Junction Stability Study of a Fishbone Well, Offshore East Coast Canada

This manuscript presents a recent study on fishbone junction stability for a well in Offshore East Coast Canada, positioned in shallow marine storm deposited sandstone. The objective was to analyze the feasibility of the fishbone design, and to estimate the extent and type of failure at the vicinity of the fishbone junctions. A 1D geomechanical model was previously built and carefully calibrated for this field. A finite element model including formation rock and the wellbore was constructed. The geometry and curvature of the wellbore were accurately represented in the model to reflect the designed trajectory. P10 rock strength and mechanical properties were implemented to capture the behavior of weaker formations. Finite Element simulations were then performed to analyze the junction stability due to drilling of the fishbone, drilling of the main wellbore and subsequent production drawdown. Post yield plastic deformation of the rock was modeled to provide a more realistic estimation of rock failure, as calibrated by experimental data. Results of the simulation revealed the development of both tensile and shear failure zones. Drilling-induced tensile fractures occur in tensile zones. Shear failure manifests itself both at the junction and further along the main wellbore and fishbone as breakouts. Overall, the expected failures appear to be manageable with limited risk on the operations, thereby supporting the application of fishbone design in the field.