Time-lapse acquisition advances with ghost-free dual-sensor streamer acquisition

Abstract

A time-lapse experiment was performed in the North Sea whereby a monitor survey was acquired using dual-sensor streamers at 15 m depth over a baseline survey that had been acquired a few months earlier using conventional streamers at 8 m depth. Wavefield separation was performed for the dual-sensor streamer data and the upand down-going pressure fields independently redatumed from 15 m to 8 m depth and summed to emulate the total pressure field acquired using the conventional streamer. The data were then processed using a modern time-lapse processing flow. The differences between the two datasets were found to be minimal as expected given that there was no production in the survey area during the months between the two surveys. A final normalized RMS difference in the target area of 11% was observed despite quite significant differences in acquisition geometry. This result validates the integrity of the wavefield separation and redatuming steps applied to dual-sensor streamer data. The down-going pressure wavefield carries information about the sea-surface shape, and thus introduces non-repeatable noise into the total pressure wavefield recorded by conventional (hydrophone-only) streamers. Conversely, the up-going pressure wavefield output by data processing is high resolution and noise-free. When combined with complementary acquisition technologies and shooting strategies, dual-sensor streamers represent the preferred platform for towed streamer 4D.