Abstract
Water jet drilling is widely used to develop coalbed methane reservoirs. The water jet drill bit is the core component, and a self-rotating bit is an economical bit because of its high rock-breaking efficiency and low energy consumption. Because the important parameters concerning the rock-breaking efficiency of these drill bits are unclear, this study carried out rock-breaking experiments on water jet rotation under different conditions of drill bit rotation speed, jet pressure, and jet impact angle. How the rock was fractured and eroded under these different conditions was analyzed. The results show that the volume of rock broken under rotary jet erosion increases exponentially with increasing jet pressure. The rock-breaking depth is the most important factor that influences the volume of rock broken, whereas the diameter of the area broken is a secondary factor. There is an optimum water jet rotation speed for the most efficient rock breakage, and this rotation speed is positively correlated with jet pressure. There is also an optimum water jet impact angle for rock breaking, and, in our experiments, this angle was 10°. The rotary impact of the water jet causes the rock to be in a three-way tension state, and this reduces the water cushion effect and jet reflection. This study can be used as a reference and guide for optimizing the design of self-rotating water jet bits and the determination of reasonable drilling parameters.
Highlights
Coalbed methane (CBM) is a high-quality source of clean energy and the main factor responsible for coal mine gas disasters
Some methods have been employed to improve the permeability of coal seams and some results have been achieved, with techniques such as hydraulic fracturing [3,4], deep hole pre-splitting blasting [5], water jet drilling [6,7], and other techniques used to increase CBM production
Differentjet jetstream streampressures, pressures, impact angles, water jetrotation bit rotation rotation speeds were to used to Different jet stream pressures, impact angles, and water jet bit speeds were used to the effects of water jets on the specimens
Summary
Coalbed methane (CBM) is a high-quality source of clean energy and the main factor responsible for coal mine gas disasters. It is necessary to adopt methods for increasing the permeability of coal seams. Some methods have been employed to improve the permeability of coal seams and some results have been achieved, with techniques such as hydraulic fracturing [3,4], deep hole pre-splitting blasting [5], water jet drilling [6,7], and other techniques used to increase CBM production. Water jet drilling is widely used for CBM development. It has the advantages of temperature reduction and dust removal, and this drilling technique does not produce sparks and is very effective at breaking rock [8]. Existing water jet bits include rotary jet bits, combined jet bits, and straight-swirling integrated
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