Abstract
As the exploration and drilling of oil, natural gas and geothermal wells are expanding continuously, research into high-efficiency rock drilling technology is imperative. High-voltage electro pulse boring (EPB) has the advantages of high rock breaking efficiency and good wall quality, and is a new and efficient potential method of rock breaking. The design of electrode drill bits and the selection of drilling process parameters are the main obstacles restricting the commercialization of EPB. Accordingly, it is necessary to determine the influences on high-voltage EPB. In this study, based on the equivalent circuit of high-voltage electro pulse breakdown, a mathematical model of high-voltage electro pulse discharge in rock is established. Meanwhile, a numerical simulation model of high-voltage EPB of hard granite is established based on a coaxial cylindrical electrode structure, which is often used for electrode drill bits. The simulation analysis software Comsol Multiphysics (Comsol Multiphysics®5.3a, COMSOL Co., Ltd., Stockholm, Sweden) is used to study the influences of granite composition, electrode spacing and electrode shape on the high-voltage EPB process. In addition, the influences of electrical parameters on high-voltage EPB are calculated according to a model of high-voltage electro pulse discharge in rock. Finally, it is demonstrated that high-voltage EPB is influenced by granite composition, electrical parameters, electrode spacing, and electrode shape, and the relationships between these factors are obtained. This study is of guiding significance for improving rock breaking efficiency, reducing energy loss, designing electrode drill bits and selecting drilling process parameters.
Highlights
The exploration and drilling of oil, natural gas and geothermal wells are expanding continuously.Traditional mechanical drilling techniques have the disadvantages of low efficiency and high cost when used for deep and ultra-deep holes and hard rock such as granite
This paper presents models of (1) the high-voltage electro pulse boring (EPB) of hard granite and (2) high-voltage electro pulse discharge in rock
A mathematical model of high-voltage electro pulse discharge in rock, and an EPB numerical simulation model are described
Summary
The exploration and drilling of oil, natural gas and geothermal wells are expanding continuously. EPB [1], a type of high-voltage electro pulse discharge drilling, has high rock-breaking efficiency and produces good wall quality. With high-pressure pulse with a rising time of less than 500 ns [5,6], the breakdown field strength of the rock is less effect is called electrohydraulic rock breaking. Electrode drill bits and the selection of drilling process parameters are the main obstacles to the commercialization of high-voltage electro pulse rock breaking. To improve the rock breaking efficiency and energy utilization of the electrode drill bit, it is necessary to analyze the influences on high-voltage. Broken rock is returned to the ground by the circulating water medium
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