Conglomerate reservoirs present significant technical challenges during drilling operations due to their complex mineral composition and heterogeneous characteristics, yet the quantitative relationships between mineral composition and microscopic mechanical behavior remain poorly understood. To elucidate the variation patterns of conglomerate micromechanical properties and their mineralogical control mechanisms, this study develops a novel multi-scale characterization methodology. This approach uniquely couples nanoindentation technology, micro-zone X-ray diffraction analysis, and machine learning algorithms to systematically investigate micromechanical properties of conglomerate samples from different regions. Hierarchical clustering algorithms successfully classified conglomerate micro-regions into three lithofacies categories with distinct mechanical differences: hard (elastic modulus: 81.90 GPa, hardness: 7.83 GPa), medium-hard (elastic modulus: 54.97 GPa, hardness: 3.87 GPa), and soft lithofacies (elastic modulus: 25.21 GPa, hardness: 1.15 GPa). Correlation analysis reveals that quartz (SiO₂) content shows significant positive correlation with elastic modulus (r = 0.52) and hardness (r = 0.51), while clay minerals (r = −0.37) and plagioclase content (r = −0.48) exhibit negative correlations with elastic modulus. Mineral phase spatial distribution patterns control the heterogeneous characteristics of conglomerate micromechanical properties. Additionally, a random forest regression model successfully predicts mineral content based on hardness and elastic modulus measurements with high accuracy. These findings bridge the gap between microscopic mineral properties and macroscopic drilling performance, enabling real-time formation strength assessment and providing scientific foundation for optimizing drilling strategies in heterogeneous conglomerate formations.

Axial–torsional coupled impact drilling (ATCID) technology represents a promising solution for overcoming the drilling challenges posed by conglomerate formations, which are characterized by strong heterogeneity, high abrasiveness, and poor drillability. However, the optimal parameter matching relationships and their influence patterns on mechanical specific energy (MSE) remain unclear. This study employed self-developed true triaxial impact rotary rock breaking equipment with conglomerate cores from the Junggar Basin to systematically investigate the effects of weight on bit (WOB), rotational speed (RPM), axial impact frequency, and torsional impact frequency on MSE through orthogonal experimental design. The results demonstrate that the parameter influence ranking on MSE is as follows: torsional impact frequency > WOB > RPM > axial impact frequency, with torsional impact frequency exhibiting the largest range value (87.5 MPa). ANOVA reveals that the interaction between axial and torsional impact frequencies is the dominant controlling factor, contributing 22.8% to MSE variation with high statistical significance. The optimal parameter combination yields the minimum MSE (103 MPa): 19 kN WOB, 20 r/min RPM, 20 Hz axial impact frequency, and 20 Hz torsional impact frequency, representing a 69.1% reduction compared to the maximum value. Response surface analysis revealed that increasing WOB significantly reduces MSE, RPM exhibits positive correlation with MSE, and synergistic effects occur when both impact frequencies reach high values simultaneously. A nonlinear MSE prediction model incorporating main effects, quadratic terms, and interaction effects was established with R² = 0.8240 and a mean absolute percentage error of 9.26%. The research findings provide an essential theoretical foundation for parameter optimization and engineering applications of ATCID technology, offering significant implications for enhancing drilling efficiency in conglomerate and other challenging hard rock formations.

Subglacial drilling through polar ice–rock transitional zones is frequently hindered by severe load fluctuations and instability induced by strong formation heterogeneity. This study investigates the coupled drilling mechanics across pure ice, an ice–rock mixture, and bedrock using a fracture-mechanics-based finite–discrete element method (F-DEM) with a strain-softening constitutive model for brittle ice. The simulations quantify the evolution of drilling force components and torque under varying gravel content, weight on bit (WOB), and rotational speed. Results show that drilling responses are strongly governed by formation-dependent mechanical behavior, transitioning from stable periodic fluctuations in pure ice to impact-dominated irregular variations in mixtures, and finally to high-level continuous resistance in bedrock. Rotational speed significantly influences drilling stability through its interaction with formation properties; lower speeds effectively suppress transient load fluctuations in pure ice and mixtures, whereas moderate speeds mitigate stick–slip effects in rock. Conversely, WOB primarily controls axial penetration while also influencing load fluctuation characteristics. The optimal WOB is identified as 10 kN for stable shearing in pure ice, reduced to 7.5 kN in mixtures to buffer lateral impacts, and increased to 10 kN in rock for efficient penetration and stable cutting. Furthermore, increasing gravel content amplifies force and torque sensitivity, transitioning the system from stable periodic behavior to impact-driven instability. These findings emphasize the necessity of a layer-dependent adaptive control strategy, providing a quantitative framework to optimize parameters and drill-bit design for safer, more efficient subglacial operations.