Optimisation of temperature observational well selection

In wellbore climatology the method of temperature inversion to determine the trends in ground surface temperature history (GSTH) assumes that the process of a well's thermal recovery is practically completed. However, for deep wells (>100-300m) the drilling process, due to the lengthy period of drilling fluid circulation, greatly alters the temperature of formation immediately surrounding the well. As a result, the determination of the formation temperature (with a specified absolute accuracy) at any depth requires a lengthy period of shut-in time. The objective of this study is to determine how long it takes before the error caused by mud circulation is small compared to the change arising from the change in surface temperature. In this paper we suggest two techniques, Slider's method and utilisation of the γ-function, which enable us to estimate the rate of temperature decline and the difference between the formation and shut-in temperatures.