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Detect Water Velocity Variations with Direct Arrivals and Water Bottom Multiples from 3D Subsurface Seismic OBN/DAS-VSP
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 3rd EAGE Workshop on Borehole Geophysics, Apr 2015, cp-447-00023
- ISBN: 978-94-6282-144-6
Abstract
Nodes (OBN) survey geometry is similar to that of the Vertical Seismic Profile (VSP), except no sensors in a borehole. Thus, VSP 3C analysis methods are applicable to 4C OBN. Li and Hewett (2013) developed a time-angle diagnosis method to quantify velocity uncertainties in a model using the VSP first arrival times (FAT) and first arrival angles (FAA). We applied this method to FAT/FAA from a 2012 OBN survey in the Gulf of Mexico to diagnose water velocity models and to detect spatial variations in the water velocity. Arrival times and angles of water bottom multiple (WBM), which was typically treated as “noise” to be eliminated, were used to characterize the water velocity uncertainties. We also investigated feasibility to use FAT and WBM from DAS-VSP concurrently acquired with the 2012 OBN to constrain the water velocity models. Diagnoses with OBN FAT indicate that the maximum RM of water velocity is -0.7% with a maximum 2-way time misfit up to ~12 ms, while OBN WBM analyses reveal lateral variation of water velocity is about +/-1%. A joint tomography using FAT/WBM from OBN/DAS/VSP is expected to be feasible for revealing details of spatial/time-variations of the water velocity.