Short summary of Hilmar Simonsen’s PhD thesis
Seismology is the oil companies’ main tool when it comes to imaging through the
layers in the subsurface. However, the raw seismic data has to be processed
before it can be used for interpretation.
The raw data for this thesis was recorded with the research vessel Magnus
Heinason in the Vestmannasund and in Skopunar Fjord. 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 that’s
proprietary to GX Technology, 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. Designature
processing is illustrated with an example of how zero phasing of the source
wavelet improves the far-field signature.
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
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 high- and low-resolution seismic
data.
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.
This project was supported by the Faroese Research Council (Granskingarráðið).
It also benefitted greatly from support of research costs by the Sindri group,
especially Statoil, and several other organizations.