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Rock Physics Constrained Estimation of Shale Anisotropy for Microseismic Processing - From VTI to ORThorhombic
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 77th EAGE Conference and Exhibition 2015, Jun 2015, Volume 2015, p.1 - 5
Abstract
Shale intrinsically exhibits transverse isotropy because of the alignment and lamination of softer and platy clay mineral and organics. The presence of preferred-aligned fractures usually cause azimuthal anisotropy. If the fractures in shale are orthogonal to fabric alignment, the intrinsic transverse isotropy and additional fracture-induced azimuthal anisotropy combine to form an equivalent orthorhombic model. Rock physics studies provide useful constraints for such orthorhombic velocity model. The fabric anisotropy of shale strongly depends on compliant and platy components of shale, e.g. clay and kerogen, but can be weakened by stiffer and non-platy minerals, e.g. quartz. We use these relationships constrain the optimization of fabric anisotropy of Horn River shales. The optimized VTI model not only improves the time misfit and locations of microseismic events, but is explicable geologicaly and physically. Schoenberg’s theory give us a simple and effective way of including the effect of fractures. Fracture-induced anisotropy is expressed in terms of normal and tangential fracture compliance. Theoretical modeling and measurements show that fracture compliances increase with fracture size and normal to tangential fracture compliances ratio ZN/ZT is less than or slightly larger than 1. The optimized ZN and ZT is consistent with other measurements in crosshole and microseismic scale.