The Field Tests for Measurement of Downhole Weight on Bit (DWOB) and the Calibration of a Real-time DWOB Model

The Drilling Engineering Research Group at the University of Calgary has been seeking better ways of improving drilling operations and decreasing costs by the use of advanced real-time modeling and simulation technologies. It is well known that the performance of a drill bit directly affects the overall drilling performance. The bit performance is often evaluated by the rate of penetration (ROP) which is dependent on the weight on bit (WOB). Therefore, obtaining actual downhole weight on bit (DWOB) is crucial in achieving good performance of a drill bit. This paper defines the procedures or steps to measure DWOB and an analytical model for calculating DWOB using typical surface collected drilling data. Field test data is used to initially calibrate the analytical model. The calibrated analytical model is next used in a forward calculation to predict DWOB on the same well. DWOB is also predicted on a second well using the same drilling rig. The results from the calibrated model are compared to the DWOB collected by the CoPilot, a Baker Inteq downhole measurement tool. The comparison shows that the DWOBs from the model match those from the CoPilot well. The model can be integrated in a new directional Autodriller system, which can in real time set the DWOB from surface measurements. The directional Autodriller can automatically conduct real-time analysis and calculations of DWOB as well as maintaining a precise DWOB for the drill bit. This will improve drilling efficiency and reduce cost.