Development of a subsea DAS acquisition system

Over the last decade Distributed Acoustic Sensing (DAS) data acquisition has seen great improvements from better interrogators, engineered fiber and lessons learned from subsea installation and acquisition. This has given us confidence that DAS cables can be installed in wells with subsea trees to be used as receivers for Vertical Seismic Profile (VSP) seismic imaging. VSP imaging for deepwater fields has shown to provide better illumination and higher frequency seismic data. Permanent DAS cable installation can be used to acquire highly repeatable time lapse (4D) data. DAS cables were installed in a number of subsea wells on two deepwater oil fields with the intention to cover the crest of these fields with high frequency seismic data. A system was developed to allow for DAS acquisition on these offshore, subsea wells with long distance tie backs using permanently installed interrogators on the floating platforms and engineered fiber in the wells. On each of these fields a DAS cable has now been installed and a subsequently a zero offset (ZO) DAS VSP was acquired for verification and commissioning. These ZO DAS VSP acquisitions showed high fidelity installations resulting in DAS VSP data with excellent data quality. These first subsea DAS acquisitions show great promise and further installations and acquisitions are planned with the ultimate goal of providing high frequency seismic images over the crest of these fields to reduce the uncertainty in decisions around reservoir management and future infill drilling.