Hu, Leon L.*1; Saleh, Saleh 1; Sliz, Krzysztof 1; Ley, Robert E.1
(1) Saudi Aramco, Dhahran, Saudi Arabia.
In the presence of complex structuring, wave equation migration (WEM) usually produces more accurate subsurface images than the ray-based methods, such as the Kirchhoff migration, but it is also computationally more expensive. Most onshore exploration targets in the Middle East are overlaid by complex geology in the near-surface. This complex near-surface remains one of the biggest challenges in onshore seismic data processing, and if it is not handled properly, poor imaging caused by wavefield distortion can mask the deeper targets.
Conventional datum static corrections can fail to resolve the complex near-surface related problems. Wave equation datuming (WED) techniques via high fidelity downward continuation algorithms can offer more accurate solutions. WED, however, can be problematic for large 3D seismic datasets for two reasons: (1) WED is computationally expensive because it downward continues the data in small depth steps, and because of the sorting of data between source and receiver domains at each depth level, and (2) the sources are usually sparsely sampled spatially, which leads to severe aliasing problems after WED. As a result, implementing WED techniques on large 3D seismic datasets can be impractical.
To overcome issues mentioned above, we propose a hybrid approach that combines a high fidelity WED algorithm with an efficient Kirchhoff prestack depth migration technique. This hybrid approach allows us to handle strong heterogeneity in the near-surface, as well as the deep structures in a practical way. To effectively handle the complex near-surface and topography, we use an explicit wavefield extrapolation WED technique. The algorithm is extended to extrapolate data directly from topography by building wavefield extrapolators with laterally variable depth steps. This is done to handle strong lateral velocity variations and large topographic changes. To avoid sorting the data and overcome the source sampling issues, we apply WED only to the receivers. This requires Kirchhoff PSDM be applied from two different surfaces; one for the source, and the other for the extrapolated receivers. We will demonstrate the implementation of this approach on a large onshore 3D seismic dataset and show how turning ray tomography was used to construct a high resolution near-surface velocity model. We will also briefly describe the modified datuming algorithm.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain