Phenomena affecting penetration mechanisms of polycrystalline diamond compact bits

Khorshidian, Hossein (2012) Phenomena affecting penetration mechanisms of polycrystalline diamond compact bits. Masters thesis, Memorial University of Newfoundland.

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Abstract

A drill setup is prepared to study the influence of borehole pressure and bit hydraulics on the performance of a drill bit. -- Experimental study of bit-rock interaction shows that the negative influence of the borehole pressure on penetration mechanisms of polycrystalline diamond compact (POC) bits, in addition to the rock strengthening under elevated borehole pressure, is the accumulation of cuttings in between the face of cutters and rock surface in the zone of penetration. -- The flow of cuttings on the surface of the cutter, results in applying a confining pressure on the zone of penetration. This confinement causes a considerable rock strengthening in the zone of penetration, which increases the mechanical specific energy and reduces the rate of penetration. The value of the confinement is observed to be related to the coefficient of friction between the cutter and cuttings and the geometry of the rockcutter interaction. -- On the other hand, utilizing a bit with an appropriate jet flow significantly improves the performance of the bit. However, the experimental results indicate that there is an optimum condition for applying the hydraulic power on the bit, which yields maximum drilling efficiency. -- In addition, in a simulation of a single POC cutter-rock interaction, using the distinct element method, it has been found that there is an optimum condition for vibrations of the bit which results in the minimum energy of penetration. The optimum condition of the cutter oscillation can be defined in terms of vertical displacement amplitude and vertical velocity amplitude of the cutter while it is moving horizontally. These parameters can be changed by adjusting inertia of the cutter with respect to the horizontal speed of the cutter.

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