Evolution of fracture permeability through fluid-rock reaction under hydrothermal conditions

Hideaki Yasuhara, Amir Polak, Yasuhiro Mitani, Abraham S. Grader, Phillip M. Halleck, Derek Elsworth

Research output: Contribution to journalArticle

136 Citations (Scopus)

Abstract

We report flow-through experiments on a natural fracture in novaculite under moderate effective stresses (∼1.4 MPa) and temperatures (20-120 °C) to examine the effect on flow and transport characteristics. The efflux of fluid and dissolved minerals were measured throughout the 3150-h experiment. After the experiment the fracture was imaged by X-ray CT, impregnated with Wood's metal, and a cast recovered of the Wood's metal-filled fracture. These measurements constrain the evolution of fracture structure, and the change in permeability that resulted from stress- and temperature-dependent dissolution at both propping asperities and fracture void surfaces. During the first 1500 h, the aperture of one fracture decreased from 18.5 to 7.5 μm, when it was loaded with constant effective stress of 1.4 MPa, at room temperature, and a flow rate decreasing with time from 1 to 0.0625 mL/min. This reduction is attributed to the removal of mineral mass from bridging asperities. After 1500 h the fracture aperture increased, ultimately reaching 13 μm. Apparently the dominant dissolution process switched from prop removal to etching of the void surfaces. We used X-ray CT images, digital radiographs, and fracture casts as independent methods to constrain the resulting architecture of the evolved fracture porosity, and developed a simple process-based model to examine the relative roles of asperity removal and free-face dissolution. The comparison of the model with the measurements identifies the relative importance of mass removal at fracture faces and at propping asperities. The experiments underscore the importance of dissolution in determining the sense, the rates and the magnitude of permeability-enhancement within rock fractures stimulated by chemical permeants in geothermal and petroleum reservoirs, and to a lesser degree under natural conditions pushed far-from-equilibrium.

Original languageEnglish
Pages (from-to)186-200
Number of pages15
JournalEarth and Planetary Science Letters
Volume244
Issue number1-2
DOIs
Publication statusPublished - Apr 15 2006

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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