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The Gateway to Libra

27th October 2014

CGG’s experience, knowledge and new broadband coverage offshore Brazil bring insight to the potential of the 11th Round pre-salt acreage.

New BroadSeis coverage in the Campos Basin highlights exciting pre-salt potential (data courtesy of CGG Data Library)

In 2013 Brazil had a hat-trick of licensing rounds after a five-year hiatus which sparked a resurgence in marine seismic activity in the country. The excitement of this year’s soccer World Cup may have faded, but there is still plenty to get excited about in the new 11th Round acreage with extensive tracts of prospective pre-salt plays to explore.

With 50 years’ experience of local operations, and considerable knowledge of the geological and geophysical challenges in Brazil, CGG was poised to take advantage of this opportunity as operators committed to significant seismic programs. As a result, CGG was awarded four multi-client survey contracts in the Equatorial Margin and Espirito Santo and Campos Basins, totalling 43,130 km2. This is a significant addition to CGG’s existing impressive library of seismic, gravity, magnetic and offshore seeps data in the area.

These new surveys have been acquired with BroadSeisTM, CGG’s benchmark broadband solution. BroadSeis is well suited for 11th Round license areas as its broad bandwidths eliminate the need for compromise in targeting either high frequencies for shallow imaging or low frequencies (with good signal-to-noise down to 2.5Hz) for the deep. With BroadSeis ghost-free data it is possible to deliver the best images throughout the section.

So what’s in store in the 11th Round acreage?

In the past, the main exploration targets in the Campos and Santos Basins were within the shallow post-salt successions, but since the discovery of the Lula oil field, interest has turned towards the pre-salt. Significant finds have since been made and the presence of Lower Cretaceous carbonate reservoirs has been established in the upper syn-rift and post-rift.

The new BroadSeis surveys have highlighted a number of mega-sequences in the pre-salt, with the oldest being highly-faulted basement which influenced the deposition of pre-salt reservoirs. Directly above the lacustrine shale and mudstone source rocks are thick syn-rift sequences which can be easily differentiated on the new images. The upper syn-rift is important for exploration in the northern Santos and Campos Basins as it provides the main carbonate coquinas reservoirs for the Libra and Franco fields. In the post-rift sequences, non-marine microbial carbonate potential reservoirs were deposited, as observed in the Lula field. All pre-salt reservoirs are sealed by a thick sequence of evaporites.

The geology in these basins creates some interesting imaging challenges which have kept the geophysicists in CGG’s Rio center on their toes. As well as deploying an advanced subsalt imaging toolbox including FWI, they have been busy applying new Internal Multiple Attenuation technology and using iterative velocity updates to image below the igneous intrusions.

In the new acreage of the Equatorial Margin, the westernmost Foz do Amazonas Basin experienced very high sedimentation rates which led to the formation of a thick deltaic sequence. Basins in this region were affected by large gravity slides and potential reservoirs in the Foz do Amazonas include Tertiary deltaic sands, turbidites, fractured carbonates and talus deposits which are structurally and stratigraphically trapped. Paleo-canyons in this basin proved to be another imaging challenge which was ably tackled by CGG’s geophysicists.

To the east of the delta, the Barreirinhas Basin is much less affected by the Amazon sediment load, but a steep margin led to mega-slide complexes forming. This basin is the conjugate to Ghana and Togo, where large fields are already producing. Large en-echelon folds, rollovers and tilted fault blocks provide structural traps and marine shales source Late Cretaceous reservoirs which are stratigraphically sealed.

If you’re passionate about your Brazilian pre-salt geology visit CGG booth # 1339 to see its “Gateway to Libra” display and talk to its Multi-Client & New Ventures team and Robertson geologists. You’ll also find CGG SubSurface Imaging presenting some of the new technology applied here in the SEG technical sessions, and join CGG on the booth at 4pm on Monday for its Brazil Happy Hour presentation to learn more about the SubSurface Imaging expertise behind these stunning new displays.

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