Influence of Weight-on-Bit on Percussive Drilling Performance

Abstract

A phenomenological model for percussive drilling systems is proposed in this paper to explain the experimentally demonstrated existence of an optimal weight-on-bit (WOB), for which the rate of penetration (ROP) is maximized. Several hypotheses have been previously proposed to explain this universal characteristic of percussive drilling, including increased wear of the bit, reduced indexing, and poor cleaning of debris under excessive WOB. Motivated by experimental evidence, we instead consider an increase of the pseudo-stiffness of the bit-rock interface (BRI) with increasing WOB, and investigate its effect on the impact energy transmitted to the rock. The 1D 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 BRI pseudo-stiffness influences the incident wave and associated energy transmitted from the bit to the rock. As a consequence, the drilling efficiency is affected by the dependence of the BRI stiffness on the WOB. The model indicates that there exist optimal conditions for the energy transfer from the bit to the rock in terms of the impedance ratio and the BRI stiffness/WOB. Thus it confirms that there is a sweet spot as seen in practice, which suggests that the root cause of the existence of a sweet spot in the ROP-WOB relationship lies in the nature of the BRI laws, rather than with issues related to bit indexing, bit wear, and/or cleaning of the debris.

Recent advances in DNA-encoded dynamic libraries

“…DEDL selection is compatible with non-immobilized targets, making it an attractive method of choice for interrogating complex biological targets, such as endogenous proteins, membrane proteins on live cells, or even intracellular targets. 10,60,158 Furthermore, multivalency is ubiquitous and plays pivotal roles in biology; nature has exploited multivalency to achieve strong, specific, but reversible molecular interactions in biological systems. 159 DEDLs may be particularly suitable for discovering novel multivalent binders, because of their reversible, dynamic nature and their programmability in ligand assembly.…”

“…In the past two decades, the emergence of the DNA-encoded library (DEL) technology, also called DELT, has replaced spatial encoding with DNA encoding in chemical libraries, thus overcoming the throughput limit of traditional HTS and being much more affordable and accessible to researchers. [2][3][4][5][6][7][8][9][10][11] For instance, many companies and institutions are offering DEL selection services: premade DEL kits 12 for direct use in selections, and reagent kits 13 for custom DEL synthesis are also available to meet the needs of individual researchers. Furthermore, with the recent expansion of DNA-/DEL-compatible reaction toolkits, 2,6,7,[14][15][16] DELs can access much greater chemical space, which has been a major driver for its adoption in the pharmaceutical industry.…”

DNA‐Encoded Libraries: Towards Harnessing their Full Power with Darwinian Evolution

“…[123,124] Li and co-workers have extensively worked with photocrosslinking groups (aryl azide, benzophenone, diazirene) to identify the best binders in DEL selections. [125] Their first design utilized a short 8 nt ssDNA containing the photocrosslinking group (PC-DNA) which hybridizes with a primer binding site (PBS) of the DEL, close to the binding moiety (Figure 5B). Upon protein binding and short light irradiation, the binders and their PC-DNA strand become covalently linked to the target.…”

Peculiarities of drilling hard rocks using hydraulic shock technology

“…According to the conditions of occurrence, groundwater is divided into three types: groundwater located in the uppermost layer of soil; soil lying on the fi rst permanent waterproof layer from the surface; interstratal type, located between two waterproof layers. They are widely used for the needs of industry and housing and communal services and irrigation of pastures [3]. One of the most eff ective drilling technologies in soft and medium-hard rocks is drilling with hydropneumatic transport of destroyed material along a double concentric column and in rocks of high hardness, the technology of percussive-rotary drilling using hydro and pneumatic hammers, and pneumatic installations [4].…”