Abstract
High voltage pulsed discharge in water (HVPD) is used throughout industry for fracturing both natural and man-made materials. Using HVPD, we modeled crack propagation of rocks under homenergic water shock waves (HWSW) with different characteristics and combination forms using a combination of experimental analysis and numerical simulation. The experimental results show that, under the same discharge energy (2 kJ), water shock waves (WSW) with different characteristics fractured the rock mass distinctly different. With a higher the peak pressure (PP) of WSW, more long cracks and microcracks were formed, creating a larger damage area. The numerical simulation results show that a single HWSWs impact with different characteristics will still only cause three long cracks to be well developed and almost no microcracks, whenPPof HWSW was 3 MPa. With the increase ofPP, the number of both long cracks and microcracks increased. This is consistent with the experimental results. When the peak pressure became greater than 15 MPa, crack propagation gradually became concentrated and the surrounding borehole wall became more severely broken. The rock model had optimal fracturing under the impact of the HWSW with aPPof 10 MPa. Also, the simulations showed that, under repeated-impacts of HWSWs with consistent characteristics, the fracturing characteristics were basically identical to those by a single-impact. While under the repeated-impact of HWSWs with variable characteristics, there was almost no relationship between the fracturing effect and the sequence of repeated-impacts. Finally, under a single-impact of HWSW with lowPPand hydrostatic pressure (PH) acting within an initial crack (similar to hydraulic fracturing in a hydrocarbon well), the initial crack had excellent propagation with an increase in hydrostatic pressure. However, whenPPof HWSW was too high, increasingPHhad no effect on initial crack propagation.
Highlights
High voltage pulsed discharge in water (HVPD) has primarily been used in the mineral industry, including but not limited to such practices as breaking down oil and gas wells [1], rock breaking and well drilling [2], and natural gas extraction [3]
The studies in recent years found that the dynamic characteristics of water shock wave (WSW) produced by HVPD were influenced by many factors, including discharge voltage, capacitor value, discharge energy, electrode gap and type [5], and water conductivity [6]
We studied the dynamic response and characteristics of rock fracturing under a single-impact and repeated-impacts of homenergic water shock waves (HWSW)
Summary
High voltage pulsed discharge in water (HVPD) has primarily been used in the mineral industry, including but not limited to such practices as breaking down oil and gas wells [1], rock breaking and well drilling [2], and natural gas extraction [3]. A single-impact with a higher WSW amplitude more clearly damaged the rock sample, and there was cumulative damage of the rock mass under repeated-impacts [12]. These studies greatly improved the understanding of HVPD on rock fracturing; they. At lower stress-loading rates, the number of crack and crack arrest caused by stress released at adjacent cracks is reduced. This leads to greater crack extension [13]. Whether or not different characteristics of rock fracturing are caused by different WSWs’ energy needs further study. This research was accomplished through numerical simulation and single pulsed HVPD experiments on concrete, providing a theoretical basis for improving the technology principle of HVPD in rock fracturing, optimizing the effect of rock breakage and improving the working efficiency of oil and gas reservoir fracturing
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