C-wave Spectral Broadening to Match P-wavelengths for Improved Fracture/Lithology Characterization
Gaiser, James 1; Verm, Richard 2; Chaveste, Alvaro 3; Hall, Michael A.*4
(1) Geokinetics Inc., Centennial, CO. (2) Geokinetics Inc., Houston, TX. (3) Geokinetics Inc., Houston, TX. (4) Geokinetics Inc., Calgary, AB, Canada.
The Marcellus shale has become an active area for gas exploration, and has fracture and lithology characteristics that make it a good candidate for multicomponent data. It is well established that similar vertical wavelength ranges must be preserved in multicomponent data and that wavelengths of P- and S-waves must match in order to sample reflectivity in an equivalent manner. Although registration functions align corresponding stratigraphic events of the P-wave and P- to S-wave (C-wave) reflections, they distort the seismic wavelet because global average velocity properties are independent of local interval properties that define wavelength.
In this study we apply a velocity-based wavelet correction method to C-waves, which is expressed as a function of interval and average VP/VS, to match wavelengths of the P-wavefield. Also, we examine the effect of this function for both land and marine data examples and find that surveys with shallow targets are more dramatically affected, and may require spectral broadening of the wavelet. Data from the Marcellus shale and the encasing carbonates in northeast Pennsylvania, show significant bandwidth improvements for C-waves when wavelet corrections based on velocity match their wavelengths with P-waves. Application of these wavelet corrections should benefit spatial resolution for Kirchhoff prestack migration, registration fidelity, joint AVO/A (offset and azimuth) inversions and attribute analyses.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain