A continental shelf extends from the coastline of a continent to a drop-off point called the shelf break. From the break, the shelf descends toward the deep ocean floor in what is called the continental slope. The continental shelves occupy 7.6% of the total area of the oceans and seas. In the Atlantic Ocean the continental shelf occupies 13.3% of its total area, but in the Pacific and Indian Oceans the percentage is 5.7 and 4.2 respectively.The average width of continental shelves is about 80 km (50 mi), the depth of the shelf also varies, but is generally limited to water shallower than 150 m (490 ft).Though the continental shelf is treated as a physiographic province of the ocean, it is not part of the deep ocean basin proper, but the flooded margins of the continent.The shelf area is commonly subdivided into the inner continental shelf, mid continental shelf, and outer continental shelf, each with their specific geomorphology. There have been various hypotheses regarding the origin of shelf. However, all these views regarding the origin of continental shelf are open to criticism. But it is undoubtedly true that continental shelves in different areas were formed by different processes. Thus, it is unlikely that any one explanation accounts for all the continental shelves of the world.
The offshore area bordering the Nigerian coast consists of a narrow shelf between 15km offshore Lagos to about 75km off the shore of the Niger Delta and about 85km off Calabar along the strand coast. The Nigerian continental shelf is grooved by three major canyons namely: Avon canyon just east of Lagos, Mahin canyon off the mahin mud coast and Calabar canyon off Calabar. The Nigerian coastal zone sprawls a total of nine coastal states namely; Akwa Ibom, Bayelsa, Cross River, Delta, Edo, Lagos, Ogun, Ondo and Rivers.
The Nigerian coastal environment is divided into four main physiographic zones which includes the Barrier Lagoon Coast, the mahin mud coast (Transgressive mud coast), the Niger delta and the strand coastline. The origin of the Nigerian continental shelf is linked to the origin of the Gulf of Guinea basin of the South Atlantic Ocean which began with the separation of South America from Africa about 180 million years ago. The Nigerian coastline is characterized by a mixture of sand and mud deposits consisting of Pleistocene/Holocene sands and recent muddy silts. Several types of minerals that are characteristic of the continental shelves of the world would be expected to occur in the Nigerian shelf. These mineral deposits of the shelf include; placer deposits, glauconite, phosphorite, biological resources, sand and gravels including vein minerals, oil and gas.Today, petroleum resources account for about 99% of the national economy. In the global scene, Nigeria is ranked 6th in OPEC and 14th in the World in terms of oil production and current production of oil and gas in Nigeria comes entirely from the Niger Delta onshore and offshore. The current push by the Federal Government to have the country’s continental shelf extended by 350 nautical miles may expand the nation’s subterranean resources, which include oil, gas, gold and diamond.
Agbami Fieldis an oil field located 220 miles south-east of Lagos and 70 miles offshore Nigeria. Discovered in late 1998, it was the second major deepwater oil field discovered off the Niger Delta, the first being Bonga Field by Shell. The field is located in nearly 1,500 meters (4,900 ft) of water off the central Niger Delta. The operator of the field is Star Deep Water Limited, an affiliate of Chevron. Production began in 2008 at over 70,000 barrels per day (11,000 m3/d) with peak production estimated to be at approximately 250,000 bls/d. The Floating Production unit is the length of three football fields and cost over $US4 billion to build. The Agbami field is the largest deepwater discovery to date in Nigeria, with estimated recoverable reserves of 900 million barrels. Production from Agbami will now bring new energy supplies to the world market and help provide long term, sustainable returns. Oil from the reservoir is light (47° API), sweet crude with low levels of contaminants.