Estimation of Fracture Density and Orientation Through Azimuthal Processing and Interpretation of Seismic Data

摘要

The determination of fracture density and orientation is important in plays in which reservoir permeability is associated withmicro-fractures. In these reservoirs, effective porosity is dependent upon the density of open fractures and permeability has adirectivity component associated to the fractures' orientation. Accurate determination of fracture density and orientationusing surface seismic helps, then, in determining locations of good reservoir storability, as well as directional drillingorientation for optimum permeability. The anisotropy of P- and S-wave velocities is commonly associated with themagnitude and orientation of stress fields or open fractures and hence, is the medium through which factures can becharacterized using surface seismic data. A case study in the Marcellus Shale (NE United States) is presented in which PP and PS wide azimuth seismic data,acquired and processed to preserve the amplitude and velocity information of the source-receiver azimuth, are used tocompute anisotropic attributes from which a qualitative analysis of fracture density and orientation is done. The Marcellus Shale is known to have two sets of fractures (joints) associated to different tectonic events. Particular tothis play is that one set of joints is perpendicular to the co-located macro-fractures. In this case, although curvature or othergeometric attributes reveal the strike of macro-fractures, this does not correspond to the joint sets, which are at sub-seismicresolution. Anisotropy analysis through elliptical inversion of P-wave velocities identifies both sets of micro-fractures andverifies their expected position in relationship to the oroclinal belt and the macro-fractures. Analysis of PS migrated stackssupports these observations.