Improving well-drilling technology is increasingly important in the oil and gas industry. Among these efforts, the continuous improvement of the polycrystalline diamond compact (PDC) drill bits is particularly significant. The PDC cutter is a crucial element of a PDC drill bit and the determining factor for the bit performance. Thus, optimizing the design of PDC cutters will improve drilling efficiency and reduce operational costs. Using the finite element method, this paper aims to develop a numerical model to accurately evaluate the cutting efficiency of 3D shaped PDC cutters and, in turn, facilitate the cutter shape design optimization. In this study, we used the Drucker-Prager plastic model with a damage law to simulate the constitutive behavior of the rock. The parameters used in the Drucker-Prager model were obtained by matching the numerical rock unconfined compressive strength (UCS) test results with the actual rock UCS testing data. We simulated the rock cutting process using the developed rock model. We compared the cutting forces, normal forces, and mechanical specific energies (MSEs) of various 3D-shaped cutters with those of the flat cutter. Finally, we verified the accuracy of the numerical model with lab tests and field trials. From numerical results, we found that 3D-shaped cutters’ cutting forces, normal forces, and MSEs are significantly smaller than those of the flat cutter, and such differences become more and more pronounced as the depth of cut (DOC) increases. Specifically, the difference of MSEs between the 3Dshaped cutters and the flat cutter increases from 8% at DOC of0.5mm to 23% at DOC of 4mm. The lab results verified the accuracy of the numerical results. Through field tests, we further compared the performances of the 3D-shaped cutter PDC bits with the flat cutter PDC bit. The 3Dshaped PDC bits had increased footage by 28% and a rate of penetration (ROP) of 9% in real-life applications. In this study, we developed a field-proven rock cutting finite element model which effectively and reliably facilitated the design of 3D-shaped cutters. Compared with lab-based methods, the numerical model can predict the cutting efficiency of 3D-shaped cutters at a much lower cost. By utilizing the numerical model, we can efficiently evaluate and thus quickly optimize the performance of the design of 3D-shaped PDC cutters.

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The Weiyuan shale gas field faces problems of long drilling cycles and high development costs. Improving the drilling efficiency of polycrystalline diamond compact bits in shale formations will significantly reduce the overall well cost and duration. Previous applications have demonstrated that conventional PDC bits on the market cannot meet the demand for drilling acceleration. In this work, a new three-dimensional concave-shaped PDC cutter was proposed to improve drilling efficiency. The special 3D concave-shaped cutter has two symmetrical curved ridges on the concave surface and a circular plane at the center. The cutting mechanism of the new 3D concave-shaped cutter has been studied by laboratory experiments and numerical simulations. The research data revealed that, compared with a flat cutter, the tangential force of the original 3D concave-shaped cutter was reduced by 1.4%–35.0%, the axial force was reduced by 6.7%–37.6%, and the mechanical specific energy (MSE) was reduced by 1.6%–35.59%. Simulations showed that the shear action of the 3D concave-shaped cutter was divided into two continuous parts, with the sides and the center surface being stressed successively, which is helpful for extending shear cracks, forming trilobal cuttings, and improving cutting efficiency. With the special 3D concave-shaped cutter, an 8½-inch drill bit was designed and manufactured and tested on the Longmaxi shale in the Weiyuan block. Through field tests, we further compared the performance of the 3D concave-shaped cutter PDC bit with that of the flat cutter PDC bit. The 3D concave-shaped PDC bit had a 41.8% better footage and 22.6% better rate of penetration (ROP) in field test.