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Seismic Forward Modeling of Deltaic Sequences
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Petroleum Engineering and Applied Geophysics.
2013 (English)MasteroppgaveStudent thesis
Abstract [en]

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.
URN: urn:nbn:no:ntnu:diva-22226Local ID: ntnudaim:9444OAI: diva2:648681
Available from: 2013-09-16 Created: 2013-09-16 Last updated: 2013-09-16Bibliographically approved

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