Key Takeaways & Executive Findings
- •• Multi-dimensional percussion (axial + torsional) enhances rock fragmentation in HDR formations, promoting brittle-ductile mixed failure in granite and brittle fragmentation in carbonatite. • Frequency-domain analysis of penetration force signals reveals increased net drilling energy and intensified fragmentation under multi-dimensional percussion. • Optimal impact frequency combinations are 15 Hz axial + 15 Hz torsional for granite and 30 Hz axial + 15 Hz torsional for carbonatite, maximizing drilling efficiency. • Field validation in geothermal well Fushen-1 confirms the reliability of the optimization approach for practical HDR drilling.
Abstract
Percussion drilling is a promising approach for hot dry rock (HDR) fragmentation. However, understanding of HDR fragmentation mechanism under multi-dimensional percussion remains limited and hinders the corresponding drilling performance. Herein, an innovative true triaxial multi-dimensional percussion device was developed for the study of HDR fragmentation mechanism under in-situ temperature and stress conditions. Multi-dimensional percussion, involving both axial and torsional components, was applied to drilling in granite and carbonatite rocks sampled from the typical HDR target areas. Multi-scale visualization techniques and a whale optimization-variational mode decomposition algorithm were employed to investigate the rock failure patterns and drilling energy characteristics. Results indicated that multi-dimensional percussion enhances brittle-ductile mixed failure in granite, characterized by transgranular, intergranular, and combined fracture patterns that promote rock cracking. In contrast, carbonatite drillhole displays enhanced brittle fragmentation and tortuous failure surface dominated by transgranular fracture pattern. Frequency-domain characteristics of penetration force signals for multi-dimensional percussion, especially the significant dominant frequency, amplitude, and high-frequency dissipation, indicate an increase in net energy for drilling into HDR and intensified rock fragmentation. Further, the effect of impact frequency on rock fragmentation performance was emphasized to maximize drilling efficiency. The optimal regulation schemes between axial and torsional impact frequencies are identified as 15 Hz + 15 Hz for granite and 30 Hz + 15 Hz for carbonatite. The reliability of the optimization approach was validated through a field test that employed a novel impactor in the geothermal well Fushen-1.
1. Introduction
Hot dry rock (HDR) geothermal resources represent a green, efficient, and stable form of renewable energy with substantial potential to replace fossil fuels for cleaner production in deep geological settings. The energy stored in HDR at depths of 3–10 km within the Earth’s crust is estimated to be approximately 30 times greater than that in global oil, gas, and coal reserves [1,2]. The enhanced geothermal system (EGS) is a promising method for exploiting HDR resources. However, the high drilling cost remains a major barrier to the economic feasibility of EGS, typically accounting for 30%–60% of the total investment in hydrothermal power plants [3,4]. This can be explained by the complex geological conditions of HDR formations, which are characterized by high-temperature, high-pressure, and greater rock hardness compared to oil, gas, and medium-low temperature geothermal reservoirs [5]. Construction of EGS wells requires drilling into the basement of the continental crust, composed of hard crystalline igneous or metamorphic rocks, making the well drilling difficult.
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Zhaowei Sun, Xiaoguang Wu, Zhongwei Huang, Gensheng Li, Xianzhi Song, Zongjie Mu, Huaizhong Shi, Wenhao He, Berdiev Alisher (2025). A multi-dimensional percussion method for efficient drilling in HDR formations: Rock fragmentation mechanism, drilling energy analysis, and performance optimization. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.07.005
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Frequently Asked Questions
What is multi-dimensional percussion drilling?
Multi-dimensional percussion drilling involves applying both axial and torsional impact components to the drill bit, enhancing rock fragmentation efficiency compared to conventional axial-only percussion.
How does multi-dimensional percussion affect rock fragmentation in HDR formations?
It promotes brittle-ductile mixed failure in granite, characterized by transgranular, intergranular, and combined fractures, while in carbonatite it enhances brittle fragmentation with tortuous failure surfaces dominated by transgranular fractures.
What are the optimal impact frequencies for granite and carbonatite?
For granite, the optimal combination is 15 Hz axial and 15 Hz torsional; for carbonatite, it is 30 Hz axial and 15 Hz torsional.
How was the optimization approach validated?
The approach was validated through a field test in the geothermal well Fushen-1 using a novel impactor, confirming its reliability for practical HDR drilling.
What is the significance of frequency-domain analysis in this study?
Frequency-domain analysis of penetration force signals reveals increased net drilling energy and intensified rock fragmentation under multi-dimensional percussion, providing insights into the drilling energy characteristics.
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