Optimizing Drawdown Program for a Miocene Field by Applying Geomechanical Modelling to Quantify Casing Integrity Risk Available to Purchase

The field studied in this work is a deepwater Gulf of Mexico asset, producing from six (6) subsea wells. To fully understand well integrity risk and access additional reserves, a finite element geomechanics study was conducted to check for critical stress/strain limits when increasing drawdown on producers. Aside from including cement and casing as structural elements, the modelling incorporated a subsurface u stress model, geological horizons from a full-field geomodel, and pore pressure profiles from a reservoir simulator. The goal was to define specific failure onset time and location resulting from a number of potential drawdown scenarios. Given the logging evidence of cement quality and stratigraphic barriers above and below producing intervals, the production liner was considered the primary well integrity barrier, with modelling configured to evaluate the depletion required to reach both minimum yield strength, and a 0.2% plastic strain, a common industry material failure metric. Prior to this study, the operating flowing bottom hole pressure limit had been constrained based on a previous stochastic failure model conducted before the onset of field production. This previous model omitted well geometry, casing, and cement, all of which are critical elements to an appropriate geomechanics modeling. The results showed that at current drawdown and depletion levels, some wells had exceeded the nominal yielding strength of their liner, requiring a second level of screening based on critical plastic strain. This strain-based criterion provides a more insightful view into the mechanical integrity of the liner, allowing for a better informed decision on whether to proceed or not with further drawdowns. For simulations using a conservative drawdown program forecast, it was identified that the wells with the highest risk of failure would not exceed 0.8% plastic strain over the life of the field. This finding indicated that despite exceeding the nominal strength (stress-based criterion), limited plastic deformation of the liner is to be expected, but sufficiently small as to not compromise the mechanical integrity of these wells during the lifetime of the field.