HR: 15:25h
AN: H12H-08    [PDF]
TI: Clay in Contact Zones: NMR and Ultrasonic Effects
AU: * Prasad, M
EM: manika.prasad@stanford.edu
AF: Geophysics Department, SRB, Stanford University 397 Panama Mall, Stanford, CA 94305 United States
AU: Bryar, T
EM: tbryar@hotmail.com
AF: Stanford Environmental Geophysics Laboratory, Stanford University 397 Panama Mall, Stanford, CA 94305 United States
AB: Presence of clay minerals in soils can affect acoustic impedance considerably. Clay in the contact area lowers the micro- and macrostructural impedance of the formations. We have investigated changes in acoustic properties as the clay dries and changes from a damping to a cementing agent. The study is aimed at understanding the role of clay minerals in saturated to partially saturated soils. METHODS: Acoustic waves were propagated through two discs in contact. The contact zone between the discs was filled with thin layers of dry clay, clay slurry that was allowed to dry slowly, and air. We monitored water content by weighing. Pore size distribution was measured by NMR experiments. We report here waveforms of P- and S-wave signals transmitted through the air-coupled, dry clay-coupled, and cemented clay-coupled quartz discs. RESULTS: We find that the state of the clay changes the wave propagation characteristics in a very pronounced manner. Addition of a water saturated clay layer to quartz discs dampens waves significantly. Significant signal damping occurs after applying a 0.05 mm thick clay layer in the contact region between glass discs. The effect is more pronounced in the S-waves than in the P-waves. However, as the clay dries, it acts as a strong cementing agent and enhances wave propagation through the clay-cemented quartz discs. The NMR experiments allowed us to measure the pore size distributions corresponding to the acoustic measurements. As the average water content decreases, the average water layer thickness decreases from 600 nm in the wet slurry to 56 nm in the partially saturated clay, and 7 nm in the almost dry clay cement with most of the signal coming from capillary water.
UR: http://pangea.stanford.edu/~manika/AGU2003
DE: 3929 NMR, Mossbauer spectroscopy, and other magnetic techniques
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 5114 Permeability and porosity
DE: 5144 Wave attenuation
SC: Hydrology [H]
MN: 2003 Fall Meeting