Blended Source Ocean Bottom Seismic Acquisition

Abstract

Abstract "Blended" or simultaneous source seismic acquisition has had a dramatic impact on the quality and productivity of land seismic acquisition but its application offshore has been comparatively limited to date. For towed streamer operations the principle benefit is to improve data quality by increasing the fold of the acquired data by reducing the shot spacing. There is little, if any, reduction in data acquisition time and hence no reduction in costs. For ocean bottom seismic applications, however, the situation is very different - survey durations can be almost halved with a very modest increase in costs by firing more than one source into the receiver spread "simultaneously." In this paper we will describe the acquisition of what is believed to be the world's largest ocean bottom survey, more than 2200 square km, using two blended sources and a very large receiver spread - more than 4200 ocean bottom receiver nodes. By firing each source wholly independently on a pseudo-random distance basis not only is blended source residual noise reduced but also operational efficiency is improved since downtime on one source vessel has no impact on the other. Since ocean bottom data are extensively used for production and development applications to provide wide azimuth data in congested producing fields the usability of blended sources for 4D or timelapse is critical and this will be examined in the presentation.