Optimizing of a Das VSP Image for 4D Assessment at the Culzean Field

We discuss the processing and imaging solutions designed to assess 4D signal in a monitor Vertical Seismic Profiling (VSP) survey acquired with Distributed Acoustic Sensing (DAS) over the Culzean field, Central North Sea. With a baseline DAS VSP survey acquired during a pilot programme in 2019, a monitor survey acquired in 2021 aimed to provide the means to assess reservoir and overburden time shifts in the Culzean field ahead of full field 4D seismic acquisition. We show how a 4D compliant processing workflow effectively tackled non-repeatability aspects of the monitor survey including significantly increased background noise levels compared to the baseline and variation in the source signatures and the recorded data. An improved de-multiple workflow utilizing Wave Equation Deconvolution Imaging and final imaging with Reverse Time Migration, achieved a high quality image in the overburden and at the key reservoir section for analysis of 4D time shift signal.