Borehole Breakouts in Black Shales - Experimental Investigations of a Transverse Isotropic Material

Within this laboratory study we try to simulate a deviated drill path frequently used in the oil- and gas as well as geothermal industry. Especially the exploitation of unconventional resources, like oil and gas shale, requires deviated drilling techniques to increase the intersection of the borehole with the low permeable rock. The rock is therefore penetrated with different drillbit sizes and orientations creating a complicated stress concentration in the circumference of the borehole. In case the stress exceeds the strength of the rock borehole breakouts develop. These failures can lead to a loss in drilling fluid, stuck pipe, reaming and the necessity to side-track a lost hole as for example observed in high-angle wells drilled in a organic-rich shale formation in the North Sea by Økland and Cook (1998).