Publications

This paper summarizes a recent success in application of multi-component imaging technology in the OBC4C survey on Mahakam PSC block, Indonesia, where the data quality of conventional P-wave suffers from serious wipeouts and distortion due to shallow gas in the central zone on the top of the Bekapai field structure. Shear waves are not affected by gas clouds and are used as a good alternative to image subsurface structures in the area. The detailed survey design and advanced processing technologies are the key to the success. The Bekapai OBC acquisition has produced a high fold coverage and good quality wide azimuth 4C dataset. Dedicated processing flows for both PP and PS waves were laid out to improve the structural and reservoir images. Particularly for PS converted wave data, apart from the conventional processing steps, such as wide azimuth noise attenuation, surface consistent amplitude correction and deconvolution, special technologies have been utilized to improve imaging quality. These include shear wave statics, a double square root moveout solution to handle different elevations of shots and receivers of OBC data, iterative converted-wave velocity (vc) and effective vp/vs ratio (e) analyses and prestack converted wave migration. In the gas cloud affected areas, the quality of P- wave images is poor, thus the velocity from P-wave data analysis is less reliable. Using converted-wave data only to update vc and e the prestack time migration was carried out to get a better solution. The final PS converted wave migration results have demonstrated superior images to P-wave and clearly unmasked subsurface structures under the gas clouds. Much better event continuities and fault definitions are observed, which provide very useful information for interpretation compared with obscured P-wave data.