Reducing Uncertainty in North Sea Injectite Fields using PGS LSM

In areas with localized steep dipping geology and low contrast sequences, seismic data can be contaminated by areas of weak reflectivity, leading to uncertainty in reservoir characterization.

In this case study PGS LSM is used to improve an already high-quality dual-azimuth Kirchhoff PSDM image of two complex fields, consisting of steeply dipping injectite sands and areas of weak reflectivity. The target structures at the Frosk and Bøyla fields are characterized by convoluted steep dipping sand systems, embedded in thick low contrast sedimentary sequences, leading to difficulty in determining field limits, and uncertainty in the associated amplitude response.

When compared with a standard migration, PGS LSM shows improvements (orange box) in the structure and focusing of small details in the target sand injectite sequences. In addition, there are benefits in signal clarity for areas characterized by low impedance contrasts between the target sands to the background sediments. This is visible on both reflectivity images and relative impedance.

Structural mapping of the steeply dipping injectite sand system is the main objective with PGS LSM in the Viking Graben, North Sea. This comparison of reflectivity for standard Kirchhoff migration and PGS LSM shows how the cemented sands in the overburden cause distortions and diming deeper in the section and how these are corrected with PGS LSM.

 

This comparison of relative impedance for standard Kirchhoff migration and PGS LSM shows how LSM enhances the signal below the dim zone and reveals finer details within the target injectite sands as well as improving the fault imaging compared to the conventional migration.