From Fracture Gradient to Spectrum of Lost-circulation Pressures: A Paradigm Shift?

Abstract

In a naturally-fractured formation, the maximum mudweight (the lost-circulation pressure gradient) allowed along the interval is distributed between the minimum and maximum in-situ stress gradients. For a vertical wellbore drilled in an extensional stress environment, the spectrum of lost-circulation pressure gradients is dominated by the values close to the maximum (vertical) in-situ stress gradient. For a vertical wellbore drilled in an compressional stress environment, the spectrum of lost-circulation pressure gradients is dominated by the values close to the minimum (vertical) in-situ stress gradient. The minimum required length of the open-hole testing section increases with the length of the interval to be drilled, but there is no clear dependence of the minimum required length on the fracture density.