Introducing optimized validated meshing system for wellbore stability analysis using 3D finite element method

Abstract

Finite element method (FEM) as a powerful tool for studying stress and strain status is being extensively employed in geotechnical studies. As the initial and boundary conditions, element type, and meshing system heavily affect the accuracy and precision of the results obtained from FEM, in this research we present a novel approach which is optimized and validated by the results obtained from reality. At first a mechanical earth model (MEM) was constructed using different well logging data, results of core analysis, and drilling reports for one of the central Iranian carbonate reservoirs. Then, a depth range was selected in the pay zone of a vertical well for FEM simulation. The selected depth range consists of two different zones: the upper zone with normal faulting regime and the lower zone with strike-slip faulting regime.After studying different model sizes, mesh densities, element types, and boundary conditions, a cylindrical model consist of a combination of regular and irregular hexahedral elements for far-field region, and fine-grained tetrahedral elements for near-wellbore region was obtained. Two different approaches were selected for FEM modeling, in the first approach a pre-drilled well was considered in the model, and in the second approach the model geometry before drilling without a pre-drilled well was subjected to an initial state of stress, removal of the elements, and loading which simulate the drilling process using a certain mud weight. The results of simulating the state of strains around the wellbore using this meshing system in both FEM approaches had acceptable adoption with drilling data.