# Study of the Critical Speed of Ultra-High-Speed Diamond Drilling Technology in Marble
## 1 Introduction  
As the depths of oil and gas exploration increase, the need for drilling technology suitable for challenging conditions in deep hard rock drilling (such as high temperature and difficult drilling pressure application) becomes crucial. The emergence of ultra-high-speed diamond drilling (Figure 1) as a novel technology offers the advantage of elevated drilling speed with lower pressure and extremely high velocity, making it an ideal choice for accelerating drilling in deep hard rock formations. Borrowing from the 'Drilling on Mars' project, Baker Hughes TerraTek laboratory introduced the 'Smaller Footprint Drilling System for Deep and Hard Rock Environments'. The aim is to develop a mobile, low-energy, high-speed drilling system. TerraTek successfully tested ultra-high-speed (40,000 rpm) small kerf diamond coring in 2004 [1]. To adapt to full-hole drilling, continued coring, and the eventual development of downhole ultra-high-speed drives in oil fields, drill bits suitable for this system need to be designed. Under conventional conditions, speeds exceeding 1 m/s have not been used for oil and gas well drilling. The usual speed in petroleum drilling is around 150 rpm. The maximum speed of downhole air turbines can reach 40,000 rpm, but due to the action of a gear reduction box, the drilling speed is reduced to the normal mud motor or rotary drilling speed range (200 rpm). Using the same drill bit (electroplated diamond bit) as the 'Drilling on Mars' project, drilling experiments were conducted. In the speed range of 17,000-40,000 rpm, the drilling speed was much lower than that of Martian drilling (3.7-26.5 m/h). In 2006, furtherresearch was conducted to explore the specific energy requirements of drilling at ultra-high speeds. Experiments were conducted on Berea sandstone, and although MSE and ROP followed the hypothesized patterns, the values obtained in each test were still unstable. As a general trend, MSE decreased with increasing RPM, while ROP increased at higher RPM. Additionally, with increasing speed, the size of rock cuttings changed, suggesting a possible change in the removal mechanism at higher RPM. Beyond 40,000 rpm, the drill bit experienced significant balling, intensifying vibration, and increasing the demand for MSE [2,3]. In 2007, experiments using comprehensive drill bits were conducted. The ROP declined at higher weights, while the specific energy showed a significant decline with the larger bit and remained flat with the smaller one [4]. In 2010, the TerraTek laboratory conducted experiments with various drill bits used in conjunction with a turbine motor, all of which showed good ROP [5]. Although the amount of rock removed per revolution of the drill bit decreased, higher speeds could increase the ROP. Regarding ultra-high-speed diamond drilling technology, [PERSON] and others characterized its efficiency and adaptability to deep hard rock drilling, considering aspects such as cutting heat and stress changes [6]. Despite the preliminary investigations into the viability and efficiency of ultra-high-speed drilling technology, TerraTek Laboratory's findings reveal that optimal conditions for enhanced performance are not indefinitely scalable with increasing speed. Although a consistent downward trend in rock mechanical specific energy (MSE) is discernible, drilling efficiency exhibits instability and varies significantly across distinct rock types. A comprehensive examination of this technology's applicability to diverse geological formations necessitates further inquiry. For the successful and reliable deployment of ultra-high-speed drilling in practical settings, a stable and optimally determined speed range becomes pivotal. The intricacies of deep drilling encompass a myriad of rock compositions and distinct critical speed intervals, underscoring the complexity of the process. Building on the work of [PERSON] et al., who investigated dolomite using ultra-high-speed conditions, their findings supported improved drilling performance (lower MSE and higher ROP).