Inversion Ready Gathers- Global Geophysical Services
Inversion Ready Gathers
Useful amplitude and velocity information resides in the 30 - 50 degree incidence angles of 3D seismic data. Including these far-angular offset amplitudes in pre-stack inversions reduces uncertainty in acoustic impedance, elastic impedance, and density estimates of various geologic layers. Further, quantifying how far-offset amplitudes and velocities vary with azimuth may reveal rock fractures.
Azimuthal velocity variations in the earth, characterized as HTI anisotropy, manifest as small shot-receiver azimuth related timing distortions in 3D seismic data, especially on the higher (>30 degree) angular offsets. If not properly corrected during imaging, these timing distortions will adversely affect bandwidth and amplitudes during Kirchhoff summation into final offset traces. This far-angle bandwidth and amplitude distortion of the final migrated gathers negatively impacts pre-stack inversion and the accuracy of rock property attributes, especially shear velocity and density attributes.
The solution is to process the data in an offset and azimuthally friendly manner, incorporating both VTI and HTI anisotropy into the pre-stack migration step. By doing so, Global's processing produces accurately positioned steep dip and fault planes, and also helps preserve far-offset amplitude information. Our patented technology produces offset and azimuth amplitude preserved final gathers, which are flat in both offset and azimuth out to 55 degrees of angular offset. Having accurate amplitude information at the far-angular offsets is crucial to estimating rock properties using elastic inversion techniques. Global calls offset-azimuth gathers that preserve true amplitude and are flat in offset and azimuth domains "Inversion Ready Gathers."
Characterizing both Velocity vs. Azimuth (VVAz) and Amplitude vs. Azimuth (AVAz) using the "Inversion Ready Gathers" approach produces two independent attributes directly related to the Thomsen anisotropy parameters, and potentially related to fracture density and direction. These attributes may be co-rendered and visually related to well productivity. They also may be integrated with a full suite of post-stack and pre-stack seismic attributes to create 3D predictive models. Reliable well productivity predictions can equate to better well planning, reduced risk and field development costs, and optimal field productivity.
Global's seismic solutions include data acquisition, ambient seismic monitoring and analysis, data processing, reservoir geophysics and integrated interpretation and consulting services. Our objective is to help oil and gas companies reduce field development cost through optimized well placement and well completion.