Petroleum exploration in Nigeria began as far back as 1908. In 1956 the first commercial oil discovery was made at Oloibiri in the onshore Niger Delta and production of the crude oil commenced in 1958. Since that time, petroleum has played a progressively prominent role in the social and economic development of the Nigeria. 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.
Current production of oil and gas in Nigeria comes entirely from the Niger Delta onshore and offshore. Some exploration campaigns have been undertaken in sedimentary basins of Northern Nigeria with the aim to expanding the national exploration and production base and to thereby add to the proven reserves asset. Sedimentary basins of Northern Nigeria comprise the Middle and Upper Benue Trough, the southeastern sector of the Chad Basin, the Mid-Niger (Bida) Basin, and the
Sokoto Basin. However, these inland basins have continued to frustrate the efforts of many explorers, principally because of the poor knowledge of their geology and the far distance from existing infrastructure (discovery must be large enough to warrant production investments),and for these reasons, many international companies have turned their focus away from frontier onshore to frontier deep-water and ultra deep-water offshore.
Within the sedimentary basins of Northern Nigeria, the Nigerian National Petroleum Corporation (NNPC)through its frontier exploration services arm (NAPIMS) has drilled some wells in the Nigerian sector of the Chad Basin and only gas shows were encountered. The first well in the Benue Trough region, Kolmani-River-1, drilled by Shell Nigeria Exploration and Production Company(SNEPCO) to a depth of about 3000 m in 1999 encountered some 33 billion standard cubic feet of gas and little oil (that has been the only well drilled by that company in that area to date).
Total and estimates
In 1997, Nigeria’s proven oil reserves measured approximately 16.8 billion barrels and gas reserves were 3.3 trillion cubic metres, which represented 1.6% and 2.2% of the world’s total reserves. In 2007, Nigeria had proven reserves of approximately 36 billion barrels. This phenomenal growth is being fueled by recent large deep-water discoveries. Approximately, 65% of Nigeria’s crude oil production is light and sweet (low sulphur content).
Offshore activities have intensified in recent years and have accounted for over 50% of oil production in Nigeria. The deep-water extraction plants are less disturbed by local militant attacks, seizures due to civil conflicts, and sabotage. One significant deep-water discovery is the Agbami field that holds more than 1 billion barrels of reserves and ranks among the single largest deep-water discoveries in the world.
According to Department of petroleum resources (DPR), probable and proven oil reserves as at 2013 stands at 31.81 billion barrels of oil, while condensate reserves is 5.35 billion barrels. Total oil and condensate reserves stands at 31.16 billion barrels. Compared to the same period in 2012, the oil reserves dropped by 1.6 billion barrels (4.79%); condensate reserves increased by 0.152 billion barrels (2.92%).
Other minerals includes
Placer Deposit
Gold in Nigeria is found in alluvial and elluvial placers, and primary veins from the several parts of super crustal belts in the southwest and northwest of Nigerian continental shelf regions. There are also a number of similar occurrences beyond these major areas.
Phosporite
Phosphorite or phosphate rock is a major industrial source of phosphates and of immense importance of chemical fertilizers. It is useful in the manufacture of elemental phosphorus from which organic and inorganic chemicals are made. Phosphorites are normally associated with areas of upwelling and therefore nutrients rich zones. Limited upwelling during July-September and possibly between November-March has been reported in offshore Nigeria by Longhurst (1962, 1964). This upwelling is taught to be wind related although the exact casual relationships are not entirely clear. However, there exist in this region, a set of upwelling inducing phenomena such as the meeting of the cool South Atlantic Central Water (SACW) and the warm Tropical Surface Water); the occurrence of counter currents; the prevalence of strong westerly winds; etc. Such a setting is ideal for a more prolonged upwelling in offshore Nigeria than is presently recognized by implication, for phosphorite deposition on the Nigerian platform. According to Dietz et al (1942), all the localities where phosphorite is found are essentially non depositional or are areas of extremely low sedimentation. Such areas have been identified on the Nigerian continental shelf by Allen (1965). One very strong support for the possible occurrence of phosphorites in Nigeria’s offshore is the existence of phosphate deposits (average P2O5 content of 30%) of decidedly marine origin in the Eastern, North-western and North-eastern Sectors of continental Nigeria (Ene 1982). It is taught that these deposits were laid down in a stand of the sea during an extensive marine transgression in the Cretaceous times. Since they is nothing to suggest that sea water chemistry in the region has changed in any appreciable way since that time, it is concluded that phosphoriteare a distinct possibility in the Nigerian platform. Products of the erosion of land based phosphate deposits would additionally enrich the forming submarine phosphates. It has been proposed that the reported low phosphate content of 0.25-0.60 mg P2O5/m3 (extrapolated by Longhurst, 1962 from published data) in the waters of the continental shelf off the West African Coast, may be indicative of an operative mechanism for the removal of phosphates from the sea water and/or its retention in sediments at the bottom to form phosphorite or phosphatic rocks. The existence of phosphatic shell debris in offshore Nigeria (Allen, 1965) is supportive of this proposal. Smirnov (1947) stated that when the bottom layers of water are forced to the surface in various upwellings, the resultant lowering of pressure and concomitant loss of CO2 will result in the precipitation of phosphates.
Glauconite
Glauconite, a hydrated potassium iron alumino-silicate reported as occurring off the West African Coast by Murray and Renard (1981) has been specifically recorded by Allen (1965) as occurring in five different forms in the Nigerian continental shelf. Allen (1965) believes that a large proportion of these forms are fecal origin while some, particularly those occurring near the Island of Fernando Poo, may have formed alteration products of ferromagnesian minerals of volcanic origin. Maximum concentration of glauconite in offshore Nigeria occurs in the outer shelf and upper continental slope in association with foraminifera and other calcareous organisms. Glauconite serves as a source of potash for use in agricultural fertilizer and a source of potassium and potassium compounds.
Sand and Gravels
This constitutes the largest of all seafloor operation used in cement and concrete for buildings, landfills and construction of artificial breaches. The annual world production is about 112 billion metric tons and the reported potential is more than 600 billion metric tons. In Nigeria, over 13.22 million metric ton of sand was dredge from the Lagos lagoon between 1984 and 1989 to sand-fill about 522 hectares of the Lekki, scheme residential project (Awosika and Dublin Green, 1994).
Sea resources
Calcareous and calcareo-phosphatic shell debris composing mostly of molluscs, echinoderm, bryozoan, crustaceans and materials of vertebrate origins occur on the Nigerian continental shelf (Allen, 1965). In addition, there is an array of planktonic foraminifera found together with benthonic forms which generally show evidence of erosion of mechanical damage and abrasion. These shells deposits could be mined for use in the manufacture of cement and lime. Some shells are attractive enough to be used as decorative materials and for jewelry mostly for the tourist trade.