Saving a Challenging Sidetrack Through Optimizing the Trajectory by Accurately Predicting the Fracture Gradient

Whilst drilling an exploration well through shallow depleted reservoirs, the heavily deviated intermediate hole section encountered uncontrollable losses, hole pack off, and ultimately was abandoned. A replacement sidetrack was proposed and the asset team requested an assessment of the drilling risks for the proposed trajectory. An integrated geomechanics approach was developed to analyze the fracture initiation pressures (FIP) of wellbores, which are dependent on well trajectories except on the field stresses and formation pressures. An FG model was elaborated with the integrated geomechanics approach analyzing the field data and the drilling history of the lost hole section. It predicted the FIPs of the initially proposed sidetrack trajectory with a value lower than the minimum required by the drilling team. The sidetrack trajectory was revised as instructed by the FG model analyses, which resulted in an increased FIP value slightly above the minimum required. The revised sidetrack trajectory observed minor losses with the ECD slightly exceeded the predicted FIP value during drilling, but the remaining section was successfully drilled by controlling the ECD under the predicted FIP value. If the primarily proposed sidetrack trajectory had been drilled, there could have been another lost-hole event due to the unmanageable drilling operation window. The integrated geomechanics approach eventually saved the challenging sidetrack through optimizing the trajectory by accurately predicting the FIPs.