Integrated Sub-surface Approach for Narrow Margin Drilling in Duva Region: A Case Study from North Sea

Lost circulation in Lower Kyrre and Tryggvason formations and shear failure in Rødby and Åsgard formations is a well-known challenge in the Duva region (southern part of North Sea). Covering above mentioned formations in one 12 ¼” section was the chosen concept, to deliver the challenging well trajectories. The pre-planning included a geomechanical forecasting of the drilling window for the planned trajectory.

Integrated approach of drilling event analysis with recently acquired image data in drilled offset geo-pilot well from the Lower Kyrre and Tryggvason formation provided valuable information on fractures and drilling events in the region. Core test results used to create empirical correlation to estimate rock strength properties of the formations. Correlations available in public domain for North Sea (Fuller correlation for static rock properties and internal friction angle from gamma ray) used to estimate mechanical properties. Poro-elastic approach with strain terms derived from the available leak-off test data and lost circulation events provided the realistic horizontal stress profile. A final drilling window was prepared using Modified Lade failure criterion. Integrated geomechanics support in real-time and equivalent circulating density management helped successful drilling in the region.