Remote sensing of hydrocarbon layers by seabed logging (SBL): Results from a cruise offshore Angola

Abstract

Detecting and assessing hydrocarbon reservoirs without the need to drill test wells is of major importance to the petroleum industry. Seismic methods have traditionally been used in this context, but the results can be ambiguous. Another approach is to use electromagnetic sounding methods that exploit the resistivity differences between a reservoir containing highly resistive hydrocarbons and one saturated with conductive saline fluids. Modeling presented by Eidesmo et al. (2002) demonstrates that by using seabed logging (SBL), a special application of frequency domain controlled source electromagnetic (CSEM) sounding, the existence or otherwise of hydrocarbon bearing layers can be determined and their lateral extent and boundaries can be quantified. Such information provides valuable complementary constraints on reservoir geometry and characteristics obtained by seismic surveying. In November 2000, a full-scale trial survey was carried out from the research ship RRS Charles Darwin offshore Angola, in an area with proven hydrocarbon reserves. The project was a collaboration among Statoil, Scripps Institution of Oceanography, and the Southampton Oceanography Centre. The object was to demonstrate that SBL, developed by Statoil (Eidesmo et al., 2000; Ellingsrud et al., 2001), could direct detect hydrocarbon-filled layers in the subseafloor. The petroleum prospects offshore Angola are in a deep Tertiary basin consisting of a thick (10-20 km) sequence of prograding sands and shales. The area is characterized by allochthonous salt of Aptian age, and deepwater channel sands with petroleum potential. Well logs show sediment resistivities typically around 0.7 Ωm that rise to around 100 Ωm in petroleum reservoirs. The survey site was on the continental slope in water depths of about 1200 m, with a known petroleum reservoir about 1100 m below seafloor. Shallow salt occurs in the northeast corner of the area.

West Coast Regional Carbon Sequestration Partnership - Report on Geophysical Techniques for Monitoring Co2 Movement During Sequestration

“…Several commercial contractors are now offering this technique as a survey tool, most notably, in the offshore environment where it is currently being used as an exploration tools (Ellingsrud et al 2002). The equipment and service providers exist to apply this technique for monitoring in the future.…”

Investigation of novel geophysical techniques for monitoring CO₂ movement during sequestration. Final report, CRADA

“…However, EM technology is currently the subject of a significant upsurge in industry interest. Several commercial contractors are now offering this technique as a survey tool, most notably, in the offshore environment where it is currently being used as an exploration tools (Ellingsrud et al 2002). The equipment and service providers exist to apply this technique for monitoring in the future.…”

Green's Tensors for the Diffusive Electric Field in a Vti Half-Space

“…Throughout the manuscript, subscript notation is used for Cartesian tensors wherever convenient, the summation convention is applied to repeated subscripts, and the lower case Greek subscripts run over the values (1,2), while lower case Latin subscripts run over the values (1,2,3). In the domain of the horizontal wave number, the electric field Green tensor for an electric dipole in the VTI half space is known.…”

“…Transient and frequency domain electromagnetic methods have potential for hydrocarbon exploration in marine environments and on land [1][2][3]. Solutions for the two half spaces configuration are of interest in electric field integral equation solutions and approximations thereof [4][5][6][7][8].…”