Angus, DA, Hildyard, MW, Verdon, JP et al. (1 more author) (2012) Exploring trends in microcrack properties of sedimentary rocks: An audit of dry and water saturated sandstone core velocity-stress measurements. Geophysical Prospecting, 3 (4A). 822 - 833. ISSN 2156-8359
Abstract
Stress dependent rock physics models are being used more routinely to link mechanical deformation and stress perturbations to changes in seismic velocities and seismic anisotropy. In this paper, we invert for the effective non-linear microstructural parameters of 69 dry and saturated sandstone core samples. We evaluate the results in terms of the model input parameters of two non-linear rock physics models: A discrete and an analytic microstructural stress-dependent formulation. The results for the analytic model suggest that the global trend of the initial crack density is lower and initial aspect ratio is larger for the saturated samples compared to the corresponding dry samples. The initial aspect ratios for both the dry and saturated samples are tightly clustered between 0.0002 and 0.001, whereas the initial crack densities show more scatter. The results for the discrete model show higher crack densities for the saturated samples when compared to the corresponding dry samples. With increasing confining stress the crack densities decreases to almost identical values for both the dry and saturated samples. A key result of this paper is that there appears to be a stress dependence of the compliance ratio BN/BT within many of the samples, possibly related to changing microcrack geometry with increasing confining stress. Furthermore, although the compliance ratio BN/BT for dry samples shows a diffuse distribution between 0.4 and 2.0, for saturated samples the distribution is very tightly clustered around 0.5. As confining stresses increase the compliance ratio distributions for the dry and saturated samples become more diffuse but still noticeably different. This result is significant because it reaffirms previous observations that the compliance ratio can be used as an indicator of fluid content within cracks and fractures. From a practical perspective, an overarching purpose of this paper is to investigate the range of input parameters of the microstructural models under both dry and saturated conditions to improve prediction of stress dependent seismic velocity and anisotropy observed in time-lapse seismic data due to hydro-mechanical effects related to fluid production and injection.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | (c) 2012, Angus, DA, Hildyard, MW, Verdon, JP and Fisher, QJ. This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. |
Keywords: | Compliance ratio; microcrack properties; saturated; stress dependent velocities; ultrasonic |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 04 Mar 2014 09:59 |
Last Modified: | 29 Mar 2018 03:56 |
Published Version: | http://dx.doi.org/10.4236/ijg.2012.324083 |
Status: | Published |
Publisher: | Scientific Research Publishing |
Identification Number: | 10.4236/ijg.2012.324083 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:77937 |