Coherence Technique and Its Application in Xisha Offshore

Taotao, Yang

Coherence Technique means that the geology evidence can be provided through appraising the similarities of seismic data and transforming the seismic to coherence data. Since Bahorich put forward the coherence technique for the first time in 1995, there have been 3 generations of coherence technique, including C1 based on cross-correlation algorithm, C2 based on multi-traces similarities algorithm and C3 based on matrix eigenvalue. These three have all been used widely. Coherence technique can reflect a point's geology feature by condensing multi-lines, multi-traces and multi-points onto a point trough space combination of seismic trace in different forms. In other words, coherence technique means the common enrichmen of abnormal bodies, so it is very sensitive to discontinuity. Trough the calibrated coherence bodies corresponding with the geology bodies, the distinct geology body can be reflected. In application, the conclusion has been got that coherence technique is accurate and practical, which has been used widely for oil & gas exploration.

Xisha offshore lies in northern South China Sea, with water depth 0~3000m, and wholly there are a central uplift and depressions around. The conclusion has been got that there is a favorable geology condition in Xisha offshore. Exploration in deepwater area started late, and now there is no well targeting on oil&gas which limited the geology study in this area. Because of the high exploration risk and cost, it's necessary to study the coherence technique and apply it on the deepwater exploration. This paper verified the validity of coherence technique, and the better algorithm was applied on the actual research work trough analyzing the algorithms. Firstly, faults can be recognized through coherence technique, while the faults' trends and their interaction cutting relations were clear on the coherence data. Secondly, the whole trend of channel, meander, and lateral erosion characteristics were clear on the coherence data for its emphasizing intensive amplitude and border detection. Thirdly, the coherence technique can reflect that the lithology was uniform in reef core, mixed and disorderly in the fringe parts. Finally, the coherence technique can reflect the volcanic development process that magma upwelled and destroyed the early sedimentary formation, and formed the radial faults while volcanic rock in the center. The application of Coherence technique supported and promoted the geology study in Xisha offshore.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013