Pore-pressure depletion arising from oil production can cause subsidence of overburden formations as well as casing failures. The reduction of casing failure in a field containing compactable reservoirs is particularly significant to the reduction of non-productive time. Casing integrity can be influenced by various factors, including formation loading and inner pressure applied to the casing. This paper focuses primarily on a numerical analysis of casing failure caused by the formation geostress load related to pore- pressure depletions. Three-dimensional (3-D) numerical analyses of formation subsidence and related casing failure of a deviated well in a field of offshore Brazil was performed. The calculations considered pore-pressure depletions in the area around a production well and of nearby wells. A fully-coupled hydro-mechanical model was adopted to simulate the porous flow that occurred simultaneously with matrix deformation. Submodeling technique was adopted to address the discrepancy between the scale of the oilfield and that of the casing section. A full-field scale was used to simulate seabed subsidence at a global level. Casing failure was calculated at a local level at the scale of 10 m. The subsidence contour at the field level was plotted as cross- sections of the areas under study for the total formation depth of 10 km. The key casing section along the entire trajectory length was selected by using the finite-element method (FEM). For a given three-year period of production, two submodels were selected, which correspond to the various key-casing sections selected. Plastic deformations of each key casing section with different maximum formation loadings for the two different pore-pressure depletions have been given out. The numerical results of seabed subsidence simulations closely correlate with the measured data from references. The casing failure analysis also matched the observed phenomena. The proposed numerical procedure provides an effective tool for casing integrity estimates and prediction of production-related subsidence.

You can access this article if you purchase or spend a download.