Determination of formation temperatures from temperature logs in deep boreholes: Comparison of three methods

The most important data on the thermal regime of the Earth's interior come from temperature measurements in deep boreholes. The drilling process greatly alters the temperature field of formations surrounding the wellbore. The temperature change is affected by many factors and the exact determination of formation temperature at any depth requires a certain length of shut-in time. In theory this shut-in time is infinitely long. There is, however, a practical limit to the time required for the difference in the temperature between the well wall and surrounding reservoir to become a negligible quantity. In this paper, we conducted a comparison of three methods of predicting the undisturbed formation temperatures from shut-in temperature logs in deep wells. Long-term temperature surveys in five wells were selected to estimate the formation temperatures and to compare measured and predicted transient formation temperatures. It was found that the best agreement is observed with values calculated by the 'three-point method' and measured during shut-in period transient temperatures.