High Fidelity Velocity Model Building, Imaging and Reflectivity Inversion – A Case Study over the Viking Graben Area, Norwegian North Sea

Abstract

A case study was carried out over the Viking Graben area with special focus on the Volund field, where a high fidelity velocity model was built to solve the complex velocity variations in the overburden resulting from a widespread presence of channels and numerous small-scale sand injectites. Significant improvements to the image quality were achieved with the use of the detailed velocity model and by incorporating a variable quality field to compensate for visco-elastic effects. Alternative imaging algorithms and reflectivity inversion techniques were explored to overcome limitations of the imaging system. This further improved the spatial resolution, enhanced the signal and helped the interpretation of the remobilized sand system over the Volund field.

Broadband Least-Squares Wave-Equation Migration

“…Another example of 3D narrow azimuth (NAZ) data from North Sea further illustrates the advantages of applying LS-WEM to strongly attenuative media with a high resolution velocity model (Korsmo et al, 2017). Figure 4 shows a comparison of the results from WEM and LS-WEM.…”

“…Later, Prucha and Biondi (2002) derived less restrictive broadband wave equation solutions. The advantage of broadband wave-equation extrapolators is that they make better use of the high-resolution earth models derived with advanced processing technologies such as Full Waveform Inversion (FWI: Korsmo et al, 2017).…”

Least-squares full-wavefield migration

“…Since FWM images both primary and multiple reflected energy simultaneously, it can produce improved images in comparison to standard migration of primaries only. However, it is challenging to balance the primary and multiple ( Korsmo et al, 2017). The standard migration images are severely contaminated by the acquisition footprint that is typical for shallow-water environments (Figure 6a).…”