Overcoming the challenges of a shallow water sparse wide azimuth survey to improve deep reservoir imaging in the East China Sea
A new broadband wide azimuth towed streamer (WATS) survey was acquired to better resolve reservoir compartments in a shallow water region of the East China Sea. To offset the shortcomings of narrow azimuth acquisition along the strike direction, two vessels were added side by side as additional source vessels to form the WATS acquisition geometry for this survey. This WATS acquisition was much sparser than typical WATS surveys used in deepwater environments due to its one sided configuration. The combination of sparse acquisition, shallow water, and deep targets set the challenge of how to optimally reveal the potential of side gun data to improve the final image. Three dimensional effects and severe aliasing in the crossline direction pose significant challenges for side gun data processing. We present a comprehensive workflow to resolve these challenges consisting of 3D deghosting, 3D model based water layer demultiple, 3D surface related multiple elimination, and 4D regularization for sparse and shallow water wide azimuth data. A tilted orthorhombic velocity model is built with better constraints from the wide azimuth data, leading to improved fault positioning and imaging. Side gun data clearly enhance the final target reservoir image and tie better with well data due to improved illumination. A new channel is discovered based on interpretation from the inverted VP/VS, explaining the previous incorrect prediction for one failed well that was drilled into a thinner and shallower channel unconnected to the main reservoir. An analysis of the impact of side gun data from different offsets and azimuths shows that better azimuthal distribution within middle offset ranges had a more significant impact than far offsets in the final image of this survey. This information provides valuable reference in similar geologic conditions for future acquisition designs.
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