# Characterization of Dolomite Stone Broken Under Axial Impact
## 1 Introduction  
The progress in oil drilling technology, especially in the exploration of deeper geological layers for the extraction of ultra-deep oil and gas, is critically significant for maintaining national energy security. However, initiatives focused on deep and ultra-deep drilling encounter numerous challenges, such as inefficiencies in rock fragmentation, slow mechanical drilling rates, high operational expenses, and considerable difficulties in achieving cost reductions [1; 2; 3; 4]. The optimization of efficiency and performance in rock-breaking mechanisms utilized in drill bits has become a focal point of research within the discipline. To tackle the complexities associated with the effective fragmentation of deep, hard rock formations, a range of acceleration techniques has been developed. These techniques encompass vibratory percussion drilling technology, high-pressure jet drilling technology, laser drilling technology, plasma rock-breaking technology, and high-pressure pulsed current-assisted rock-breaking technology, among others. High-pressure jet drilling technology leverages hydrodynamic principles and has demonstrated effective performance in medium-soft geological formations [5; 6; 7]. In contrast, laser drilling and plasma rock-breaking technologies have primarily been confined to laboratory studies, lacking straightforward and efficientimplementation tools and methodologies [8; 9; 10; 11; 12; 13]. Axial vibration impact rock-breaking technology employs downhole impact tools to generate force on the drill bit, thereby enhancing the conventional shear rock-breaking mechanism. This approach significantly improves rock-breaking efficiency while minimizing drill bit wear [14; 15]. The vibratory percussion drilling technology has established itself as one of the most prevalent methods employed in current practices [16; 17]. Unlike traditional hydraulic pulse-assisted rock-breaking methods, vibro-impact technology exhibits reduced reliance on drilling equipment and does not necessitate the upgrade of high-pressure pumps. By utilizing a periodic alternating load to apply axial impact forces on the drill bit, this technology increases the penetration depth of the drill bit's cutting cutters, effectively improving the stress conditions of the rock at the well's bottom and mitigating the repetitive cutting associated with pressure-holding effects [18]. Furthermore, the alternating load facilitates brief contact between the PDC cutter and the rock, resulting in a significantly smaller contact area compared with conventional rock-breaking techniques. This reduced contact time and area effectively diminish the high temperatures generated during drilling, thereby alleviating wear and extending the drill bit's lifespan. The adaptability of drilling parameters, such as drilling pressure, rotational speed, and impact frequency, allows for optimization based on the lithology of various formations, thereby broadening the applicability of this technology. By vigorously carrying out the research and technology promotion of axial impact rock-breaking drilling speed-up technology, it is expected to overcome the technical pain points of low penetration and difficult speed-up of high-temperature and high-pressure hard rock strata in deep earth and effectively accelerate the pace of exploration and development of domestic oil and gas resources, which is not only related to the national economy and people's livelihoods but also related to the national energy strategic security [19; 20]. Numerical simulations can proficiently delineate the interaction dynamics between the tool and rock throughout the impact process [21; 22; 23]. The kinetic model provides an explanation for the experimentally observed decrease in drilling speed by proposing a dry friction mechanism. This mechanism adeptly replicates the nonlinear characteristics linked to the intermittent impact process through a dual friction framework, resulting in a pattern that closely mirrors the actual impact force.