Reviving Legacy 4D Seismic Data to Reveal Subtle Oil Slumping Signals in the Grane Field

Summary The Grane field, located in the North Sea, has been producing heavy oil from Paleocene Heimdal Formation sandstone since 2003. To maximize oil recovery and reduce Gas-Oil Ratio (GOR), production strategies have evolved, including deeper well placements and water/gas injection. Some remaining reserves lie in structurally low areas at the reservoir base, where oil has displaced originally present water—creating “slumped oil” zones. These are key targets for late-life production optimization. To better identify these zones, legacy towed streamer seismic data (1993–2013) were reprocessed, since the slumping occurred before the 2014 onset of permanent reservoir monitoring (PRM). The reprocessing incorporated modern 4D seismic techniques: adaptive deghosting, advanced debubble corrections, water velocity corrections, and pre-stack depth migration (PSDM) using full-waveform inversion (FWI) models. Iterative workflows refined sail-line corrections and enhanced alignment, particularly in problematic undershoot areas. Results showed significantly improved imaging quality and reduced noise, especially in overburden and time shift artifacts. This allowed clearer detection of subtle 4D signals associated with slumped oil. The study illustrates the value of applying modern processing techniques to legacy seismic data for improved subsurface interpretation and recovery potential in mature fields like Grane.