2019 AAPG Annual Convention and Exhibition:

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Exploration in the Atlantic Conjugate Margin Using CSEM Data as Part of an Integrated Workflow

Abstract

The Atlantic conjugate margin is an attractive exploration area with large Cretaceous discoveries such as Jubilee in Ghana, Zaeydus in French Guyana, Liza in Guyana, Moita Bonita in Brazil and SNE in Senegal. In addition, the recent Hammerhead well in Guyana opens a new Tertiary play. Despite recent exploration success on both the Africa and South-American side, several dry wells were drilled the last years targeting analogue prospects. According to Richmond Energy Partners only 9 of 110 frontier wells drilled on the Atlantic margin in the period 2007-2015 are considered commercial. Many of the prospects are basin floor fans with a large degree of stratigraphic trapping. The latter is also considered high risk. AVO and flat-spots are reported on dry prospects and should therefore be handled with care. To improve the success rate of frontier wells, we propose an integrated workflow including Controlled Source Electromagnetic (CSEM) data. CSEM data is a geophysical technique providing subsurface resistivity models ready to be integrated with seismic, well and geological data. Numerous worldwide examples prove how such integrated interpretation can de-risk seismic DHI prospects. The CSEM value of information is in many cases highest in frontier basins where regional CSEM acquisition effectively improves the drilling sequence of seismic prospects by downgrading prospects with low hydrocarbon volume potential. To make such assessments successfully, it is important to also consider possible CSEM interpretation pitfalls. Typical pitfalls are omittance of information on sensitivity to reservoir target, complex geology causing imaging challenges and resistive lithologies creating anomalies similar to a hydrocarbon reservoir response. In this paper we will demonstrate use of CSEM data in integrated interpretation through real data case examples from the Atlantic conjugate margin. We will identify various CSEM pitfalls and implement such knowledge to make systematic risk assessments for prospects with both presence and absence of resistive anomalies. Results will be compared to drill results where available.