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Hydraulic fracturing and permeability enhancement in granite from subcritical/brittle to supercritical/ductile conditions
Author(s) -
Watanabe Noriaki,
Egawa Motoki,
Sakaguchi Kiyotoshi,
Ishibashi Takuya,
Tsuchiya Noriyoshi
Publication year - 2017
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2017gl073898
Subject(s) - hydraulic fracturing , supercritical fluid , borehole , brittleness , permeability (electromagnetism) , geothermal gradient , overburden pressure , geology , pore water pressure , geotechnical engineering , materials science , petroleum engineering , mineralogy , composite material , thermodynamics , chemistry , membrane , biochemistry , physics , geophysics
Hydraulic fracturing experiments were conducted at 200–450°C by injecting water into cylindrical granite samples containing a borehole at an initial effective confining pressure of 40 MPa. Intensive fracturing was observed at all temperatures, but the fracturing characteristics varied with temperature, perhaps due to differences in the water viscosity. At the lowest considered temperature (200°C), fewer fractures propagated linearly from the borehole, and the breakdown pressure was twice the confining pressure. However, these characteristics disappeared with increasing temperature; the fracture pattern shifted toward the formation of a greater number of shorter fractures over the entire body of the sample, and the breakdown pressure decreased greatly. Hydraulic fracturing significantly increased the permeability at all temperatures, and this permeability enhancement was likely to form a productive geothermal reservoir even at the highest considered temperature, which exceeded both the brittle‐ductile transition temperature of granite and the critical temperature of water.