Geomechanical and Decision Analyses for Mitigating Compaction-Related Casing Damage

Abstract

Summary Reservoir compaction and its associated bedding plane slip and overburden shear have induced damage to hundreds of wells in oil and gas fields throughout the world. Critical casing damage mechanisms observed in a variety of structural settings include overburden shear damage on localized horizontal planes, shearing at the top of production and injection intervals, and compression and buckling damage within the production interval, primarily around perforations. Analytical solutions are readily available to estimate compaction, subsidence, and casing damage risks. These should be applied as initial screening tools at an early stage in reservoir development planning. They also can be applied to estimate relative risks for various well locations and trajectories. Geomechanical models of increasing complexity, including 2D and 3D finite element type techniques, have been used with good success to assess formation deformation and casing damage risks in several reservoirs and are described herein. Three-dimensional geomechanical models at the wellbore scale are required to evaluate shearing deformation on specific well designs and are used to assess damage mitigation effectiveness for varying completion strategies. An economic decision tree model is applied to compare the costs and benefits of alternative well designs while taking into account inherent uncertainties in model input data, the well's damage location, and the effectiveness of various mitigation strategies. In some instances, the appropriate action is not to change the completion design, but simply to accept damage risk.