Dual-sensor data and enhanced depth imaging sheds new light onto the mature Viking Graben area

Abstract

The Viking Graben area in the Central North Sea was the initial focus of a series of early 3D GeoStreamer dual-sensor surveys between 2009 and 2012 (Figure 1). These MultiClient surveys immediately demonstrated significant image quality improvements achieved with the dual-sensor towed streamer seismic in an area characterized by significant subsurface complexity. After more than 50 years of active exploration, the Viking Graben is widely regarded as a mature basin whose petroleum system is thought to be well understood. Many of the classic hydrocarbon targets of the region, including the large rotated Jurassic fault blocks of Gullfaks and Oseberg, and the Paleocene and Eocene fan systems of the Heimdal and Frigg fields, have already been exploited. Challenges remain to stratigraphic interpretation and mapping of sands within the Upper Jurassic and it is therefore important to have data which has sufficient penetration and accurate positioning of reflectors to continue to explore these levels. Determining the exploration opportunities beyond these classic targets also requires optimization of the seismic data. The Eocene sands have been extensively mapped, but the Paleocene fans are less well known. Although the play is proven, the more subtle sands of the Ty and Maureen formations have been masked by artefacts caused by shallow events. In addition, several of the classic plays have now become the subject of re-evaluation. Better resolution and deeper signal penetration with dual-sensor data has provided detailed insight into many of these plays and also improved the understanding of the overall connectivity of several highly compartmentalized reservoirs that are often comprised of a variety of barriers and baffles. In order to improve the understanding of the geology within this established area and to be able to exploit the fields to their full potential, modern seismic data need to be consistently re-evaluated and subjected to new processing techniques. The remobilized and injected reservoir sands of the Volund field were considered unique at the time of its discovery in 1994, however, many other recent discoveries are also now considered to be the result of remobilized sands. Potentially, known fields such as Balder, with its steep sided reservoir, may also be re-categorized as an injectite rather than a deep marine fan reservoir. Utilizing a depth migrated seismic dataset with reduced artefacts from shallow anomalies may validate this and enable additional fields to be discovered.