Technical Paper: Stress and Seismic Anisotropy Near Salt Bodies – Numerical Modeling and Observation from Wide-Azimuth Marine Data

Society: EAGE
Paper Number:
Presentation Date: 2007

Wide-azimuth marine data enable us to observe and analyze the azimuthal response of marine sediments. Modeling the stress near salt bodies using realistic salt geometry and a finite-element solver, we show that the presence of salt bodies cause changes in the orientation of the stress in the sediment near the salt. Thus, horizontal stresses magnitude and direction may vary near salt bodies. We use third-order elasticity (TOE) theory to quantify the expected stress induced changes in elastic stiffness and seismic velocity. We show that if we assume orthorhombic media, we can expect changes in azimuthal velocity as the maximum and minimum horizontal stresses are different. The magnitude of the stress changes depends on the TOE coefficients. Using published values from the Gulf of Mexico shales, we can expect the azimuthal anisotropy to be anywhere between 20m/s to more than 300m/s. We show that azimuthal analysis of wideazimuth seismic data can be used to derive the direction of maximum and minimum stresses. These results show that, in principal, wide-azimuth marine seismic data analysis can provide useful information with respect to the state of stress and potential drilling hazards in the formation near the salt.

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