Seismic Forward Modeling of Deltaic Sequences
The seismic forward modeling is a useful tool to predict the seismic response from a known
geological model. A seismic forward modeling process contains two main steps, a model
building step and a seismic forward realization part. The geological model may be built
from scratch or an interpretation of some real seismic might be used as an input to the
forward seismic realization algorithm.
In this work both the steps in a seismic forward modeling process are done. The first
step is to build the geological model, which is based on an outcrop study from Storvola.
Storvola is located alongside Van Keulenfjorden in the Central Basin on Svalbard. The
sediments are from late Paleocene and Eocene time and are deposited from west to east.
The Deltaic section exposed at Storvola has been buried and undergone high pressure,
deformation and faulting. The purpose of this study was to reverse this deformation by
flattening the model so it represents a newly deposited delta.
An outcrop study has been performed by Johansen et al. (2007) in this area, where the
exposed layers have been mapped and the properties have been measured. The mapped
geology was digitized by using the software Petrel. The model building was based on
the digitized data which the property models could be built out of. The three property
models were the P-velocity, S-velocity and density. These properties were exported to the
ECLIPSE file format which again was converted to the RSF format.
The second step in the seismic forward modeling process is the seismic realization.
The open source software Madagascar is used to simulate a seismic survey, which predicts
the responses from the subsurface by solving the center finite difference discretization of
the elastodynamic equations. These equations use the property models as input. As a
source a Ricker wavelet with a maximum spectre frequency of 100 Hz was used.
The resulting synthetic seismic gets re-sampled to reduce the amount of data and to
speed up the processing, but carefully to not remove important data. Unwanted signals
are removed or muted from the re-sampled data like the direct arrival. Common midpoint
gathers are generated to simplify the generation of pictures of the subsurface before the
data becomes migrated. The migration algorithm used is the 2-D prestack Kirchhoff time
migration, which moves the reflectors to their correct position.
The migrated data is interpreted and compared to the original geological model. Almost
all the thick layers with a high velocity contrast could be recognized, but some visualization problems were detected in areas with many thin layers.
Place, publisher, year, edition, pages
Institutt for petroleumsteknologi og anvendt geofysikk , 2013. , 86 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-22226Local ID: ntnudaim:9444OAI: oai:DiVA.org:ntnu-22226DiVA: diva2:648681
Johansen, Ståle Emil, Professor