Revisiting an Old Prospect by Integrating Seismic, CSEM and Well Data. A Case Study from the Norwegian Shelf (Best of EAGE)

Sperrevik, Susanne ¹; Rykkelid, Jon Ivar ²; Cumming, Daniel ²; Hesthammer, Jonny ¹; Maxwell, Gregor ²; Boulaenko, Mikhail ²; Berry, Kate ³; Ekeli, Christine ³
(1) Emergy Exploration, Bergen, Norway. (2) Rocksource ASA, Bergen, Norway. (3) Envision, Stavanger, Norway.

License PL559 is located on the Nordland Ridge in the Norwegian Sea, and the area was first awarded to PL 128 in 1986. PL128 has undergone a stepwise area reduction from 2005 to 2009, and the relinquished acreage has been made available to other players through the APA licensing rounds.

In 2003, PL128 acquired CSEM data which showed a response related to the identified Linerle prospect (Statoil 2004). Drilling of Linerle the same year proved oil, and it was taken as a “proof” that CSEM technology was able to de-risk prospectivity in the area (Statoil 2005). The EM line also showed an elevated response to the NE of Linerle, corresponding to the prospect referred to as Valkyrie (Statoil 2005). A further EM survey consisting of several lines was thereafter acquired, and the main part was testing the Valkyrie prospect. Several of the lines showed an elevated response over the prospect, but clear variation is observed along the EM lines (Statoil 2005). Valkyrie was drilled in 2006 and the well 6608/11-5 was practically dry. The Valkyrie case was therefore taken as evidence that the EM tool was problematic to apply in this area and a model was made where a highly anisotropic layer was introduced in order to explain the results (Statoil 2006).

In the current project special studies have been carried out to assess whether the observed EM anomaly over Valkyrie really can be explained by electrical anisotropy, or whether the well actually did not test the EM anomaly. These studies show that it is very improbable that even an extreme case of anisotropy could cause the observed anomaly, whereas synthetic models with a resistive hydrocarbon filled target located just NE of the well gives a good match to the real data.

Although the study of the public information was encouraging for the area, it was clear that the published information about the EM data was very limited, and the survey was old (raising questions about quality). It was therefore decided to acquire new EM data in 2010. These data confirm the presence of a clear resistivity anomaly. A new well will be drilled in the license in 2011, and although the final well location is yet to be decided it will likely test the resistivity anomaly.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.