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Exploration Lessons and Trends from the Gondwanan Basins*
By
Ian Longley1, Kristan Reimann1, Christiane Buessenschuett1 and Ciaran Lavin1
Search and Discovery Article #70029 (2007)
Posted January 21, 2007
*Adapted from oral presentation at AAPG International Conference, Perth, West Australia, November 5-8, 2006
1Woodside Energy (UK) Ltd., London, UK ([email protected])
Gondwanan Basins in a Global Context
Gondwanan basins contain approximately 50% of the world’s discovered 2P (proven plus probable) reserves.
· Arabian basin contains approximately 65% of Gondwanan 2P reserve volumes.
· Remaining 35%, 744 BBOE, equals approximately 20% of the globally discovered volumes. It is concentrated in a few key major oily basins.
o Mainly along the South Atlantic margins
o In Venezuela
· The eastern Gondwanan basins of East Africa, India, and Australia are relatively smaller and are gassier in comparison to their western cousins.
Since January 1, 2000, approximately 70% of all large discoveries have been in Gondwanan basins. These represent approximately 70% of the oil and gas volumes found globally.
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If we exclude the Middle East, the major hydrocarbon resources in Gondwana are typically onshore or within shelfal areas with effective oily Cretaceous source rocks or gassy Jurassic and Palaeozoic source rocks. The resource base of the major basins of Gondwana tends to get larger with time. The deep water has been the major recent contributor to recently discovered volumes, but this trend is diminishing--the deep water is maturing. In the onshore basins there have still been numerous significant but more minor discoveries.
The Middle East has an estimated 1070 BBO and 2254 TCFG reserves, equating to an oil proportion of 74% by BOE. The recent rate of hydrocarbon discovery is 3.8 BOE/year. The remaining exploration potential within the area is very large. The region is dominated by the Arabian Basin, and the exploration/discovery trends are more influenced by politics and the development/exploitation plans of NOC’s than by competitive exploration efforts.
West Gondwana is oily, with deep water dominating recent discoveries. Main contributing basins are Campos, Niger Delta, and Congo. Recent key subsalt discoveries are in Brazilian Santos basin. Key failures have been in the Amazon Fan, Ghana, Togo, Benin, and Morocco. The ultra-deep-water “toe-thrust” Nigerian failures reflect no source maturity. No significant new basins have been discovered outside of proven basinal areas since the Woodside-led Mauritanian successes of 2001-2003. Main hydrocarbon systems are known and well mapped with many failures outside of proven areas. The focus is now on new/deep plays in proven basins.
Although less oily than West Gondwana, Central Gondwana is also oily. Onshore and deep water are the main contributors, with onshore Sudan, Nile Delta, and Ghadames as main recent contributors. Key finds include Western Desert 2003 Apache El Qasr discovery (2.8TCF from deep Jurassic)), and Nile Delta 2004 BP Raven discovery. Areas of particular interest also include Central African Rift System (Muglad/Sudan), modern rift system (Uganda [Tullow/Hardman project]), and offshore Libya, with tests in 2007.
This is a gassy region, and all terrains and many basins contribute to the reserves. Three key areas are Indian sub-continent, East Africa, and Australian North West Shelf. With the increase in oil price, greenhouse, and security issues gas has become progressively more important over the last few decades, and now exploration is turning to East Gondwana, where exploration has lagged behind the oilier areas of Gondwana (and the world).
The Middle East is dominant, but exploration is not the focus there.
Of the three other Gondwanan regions, West and Central Gondwana areas: · Are oily. · Have generally maintained recent discovery rates mainly through deep-water exploration discoveries. · Are within a few selected large basins.
The rates of discoveries are now slowing, and these areas look mature. Few new basin discoveries have been made outside of proven areas.
East Gondwana: · Is oily. · Has a leaner hydrocarbon endowment which is spread amongst more numerous and varied smaller basins.
Discovery rates here are accelerating due to the increasing global importance of gas and the relatively low level of exploration which has left significant remaining exploration potential.
Comparison with Laurasian/Global Trends / Conclusions Exploration trends are developed faster and more aggressively in major Laurasian basins than in Gondwana (especially eastern Gondwana). Many major Laurasian basins are now mature. Many of the technologies developed in Laurasia have not been rigorously applied to Gondwanan basins. Why do technological developments start in Laurasia—are they cleverer? We believe Laurasians are not cleverer than Gondwanans; rather we have better things to do with our time than to develop exploration ideas—like sport and drinking wine, and we are happy to be fast followers. We are fast copiers and catch up quickly. Many Gondwanan basins have significant remaining exploration potential which can be realized utilising established Laurasian exploration technologies.
Hull, Jonathan J., 2006, Offshore Lamu Basin, Kenya: deepwater fold belt (abstract): Search and Discovery Article #90061 (2006) (http://www.searchanddiscovery.net/abstracts/pdf/2006/intl_perth/abstracts/hull.pdf). Modica, Christopher J., and Eugene R. Brush, 2004, Postrift sequence stratigraphy, paleogeography, and fill history of the deep-water Santos Basin, offshore southeast Brazil: AAPG Bulletin, v. 88, p. 923-945.
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