In order to evaluate the behavior of a high power pulsed underwater electrical discharge, and especially characterize the pressure generated by such a discharge, we implemented several optical diagnostics. We first observed directly the expansion of the plasma produced by the dielectric breakdown of the water between the electrodes and the resulting gaseous pulsating bubble. This observation led to an estimate of the pressure inside the bubble with respect to time. We then visualized the propagation of the pressure wave generated by the discharge with shadowgraph and Schlieren setup. The obtained velocity was then used to evaluate the theoretical maximum pressure at the pressure front. Finally, we measured the velocity induced by the pressure wave on a thin aluminum disk with a heterodyne velocimeter and used numerical simulation to obtain a temporal form of pressure. These methods and results can be used to develop and assess performances of processes using underwater electrical discharges to generate pressure waves such as electrohydraulic forming.

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Optical diagnostics for high power pulsed underwater electrical discharge characterization

Bit optimization method for rotary impact drilling based on specific energy model

Plasma based fracking in unconventional shale – A review

Anti-drilling ability of Ziliujing conglomerate formation in Western Sichuan Basin of China

In the work the problem of directed chipping of facing stone material by means of managing of explosion process is considered. The technology of the mining of decorative stone by the use of explosion energy means the very rapid transfer of potential energy of elastic deformations to kinetic energy. As a result, the explosion impulse, in the expanse of the inertia of rock massive, does not cause the increase of existing cracks. In the course of explosion, the shock wave is propagated by ultrasonic velocity and in this case the medium parameters (pressure, density, temperature, velocity) increase in spurts. In spite of this fact the all three conservation laws of mechanics remain valid on basis of three laws the equations are derived by which the parameters of shock wave may be defined by means of the rock physical-mechanical properties. The load on the body volume at breaking under explosion acts over very small period of the time. Therefore, stressed-deformed state of the rock was studied when the impulse load acts on the boundary. It was considered that the mining of the blocks of facing stone is performed from the hard rocks. This means that the breaking proceeds in the zone of elastic deformation. In the conditions of mentioned assumptions, the expression of the stress tensor and displacement of vector components initiated by stressed-deformed state in the rock are written.

https://iopscience.iop.org/article/10.1088/1755-1315/44/5/052005/pdf

Rock Directed Breaking Under the Impulse Load

Similarity evaluation of stratum anti-drilling ability and a new method of drill bit selection

Shale oil and gas reservoirs, as well as compact oil and gas reservoirs, are important oil exploration resources. However, their tight lithology and extremely low permeability and porosity hinder extraction. Production stimulation measures, such as reservoir fracturing transformation, are needed to increase production by low-permeability oil and gas reservoirs. This study explored a new type of fracturing technology, namely, pulsed-plasma rock fracturing, to increase rock fracturing efficiency and recovery. First, a model of stress distribution on the sidewalls of open holes was established. Then, a fracturing experiment was conducted on polymethyl methacrylate (PMMA). Morphological features were analyzed on the basis of the visual characteristics of PMMA, and the influential factors of fracture breakdown were summarized. Meanwhile, the stress-changing rule was analyzed by simulating pulsed-plasma shock-wave rock fracturing with LS-DYNA. Results show that pulsed-plasma fracturing can generate valid cracks with actiniform and wave-form features. High discharge voltages and loads on rocks associate with long crack lengths. In the simulation, applies load strengths form 9 MPa to 30 MPa, and the crack lengths increase from 16 mm to 67.5 mm. At the same time, the width and number of fractures show an increasing trend, and radioactivity and multi-branched cracks inside the rocks become increasingly complex. This study provides a practical and reliable reference for the technology of pulsed-plasma rock fracturing.

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Visualization Experiment and Numerical Simulation of Cracks Caused by Pulsed- Plasma Rock Fracturing

The invention relates to a double-pulse plasma rock breaking generation device. The double-pulse plasma rock breaking generation device comprises a charge power supply, a negative peak preventing inductor, a first discharge electrode group, a second discharge electrode group and a current transformer, wherein the charge power supply is separately connected with the negative peak preventing inductor and a free-wheel diode, the other end of the negative peak preventing inductor is separately connected with a bleeding switch and two parallel energy storage capacitors, the two parallel energy storage capacitors are then connected with an energy storage discharge loop in parallel, the energy storage discharge loop is formed by the series connection of a first wire inductor, a first discharge electrode group, a second discharge electrode group, a current transformer and a second wire inductor, the two parallel energy storage capacitors and the second wire inductor are all grounded, the free-wheel diode is grounded, the bleeding switch, a first bleeding resistor and a second bleeding resistor are connected in series, and the second bleeding resistor is grounded. Each discharge electrode group consists of an electrode external nut, an epoxy protective bushing, a grounding electrode, an insulating protective bushing and a high-voltage electrode. The crack density of broken rocks can beincreased, crack extension is promoted, and the breaking effect is improved.

Double-pulse plasma rock breaking generation device

The invention relates to a water-driven drill bit impactor comprising a shell, a spiral blade, a middle cavity, a spring, a vibrator, an upper toothed ring, a lower toothed ring and a drill bit. A rotating disk rail is installed on the upper part of the shell. The rotating disk is embedded into the rotating disk rail. The outer side of the spiral blade is installed on the inner wall of the rotating disk. The upper end of the connection column is installed on the spiral blade. The lower end of the connection column penetrates through the middle cavity to extend into the vibrator and is fixedlyconnected with the lower toothed ring. The middle cavity is installed in the shell and located below the rotating disk rail. The vibrator is arranged in the middle cavity. The lower end of the springis connected with the vibrator. The upper end of the spring is connected with the middle cavity. The wall of the middle cavity is provided with a hole channel. The upper toothed ring is arranged in the vibrator and corresponds to the lower toothed ring. The outer wall of the vibrator is symmetrically provided with two clamping sheets. The inner wall of the middle cavity is provided with vibrationgrooves. The two clamping sheets are located in the corresponding vibration grooves correspondingly. The vibrator and the drill bit are connected through the connector. The water-driven drill bit impactor achieves a quite remarkable acceleration effect, saves energy and reduces consumption.

Shao Yang

Papers

Similarity evaluation of stratum anti-drilling ability and a new method of drill bit selection

Visualization Experiment and Numerical Simulation of Cracks Caused by Pulsed- Plasma Rock Fracturing

Double-pulse plasma rock breaking generation device

Water-driven drill bit impactor