Abstract
The Brazilian pre-salt operation presents many technological challenges. Among the key aspects for a successful operation, the choice of drilling fluid is important to avoid structural problems and predict the final well caliper. Drilling operation simulations can be used to indicate operational conditions and assist the choice of the drilling fluid. A simulator has been developed to represent drilling, circulation and static operations involving well drilling processes considering simultaneous effects of solubility and salt creep. The main objective is to avoid wellbore enlargement due to salt solubility in water-based fluids. A bad fluid choice can lead to column imprisonment or a wellbore caliper increase; both effects could compromise the well structure and add difficulties and costs in drillings operations. The model implemented is based in salt transport equations and mass transfer adjusted correlations. The common ion effect is considered in presence of more than one salt. Initial development did not include salt creep and influence of drill cuttings size. The present work adds these effects and evaluates their influence in the final caliper. The salt creep effect is computed as a decrement in well radius, which is obtained in a deformation rate table as a function of fluid density and depth. The authors propose an analysis of salt creep effect and drill size cuttings in a real case study. The need for new adjustments in mass transfering correlations in the solubilization modelling is evaluated and its impacts are presented. The change in the well geometry during drilling, due to solubilization and creep of the salt formations is computed in a dynamic mesh. The application estimates a final wellbore caliper after a sequence of operations in a drilling phase. Such estimate provides arguments for an optimized drilling fluid selection. This work contributes to improve salt drilling operations, avoiding well losses and reducing drilling time and cost.
