3D DAS-VSP Processing and Learning - Velocity Diagnosis and Update for Seismic Imaging Improvement

Abstract

SUMMARYIn 2012, Shell acquired its first dual-well 3D DAS-VSP (Distributed Acoustic Sensing -Vertical Seismic Profiling) data concurrently with an OBS survey in a deep water environment in the Gulf of Mexico. A work flow was developed to process the 3D DAS-VSP data and use the VSP first arrival times to diagnose the velocity models which were derived from previous surface seismic surveys for selecting a suitable initial velocity model to be updated with the travel time tomography inversion. The VSP diagnosis method was applied again to the updated VTI-inversion model to ensure the velocity updating effort is in the right track. Both DAS-VSP and OBS data were migrated with the initial VTI velocity model and the updated VTI-inversion model. It is found that both borehole and surface seismic images generated with the VTIinversion model are significantly improved from those obtained with the initial model, especially for the seismic amplitudes at the target event. In this paper, we will share our processing procedure and some learning from our practices of processing marine 3D DAS-VSP data. Processing results from borehole seismic data acquired in Well 1 will be presented as examples.

Borehole seismic quantitative diagnosis of a seismic velocity model for 3D seismic imaging of subsurface structures

“…An initial velocity model was diagnosed with the FAT method using over a million source‐receiver pairs of 3D DAS‐VSP data and then it was updated using the TTT method with this huge amount of data, preliminarily resulting in much better ‘flat gathers’ and significant improvements of both borehole and surface seismic images of subsurface structures (Wu et al . ).…”

“…Although our first arrival time diagnostic method has been used with 3D VSP and surface seismic data to guide velocity model updating practices and make improvements of subsurface seismic images (e.g., Wu et al . ), unfortunately, there is no 3D VSP data available in the area under study in this paper. However, it is worth testing that if such a simple diagnostic method with limited multi‐azimuth OVSP and VIVSP data can be used as a simple and practical tool for seismic velocity updating and image improvement, since many exploration and development areas may only have multi‐azimuth VSP data rather than 3D VSP data.…”