Schlumberger

Technical Paper: Broadband Acquisition–Imaging Below the Shallow Gas

Society: Other
Paper Number: PGCE P32
Presentation Date: 2013
 

Abstract

In this deep water marine seismic dataset, it has been observed that imaging and resolution of the deep section is poor. The amplitudes of the events at depth are deemed to be affected by the shallow gas clusters.

WesternGeco was contracted to perform a 3D Marine Survey Evaluation & Design (SED) study by JX Nippon Oil & Gas Exploration (Deepwater Sabah) Limited, hereinafter referred as JX Nippon. The aim of the study is to aid in optimizing the survey acquisition parameters as well as to evaluate the suitable acquisition technology based on 3D target reflector illumination modeling and analysis for seismic acquisition over the DW-R Block.

DW-R block is situated 98km north-west of Labuan in South China Sea with water depth range from hundred at south to over a thousand meter at north. The field acreage is approximately 700sqkm. There is an existing 3D surface seismic which adequately imaged the shallow reflector but imaging and resolution for the deep structure is poor. The target has low signal levels and low bandwidth likely due to the overlaying shallow gas cluster. The vintage 3D survey was acquired in strike direction, resulting inadequate crossline sampling to properly image structure beneath. Furthermore, complex anticline structures contributed to the un-even illumination and poor imaging of the target.

A 3D illumination study was carried out to determine the illumination characteristics of the proposed multi-azimuth acquisition geometry. Of main interest is the comparison between the amplitude maps corresponding to the conventional towed marine and broadband type seismic acquisition.

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