An Integrated Geomechanical Approach to Accurately Predicting the Fracture Gradient for Mitigating Drilling Losses of Challenging Wellbores

Abstract

Fracture gradient (FG) of wellbores is the function of not only stresses, formation pressure and rock mechanical properties but also well trajectories. An accurate FG prediction is critical for safe well drilling. However, the existing methods do not account for the trajectory effects. An integrated geomechanical approach has been developed to more accurately predict the FG of wellbores subject to various trajectories. The approach deploys the Kirsch equations and takes into account the effects of formation pressure variations on stresses. It further integrates the elaborated individual procedures for deriving the geomechanical input parameters from regional field data to form a FG model. After verifying the losses test and offset well drilling data with necessary modifications, the calibrated FG model is then able to more accurately predict the fracture initiation pressure (FIP) of wellbores to mitigate the drilling losses for not only vertical but also deviated wellbores by guiding the equivalent circulation density (ECD) management. The integrated geomechanical approach has been applied to the planning and drilling of more than 30 new wells at Brunei Shell Petroleum (BSP). It has significantly mitigated the drilling losses for the challenging wells of a field redevelopment project in which about 50 deviated wells were expecting narrow drilling windows due to penetrating heavily depleted reservoirs. In another drilling campaign, it saved the sidetrack of a lost hole section by revising the trajectory as instructed by the FIP predictions. The integrated geomechanical approach is an algorithm that can effectively mitigate drilling losses by accurately predicting the FG for any arbitrary wellbores.