Shale anisotropic elastic modelling and seismic reflections

Wu, Xiaoyang; Uden, Richard; Chapman, Mark. 2016 Shale anisotropic elastic modelling and seismic reflections. Journal of Seismic Exploration, 25 (6). 527-542.

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Abstract/Summary

Shales are rocks with various mineralogies and complex fabric, which exhibit strong anisotropy. The change in effective velocities due to kerogen content and pore geometry influences the AVO (Amplitude Versus-Offset) behavior of shale-gas formations. How the conventional seismic survey plays its role in the exploration of unconventional shale gas is a key issue. In this paper, we present a method for estimating the anisotropic elastic stiffness of organic shales. The model takes mineralogy, kerogen, pore geometry and cracks, as well as the saturated fluids into consideration. A compaction-dependent Orientation Distribution Function (ODF) is incorporated to quantify the anisotropy originating from the preferential orientation of non-source shale inclusions. Comparison of the estimated elastic stiffnesses with experimental measurements of shale core sample from the Bazhenov formation indicates this method has the potential to estimate the elastic properties of organic shales. We also use another example from Eagle Ford formation to study the feasibility of distinguishing between proppant suspending hydraulic fluid and contacting with matrix during hydraulic stimulation stage. A half-space model with anisotropy due to multi-set of cracks is constructed to investigate the AVAZ reflections from the interface. The results indicate that the AVAZ behavior of PP reflection is different between proppant suspending fluid case and contacting with matrix case. The converted P-SH wave and SH-wave exploration may also offer detection of crack properties (distribution and intensity) to optimize shale gas production.