HR: 0800h
AN: H41B-0409    [Abstracts]
TI: Seismic Monitoring of Fracture Formation
AU: * Pyrak-Nolte, L J
EM: ljpn@physics.purdue.edu
AF: Department of Physics, Purdue University, 525 Northwestern Ave., West Lafayette, IN 47907-2036 United States
AU: * Pyrak-Nolte, L J
EM: ljpn@physics.purdue.edu
AF: Department of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907-2051
AU: de Pater, C J
EM: c.j.depater@mp.tudelft.nl
AF: Faculty of Mining and Petroleum Engineering, Delft University of Technology, Mijnbouwstraat 120, Delft, 2628 RX Netherlands
AU: Jocker, J
EM: J.Jocker@CITG.TUDelft.NL
AF: Faculty of Mining and Petroleum Engineering, Delft University of Technology, Mijnbouwstraat 120, Delft, 2628 RX Netherlands
AB: Seismically tracking fracture formation is an important step in the monitoring of subsurface sequestration reservoirs. In this paper we report on laboratory experiments that were performed to investigate seismic transmission across a slowly propagating fracture to monitor how fracture heterogeneity varied due to changing stress conditions. Experiments were performed on a cube of Pierre Blue limestone with dimensions 0.3 m by 0.3 m by 0.3 m in a tri-axial pressure machine consisting of three independent loading frames. Two seismic arrays were used to propagate compressional and shear waves through the sample prior to, during, and after fracturing. Each array was composed of sixteen piezoelectric transducers (eight compressional-mode and eight shear-mode) with a central frequency of 1 MHz. After the sample was removed from the triaxial frame, a laser profilometer was used to measure the geometry of the fracture surfaces. The seismic array data produced a time-dependent two-dimensional map of the propagating fracture tip and the resulting fracture. The transmitted signals showed a 5%-10% increase in amplitude as a precursor to the main fracturing event after which the transmitted energy decreased to 1%-15% of its original value. The observed increase in amplitude prior to major failure is caused by constructive interference from diffraction from the tip of the fracture before the fracture tip was even under the sensors. Numerical simulation shows that the precursory increase in amplitude is a function of the specific stiffness of the fracture tip and the frequency of the signal. Post-fracturing characterization of the fracture topology identified anisotropic features in the fracture aperture that correlated with the direction of fracture propagation observed in the seismic data. The seismic signal, combined with the fracture characterization, supports the hypothesis that seismic signals can provide specific information about fracture formation and the resulting fracture geometry. This work demonstrates the potential for developing seismic methods for characterizing time-dependent fracture formation and fracture properties. Acknowledgments: LJPN wishes to acknowledge the Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy, the University Faculty Scholar program at Purdue University, and the Delft University of Technology
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 5102 Acoustic properties
DE: 5114 Permeability and porosity
DE: 5144 Wave attenuation
SC: Hydrology [H]
MN: Fall Meeting 2005