CSEM Technology Reduces Exploration Risk in Toe Thrust Area of Block 2F Sarawak Deep Water — Malaysia

Robert Wong, Arthur Van Liet, Alwyn Chuang, and Eng Yao Wong
Petronas, Kuala Lumpur, Malaysia

Block 2F, located within the Sarawak deep water basin in 500-2000 meters water depth, has one well drilled in June 2004 which encountered minor gas shows in thin sands. The block is also covered by both high quality 2D and 3D seismic data. Interpretation and mapping of the seismic data in the block revealed mainly toe thrust structures and low relief features containing the Late Miocene - Pliocene turbidites derived from Rajang Delta in the south to southwest. Further amplitude analysis, particularly Amplitude-Versus-Offset (AVO) highlighted the top ranked prospects in the block.

In order to further derisk the uncertainties of both the toe thrust structures and low relief features, particularly on the reservoir thickness and fluid containment. Controlled-source electromagnetic (CSEM) survey over 5 high-ranked prospects in the toe thrust and low relief plays was carried out in September 2007. Project objective is to identify the choicest prospects in terms based on CSEM anomalies observed which will then be considered as the drilling candidates in the very near future, probably in year 2008. One CSEM line each along the strike of the prospect was acquired in order to capture the thickest part of the reservoir. Based on the CSEM technology, when a CSEM anomaly is observed after processing the acquired CSEM data, it is mostly likely related to hydrocarbon saturated thick stacked sand bodies.

The CSEM processing results which include depth migration, have shown anomalies in both toe thrust structures and low relief features. The anomalies are based on comparison between both amplitude and phase of the processed CSEM data on the targeted reservoir versus the background water bearing reservoir. The strongest anomalies are observed in the toe thrust structures and hence they are confirmed as the best ranked play-type.

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