AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Atlantic Margin, Stratigraphic Play: An Integrated CSEM-Seismic Approach to De-Risk Fluids?


In 2013 during the latest offshore exploration bid round the oil giant TOTAL was awarded the operatorship of 5 deep water exploration blocks of total 3800 sqkm located in the Atlantic margin. TOTAL has signed high commitments including large 3D seismic acquisition and high number of wells drilling program for next 5 years. Given basin is remaining underexplored due to the remoteness of the area and poor exploration results up to now (only 10 shelf wells with HC traces). The working petroleum system of the basin was proved by Shell's recent drilling campaign in the neighbour country to the North. From the current evaluation the considered exploration blocks represent 4 Gboe of unrisked mean resources for TOTAL. Depth processing project of large 3D broadband seismic multi-client campaign (more than 11,000 sqkm) was terminated only in December 2015. It enabled a definition of large variety of plays dominated by upcurrent stratigraphic trapping in the Upper Cretaceous. There are massive reservoir sands concentrated inside large multi-storey turbiditic channel complexes in the middle slope sealed by overpressured shales. Trapping mechanism is explained by having a by-pass in the upper slope, fairways are shale plugged during highstand. The AVO and rock physics studies have played an important role in the prospect interpretation. The available 3D seismic data is an excellent lithological indicator allowing mapping of sands. Nevertheless mineral content of reservoirs, burial, specific petrophysical parameters and high fluid pressure make the Upper Cretaceous reservoirs the Class I AVO sands without a fluid effect from the seismic data (calibration from offset wells). In de-risking fluid content, EMGS 3D CSEM 3,600 sqkm dataset was licensed (acquired as multi-client survey in 2013). A confident start model (2.5D, 3D unconstrained and constrained) has been created after tens of iterations through the proprietary inversion project (2015-2016). Different inversion results were largely challenged by asset team providing finally set of robust resistive anomalies potentially related to HC presence in the target interval. When the AVO is not a fluid indicator, the CSEM technology in some circumstances when calibrated can be used as a potential DHI. However it requires high level of geological integration by the operator from inversion to interpretation stages. A case study of a CSEM anomaly supported prospect will be described.