Subsea Fiber Topology and Effect on 3D and 4D Subsea DAS VSP Images

Summary Distributed acoustic sensing (DAS) is a rapidly evolving, conveyance-agnostic technology for both seismic and reservoir diagnostic applications. Despite maturity in dry-tree and retrievable applications, there are significant challenges associated with DAS for subsea applications. While fiber optic engineers understand the complexities and subtleties of the sources of optical losses and their respective hardware compensations, very little has been provided to help geoscientists understand the impact of the net signal-to-noise (SNR) impacts on vertical seismic profile (VSP) data, and its 3D and 4D answer products. This is particularly critical to quantify as time-lapse VSP is a primary basis of design for subsea DAS. This paper enumerates the sources of subsea optical signal losses and their respective compensations in different subsea sensing configurations, and then demonstrates their systems-level SNR effects on 3D and 4D VSP imaging relative to the dry-tree base case that geoscientists are familiar with today.