A Timescale Analysis of Percussive Drilling
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/2739532Utgivelsesdato
2021Metadata
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Sammendrag
Percussive drilling (PD) tools are widely recognized to be more efficient for drilling hard rock formations than conventional rotary drilling equipment. Thus, PD tools have been used to drill blast holes in mining and construction operations, to explore shallow oil and gas reservoirs, and to harvest deep geothermal energy. However, negative factors such as risks in drilling operations and economical uncertainties have limited its widespread applications in the oil and gas industries. Therefore, more research, for instance, on the optimal design of the PD tools and on the determination of the optimal drilling parameters, is required to advance the knowledge of this technology.
A 1D dynamic model based on scalar wave theory is first developed in the thesis to understand the PD behaviors and associated drilling performance. The model approximates the dynamics underlying the drilling process by assuming that the impact of the hammer generates a longitudinal wave in the bit. It is shown that the bit-rock interface (BRI) pseudo-stiffness influences the stress and associated energy transmitted from the bit to the rock. According to this model, there exists an optimal BRI stiffness for the energy transfer from the bit to the rock, provided that the bit/rock impedance ratio is small.
A further insight into the PD tools reveals that the PD dynamics is primarily characterized by different time scales that arise from the production, propagation and reflection of the impact wave. Accordingly, the drilling performance of the different classes of percussion tools can be analyzed within a unified theoretical framework, where the models are reduced to their most essential components. Our analysis identifies the maximum efficiency in the parametric space of time scale ratios; the efficient impact energy transmission can be understood as representing an optimum match of the different time scales. For instance, maximum performance is achieved with a simplified top-hammer PD tool if the two time scales that characterizing the duration of the response of the bit/rock interface to an impulse load and the duration of the pulse generated by the impact of the hammer are equal.
Furthermore, a more comprehensive phenomenological PD model is proposed, which accounts for the hammer/bit impedance contrast, as well as for the hammer/ bit and bit/rock interactions. The model is employed to investigate the unloading slope, the rock radiation effect and the nonlinear bit-rock interaction on the impact transmissions and associated energy partitioning. It is of particular interest to note that there is an optimal BRI pseudo-stiffness to maximize the energy transmission on rock fragmentation. This result is further investigated by introducing an experimentally observed nonlinear force-penetration response as the boundary condition at the BRI. The analysis shows that an optimal weight-on-bit (WOB, also known as thrust force/feed force) force exists to preload the BRI to reach an optimal pseudo-stiffness that can maximize the energy transmission. In this case, this study successfully reproduces an optimal WOB as observed in the PD tests. This is different from the traditional view of the optimal WOB, which corresponds to the minimum thrust required to counteract the rebound of the drill before the next impact. This analysis thus could provide a new insight into the optimal drilling operation. However, this needs further investigation, in particular, a rigorous comparison between the threshold WOB from the traditional view and the predicted WOB in this thesis.
Består av
Paper 1: Song, Xianfeng; Aamo, Ole Morten; Kane, Pascal-Alexandre; Detournay, Emmanuel. A Phenomenological Model of Percussive Drilling: Review of Experimental Evidence. I: ARMA-CUPB Geothermal International Conference. American Rock Mechanics Association (ARMA) 2020 ISBN 9781510857582.Paper 2: Song, Xianfeng; Aamo, Ole Morten; Kane, Pascal-Alexandre; Detournay, Emmanuel. Influence of weight-on-bit on percussive drilling performance. Rock Mechanics and Rock Engineering 2020 s. 1-15 https://doi.org/10.1007/s00603-020-02232-x
Paper 3: Song, X., Aamo, O.M., Kane, P.A. and Detournay, E., 2020. A Time Scale Regard on Percussion Drilling
Paper 4: Song, X., Aamo, O.M., Kane, P.A. and Detournay, E., 2020. A comprehensive phenomenological model of the percussive drilling tools.