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Velocity Anisotropy of Unconsolidated Sands and its Relation to Induced Stress Response
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 76th EAGE Conference and Exhibition 2014, Jun 2014, Volume 2014, p.1 - 5
Abstract
Velocity anisotropy is an important parameter in seismic imaging, AVO analysis, and sonic log interpretation. Isotropic sands or sandstones can behave anisotropically if subjected to anisotropic stress. The variations in velocity anisotropy in sands can also be due to discontinuity of the boundary between sand grains influenced by mineral and textural differences. Since the velocity anisotropy can be induced by stress, the velocity anisotropy in rocks can indicate stress anisotropy. This study investigates velocity anisotropy and its relation to induced stress response (stress anisotropy) affected by mineralogy and textures of seven unconsolidated natural sands by experimental mechanical compaction under uniaxial strain condition. The results show that velocity anisotropy and its relation to induced stress response are significantly affected by mineral compositions and textural differences. Our findings have potential applications in velocity anisotropy and induced stress anisotropy in shallow sands where compaction is mainly mechanical. The close correlation between these two anisotropic parameters (velocity and induced stress response) can also be used for detecting stress anomalies using velocity anisotropy. By inverting the stress anisotropy, induced horizontal stress changes can be obtained and can be useful for many in-situ stress applications i.e. fault seal analysis, wellbore stability, and compaction and subsidence studies.