Geomechanics of fracture caging in wellbores

Abstract

This study highlights the occurrence of so-called 'fracture cages' around underbalanced wellbores, where fractures cannot propagate outwards due to unfavourable principal stress orientations. The existence of such cages is demonstrated here by independent analytical and numerical methods. We explain the fracture caging mechanism and pinpoint the physical parameters and conditions for its control. This new insight has great practical relevance for the effectiveness and safety of drilling operations in general, and hydraulic fracturing in particular. Fracture caging runaway poses a hazard for drilling operations in overpressured formations. Recognition of the fracture caging mechanism also opens up new opportunities for controlled engineering of its effects by the manipulation of the Frac number in wells in order to bring more precision in the fracking process of tight formations. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.