Azimuthal anisotropy investigations for P and S waves: a physical modelling experiment

Khaled Al Dulaijan, Gary F. Margrave, and Joe Wong

ABSTRACT

Information related to fracture orientation and intensity is vital for the development of unconventional hydrocarbons, such as tight sand gas and shale gas. Numerical modeling provides a valuable tool for geophysicists to test and validate their methodologies that provide them with information about reservoirs. Fractures make numerical modeling more complicated and introduce complexities that might even require geophysicists to validate their numerical models before using them to assess their methods. Alternatively, physical modeling provides a unique opportunity to test, validate, and develop methods for characterizing fractured reservoirs. This report utilizes seismic physical modeling for fracture characterization.

A two-layer model was built using vertically laminated Phenolic overlain by Plexiglas to represent a fractured reservoir overlaid by an isotropic overburden. The first dataset was acquired over that 2-layer model and consist of three 9-component common-receivers. P-wave first-arrival times were analyzed on all three gathers and fracture orientation was predicted. An Alford rotation was applied to the four horizontal components and successfully minimized energy on components other than those two that are related to the fast S wave and slow S wave. However, the angle between natural and acquisition coordinate systems was not predicted correctly. One possible reason could be the contact between the two media. Therefore, another dataset was acquired using a single Phenolic layer. Alford rotation was applied and the angle between natural and acquisition coordinate system was predicted correctly. That dataset was used too to measure the stiffness coefficients tensor using group velocity data.

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