Abstract
<title>Abstract</title> <p>To address challenges such as unclear rock-breaking mechanism, slow drilling speed, and high costs in plastic mudstone formations of the southwest Weizhou, this paper proposes three novel-shaped cutters: forward-inclined cutter, concave axe cutter, and thorn cutter. First, based on the rock mechanics experiments of the target mudstone, a new shaped cutter-mudstone thermomechanical coupling model was established using the D-P constitutive model. Then, numerical simulation studies revealed the rock-breaking mechanism of the shaped cutters: The unique cutter surface structure of the forward-inclined cutter forms a "scraping" rock-breaking mode, which enhances the chip-breaking ability of the cutter, and reduces repeated rock crushing at the bottom of the well; The concave axe cutter and thorn cutter engage the rock formation through point-and-line contact, achieving "plowing" and "puncture" effects in mudstone. This enhances the teeth's penetration capability and improves rock-breaking efficiency. Through rock-breaking simulations of the novel shaped cutters with different structural characteristics, cutting parameters, and cutter arrangement parameters, the optimal parameters for the target formation were obtained: forward-inclined cutter with a tooth surface angle of 12°, diameter of 19 mm, back rake angle of 3°, and tooth spacing of 7.6 mm; thorn cutter with a tooth edge length of 1.5 mm, diameter of 16 mm, back rake angle of 15°, and tooth spacing of 6.4–8.0 mm; concave axe cutter with a tooth edge height of 1.6 mm, diameter of 16 mm, back rake angle of 10°, and tooth spacing of 4.8–6.4 mm. Based on the above research results, three types of personalized PDC bits with novel-shaped cutters were designed and developed, all of which achieved good results in field applications. The average rate of penetration (ROP) was increased by 20–127%, providing effective support for drilling speed-up in marine plastic mudstone and other formations.</p>