Tilted orthorhombic velocity model building and imaging of Zamzama gas field with full-azimuth land data

摘要

Many geologic plays show indications of azimuthal an-isotropy caused by azimuthal stress differences and fractures, which need to be accounted for during velocity model building and depth imaging. To fully observe azimuthal anisot-ropy, 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.