【作者】 章志成；

【导师】 闫克平；

【作者基本信息】 浙江大学 ， 化学工程与工艺， 2013， 博士

【摘要】 随着陆上油气资源的日益枯竭,海上油气资源的勘探和开发变得日益迫切,基于脉冲放电破碎岩石的钻井技术受到了广泛的关注。现有的高压脉冲放电破岩装置,使用的脉冲电源单次能量都是几百甚至上千焦耳,该能量等级下电源工作的重复频率、能量效率和电极的使用寿命等问题都会受到一定的限制。减小单次放电能量和工作电压,有可能实现装备的小型化,快重复频率和长使用寿命,并增强设备使用的安全性。本论文开展了幅值电压30～50kV、单次能量10～20J下脉冲放电破碎岩石的理论和实验研究。脉冲放电破碎岩石主要分为液电效应破碎和电破碎两种形式。液电效应的研究历史较早,理论相对成熟。本文重点讨论了电破碎岩石过程及机理。从电场的角度分析了气泡对岩石电击穿场强的影响。利用等效电路的方法,分析了储能电容上的能量注入到等离子体通道中的过程,模拟结果显示：等离子体通道在电击穿后,其阻抗在Q量级。借鉴经典的爆炸理论,将岩石看作为均匀、各向同性、不可压缩性流体,建立了一个基于动量传递观点的等离子体通道破碎岩石模型。储能装置上的能量快速地注入到等离子通道,引起通道迅速膨胀,对通道周围的岩体产生一个比冲量。岩石以一定的速度开始运动,但由于获得的初速度并不一致,相对运动产生的位移差将会使岩石变形。当岩石的变形能超过其应力强度时,破碎发生。岩石的电击穿场强是研究电破碎岩石的核心问题。本文考察了针—板电极条件下岩石的电击穿场强。黄砂岩、黑大理岩、白大理岩、黑花岗岩和白花岗岩在50%击穿概率下平均电击穿场强分别为70kV/cm、105kV/cm160kV/cm、135kV/cm和120kV/cm。实验证实了岩石的孔隙率跟其电击穿场强的相关性：孔隙率越大,电击穿场强越小。岩石的电击穿场强随厚度的增减而减小。利用小能量的Marx发生器在针—板电极下对岩石进行电破碎实验。岩石发生破碎需要电源提供的单次能量不能低于8J。针对高压脉冲放电破碎岩石的工业应用,本文开展了下针—针电极放电破碎岩石的实验研究。高压脉冲放电对岩石破碎的结果表明：电场强度、脉冲能量、电导率等因素对岩石的破碎均有影响。加载在放电电极上的电压越高、单次脉冲能量越大、水电导率越小,则岩石越容易发生破碎。实验证实了在电极间距2～4mm,自来水的电导率300μS/cm幅值电压30～50kV、单次能量10～20J的脉冲放电是可以实现对硬岩的破碎。基于前期的理论和实验研究,设计了一套高压脉冲放电破碎岩石的钻井工艺,搭建了一台脉冲等离子体钻井设备。提出利用线性的电容和非线性的脉冲形成线的组合来实现电源同负载的阻抗匹配。自行设计并搭建了一台LCR触发多级多通道火花开关。实验结果表明：该火花开关具有稳定的电压输出,较小的能量损耗,电压的上升沿小于40ns,可以作为钻机的短脉冲形成开关。开发了一种低波阻抗同轴水电缆,电缆的波阻抗小于10Ω,将进水管放置于中心导体内,实现了电缆和水缆的结合。设计并搭建了一套可行的钻机机构,该机构由机架、钻井杆、重力压盘和导向杆等部件组成。钻井杆采用多级连杆组合的方式实现足够的机械连接,并可以根据进钻的深度调节钻井杆的长度。钻井机构能够满足持续的深井钻孔的要求。利用搭建好的钻机开展了岩石钻孔的实验研究。钻头电极采用同轴圆柱结构,接地电极的外直径54mm,电极壁厚5mm,高压电极为内电极,直径为40mm,高、低压电极间距为2mm。当采用自制的低波阻抗脉冲传输线时,受限于传输线的工作电压,钻机无法实现对天然岩石的钻孔。当采用RG218电缆作为传输线,电压30～45kV、单次能量10～20J的脉冲放电数次后,岩石的表面在与放电间隙对应的位置有凹槽,与高压电极接触的岩石无变化,钻机也无法实现对岩石的有效钻孔。利用多根细电缆制成的钻头电极,高低压电极对为10对,电极间距为3～3.5mm集成后电极的直径为40mm。实验发现不同种类的岩石,在不同的电压等级下,能耗的差别较大。实验选取了建筑红砖、黑大理岩、黄砂岩、白大理岩和黑花岗岩等作为实验石材。建筑红砖的能耗最低,在30kV电压时,钻孔能耗为100J/cm3,当升高电压至45kV时,钻孔的能耗降至45J/cm3。钻孔的能耗随着电压的上升而下降。芝麻白花岗岩和珍珠黑花岗岩在40～50kV电压等级下的钻孔能耗约为1000J/cm3。更多还原

