Acquisition, processing and geologic interpretation of marine seismic data from high-resolution and deep-penetration surveys in the Vestmanna Sound and Skopunar Fjord region, Faroe Islands

Abstract

This thesis spans over three main scientific goals, which may be categorized as: 1) development of strategies for optimal data acquisition and processing of reflection seismic data, 2) tying of wells and seismic sections, and 3) testing of two geological hypotheses: the first is to test a geologically inferred strike-slip fault in Skopunar Fjord; and the second to test thickness variations of the Malinstindur Formation, applying joint interpretation of shallow- and deep-penetration seismic data.

It is evident that the fold of coverage is crucial to create good-quality seismic images, even if it means a drop in air gun pressure due to denser shooting. The acquisition should be planned so that the CMP fold is high, and no less than about 24.

Swell-noise attenuation of the raw data was initiated with an f-x technique, while residual noise attenuation was done cautiously with f-k filtering. Attacking the water-bottom multiples in this shallow-water area with a combination of τ-p deconvolution and SRME, then followed by post-stack deconvolution was quite successful. Migration was performed with the fast and accurate Stolt f-k algorithm. The final processed data show reflections that correlate with intrabasaltic horizons.

In my data, there is no visible sign of any fault in Skopunar Fjord with a throw of 200-300 m, as has been suggested by others. If this fault existed, it would have had a temporal displacement of 100-200 milliseconds that would have been easily observed on the seismic data. If the fault should exist anyway outside of the study area, a good approach would be to collect more seismic, at least two lines north and south off Sandoy. These lines would inevitably traverse the fault if it existed.

Joint interpretation of shallow- and deep-penetration seismic data can be significantly more rewarding than the interpretation of one of these alone. This made it possible to interpret confidently an intrabasaltic stratigraphic sequence with an average thickness of about 1300 m. Isochore calculation shows ~100 m thinning over a distance of ~30 km.

Date of Award	2013
Original language	English
Supervisor	Robert James (Jim) Brown (Supervisor)