等离子体电脉冲钻井破岩机理的电击穿实验与数值模拟方法

等离子体电脉冲钻井技术为一种高效破岩钻井技术。对4种岩石在80 kV固定输出电压、重频率为2.5 Hz下进行了电脉冲击穿实验。实验发现,电脉冲破碎结果中存在贯穿破碎和未贯穿破碎2种状貌,并针对产生这两种状貌的原因进行了分析。从电击穿角度明确了单次脉冲破岩效率的评价指标——能量转换效率η_e,并提出了一种新的岩石介质击穿模型——概率发展模型(PDM),借助PDM和简化的电击穿电路研究了单脉冲击穿时电路结构参数对破岩能耗分配的影响规律。基于电脉冲击穿实验参数和PDM生成的等离子体通道轨迹提出了等离子体电脉冲钻井破岩机理研究的数值模拟方法,利用该数值模拟方法研究了在地层压力为0～30 MPa下、直径为41 mm的电极钻具在加载峰值电压为60 kV时的破岩规律。

Electrical breakdown experiment and numerical simulation method of rock-breaking mechanism of plasma electric pulse drilling

This paper introduces and studies a kind of high-efficiency rock breaking drilling technology, i.e., plasma electric pulse drilling technology. First, electric pulse breakdown experiments were carried out on 4 kinds of rocks at a fixed output voltage of 80 kV and a dual frequency of 2.5 Hz. The experiment results present two types of crushing morphology, i.e., throughout crushing and non-throughout crushing, and the relevant reasons are also analyzed. Then, from the perspective of electrical breakdown, this paper first determines the evaluation index of single-pulse rock breaking efficiency, namely energy conversion efficiency η_e, and proposes a new dielectric breakdown model for rock, namely the probabilistic development model (PDM). With the help of PDM and the simplified electrical breakdown circuit, this paper studies the general influence laws of the circuit structure parameters on the distribution of rock-breaking energy consumption during single-pulse breakdown. Finally, based on the parameters of the electric pulse breakdown experiment and the trajectory of the plasma channel generated by PDM, this paper proposes a numerical simulation method for studying the rock-breaking mechanism of plasma electric pulse drilling technology, and studies the rock-breaking law of the electrode drilling tool with a diameter of 41 mm at the peak voltage of 60 kV under the formation pressure of 0-30 MPa.