A drilling campaign in a mature field presents challenges beyond extended-reach drilling (ERD) profiles, with water-based mud and depleted reservoirs introducing added complexities such as abnormally high friction factors and narrow drilling windows. Iterative torque and drag (T&D) and buckling (stiff-string model-based) and hydraulic simulations were conducted for multiple tapered string combinations. The results, combined with operational constraints, guided the selection of a string configuration that allowed planned total depths (TDs) to be deemed feasible.
Methodology
The industry has used conventional models to simulate T&D in the vast majority of cases, subsequently combining them with hydraulic simulations to cross-check and validate equivalent-circulating-density (ECD) evolution. However, conventional T&D models are in essence soft-string models of the tubulars (assuming that the drillstring is a soft and malleable assembly always on the low side of a deviated borehole). While these models provide a good approximation of forces and contact loads in perfectly smooth well trajectories, they become completely inappropriate in realistic scenarios where trajectories become more complex or where tortuosity (micro or macro) and local doglegs are in play.
