HR: 11:25h
AN: H22B-05    [Abstracts]
TI: The Effect of Mineral Deposition on the Hydraulic and Seismic Properties of Fractures
AU: Gilbert, Z A
EM: gilbertz@purdue.edu
AF: Department of Physics, Purdue University, 525 Northwestern Ave , West Lafayette, IN 47907 United States
AU: * Acosta-Colon, A A
EM: aacosta@physics.purdue.edu
AF: Department of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Dr, West Lafayette, IN 47907 United States
AU: Pyrak-Nolte, L J
EM: ljpn@physics.purdue.edu
AF: Department of Physics, Purdue University, 525 Northwestern Ave , West Lafayette, IN 47907 United States
AU: Pyrak-Nolte, L J
EM: ljpn@physics.purdue.edu
AF: Department of Earth & Atmospheric Sciences, Purdue University, 550 Stadium Mall Dr, West Lafayette, IN 47907 United States
AB: Fractures and other subsurface discontinuities can be altered over time from geochemical interaction with the pore fluids. Alteration of the pore space in a fracture will affect the seismic and hydraulic properties of a fracture. Mineral deposition can alter the fracture specific stiffness by changing the size and strength of the contact area and/or filling-in the void space which will reduce the flow rate. We performed acoustic imaging experiments on single fractures in granite to determine the effect of mineral deposition on the seismic and hydraulic properties of single fractures. Prior to and after mineral precipitation (CaCO3), the samples (110 mm x 104 mm x 70 mm) were imaged over a 64 mm by 64 mm region using transmitted compressional waves (~1 Mhz). Eight ports were distributed around the perimeter of the fracture to measure the variation in flow as a function of position, as well as prior to and after chemical invasion. After mineral precipitation, the flow rate decreased by approximately 90%. The decrease in flow rate can be attributed to reduction of the fracture aperture and blocking of flow paths by mineralization. We observed that the initial void geometry controlled the amount and spatial distribution of mineral deposition within the fracture. The most reliable seismic indicator that the fracture had been altered was a reduction in the variance of the frequency distribution of the received signal. The reduced variance indicates that the fracture is homogenized by mineral deposition in the fracture voids (i.e. tending toward a move uniform fracture stiffness). Homogenization occurs because the mixing predominantly takes place in the dominant flow paths within the fracture, which tend to have lower fracture stiffness. The results indicate that acoustic imaging techniques are required in this characterization because they provide statistical indicators that help monitor changes in fracture geometry caused by mineral deposition. Acknowledgments: Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy. LJPN wishes to acknowledge University Faculty Scholar program at Purdue University
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 1832 Groundwater transport
DE: 1894 Instruments and techniques
DE: 0400 Biogeosciences
DE: 0900 EXPLORATION GEOPHYSICS
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting