--> CSEM Ranking of Transform Margin Prospects

2018 AAPG International Conference and Exhibition

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CSEM Ranking of Transform Margin Prospects

Abstract

The Transform Margin play is a prolific HC play explored along the equatorial margins of Africa and South America. Significant discoveries include Jubilee (Ghana) and Liza (Guyana). The play consists of Late Cretaceous deep water slope and basin floor channels & fans with structural/stratigraphic trapping. While prospects are typically well mapped with seismic and commonly exhibit seismic DHI’s, their stratigraphic nature implies high risk and commercial drilling success rate has been declining recently, e.g. Fatala (Guinea). The highest risks typically are seal integrity and charge. De-risking with seismic DHI’s is notoriously difficult due to the strong response from low saturation HC. As exemplified by the successful CSEM track record in Norway for both structural & stratigraphic plays, integration of resistivity from CSEM with seismic can de-risk seal and charge by distinguishing high from low saturation HC. Moreover, CSEM can reduce uncertainty in the prospect resources. Hence CSEM is a very valuable tool for de-risking AVO and seismic amplitude driven prospects, particularly in deep water where only large volumes are commercial. Existing CSEM data at the West African equatorial margin dates from the early years of commercializing CSEM technology (2002-2007). While some of these data proved the capability of CSEM to de-risk stratigraphic prospects (e.g. Fortuna in Eq. Guinea), the legacy data mostly failed to be of value due to immature products: the lack of imaging and non-existence of workflows to embed CSEM in prospect evaluation. These early shortcomings have now been overcome by tremendous technological advances and experience building from worldwide CSEM application. To illustrate the ability of modern CSEM to increase exploration performance for the Transform Margin play, we studied a drilling commitment for a hypothetical portfolio of 4 prospects in deep water Guinea. The setting is analog to the Fatala prospect with high resource potential but significant uncertainty. We model the impact of CSEM information on the PoS and volume distribution of each prospect. Due to excellent CSEM sensitivity to the Late Cretaceous, only small volumes are undetectable and thus a prospect without a resistive anomaly has very low probability of commercial success (Pc). We then simulate a drilling candidate selection and show that by downgrading prospects without a resistive anomaly the Pc of the 1st well is at least as high as drilling 2 wells without CSEM.