Sparse Ocean Bottom Node on the Alwyn Field - From Acquisition to Joint PP-PS Imaging

This case study presents the first ocean bottom node (OBN) survey acquisition and processing over the Alwyn field. The objectives of this sparse acquisition were the enhancement of lateral and vertical resolution of Triassic reservoir. Vintage seismic data consists of three conventional towed streamer surveys acquired in 1981, 1995, and 2000, suffering from limited illumination and none are repeat surveys. This new OBN survey, full azimuth, long offset seismic provided both P and PS-waves datasets for imaging and pre-stack AVO joint inversion.

The objective of this paper is to present the acquisition and processing of both P and PS-wave. Early P-wave output, obtained three months after start of processing, showed the potential of OBN data. This volume confirmed the step change in imaging over existing vintage data. PS-wave intermediate images could only be compared with P-wave due to lack of legacy PS data; structural imaging using PS data remained a challenge, however results are expected to bring value at the joint pre-stack PP-PS inversion stage.

This project demonstrated the ability of sparse OBN data to provide improved P-wave imaging at reservoir levels. Parallel P & PS-wave processing allowed a reduced turnaround time for an early PP & PS joint AVO inversion.