A new approach to determine the rock/shale compressive strengths using drilling data

ABSTRACT: The objective of this paper is to investigate the influence of rake angle on the magnitude of the intrinsic specific energy and the inclination of the force acting on the cutting face of a Polycrystalline Diamond Compact sharp cutter while tracing a groove on the surface of a rock/shale sample. An extensive and comprehensive set of cutting experiments are performed on a range of quarry rock samples and black/red shale formations using a state-of-the-art cutting equipment. Additional uni-axial compression (UC) tests were conducted on the specimens to independently estimate the compressive strength of each individual specimen. The results conform with the previous studies by other researchers; the intrinsic specific energy (𝜀) is in good agreement with the uni-axial compressive strength (𝑞) of the samples when the cutter is positioned at back rake angles between 5° and 20°. New results on a few rock samples were also obtained by performing novel experimental tests at very large rake angles (𝜃> 70°) as well as negative rake angles, showing that the intrinsic specific energy increases dramatically once the back rake angle exceeds 75°.