Bottom-hole temperature correction – the Chad Basin, N.E., Nigeria case study

Abstract

Correction of the effects of drilling on bottom-hole temperatures, BHTs, measured in drilled wells require multiple measurements in the same well at the same depth but at different elapse times in order to predict true formation temperatures, TFTs. The relaxation of the same-depth requirement for depths differing by less than 100 m allowed the application of two such methods to a qualifying pair of single BHTs from where estimates of Horner plot slope and thermal diffusivity, κ were obtained. By assuming both the slope and к to be typical of the basin, several correction methods were employed to estimate TFTs from a dataset collected from the log-headers of wells drilled for oil and gas exploration in the Chad basin, N.E., Nigeria. Although the different TFT estimates did not agree, sensitivity of the methods to variations of either the slope or к enabled the results to be used to define the range within which the actual TFTs lie. TFT estimates obtained using empirical temperature correction methods were observed to fall within the defined range, and suggest that the data are amenable to empirical correction. Based on significant correlations, empirical equations relating correction and drilled well parameters were therefore derived.

Keywords: bottom-hole temperature (BHT), true formation temperature (TFT), horner plot slope, thermal diffusivity, same-depth relaxation

Global Journal of Geological Sciences Vol. 3(2) 2005: 133-142