Underwater plasma breakdown characteristics with respect to highly pressurized drilling applications

Abstract

Deep earth drilling is a key technique to extract oil, gas, and geothermal heat from the earth. Many complex energy focusing methods have been explored as an alternative approach to reach these resources but most of them require high energy. However, by utilizing short time span liquid plasma discharges, energy focusing can be achieved within traditional drilling systems. These discharges induce a rapid expansion process and a resulting shockwave. It is believed that this focused energy will lower the required cutting force to progress through the rock. Lowering the required cutting force will allow for lower drill bit wear, quicker rate of penetration, and an overall cost savings of the project. Plasma breakdown characteristics at drilling relevant pressures, ranging from 1 to 350 atm, were studied. A resistance–capacitance circuit with an air gapped spark switch was utilized to generate pulsed plasma between the pressurized electrodes. It was found that the required breakdown voltage increases as the pressure increases. It was also found that a plasma channel formation and an associated breakdown may or may not occur between the electrodes at different pressures due to variation in required breakdown voltages. Breakdown time-lag in the dielectric medium (tap water, 780 μS cm−1) increased as the pressure was increased, which indicated a higher voltage drop at higher pressures (>100 atm). The plasma generated cavitation bubble with an associated shockwave occurred as pressures were increased. However, the bubble radius and the bubble duration decreased as the pressure was increased. The plasma generated shockwave speeds fall within the expected speed of sound in water. Finally, preliminary rock cracking tests were performed on granite at high pressures (340 and 272 atm) and it was found that plasma is able to create cracks in the rock.

Study on Mechanism and Regularity of Rock Breaking by Pulsed Water Injection with Particles

“…Advantages Shortcomings Laser [16,17] Low cost, high efficiency, low pollution Use of high power is limited Plasma [10,11] Higher rate of penetration Large energy consumption Microwave [12,13] Fast heating, strong penetration, and easy process control It takes some time for the radiation to take effect Rotary percussion drilling [14,15] High stability and drilling efficiency High pressure resistance of drill bit is required…”

“…With the development of modern science and technology, some new rock-breaking technologies have emerged. Examples include plasma rock-breaking [10,11], microwave rockbreaking [12,13], rotary percussion drilling [14,15], laser drilling [16,17], and other rockbreaking methods [18]. However, in addition to the shortcomings shown in Table 1, a lot of energy is required from the bottom of the hole or the ground to maintain drilling, and recently, the engine power, cable transmission efficiency, underground equipment anti-electromagnetic interference, and other capabilities have begun adding to these high requirements.…”

Characteristic simulation of underwater microsecond high-current pulsed arc discharge plasma

“…Currently, experimental research on underwater pulsed arc discharges is quite extensive. This includes capturing images of the arc channel morphology and shockwave wavefront using techniques such as shadowgraphy, schlieren imaging, and high-speed photography [8][9][10]. For underwater pulsed corona discharges, spark discharges, and bubble discharges of low energy and intensity, emission spectroscopy has been employed for diagnosing the electron density and temperature of the plasma [11][12][13][14][15][16].…”