Velocity Anisotropy of shales and sandstones from core sample and well log on the Norwegian Continental shelf

Abstract Velocity anisotropy referse the directional inequality of velocity on the subsurface. Often sedimentary rocks are anisotropic and occurse at all scales from core plugs to reservoirs. In this thesis velocity anisotropy of shale and sandstone was analysed from core sample and well log data. The core sample was taken at a shallow and intermediate depth from the northern North Sea (Gullfaks and Statfjord Fileds) and deeply buried, the Haltenbanken Area. The well log data were vertical and deviated well bore from Statfjord Field. The estimated velocity anisotropy from the core sample varied from weak (å=0.11 and ã= 0.11) for immature source rock type Draupne Formation, å=0.02 and ã= 0.07 for calcite cemented Broom Formation (Brent Group) and å=0.15 and ã= 0.27 for cap rock type Lange Formation from the Haltenbanken Area. Velocity anisotropy from the well log data also show evidence of anisotropy on the Statfjord Field shale formations. The predicted velocity anisotropy from the well log data was substantial due to layer induced anisotropy (~ å=0.15 - 0.25 and ~ã= 0.43 - 0.531) shale formations. The observed degree of anisotropy from the core sample and well log data was dependent on: the volume and type of clay minerals, the provenance, the depositional environment, diagensis, compaction, kerogen (TOC) content. This study also observed how velocity anisotropy can make huge difference to a reservoir performance and subsurface imaging by emplmenting the estimated anisotropic parameters.The methods and the results obtained on this study may be used as potential indicator of remote detection of source rock, reservoir rock and cap rock.