Contribution to Prospect De-risking on the Veslemøy High, SW Barents Sea - An Offshore Vertical Source, Vertical Receiver CSEM Survey

Leon, Enric ¹; Børven, Jon-Mattis ²
(1) Concedo ASA, Asker, Norway. (2) PetroMarker, Stavanger, Norway.

Integration of electromagnetic methods with seismic measurements has gained acceptance in the petroleum industry as a powerful tool for prospect de-risking. A time domain controlled-source electromagnetic (CSEM) method for marine hydrocarbon prospecting developed by the Norwegian company PetroMarker has been utilized in connection with the 21st License Concession Round application. The objective of this work was to evaluate a prospect defined by a small fault-bounded closure. This structure is located on the Veslemøy High, a prominent feature developed on a sheared margin setting in the SW Barents Sea. The stratigraphy beneath the high is not fully understood due to limited seismic resolution and lack of exploration wells. A geological model depicting a Jurassic or Cretaceous reservoir prospect at the top of the structure is proposed. In order to mitigate the risking factor prior to license application, a 2D EM survey was acquired over the target structure, with the prospect expected at ~2.5 km depth. The layout of the survey was designed to obtain optimal data coverage both above and outside the target.

This EM technique is characterized by vertical, stationary transmitters and receivers which operate at short offsets (typically ~1 km). The strong depth penetration and high lateral resolution of the method makes it particularly suitable in cases where target width and target burial depth are of comparable dimensions, like in the structure investigated herein.

The results of the 8.5 km acquisition profile revealed a prominent resistivity anomaly at the NW end of the line, coincident with the position of the target structure.

Data inversion was performed using a 1D Marquardt-Levenberg inversion scheme incorporating anisotropy, using both unconstrained and constrained approaches. In both cases, the results confirm the presence of a resistor at the position of the target structure, consistent with pre-inversion apparent resistivity results.

From the exploration company’s point of view, the contribution of this method in the de-risking workflow is considered as valuable because of the great potential showed in the detection of relatively small prospects. A more comprehensive evaluation of the method can be achieved after an eventual drilling of the prospect.

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