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oa Depth versus Time Imaging of 3D seismic data – Tabu Field
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, PGCE 2005, Dec 2005, cp-257-00008
Abstract
This paper describes the Kirchhoff Pre-stack Depth Migration processing of marine 3D seismic data acquired over the Tabu prospect, offshore Peninsular Malaysia and compares the results with the Pre-stack Time Migration. The survey covered an area of approximately 230 km2 and was processed through pre-stack time migration and Pre-stack Depth Migration processing flow. There are three target zones that can be identified on a crossline passing through the crest of the anticlinal structure: 1.5 s, 1-1.2 s, and 3.2 s. and the primary objective of the PSDM was to improve the stratigraphic definition of the reservoir obtained from the Kirchhoff pre-stack time migration processing. A new smooth velocity model approach was applied, where the initial model building consisted of a simple Dix conversion of the pre-stack time migration velocities and subsequent smoothing. The resultant velocity model is then perturbed to varying degrees in order to find the percentage of the velocity model which, when applied, will slightly over-correct the CRP gathers. The reason being as slightly overcorrected gathers provide optimum input to the inversion phase. There is a clear trend in the industry to analyze the physical parameters of the subsurface much more densely than previously done. For this kind of dense data, CGG has implemented a new methodology for imaging velocity analysis, based on the RMO inversion method and aimed at: • Improving resolution using the dense automated velocity analysis for model building.<br>• Reducing overall project turnaround by using automated picking and multi-layer inversion. Compared with the Pre-STM result, the Pre-SDM has resulted in the following: a. sharper fault definition; b. correction for the pushdown due to shallow gas pockets; c. a better understanding of the structure of the deeper events (in some cases a relatively flat structure interpreted at later times on the Pre-STM volume appeared to have a lot more folding associated with it than first thought).