A Seismic Modeling Study of Sand Injectites
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In this thesis 2D seismic modeling of various injectites with the aim of understanding seismic responses better, is performed and documented. A study of sand injectites from the Tampen Spur Area, North Sea, provided a set of geophysical values which allows for elastic modeling. The two dimensional wing like large anomalies that sand injectites are seen to appear in on 2D seismic data are the main focus of this modeling study of sand injectites. Sand injectites are characterized by their non-depositional intrusional nature in various host lithologies; most typically this host appears to be younger mudstones. The injectites are seen to crosscut, or intrude with respect the depositional stratigraphy. Recently, recognition of sand injectites has emerged in the petroleum industry, as sand injectites do seem significant in the exploration business as well as for production measures. The attention is directed at the outcrop studied and predicted connectivity of sand injectite complexes, and also at unexpected encountering of high porosity units while drilling, the reservoir potential of large injectites with often exceptional porosity in a sealing host, and moreover; that sand injectites seem to be unrestrained to neither specific geographic locations or depositional environments. Constructed models are varied consequently in size and thickness, some with different geophysical values to allow for comparability. The model database is assessed with a simplified model of a one of the most complete sand injectite complexes in the world, located in California; The Panoche Giant Injectite Complex. From in total 12 models, different effects caused by both the seismic processing and the seismic resolution limits on the actual models are consequently interpreted and discussed. Seismic processing artifacts like multiples, distortion of layers underneath the modeled structures that could mistakenly be interpreted to be feeder systems injectites are pointed out. A result of an imaginary velocity updating iteration is presented as well, as migration of data using the exact velocity model as input, is believed to produce a similar outcome for the cases studied. A velocity model update by using available stacking velocities from time migrated data on sand injectites is discussed, as this is performed in the industry, and it is by discussion found not to be a sufficient starting point for data with complex sand injectite configuration. Due to the geometries sand injectites often exhibit, depth migration is suggested as superior and a necessity in areas where structures in the limits of resolution are present in sand injectites complexes.