Multi-source design and penta source case study from the NWS Australia

Abstract

Marine towed streamer acquisition has been largely restricted to just a few geometries which are determined by the streamer separation and number of sources. Most acquisition uses two sources with 100m streamer separations, or sometimes 75m and 50m for higher resolution surveys. Greater flexibility can be gained by using more than two sources and this leads to a range of design options more commonly associated with land acquisition. The aim here is to allow greater tuning of the acquisition to meet efficiency, quality or time restraints of the survey so that so a better match is obtained between the actual and desired survey. The use of multiple sources is in part enabled by the commercialisation of interfering shot energy removal which has long been practiced in land seismic, but is much more challenging with marine streamer data due to the lack of azimuthal and offset variation of the source positions relative to the receivers. The ability to remove interfering shot energy means shotpoint intervals can be reduced, enabling multi-source designs by increasing inline fold, which is needed for successful processing of the data in domains such as 2D CMP and common-trace. With triple sources we show that the options are greatly increased to either improve efficiency or quality and sometimes both, but we can also consider 5 or penta sources with which we obtain very high density data — 6.25m cross-line cells — with acquisition efficiency. A 400km2 survey was acquired on behalf of Quadrant Energy using the 5 source method and in addition a smaller 50km2 using a conventional geometry. Direct comparisons can be made between the geometries and the simple fast-track processing shows the benefits of decreasing the cross-line sampling to fully realise the benefits of broadband data as high-frequencies are fully sampled in the cross-line domain.