As part of our study on "Relationships between seismic properties and rock microstructure", we have studied 1. Kerogen-rich shales using Scanning Acoustic Microscopy and ultrasonic wave propagation. We find that an increase in elastic modulus with increasing kerogen maturity can be directly related to the microstructural acoustic impedance changes. A positive relation is established between microstructural changes and velocity variations as functions of kerogen maturity. 2. Elastic properties of clay minerals using Atomic Force Acoustic Microscopy and Scanning Acoustic Microscopy. We show the effect of clay minerals in contact zones as load-bearing constituents of rocks 3. Elastic properties of unconsolidated sediments in an effort to quantify attributes for detection of overpressures from seismic and for effects of stress-induced velocity anisotropy in sediments 4. We have initiated efforts for velocity upscaling to quantify long-wavelength and short-wavelength velocity behavior and the scale-dependent dispersion caused by sediment variability in different depositional environments.4
INTRODUCTIONIn this quarter, we submit results of our research on: impedance mapping on a micrometer scale and its relation to centimeter-scale core measurements of impedance, measurements of clay modulus using Atomic Force Acoustic Microscopy (AFAM) and measurements of seismic properties of unconsolidated sediments at very low effective pressures. Five papers have been published on the work done in the first year of this project. This report presents reprints of our publications relevant to this project on impedance mapping, AFAM measurements, and overpressure analyses.
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PAPER 1Prasad, M., Reinstaedtler, M., Nur, A., and Walter A.: Quantitative Acoustic Microscopy: Application to Petrophysical Studies of Reservoir Rocks: Acoustical Imaging, Vol. 26,[493][494][495][496][497][498][499][500][501][502] We demonstrate here applications of scanning acoustic microscopy (SAM) to quantify microstructure as variations in acoustic impedance. The acoustic maps can then be used to understand the seismic response of the rock. For example, ultrasonic measurements on kerogen shales have shown that the elastic modulus increases with increasing kerogen maturity. SAM of these shales shows a stiffening of the shale framework with increasing kerogen maturity. The load-bearing material changes from low impedance kerogen to high impedance shale. The impedance values determined from SAM are comparable with those obtained from ultrasonic time-of-flight data. In contrast, the cement is load bearing in sandstones where high impedance quartz grains are cemented together by low impedance clay. The cement determines not only the total impedance of the rock but also its pressure dependence.Paper 1: Total of eight figures in paper 8
PAPER 2Zimmer, M., Prasad, M., and Mavko, . Ann. Internat. Mtg., Soc. Expl. Geophys., Expanded Abstracts, Paper RP2.5. Presence of clay minerals, hydrous aluminosilicates with grain size smaller than 2 mm, We develope...