Low-frequency seismic analysis and direct hydrocarbon indicators
Master thesis
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http://hdl.handle.net/11250/2414789Utgivelsesdato
2016-06Metadata
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Sammendrag
Low-frequency seismic analysis has been used as a possible direct indicator of
the presence of hydrocarbons in reservoirs. Laboratory examples, synthetic studies and
field examples in oil and gas exploration suggest that hydrocarbons often contribute a
low-frequency anomaly (less than 15 Hz). Th
ere are a number of
algorithms available
in interpretation software packages that
perform spectral decomposition of reflection
seismic arrivals. Using seismic and well data from the Johan Sverdrup field, central
North Sea, and the Western Graben, southern North Sea, a low-frequency analysis has
been carried out in the context of differences in lithological properties of reservoirs.
Spectral decomposition is applied to stacked seismic traces to enable low-frequency
analysis and comparison of results from these two oil-bearing reservoirs types. To look
for low-frequency anomalies, spectral sections of 5 Hz to 40 Hz have been used.
Additionally, in order to analyze anomalous low-frequency responses, so-called
frequency gathers (amplitude vs time in various narrow frequency bands) at a single
seismic trace or well location have been used. This study focuses on finding a
connection between the occurrence or non-occurrence of low-frequency anomalies and
the nature – heterogeneous or homogeneous – of the reservoir. Here, Johan Sverdrup is
considered a relatively homogeneous reservoir while the 2/7-31 discovery in Western
Graben is considered a relatively heterogeneous reservoir.
Beskrivelse
Master's thesis in Petroleum geosciences engineering