Influence of normal and shear stress on the hydraulic transmissivity of thin cracks in a tight quartz sandstone, a granite and a shale.

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    Abstract

    Transmissivity of fluids along fractures in rocks is reduced by increasing normal stress acting across them, demonstrated here through gas flow experiments on Bowland shale, and oil flow experiments on Pennant sandstone and Westerly granite. Additionally, the effect of imposing shear stress at constant normal stress was determined, until frictional sliding started. In all cases, increasing shear stress causes an accelerating reduction of transmissivity by one to three orders of magnitude as slip initiated, as a result of the formation of wear products that block fluid pathways. Only in the case of granite, and to a lesser extent in the sandstone, was there a minor amount of initial increase of transmissivity prior to the onset of slip. These results cast into doubt the commonly applied presumption that cracks with high resolved shear stresses are the most conductive. In the shale, crack transmissivity is commensurate with matrix permeability, such that shales are expected always to be good seals. For the sandstone and granite, unsheared crack transmissivity was respectively 2 and 2.5 orders of magnitude greater than matrix permeability. For these rocks crack transmissivity can dominate fluid flow in the upper crust, potentially enough to permit maintenance of a hydrostatic fluid pressure gradient in a normal (extensional) faulting regime.
    Original languageEnglish
    Pages (from-to)1262-1285
    Number of pages24
    JournalJournal of Geophysical Research: Solid Earth
    Volume123
    Issue number2
    Early online date20 Jan 2018
    DOIs
    Publication statusPublished - 20 Jan 2018

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    • Structural geology and rock physics

      Mecklenburgh, J. (PI), Covey-Crump, S. (PI), Rutter, E. (PI), Chandler, M. (PI), Ardo, B. (PGR student), Bashir, Y. (PGR student) & Tielke, J. (PI)

      Project: Research

    • Geophysics

      Mitchell, N. (PI), Mecklenburgh, J. (PI), Rutter, E. (PI), Huuse, M. (PI), Finch, E. (PI), Chandler, M. (PI), Chang, Y.-C. (PGR student), Zhao, Z. (PGR student), Shi, W. (PGR student), Bashir, Y. (PGR student), Ardo, B. (PGR student), Newton, A. (PGR student), Cox, D. (PGR student), Lloyd, C. (PGR student), Putuhena, H. (PGR student), Sarkar, A. (PGR student), Nnorom, S. (PGR student), Owolabi, O. (PGR student), Malah, M. (PGR student), Soutter, E. (PGR student), Dunlevy, E. (PGR student), Balila, A. (PGR student), Alhammami, S. (PGR student), Olobayo, O. (PGR student), Serié, C. (PGR student), Chenrai, P. (PGR student), Sharples, A. (PGR student), Le, A. (PGR student), Lamb, R. (PGR student), Harding, R. (PGR student), Gulmammadov, R. (PGR student), Calves, G. (CoI), Bureau, D. (CoI) & Muniz Pichel, L. (PGR student)

      Project: Research

    • Shining light on shale:geomechanics and 4D fracture characterization.

      Mecklenburgh, J. (PI), Lee, P. (CoI), Rutter, E. (CoI) & Taylor, K. (CoI)

      30/11/142/03/18

      Project: Research

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