With the development of time-lapse seismic and the move into deeper water environments, larger volumes of data will be acquired in order to analyze subtler changes in the reservoirs. In these conditions, the problem of seawater velocity variations will become more critical. As presented in this article, seawater velocity can be estimated by tomographic inversion. The Teal-South experiment showed spatial variations of 17 metres per second, as well as intra-survey variations (occurring during the time of the survey acquisition). The results, strengthened by metocean studies, emphasized a local northeast current. The impact on time-lapse seismic data was tackled by seismic modeling based on oceanographic studies. Seawater velocity variations had a significant impact on both pre- and post- stack data. Travel times and amplitudes are altered leaving a distortion of the time-lapse signature that cannot be extracted by conventional processing. Therefore, specific new techniques should be considered. MacKay and Fried5 propose a dynamic correction which they apply successfully to streamer data. Finally, Bertrand and MacBeth6 have developed a new method that can be applied to seabed data without any additional pre-processing or any seawater velocity knowledge. It removes the dynamic travel-time differences within a single trace and is applicable in shot domain.
|Number of pages||5|
|Publication status||Published - Apr 2003|