【Abstract】 With increasing depletion of land oil and gas resources, exploration and development of offshore oil and gas resources has becoming increasingly urgent. Recently, a drilling technology based on pulsed electrical discharge fragmentation (PEDF) of hard rocks has attracted widely attention. The energy per pulse of existing generators of PEDF is hundreds or even thousands of joules per pulse, which limits operating frequency, energy efficiency and lifetime of electrodes. With lowering energy per pulse and voltage amplitude, there may be to miniaturize the equipment and to increase the frequency rate, lifetime of the electrode, and the use of safety. In this paper, theoretical and experimental research on PEDF has been conducted with voltage amplitude of30-50kV and energy per pulse of10～20J.Electrohydraulic (EHD) and Electrical discharge (ED) are two main methods for the PEDF technology. The research on the electrohydraulic is a bit earlier and the relevant theory is relatively mature. This article mainly discusses the process and mechanism of the ED method. The effect of porosity on the electrical strength is analyzed. The process of the energy injected into the plasma channel is analyzed using the equivalent circuit method. The simulation result shows that the impedance of the plasma channel is smaller than1Ω. A model of rock fragmentation by plasma channel is established based on the momentum transfer, assuming rock as homogeneous, isotropic and incompressible fluid. The energy in the storage device quickly injects into the plasma channel and the channel expands rapidly to produce a specific impulse to the surrounding rock. The rock begins to move at a certain speed but the initial velocity obtained is not consistent, the relative movement of the displacement difference will make the rock deformation. When the deformation of the rock exceeds its stress intensity, fragmentation occurs.Electrical strength of rock is the core issue of electrical fragmentation of rock. In this research, rocks were placed between a needle high-voltage electrode and a plate grounded electrode in deionized water. The electrical strengths with50%breakdown possibility of yellow sandstone, black marble, white marble, black granite and white granite are70kV/cm,105kV/cm,160kV/cm,135kV/cm and120kV/cm respectively. The result verifies the relationship of rock electrical strength and its porosity. A rock with a higher porosity may have a lower electrical strength. Moreover, the electrical strength drops with increasing the thickness of rocks. Experiments on rock electrical discharge were taken in needle-to-plate electrodes with small energy Marx generator. Fragmentation can be realized on the condition that power supply should provide energy more than8J per pulse.Taking into account the conditions of actual industrial applications of PEDF technology, rock fragmentations with needle-to-needle electrode pulse discharge in tap water were carried out. Several factors effect rock fragmentation performance, such as electrode gap, voltage amplitude, energy per pulse and water conductivity. Higher voltage on the electrode, greater energy of pulse, smaller conductivity of the water, is more prone to destroy rock. Rock fragmentation can be realized on the condition that, electrode gap of2-4mm, water conductivity of300μS/cm, voltage amplitude of30～50kV and energy per pulse of10～20J.Based on theoretical and experimental research of PEDF, a setup of plasma drill has been designed and developed. The combined pulsed power network has been raised as the drill’s generator. The combined network combined linear capacitor and non-linear pulsed forming line, which can match with the impedance of the plasma channel. A LCR triggered, multi-gap and multi-channel spark switch has been developed. Test results shows that the switch has stable voltage output, little energy consumption. The rise time of output voltage is less than40ns. A low wave impedance transmission line with10Ω has been developed. The inlet water tube is installed in the center of the transmission line. This design has combined the water inlet tube and transmission line together. An drilling mechanism have been developed and the mechanism comprises of a drilling frame, a drilling bar, a gravity plate and guiding bars, et al. Several unites of drilling bars can connect together and realize enough mechanical strength. The length of the drilling bar can be adjusted depending on the drilling depth. The drilling mechanism can meet requirements of drilling holes.Experiments on rock drilling using the plasma drill have been carried out. A radially symmetric electrode design was used as the drill head. The drill head consistes of an internal high voltage disc electrode with diameter of44mm and an external grounded cup-like electrode with outer diameter of54mm. The annular inter-electrode gap is2mm. Rock cannot be destroyed with the low impedance transmission line for its operating voltage. When the cable of RG218is adopted as the transmission line, only a concave groove on the rock surface is formed after several discharges. The position of the groove is corresponding to the electrode gap. The rock under the high voltage electrode is undestroyed. Rock drilling with multi-cable electrodes has been carried out. The diameter of the multi-cables drill head is40mm and the gap between high voltage electrode and low voltage electrode is3-3.5mm and10pairs of electrodes are combined. Results show that specific energies for different kind of rocks under different operating voltage have great difference. The specific energy decreases as the operating voltage increases. For red brick, when the operating voltage is30kV, the specific energy is100J/cm3. The specific energy decreases to45J/cm3when the operating voltage is45kV. When the operating voltage is40～50kV, the specific energy of granite is about1000J/cm3.更多还原