Experimental study on an alternative oil stimulation technique for tight gas reservoirs based on dynamic shock waves generated by Pulsed Arc Electrohydraulic Discharges

Chen, Wen; Maurel, Olivier; Reess, Thierry; Ferron, Antoine Silvestre de; Borderie, Christian La; Pijaudier‐Cabot, Gilles; Rey-Bethbeder, Franck; Jacques, Antoine

doi:10.1016/j.petrol.2012.01.009

Cited by 92 publications

(41 citation statements)

References 5 publications

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“…To release gas or oil from the shale mass by means of shock waves generated by explosions or pulsed arc in a horizontal borehole, the fragmentation would have to be sufficiently fine to achieve a drastic increase of permeability (19). Reports on ongoing dynamic finite element simulations indicate that the shear strain rates produced by such shock waves exceed _ e D = 100 s −1 (20).…”

Section: Some Results and Discussionmentioning

confidence: 99%

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

Bažant

Caner

2013

Proc. Natl. Acad. Sci. U.S.A.

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Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.fracture mechanics | dynamic fracture | shale gas | dimensional analysis T he previous studies of high-rate dynamic fracture of rocks, concretes, ceramics, composites, and metals have dealt mainly with the nucleation, propagation, and branching of dynamically propagating cracks, their interference with elastic or shock waves, and the mechanism of development of the zones of densely distributed fractures, called the Mescall zones (1-7). However, a comminution model in the form of a macroscopic constitutive equation that could be used in large dynamic finite element programs for global response of structures is apparently still unavailable.Seeking such a constitutive model, we begin with the analysis of a simple idealized process in which the solid is comminuted to identical particles (Fig. 1). Among simple space-filling regular subdivisions in the plane of maximum shear, regular hexagons are the most likely because they give the smallest surface-to-volume ratio (Fig. 1A) and thus require the minimum energy to form. In the direction normal to the hexagons, we assume the particles to be prismatic.Consider that, at a certain moment, the strain rate (shown in Fig. 1B as a displacement regarded as infinitesimal) becomes high enough for the kinetic energy of shear strain rate to suffice for creating the fractures and interface slips that separate the particles of as yet unknown size. As that happens, the particles release their local kinetic energy, slip against each other, and regain their original undeformed shape, while the particle centers conform to the same macroscopic velocity field (Fig. 1C).For the sake of simplicity and clarity, we will first outline a 2D analysis of comminution in the plane of maximum shear strain rate denoted as _ e D , and leave the 3D generaliza...

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Section: Some Results and Discussionmentioning

confidence: 99%

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

Bažant

Caner

2013

Proc. Natl. Acad. Sci. U.S.A.

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“…where k and α in the empirical formula (1) are parameters related to the experimental environment and electrode geometry [44,45]. ese two parameters represent the energy conversion characteristics of the WSW in different experimental conditions [42].…”

Section: Data Fitting and Contrastmentioning

confidence: 99%

Experimental Study of Pulsed Discharge Underwater Shock‐Related Properties in Pressurized Liquid Water

Bian

Dong

Zhao

et al. 2018

Advances in Materials Science and Engineering

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Engineering background of hydraulic fracturing is applied to improve the permeability of unconventional gas wells, such as coal seams and shale gas wells, by a pulsed discharge mechanism. We studied the general relations between water shock wave properties (the maximum pressure, wave velocity, and energy conversion efficiency), the discharge voltage, and hydrostatic pressure during high-voltage pulsed discharge experiments in pressurized liquid water. e following observations were made: (1) when the discharge voltage increased from 7 kV to 13 kV, the maximum pressure increased from 12.6 MPa (hydrostatic pressure P H � 12 MPa) to 40 MPa (P H � 6 MPa), wave velocity increased from 1418 m/s (P H � 12 MPa) to 1454 m/s (P H � 6 MPa), and energy conversion efficiency increased from 9% to 11%, and (2) when hydrostatic pressure increased from 0 MPa to 12 MPa, the maximum pressure and wave velocity augmented and then diminished slowly (the critical hydrostatic pressure occurs in the 3 to 6 MPa range), whereas the change of energy conversion efficiency was not obvious. eir properties are explained by the variation of electrical parameters during the pulsed discharge.

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“…Oil companies have been experimenting with vari ous types of explosions in the borehole, including electric pulsed arc [34,35]. Oil companies have been experimenting with vari ous types of explosions in the borehole, including electric pulsed arc [34,35].…”

Section: The Intriguing Prospect Of Comminuting Shale Near Borehole Bmentioning

confidence: 99%

Why Fracking Works

Bažant

Salviato

Chau

et al. 2014

Journal of Applied Mechanics

164

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Although spectacular advances in hydraulic fracturing, also known as fracking, have taken place and many aspects are well understood by now, the topology, geometry, and evolution of the crack system remain an enigma and mechanicians wonder: Why fracking works? Fracture mechanics of individual fluid-pressurized cracks has been clarified but the vital problem of stability of interacting hydraulic cracks escaped attention. First, based on the known shale permeability, on the known percentage of gas extraction from shale stratum, and on two key features of the measured gas outflow which are (1) the time to peak flux and (2) the halftime of flux decay, it is shown that the crack spacing must be only about 0.1 m. Attainment of such a small crack spacing requires preventing localization in parallel crack systems. Therefore, attention is subsequently focused on the classical solutions of the critical states of localization instability in a system of cooling or shrinkage cracks. Formulated is a hydrothermal analogy which makes it possible to transfer these solutions to a system of hydraulic cracks. It is concluded that if the hydraulic pressure profile along the cracks can be made almost uniform, with a steep enough pressure drop at the front, the localization instability can be avoided. To achieve this kind of profile, which is essential for obtaining crack systems dense enough to allow gas escape from a significant portion of kerogen-filled nanopores, the pumping rate (corrected for the leak rate) must not be too high and must not be increased too fast. Furthermore, numerical solutions are presented to show that an idealized system of circular equidistant vertical cracks propagating from a horizontal borehole behaves similarly. It is pointed out that one useful role of the proppants, as well as the acids that promote creation of debris in the new cracks, is to partially help to limit crack closings and thus localization. To attain the crack spacing of only 0.1 m, one must imagine formation of hierarchical progressively refined crack systems. Compared to new cracks, the system of pre-existing uncemented natural cracks or joints is shown to be slightly more prone to localization and thus of little help in producing the fine crack spacing required. So, from fracture mechanics viewpoint, what makes fracking work?–the mitigation of fracture localization instabilities. This can also improve efficiency by fracturing more shale. Besides, it is environmentally beneficial, by reducing flowback per m3 of gas. So is the reduction of seismicity caused by dynamic fracture instabilities (which are more severe in underground CO2 sequestration).

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Experimental study on an alternative oil stimulation technique for tight gas reservoirs based on dynamic shock waves generated by Pulsed Arc Electrohydraulic Discharges

Cited by 92 publications

References 5 publications

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

Experimental Study of Pulsed Discharge Underwater Shock‐Related Properties in Pressurized Liquid Water

Why Fracking Works

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