SPECIAL SECTION: I m a g i n g m i g r a t i o n Tilted orthorhombic velocity model building and imaging AbstractMany geologic plays show indications of azimuthal anisotropy caused by azimuthal stress differences and fractures, which need to be accounted for during velocity model building and depth imaging. To fully observe azimuthal anisotropy, multiple narrow-azimuth surveys or wide-azimuth or full-azimuth surveys are required. Modern land surveys usually are shot with full-azimuth coverage, which enables one to address azimuthal velocity changes if present. A reprocessing and imaging project has been conducted of a full-azimuth land survey over Pakistani Zamzama gas field where azimuthal anisotropy is observed. The major geologic structure in this field is a large anticline split by a prominent fault zone trending north-south. The prestack depth-imaging workflow first exhausted tilted-transverse-isotropy (TTI) assumptions and then attempted tilted orthorhombic velocity model building and imaging. The processing flow, velocity model-building methodology, and successful results of final imaging with tilted orthorhombic anisotropic assumptions can be demonstrated. Success is measured with seismic to well-tie analysis.

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