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Fluid-dependent anisotropy and experimental measurements in synthetic porous rocks with controlled fracture parameters

Ding, Pinbo; Di, Bangrang; Wei, Jianxin; Li, Xiangyang; Deng, Yinghua. 2014 Fluid-dependent anisotropy and experimental measurements in synthetic porous rocks with controlled fracture parameters. Journal of Geophysics and Engineering, 11 (1), 015002. 10.1088/1742-2132/11/1/015002

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Abstract/Summary

In this study, we analyse the influence of fluid on P- and S-wave anisotropy in a fractured medium. Equivalent medium theories are used to describe the relationship between the fluid properties and the rock physics characteristics in fractured rocks, and P-wave and S-wave velocities and anisotropy are considered to be influenced by fluid saturation. However, these theoretical predictions require experimental measurement results for calibration. A new construction method was used to create synthetic rock samples with controlled fracture parameters. The new construction process provides synthetic rocks that have a more realistic mineral composition, porous structure, cementation and pressure sensitivity than samples used in previous research on fractured media. The synthetic rock samples contain fractures which have a controlled distribution, diameter, thickness and fracture density. In this study, the fracture diameter was about 4 mm, the thickness of fractures was about 0.06 mm, and the fracture density in the two fractured rock samples was about 3.45%. SEM images show well-defined penny-shaped fractures of 4 mm in length and 0.06 mm in width. The rock samples were saturated with air, water and oil, and P- and S-wave velocities were measured in an ultrasonic measurement system. The laboratory measurement results show that the P-wave anisotropy is strongly influenced by saturated fluid, and the P-wave anisotropy parameter, ε, has a much larger value in air saturation than in water and oil saturations. The S-wave anisotropy decreases when the samples are saturated with oil, which can be caused by high fluid viscosity. In the direction perpendicular to the fractures (the 0° direction), shear-wave splitting is negligible, and is similar to the blank sample without fractures, as expected. In the direction parallel to the fractures (the 90° direction) shear-wave splitting is significant. The fractured rock samples show significant P- and S-wave anisotropy caused by the fractures and controlled by the saturated fluids.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1088/1742-2132/11/1/015002
ISSN: 1742-2132
Date made live: 05 Jun 2014 15:36 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/507372

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