Real Time Surface Data Driven WOB Estimation and Control

Abstract In directionally drilled oil and gas wells, wellbore friction and tortuosity play an important role on how efficiently torque and weight-on-bit (WOB) is transferred from surface to the drill bit. Providing accurate and consistent true WOB in a real-time manner is crucial to maintaining optimum drilling efficiency. In this paper, we present a novel, automated system for estimating and controlling downhole WOB in real-time using surface data. The new system presented here automatically consumes drill-string and wellbore information while drilling to build a drill-string model with multiple sections, each with its own length, size, heading and wellbore friction factor. An automated algorithm captures and stores off-bottom hook-load data that meet certain rig-state conditions while monitoring multiple surface data streams. A numerical optimization method is then used to solve for the friction factor distribution with depth using selected off-bottom hookload data. The friction factors are put into a torque and drag model to estimate the downhole WOB. Numerical simulation shows that using the time history of surface data rather than a single hookload reading is key to ensuring a robust solution against noisy and missing data. An active control mode is also implemented in which the driller can directly control the downhole WOB through the system. The system was field tested on multiple horizontal wells drilled by the operator. Comparisons with downhole measurements show the system is capable of accurately predicting downhole WOB throughout the well including the lateral section. Solving the friction model using historical hookload data ensures the stability and robustness of the estimation. The distribution of friction factors with depth also help provides additional assessment of wellbore quality. An automated WOB control test was also conducted to demonstrate the system's ability to directly control downhole WOB by adjusting surface WOB according to the algorithm. The new system provides a novel way to use real time surface data to estimate and control downhole WOB