A Study of Downhole Weight on Bit Calibration Model and Performance Assessment on Field Trial Data

Abstract

Obtaining real downhole weight on bit (DWOB) is a critical issue in drilling. In this paper, a weight on bit (WOB) calibration model which converted measurement reading of WOB sensor to force between bit and formation, namely DWOB, was proposed. Influence factors of measurement reading such as pressure, temperature and drillstring kinetics had been discussed in the derivation of the calibration model. Moreover, the model performance assessment was also studied with field trial data. After calibration of WOB sensor reading, DWOB maintains the fluctuating trend around zero in a small range when running drillstring into hole and pulling it out of hole. In addition, calculations indicate that pressure plays a more important role in calibration model compared to other factors. The calibration model is appropriate for both vertical and inclination wells.