The main objective of this project was to quantify rock microstructures and their effects in terms of elastic impedances in order to quantify the seismic signatures of microstructures. One special focus was to understand how sub-resolution heterogeneities affect observable seismic signatures.

Stanford University
Stanford, CA

Attempts to relate microstructural properties and reservoir properties controlled by microstructure to seismic data have been problematic. One problem is that microstructure is difficult to quantify geometrically and elastically. This problem is addressed in this project by measuring, analyzing, and quantifying the impedance microstructure of sands and shales at pore-scale resolution and analyzing their relations to corresponding measurements of seismic properties.

Project Results
Acoustic microscopy and ultrasonic measurements were used to quantify microstructures and their effects on elastic impedances in sands and shales.

Benefits
The main benefit of this project was the development of key technologies for quantitatively interpreting seismic images and the linkage of seismic data with geologic models to estimate reservoir properties. For the public, ultimately, better technologies for reservoir characterization translates to better reservoir development, reduced risks, and hence reduced energy costs.

Project Summary
Over 250 scanning acoustic microscope images of impedance microstructures in shales were analyzed quantitatively. Relations were obtained between textural heterogeneity and anisotropy, and shale maturation and kerogen content. Consistent measurements of elastic moduli of clay minerals using ultrasonic methods and acoustic force microscopy were obtained. It was found that theoretical models give better predictions when the new measured values of clay were used. Empirical velocity-pressure and porosity-pressure trends were developed from P- and S-wave ultrasonic measurements on unconsolidated sands. Trends such as these are critical for better understanding and predicting the hazards posed to offshore drilling by unknown overpressures at shallow depths.

Project accomplishments include:

• Studies on the effects of sorting, compaction, and stratification in sediments on the Vp and Vs seismic signatures.
• Quantitative acoustic microscopy study of textures for reservoir rocks.
• Nanometer-scale measurements of elastic properties of clay.

The project has been completed.

$ 450,000

$115,000 (20% of total)

NETL - Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021)
Stanford U. - Gary Marko (mavko@stanford.edu or 650-723-9438)

Publications
Vega, S., 2003, Intrinsic and stress-induced velocity anisotropy in unconsolidated sands, Ph.D. thesis, Stanford University (http://srb.stanford.edu/Theses/theses04.html)

Zimmer, M., 2003, Controls on the seismic velocities of unconsolidated sands: Measurements of pressure, porosity and compaction effects, Ph.D. thesis, Stanford University (http://srb.stanford.edu/Theses/theses04.html)

Prasad, M., and Mukerji, T., Analysis of microstructural textures and wave propagation characteristics in shales, SEG Exp. Abstr., 73rd Ann. Intl. Mtg., 2003.

Vega, S., Mukerji, T., Mavko, G., and Prasad, M., Stratification in loose sediments and its seismic signature, SEG Exp. Abstr., 73rd Ann. Intl. Mtg., 2003.

Vega, S., Prasad, M., and Mavko, G., Comparative study of velocities under hydrostatic and nonhydrostatic stress in sands, SEG Exp. Abstr., 73rd Ann. Intl. Mtg., 2003.

Vanorio, T., Prasad. M., and Nur, A., Elastic properties of dry clay mineral aggregates, suspensions, and sandstones, Geophys. J. Int., 155, 2003, pp. 319-326.

Prasad, M., Reinstaedtler, M., Nur, A., and Walter, A., Quantitative Acoustic Microscopy: Application to petrophysical study of reservoir rocks, Acoustical Imaging, 26, 2002, pp. 493-502.

Prasad, M., Kopycinska, M., Rabe, U., and Arnold, W., Measurement of Young's modulus of clay minerals using atomic force acoustic microscopy, Geophys. Res. Lett., 29, 2002, p. 1238.

Zimmer, M., Prasad, M., and Mavko, G., Empirical velocity-pressure and porosity-pressure trends in unconsolidated sands, SEG Exp. Abstr., 72rd Ann. Intl. Mtg., 2002.

Zimmer, M., Prasad, M., and Mavko, G., Pressure and porosity influences on Vp-Vs ratio in unconsolidated sands, The Leading Edge, V. 21, No. 2, 2002, p. 178.