Experimental Processing of Dual-well 3D DAS-VSP Simultaneously Acquired with OBS in Deep Water Environment in GOM

A dual-well 3D DAS-VSP survey was simultaneously conducted by Shell with 2012 OBS survey in deep water in the Gulf Mexico. About 50 million traces were acquired in two wells, one is a near-vertical well and another is a strongly deviated well. Efficiently and effectively process of the large scale 3D DAS-VSP to obtain satisfactory subsurface seismic images is a great challenge. We developed the processing workflows for imaging, semi-automatic first arrival time (FAT) picking, and updating of velocity model with borehole seismic tomography inversions. The workflows were successfully applied to both wells to obtain RTM depth migrations with the VTI-initial model and VTI-inversion model derived with the borehole seismic tomography inversion. Our processing results demonstrate the ability of 3D DAS-VSP in providing higher frequency and higher resolution 3D RTM images of deep water reservoirs, possibly enabling 4D DAS-VSP as a cost-efficient, effective, on-demand monitoring technology for a deep water environment. It is found that the FAT diagnosis method can quantitatively diagnose velocity model uncertainties and monitor the process of velocity model updating. In this paper, we will present processing results of both wells and share our leanings from the 3D DAS-VSP processing practice.