Experimental and numerical investigation of drilling performance in anisotropic formations and with axial compliance at the bit

As drilling performance is a key indicator of success in the oil and gas industry, numerous academic and industry organizations have been researching how to improve drilling with regard to time and efficiency. A study is done to determine rock isotropy by applying mechanical and physical measurements, along with oriented drilling, as anisotropy has a distinct impact in drill performance. Based on these findings, the study then performs drilling experiments on anisotropic rock in order to gauge the effect of anisotropy on drill efficiency. The tests employ a dual-cutter PDC bit, 35 mm, and use several different WOB under constant atmospheric pressure and water flow. In looking at relationships of WOB, ROP and DOC, it is clear that increasing the WOB leads to a subsequent increase in DOC and ROP. Furthermore, increasing the WOB also leads to increases in cutting sizes as well as material anisotropy. At Memorial University in Newfoundland, Canada, the Drilling Technology Laboratory (DTL) has developed a passive vibration-assisted rotational drilling (p-VARD) tool which enhances drill rates of penetration (ROP) in lab tests. Previous lab experiments, including simulations, point to axial vibrations having significantly improved ROP. These experiments are carried out by applying the Discrete Element Method (DEM) simulation, using the DTL p-VARD configurations tool. To gauge the tool’s cutting efficiency, a PFC2D (i.e., particle flow code in two dimensions) numerical model is utilized in simulating micro-crack generation/propagation for the drill procedure on synthetic rocks. The pVARD tool compares the downhole vibration with the rigid drill configuration of conventional rotary drilling, using low, medium and high spring compliance. Next, output parameters for ROP, MSE, and DOC are analyzed for pVARD/ non-pVARD configurations. The overall results point to the pVARD tool having a positive impact in downhole drilling, showing improvements in DOC, MSE, and ROP.