Acoustic Emission Response of Laboratory Hydraulic Fracturing in Layered Shale

Li, Ning; Zhang, Shicheng; Zou, Yushi; Ma, Xinfang; Zhang, Zhaopeng; Li, Sihai; Chen, Ming; Sun, Yi-Fei

doi:10.1007/s00603-018-1547-5

Cited by 78 publications

(27 citation statements)

References 40 publications

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“…Only a few studies focused on geothermal reservoir stimulation in hard granite, 18,19 and no previous studies comprehensively analyzed the influences of initiation pressure, breakdown pressure, propagation time, and postfracturing pressure on hydraulic fracturing behavior. At the same time, for our HDR granite hydraulic fracturing tests, the fracture initiation was before the breakdown point could be identified, which was also found in previous studies and other rock formations hydraulic fracturing experiments 20‐27 . These two parameters both had significant effects on hydraulic fracturing behavior, and should be distinguished and analyzed in detail.…”

Section: Introductionsupporting

confidence: 82%

Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Cheng

Zhang

et al. 2020

Energy Science & Engineering

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Geothermal energy has been widely proposed as a potential renewable energy to replace traditional fossil fuel energy. Hot dry rock (HDR) reservoirs were the main geothermal energy resources and usually consist of low‐permeability hard granite without fluid. Developing HDR requires water cyclically flowing between injection and production wells to extract heat energy. Hydraulic fracturing, as a key reservoir stimulation technology, can create the path of fluid cyclically flowing. However, few studies have investigated hydraulic induced artificial fractures in HDR geothermal formations. This paper investigated HDR geothermal reservoir stimulation characteristics and fracture patterns under different injection flow rates. Numerical simulations were conducted to model the laboratory tests. Results showed they were in good agreement, and this indicated the possibility of numerical simulation to predict hydraulic fracturing behavior under different injection flow rates. With the increase of injection flow rate, the fracture initiation pressures and breakdown pressures increased, and the propagation times and postfracturing pressures decreased. The fracture geometries were observed and analyzed, mean injection power was proposed, and results showed that it could be used to roughly estimate the fracture total lengths. Moreover, the fracture permeabilities based on the pressure data were calculated. These results can provide some reasonable advice for implementing reservoir stimulations on application to field‐scale HDR operation.

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Section: Introductionsupporting

confidence: 82%

Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Cheng

Zhang

et al. 2020

Energy Science & Engineering

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“…In an attempt to better understand the hydrofracture process, numerous laboratory studies investigating fluid-driven fracturing have been developed and reported (e.g., Clifton et al, 1976;Haimson & Fairhurst, 1969a;Lin et al, 2017;Li et al, 2018;Schmitt & Zoback, 1992;Stoeckhert et al, 2015;Stanchits et al, 2011Stanchits et al, , 2014Vinciguerra et al, 2004;Zoback et al, 1977). These previous studies range from complex and costly true triaxial simulations (Li et al, 2018) to the use of effective confining triggers on critically loaded conventional samples to induce shear failure due to increasing pore fluid (Stanchits et al, 2011). While such methods allow a degree of control that is difficult in a field setting, an obvious challenge is the smaller scale of these experiments.…”

Section: Introductionmentioning

confidence: 99%

Seismo‐Mechanical Response of Anisotropic Rocks Under Hydraulic Fracture Conditions: New Experimental Insights

et al. 2019

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Unconventional hydrocarbon resources found across the world are driving a renewed interest in mudrock hydraulic fracturing methods. However, given the difficulty in safely measuring the various controlling factors in a natural environment, considerable challenges remain in understanding the fracture process. To investigate, we report a new laboratory study that simulates hydraulic fracturing using a conventional triaxial apparatus. We show that fracture orientation is primarily controlled by external stress conditions and the inherent rock anisotropy and fabric are critical in governing fracture initiation, propagation, and geometry. We use anisotropic Nash Point Shale (NPS) from the early Jurassic with high elastic P wave anisotropy (56%) and mechanical tensile anisotropy (60%), and highly anisotropic (cemented) Crab Orchard Sandstone with P wave/tensile anisotropies of 12% and 14%, respectively. Initiation of tensile fracture requires 36 MPa for NPS at 1‐km simulated depth and 32 MPa for Crab Orchard Sandstone, in both cases with cross‐bedding favorable orientated. When unfavorably orientated, this increases to 58 MPa for NPS at 800‐m simulated depth, far higher as fractures must now traverse cross‐bedding. We record a swarm of acoustic emission activity, which exhibits spectral power peaks at 600 and 100 kHz suggesting primary fracture and fluid‐rock resonance, respectively. The onset of the acoustic emission data precedes the dynamic instability of the fracture by 0.02 s, which scales to ~20 s for ~100‐m size fractures. We conclude that a monitoring system could become not only a forecasting tool but also a means to control the fracking process to prevent avoidable seismic events.

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“…This occurred because the high injection rate caused quick pressurization and decreased the time of fluid leak-off into the NFs. This mechanism has also been discussed by Li et al [58,59]. Based on the abovementioned results, the injection scheme for naturally fractured volcanic formations should be optimized.…”

Section: Discussionmentioning

confidence: 67%

Effect of Multiple Flow Pulses on Hydraulic Fracture Network Propagation in Naturally Fractured Volcanic Rock

et al. 2020

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Exploring engineering methods for increasing fracture network complexity is important for the development of unconventional oil and gas reservoirs. In this study, we conducted a series of fracturing experiments on naturally fractured volcanic samples. An injection method, multiple flow pulses, is proposed to increase fracture complexity. The results show that fluid leaked into the natural fracture network (NFN) when the injection rate was low (0.2 mL/min); hydraulic-fracture-dominant fracture geometry was created with an injection rate of 2 and 5 mL/min. Under the 2 mL/min-injection scheme with 3 pulses, the injection pressure during the intermittent stage was low (<5 MPa), resulting in a limited increase in fracture complexity. When the number of the flow pulses increased to 5, the pressure drop rate in the fourth and fifth intermittent stage significantly increased, indicating an increase in the aperture of natural fractures (NFs) and in the fluid leak-off effect. Under the 5 mL/min injection scheme containing 5 pulses, besides the enhanced fluid leak-off, a sharp injection pressure drop was observed, indicating the activation of NFs. The complexity and the aperture of the ultimate fracture network further increased. The injection method, multiple flow pulses, can be used to create complex fracture networks effectively.

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Acoustic Emission Response of Laboratory Hydraulic Fracturing in Layered Shale

Cited by 78 publications

References 40 publications

Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Experimental and numerical studies on hydraulic fracturing characteristics with different injection flow rates in granite geothermal reservoir

Seismo‐Mechanical Response of Anisotropic Rocks Under Hydraulic Fracture Conditions: New Experimental Insights

Effect of Multiple Flow Pulses on Hydraulic Fracture Network Propagation in Naturally Fractured Volcanic Rock

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