Air Gun near the Sea Floor as Shear-wave Source?

Abstract

SUMMARYThe feasibility of using an air gun near the sea floor as shear-wave source has been investigated. With an air gun near the sea floor, an evanescent P-wave in the water becomes a propagating S-wave in the sea floor, such that it seems that a pure shear-wave source has been used at the sea floor. This type of wave has been called a P*S wave. An experiment with such a set-up has been carried out at the Valhall field. For that case, modelling shows that shear-wave related event of the type of P*S waves can be expected with such a set-up. Especially at larger offsets, P*S waves can be expected. When analysing the field records and Constant-Velocity Stacks, it is hard to find P*S-wave reflected events. On the other hand, P*S-wave refracted events can be discerned in records. These events can be brought up to stack level and imaged, as shown in this paper.

Fully Autonomous Marine Seismic Acquisition Systems for Reservoir Monitoring

“…From the point of view of seismic quality, seabed sources will generate shear waves (Drijkoningen, Dieulangard, Kjos, & Holicki, 2015) which may or may not be desirable. Despite these challenges, however, should these sources become viable, the advantages would be numerous, including on-demand availability, resilience to sea surface weather, minimization of disturbance to environment and marine life, potential to deploy multiple sources simultaneously, and more effective use of the source energy being much closer to the reservoir (thus compensating for potentially small sources).…”