Evaluation of Cuttings Transport Impact on Percussive Drilling Performance

Abstract

Although pneumatic percussive tools were introduced about one century ago, fundamental knowledge about the complex process of rock drilling with such tools is still lacking, including the rock fragmentation and the cuttings transport influence on the deep drilling efficiency. In this paper, an integrated model is proposed from a hydrodynamic point of view to address the critical drilling depth that can be achieved with a Down-The-Hole (DTH) pneumatic hammer for a given pressure delivered by the compressor. A closed loop drilling system, reduced to (i) the air compressor, (ii) the pneumatic hammer and (iii) the well annulus, is combined with an empirical ROP law and an analytical multiphase (air, rock cuttings) transport model to predict the pressure loss evolution with depth. Available laboratory data have been used to calibrate the multiphase transport model and assess its ability to account for the cutting size distribution and mass flow influence on the pressure drop. The critical depths predicted by the integrated model is discussed for various drilling cases studies (hammer parameters, well geometry, compressor performance).