| dc.description.abstract | Quantitative prediction of pressure as well as saturation effects from time-lapse seismic data
is one of the topics of interest for geophysical society since the last decade. Time-lapse
amplitude variation with offset (AVO) could be used for this purpose. The conventional
pressure-saturation discrimination method suffers due to leakage between estimated pressuresaturation
changes. However, the method works reasonably well for deeper reservoirs where
the P-to-S-wave velocity ratio (Vp/Vs) is around 2. Objective of this thesis is to investigate
the applicability of the conventional inversion method for shallow unconsolidated reservoirs
where Vp/Vs is often higher than 2. In addition, it is also important to investigate the inaccuracy
in the estimates (of pressure and saturation changes) due to improper implementation
of rock physics parameters as well as consideration of first order approximations in AVO
gradient and intercept changes. I propose a new method, based on a stepwise linear approximation
to the intercept and gradient reflectivity changes, to estimate pressure and saturation
changes. Similar to the conventional method the new method utilizes the near- and far offset
seismic surveys as two independent measurements, and then estimates the pore pressure and
saturation changes from amplitude versus offset (AVO).
As the conventional pressure-saturation discrimination method has inaccuracy mainly due
to gradient reflectivity attribute, it is crucial to explore the applicability of other seismic
attributes, such as PS-reflectivity changes and travel time shifts, to discriminate between
pressure-saturation changes. I investigate the applicability of various combinations of seismic
attributes for compacting reservoir scenario.
The usefulness of time-lapse seismic data greatly depends on the repeatability of the data
between different surveys. The more repeatable the data is, the more confidently and efficiently
it may be used in reservoir management. As the refraction method is emerging as
one of the promising and complementary 4D techniques, it is therefore necessary to perform
repeatability analysis on refraction data as well. In addition, repeatability analysis on
other seismic events (such as tank noise, normal modes, sea-bottom reflection) provide more
insight on the efficient implementation of 4D seismic method. I study repeatability issues using
two seismic data sets acquired at the permanent sea-bottom array that was installed at the
Ekofisk field (North Sea) in 2010. I compare pre-stack repeatability of various seismic wave
types, such as refraction, reflection, sea-bottom reflection, tank noise and water column noise.
In carbonate reservoirs, implementation of a proper rock physics model is extremely difficult
due the more complex pore-geometry in carbonate rocks. It is therefore important to
investigate various rock physics models and their applicability for carbonate reservoir. I investigate
the applicability of various rock physics models applied in three different wells at
the Ekofisk Field, North Sea. | nb_NO |
