Experimental investigations of rate effects on drilling forces under bottomhole pressure

The purpose of this study is to examine cutting speed and bottomhole pressure effects on cutting forces acting on PDC cutters during the oil and gas drilling process. A set of single cutter tests was performed in three sedimentary rocks of different permeabilities. Dry tests were carried out at atmospheric pressure and at different cutting speeds. As previously observed in the literature, these tests show that cutting forces increase with the cutting speed, especially the normal component. The same tests were performed at 20 MPa bottomhole pressure. It appears that the cutting speed effect on cutting forces in the medium and low permeability rocks is moderate and weak, respectively. By contrast, rate effects in the highly permeable rock are significant and overcome rate effects observed in dry experiments by an order of magnitude. Interestingly, these observations are similar to those observed in submarine soil ploughing at high hydrostatic pressure. These results are believed to represent an important step into a deeper understanding of the oil and gas drilling process.