Depletion-induced extreme plasticity across multiple horizontal wellbores in reservoirs with soft formations

Abstract

Following depletion of oil and gas reservoirs with soft rocks, serious wellbore damage and a large amount of sand production result from the development of extremely large plastic deformation around wellbores. Evaluation on the development of plastic strain is crucial to wellbore instability analysis and sand production forecasting. Cap plasticity models have been developed to capture both shear and compaction failures for geomaterials. However, it has been a great challenge in accurately identifying extremely large plastic deformation around wellbores in reservoirs with soft formations using cap plasticity model coupled with fluid flow. To tackle this challenge, we have developed a fully implicit and fully coupled geomechanics and fluid flow finite element code where the Pelessone smooth cap plasticity model is consistently formulated for finite plastic deformation. In this work, with this robust and accurate computer code, we successfully investigate a detailed evolution of plastic strain up to its extreme condition around and across multiple horizontal wellbores following reservoir pore pressure drawdown.