HR: 0800h
AN: T51A-1324    [Abstracts]
TI: Hydromechanical Behavior of Country Rock Samples from the Taiwan Chelungpu-Fault Drilling Project
AU: * Chen, T N
EM: tzchen@ic.sunysb.edu
AF: Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 United States
AU: Zhu, W
EM: wzhu@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Wong, T
EM: Teng-fong.Wong@stonybrook.edu
AF: Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 United States
AU: Song, S
EM: srsong@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, Taipei, 106 Taiwan
AB: Hydromechanical behavior TCDP core samples are being investigated in the laboratory. Initial tests focused on country rock cores at depths of ~588 m and 837 m. Cylindrical samples were cored in three orthogonal directions, one parallel and two perpendicular to the core axis. Triaxial compression tests were performed at room temperature to determine the brittle strengths of the intact samples and frictional strengths of the fractured samples. Nominally dry samples were deformed under 20 MPa confining pressure, and samples saturated with distilled water were deformed under 30 and 50 MPa confining pressure and 10 MPa pore pressure. The permeabilities of samples saturated with distilled water were measured by either steady state or pulse transient technique. Two series of permeability measurements were also conducted on samples using argon as pore fluid with pore pressure oscillation technique. The shaly siltstone samples from ~837 m show significant water weakening. Presence of water resulted in ~32% reduction in the strengths of the saturated samples relative to the corresponding dry samples cored in either direction. This shaly siltstone has an interconnected porosity of 4-5 %. The high clay content made the sample mechanically weak. The friction strengths seemed to be quiet normal, in that the friction coefficients of fractured samples were determined to range from 0.68 to 0.87 under wet condition. The bedding of these shaly samples dip at ~30°, and their mechanical behavior was sensitively dependent on bedding anisotropy. The stiffness and brittle strength of samples cored vertically were somewhat lower than those of the horizontal samples. Only small amount of dilatancy was observed for the siltstone prior to brittle failure. The principal stresses for the samples cored perpendicular to the strike of the core axis and bedding simulated those in a thrust faulting regime, and the failure mode in these samples was characterized by almost planar shear faults that were aligned along the dip of the bedding, with the implication that bedding anisotropy may have dominant control over the style of faulting. The bioturbated sandstone samples from ~588 m have porosities of 15-18 %. While their brittle strengths were comparable to those of the shaly siltstone, they were elastically stiffer. Their permeabilities were relatively high, on the order of 10^-14 m² at effective pressures of 5-20 MPa. The permeability was observed to decrease with increasing effective pressure, but increase after brittle faulting had occurred. In contrast, the shaly siltstone samples from ~837 m were relatively tight, with permeabilities on the order of 10¹⁸-10¹⁹ m² at effective pressures of 5-40 MPa. Significant permeability anisotropy was observed, with the permeability of a sample cored parallel to the bedding higher than that cored perpendicular by an order of magnitude. The effects of stress on permeability in the shaly siltstone and sandstone samples were similar.
DE: 8100 TECTONOPHYSICS
DE: 8168 Stresses: general
SC: Tectonophysics [T]
MN: Fall Meeting 2005