Using 3D4C Data to Image and Interpret the Seismically Obscured Area over the Tommeliten Alpha Discovery

Abstract

A high density 3D4C seismic survey was acquired over the Tommeliten Alpha gas condensate discovery in 2005 to image a seismically obscured area caused by complex velocity and density variations in the overburden. Both full azimuth PP and PS data were used and pre-stack co-depth migrated. The result was an improved image of the previously obscured area, especially in the PS dataset. The size of the Seismically Obscured Area (SOA) was reduced also in the pre-stack depth migrated PP data, but in this outer part of the SOA the PP data gave a different image compared to the PS dataset - making the interpretation challenging. Although the resolution of the PS data is lower at the target level, and the main Ekofisk Fm reservoir target (21-24m thick) is below PS seismic resolution, the PS dataset proved very useful in mapping the structural shape and faults inside the SOA, leaving only a small central area obscured.