in the wellbore from measured inlet and outlet temperatures of drilling fluid by computer simulation even when formation temperature distribution is not known exactly. In this paper, we described the method and estimated bottom-hole temperatures during drilling for four geothermal wells. Conclusions are as follows:
(1) When the fluid is circulated in the well at a certain flow rate and the inlet and outlet fluid temperatures coincide with the given inlet and outlet temperatures respectively, the temperature distributions in the wellbore are almost the same for different formation temperature distributions.
(2) The temperature distribution in the wellbore during drilling can be estimated from the measured inlet and outlet temperatures of drilling fluid even when undisturbed temperature distribution and thermal disturbance in the formation are not given exactly.
(3) The estimated bottom-hole temperatures of mud during drilling were about 140 to 200°C lower than the undisturbedf ormation temperatures.Differences between the bottom-hole temperature and the outlet temperature of mud were only 1 to 18°C.
