Numerical Analysis on Subsalt Wellbore Stability in the Vioska-Knoll Deepwaters of the Northern Region of the Gulf of Mexico

Abstract

AbstractThe goal of this paper is to present a best practice for deep water sub-salt wellbore stability analysis. Conventional one-dimensional analytical tools and three-dimensional nonlinear finite element method (FEM) software were used jointly in an integrated manner in which the former was used to predict pore pressure with logging data, and thus provides input data for FEM analysis. Numerical results of sub-salt wellbore stability analysis were presented for the Viosca Knoll field in the deepwaters of the Gulf of Mexico. To obtain accurate stress field information around the salt, it is necessary to begin by performing an analysis at the field scale. This analysis presents correct boundary conditions for wellbore stability analysis at the wellbore-section scale. Submodeling techniques were used to manage the field-to-reservoir scale discrepancy. A field model, 10 km in depth and width, was built, and a pan-cake-shaped salt body with a diameter of 7 km was embedded in the model. Trajectory optimization was performed once the vector distribution of principal stresses was provided. At the wellbore section scale, a submodel was built and the minimum safe mud-weight gradient was numerically predicted. A variation in the axial direction of the wellbore was performed to determine the optimized wellbore direction at the salt exit. The proposed integrated approach of jointly using conventional analytical tools with FEM software offers an effective method and best practice for deepwater sub-salt wellbore stability analysis.