Recently, operators have found that deepwater wells often have higher flow rates than expected, providing a lower initial drilling cost. At the same time, the long exposure of the production flow to seawater near freezing temperatures promotes the deposition of solids - waxes, asphaltines, and hydrates - in production equipment. These are requiring additional equipment or flowline looping to inject buildup preventatives or cleaning pigs, and so require more initial testing and engineering to assure long-lived flows.
DiscoveriesThere are at least eight known deepwater fields with 1 billion bbl or more of oil in place, located offshore five countries:
- Brazil: To date, Petrobras' Marlim Field off Brazil, with 2.5 billion bbl in place, is the largest deepwater field in the world. First considered only a local anomoly when discovered early in the decade, Petrobras soon proved that the trend was extensive and involved plays in even greater depths. The Roncador discovery followed in the mid-1990s. Aware that South America and West Africa were joined in an early geological era and surrounded a body of water that was largely devoid of oxygen (requirement for petroleum formation), explorationists started examining West African deepwater geology in detail.
- Nigeria: Nigerian deepwater geology in the Gulf of Guinea proved difficult to unravel, and the shows were unpredictable. However, Shell was able to locate the Bonga Field in the OML 212 license. In-place reserves totaled 1 billion bbl.
- Cabinda: The West Africa search also moved south at the same time as the search for large fields moved into deepwater. There, off Cabinda, Chevron discovered the Banzala Field. But the greater payoff lay even further south.
- Angola: Elf's Dalia Field, at 1.3 billion bbl in place, and Girassol, at 1 billion bbl in place, are both deepwater discoveries. Chevron's Kuito Field discovery, also off Angola, also came in a 1 billion bbl. Some geological trends in deepwater may extend from Angola southward into Namibia's offshore area.
- US Gulf of Mexico: Shell has a number of discoveries in the US Gulf of Mexico that exceed 500 million bbl, although none exceed 1 billion bbl. If subsequent drilling does not undermine estimates based on early drilling and geology evaluation, EEX appears to be the first to define a 1 billion bbl field in the US Gulf of Mexico. EEX's Llano prospect appears to underlie at least nine contiguous 3-mile square tracts. Several sedimentary studies suggest that at least two more 1 billion bbl plus fields could exist in US Gulf of Mexico deepwater.
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