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

Gehne, S.; Benson, P.M.; Koor, N.; Dobson, K.J.; Enfield, M.; Barber, A.

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


Authors

S. Gehne

P.M. Benson

N. Koor

K.J. Dobson

M. Enfield

A. Barber



Abstract

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.

Citation

Gehne, S., Benson, P., Koor, N., Dobson, K., Enfield, M., & Barber, A. (2019). Seismo‐Mechanical Response of Anisotropic Rocks Under Hydraulic Fracture Conditions: New Experimental Insights. Journal of Geophysical Research. Solid Earth, 124(9), 9562-9579. https://doi.org/10.1029/2019jb017342

Journal Article Type Article
Acceptance Date Aug 24, 2019
Online Publication Date Sep 14, 2019
Publication Date Sep 30, 2019
Deposit Date Oct 8, 2019
Publicly Available Date Mar 29, 2024
Journal Journal of Geophysical Research. Solid Earth
Print ISSN 2169-9313
Electronic ISSN 2169-9356
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 124
Issue 9
Pages 9562-9579
DOI https://doi.org/10.1029/2019jb017342

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Copyright Statement
Gehne, S., Benson, P. M., Koor, N., Dobson, K. J., Enfield, M. & Barber, A. (2019). Seismo‐Mechanical Response of Anisotropic Rocks Under Hydraulic Fracture Conditions: New Experimental Insights. Journal of Geophysical Research: Solid Earth 124(9): 9562-9579. 10.1029/2019JB017342. To view the published open abstract, go to https://doi.org/ and enter the DOI.





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