Deriving shallow-water sediment properties using post-stack acoustic impedance inversion
In contrast to the use of marine seismic reflection techniques for reservoir-scale applications, where seismic inversion for quantitative sediment analysis is common, shallow-water, very-high-resolution seismic reflection data are seldom used for more than qualitative reflection interpretation. Here...
| Published in: | Near Surface Geophysics |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2015
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| Online Access: | http://nora.nerc.ac.uk/id/eprint/513007/ https://nora.nerc.ac.uk/id/eprint/513007/1/Vardy-2015.pdf https://doi.org/10.3997/1873-0604.2014045 |
| Summary: | In contrast to the use of marine seismic reflection techniques for reservoir-scale applications, where seismic inversion for quantitative sediment analysis is common, shallow-water, very-high-resolution seismic reflection data are seldom used for more than qualitative reflection interpretation. Here, a quantitative analysis of very-high-resolution marine seismic reflection profiles from a shallowwater (<50 m water depth) fjord in northern Norway is presented. Acquired using Sparker, Boomer, and Chirp sources, the failure plane of multiple local landslides correlates with a composite reflection that reverses polarity to the south. Using a genetic algorithm, a 1D post-stack acoustic impedance inversion of all three profiles is performed, calibrating against multi-sensor core logger (MSCL) data from cores. Using empirical relationships the resulting impedance profiles are related to remote sediment properties, including: P-wave velocity; density; mean grain size; and porosity. The composite reflector is consistently identified by all three data sources as a finer-grained (by one φ), lower density (c. 0.2 g/cm3 less than background) thin bed, with an anomalous low velocity zone (at least 100 m/s lower than background) associated with the polarity reversal to the south. Such a velocity contrast is consistent with an accumulation of shallow free gas trapped within the finergrain, less permeable layer. This study represents the first application of acoustic impedance inversion to very-high-resolution seismic reflection data and demonstrates the potential for directly relating seismic reflection data with sediment properties using a variety of commonly used shallow seismic profiling sources. |
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