Anti-drilling ability of Ziliujing conglomerate formation in Western Sichuan Basin of China

The conglomerate rock is usually featured by strong heterogeneity, high abrasiveness, and poor drillability due to its complex composition and texture, which brought a huge challenge for drilling efficiency. In order to guide the drill bit selection and high-efficiency drilling, the physical, mechanical, and drillability characteristics were investigated for conglomerate rock that collected from the lower Jurassic Ziliujing formation in the Western Sichuan Basin of China. The mineral composition, SEM micro-structure, P- and S-wave velocities, uniaxial and triaxial compressive testing, drillability, abrasiveness were systematically tested and analyzed. The mechanical properties and anti-drilling ability of Ziliujing formation were proposed for a typical deep well of S-07, and the distribution characteristics were analyzed. The results indicated that the Ziliujing rock is rich-in quartz and clay minerals, due to the co-existing of strong quartz gravel and weak argillaceous cement, the Ziliujing rock shows strong heterogeneity. The relationships are roughly linear among UCS, drillability, and grinding weight loss with P-wave velocity. The Young's modulus, UCS, internal friction angle, drillability, and abrasiveness meet the Weibull distribution pattern, while only the Poisson's ratio meets the Kernel Smooth distribution pattern. Logging interpretation results reval that the Ziliujing formation has the Young's modulus of 38.61 ± 17.08 GPa, the Poisson's ratio of 0.327 ± 0.006, the internal friction angle of 49.21 ± 11.00°, the drillability of 8.04 ± 1.54, and the abrasiveness grade of 4.32 ± 1.94. The mechanical properties and anti-drilling ability of logging interpretation are in good agreement with the experimental data. The Ziliujing formation is a kind of hard rock with strong heterogeneity, high strength, poor drillability, and medium abrasiveness. Based on the characteristics of Ziliujing formations, the SV516TAUL PDC bit with non-planar cutters was selected for the field application due to the good abrasion resistance, impact resistance, self-sharpening and thermal stability of the non-planar cutters. The field application shows that the average ROP of the new type drill bit in Ziliujing formation is 2.93 m/h, and the average footage is 225.9 m. Comparing with the traditional PDC bit, the ROP of the new drill bit with non-planar cutters has increased by 67.4%, and the footage has increased by 92.1%. The results of this paper can be utilized to guide the drill bit selection and high-efficiency drilling in conglomerate formation.