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Elastic Anisotropy Estimation in the North Sea from Walkaway VSP and Sonic Data
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fourth EAGE Borehole Geophysics Workshop, Nov 2017, Volume 2017, p.1 - 5
Abstract
The Hejre oil and gas field is located in the Danish Central Graben, a shallow water part of the central North Sea. The reservoir lies at depths below 5 km in a high-temperature (172°C) and high-pressure (1 kbar) environment. Seismic resolution is relatively poor due to absorption in the overburden, multiples and distortion from a complex structure. Anisotropic depth processing improved the seismic quality but the anisotropy uncertainty remained high.
In order to measure elastic anisotropy in-situ, reduce the velocity model uncertainties and allow improvements in anisotropic surface seismic processing, comprehensive Walkaway VSP and modern wireline sonic logging surveys were planned in a new deviated production well drilled in 2016.
This project represents a first step in the velocity model calibration workflow and highlights the importance of integrating measurements taken at different scales: cores, sonic, borehole and surface seismic, in order to understand the elastic anisotropy of the rocks drilled and allow reducing the uncertainties in the seismic velocity models used for depth imaging.