Abstract
Scanning and transmission electron microscopy, synchrotron X-ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub'al-Khali basin, Saudi Arabia. Kaolinite, illite-smectite, illite-mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4-6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P-wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P-wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P-wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging. © 2011 European Association of Geoscientists & Engineers.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 536-556 |
| Number of pages | 21 |
| Journal | Geophysical Prospecting |
| Volume | 59 |
| Issue number | 3 |
| DOIs | |
| State | Published - Feb 17 2011 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledged KAUST grant number(s): KUS-I1–004-21
Acknowledgements: This project is supported by NSF (EAR-0836402) and DOE (DE-FG02-05ER15637). This publication was in part supported by Award No KUS-I1–004-21, made by the King Abdullah University of Science and Technology (KAUST), which initiated the contact with researchers in Saudi Arabia, especially Edgardo Nebrija (ARAMCO). We would particularly like to thank Dr Walter Voggenreiter (Exploration Manager), Geoff Pike and other staff of the South Rub’al-Khali Company (SRAK) for providing us with shale samples and useful information. We acknowledge the Ministry of Petroleum, Saudi Arabia as well as Saudi Aramco, SRAK and Shell for permission to publish the information obtained in this study. We are appreciative for access to beamline 11-ID-C at APS and assistance from Yang Ren for diffraction experiments and access to beamline TOMCAT at SLS and assistance from Rajmund Mokso for tomography experiments. We also greatly appreciate the help from Luca Lutterotti for updating the MAUD software, Marco Voltolini for suggestions with data analysis and Kai Chen for help with tomography data processing. Hans-Rudolf Wenk is appreciative for the hospitality and access to facilities at GFZ Potsdam. We thank David Dewhurst and two anonymous reviewers for helpful and constructive comments on the first version of this manuscript.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.