By Sabo Ibrahim Hassan
Up to date, Oil remains the sole resource that keeps the wheel of Nigeria’s economy moving. As asserted by the Organization of Petroleum Exporting Countries (OPEC), oil makes up over 90 percent of Nigeria’s exports and 70 percent of its government revenue. Nigeria is the largest producer and exporter in the African continent and world’s thirteenth oil producer. According to the Oil & Gas Journal, Nigeria had an estimated 37.0 billion barrels of proved crude oil reserves by the end of 2019–the second–largest amount in Africa after Libya.
Geologically speaking, petroleum deposits occurs in sedimentary basins only. Certain elements that give birth to what is technically called petroleum system, remain the only determinants of the oil prospectivity within a given sedimentary basin. In Nigeria, Niger-Delta is the main active basin from which oil is currently produced. However, a relatively small quantity of oil is produced from Dahomey basin.
Apart from the above mentioned basins ( Niger-Delta and Dahomey) the rest are frontier (unexplored) inland basins which include Anambra basin, the rift basin called Benue Trough (which is segmented into Upper, Middle, and Lower parts), Mid-Niger or Bida Basin, Chad or Borno Basin and Sokoto Basin (Illumenden). Apart from Niger-Delta, Dahomey, Anambra and lower Benue Trough, the rest basins are all found in the northern Nigeria.
In the existence of a working petroleum system, petroleum deposit is certainly expected to be generated. For the sake of laymen reading this piece, Petroleum system is a unifying term that encompasses essential elements of petroleum geology which include the source rock (an organically rich rock that may end up yielding petroleum upon subjection to a reasonable temperature), reservoir rock ( that which stores the petroleum after it has been formed), seal and cap rock ( all capable of preventing migration of the petroleum either vertically or horizontally), as well as processes ranging from trap formation (an arrangement of rock that allows for an accumulation of petroleum in the subsurface), generation, migration and accumulation of the petroleum.
In the journey of search for oil in northern Nigeria, about 23 wells were drilled in the Nigerian sector of the Chad Basin and only gas shows were encountered. This was carried out by the Nigerian National Petroleum Corporation (NNPC) through its frontier exploration services arm (FES) which was then under NAPIMS. As elaborated by the holder of professorial chair in basinal studies, Nuhu George Obaje 2019, 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 3000m (i.e. 3km) in 1999 encountered some 33 billion standard cubic feet of gas and little oil (that has been the only well drilled by the company in that area to date). Two other wells, Kuzari-1 and Nasara-1, drilled by Elf Petroleum Nigeria Limited (TotalFinalElf) in 1999 to a depth of 1666m (1.67km) and Chevron Nigeria Limited (Chevron Texaco) in 2000 to a depth of about 1500m (1.5 km), respectively, were reported dry.
However, cost implication of seismic survey (a low impact, non-invasive method of gathering information about the location and characteristics of geological structures beneath the Earth’s surface, used to produce maps of structures identifying areas where oil and gas deposits may be found), which is more informative and precise, is more expensive on land, perhaps this is why the urge to invest in oil exploration in the north kept dying for decades especially because there was no proven oil accumulation.
With the deployment of 3-D seismic data acquisition method, more information has been unveiled which in turn remotivates the quest for hydrocarbon. It is worthy of note that the previous exploratory journeys deployed a 2-D seismic acquisition method, which is not as rich as 3-D, hence will yield lesser information. The technological advancement from 2-D to 3-D has enormously contributed to the existing knowledge of any potential petroleum system.
Seismic surveys are more expensive on land than by ship at sea because geophones have to be placed in a grid, often on uneven and difficult land surfaces. Drilling on land, however, costs much less than from offshore rigs and a much denser well spacing can be used during both exploration and production (Knut Bjørlykke, 2015).
Moreover, the Organic Geochemistry information recovered from samples taken in the areas of interest has also provided explorers with more certainty and clarity with regards the underneath reserves of the basins in question. Likes of Professor Nuhu George Obaje and M.B Abubakar have done more than excellent in that regard.
The federal government’s 2030 mission of reaching 40 billion barrels of Oil reserves and a daily production of 3 million barrels, has intensified the search for more commercial Oil reserves in the frontier basins, this has made more exploratory journeys almost compulsory especially in the unexplored or frontier basins.
The intensified search for oil in the inland basins especially of the northern Nigeria, needs more wells of greater depths to be drilled, so as to ascertain the existence or absence of a good reservoir within Gongola Basin (One of the two arms of the Upper Benue Trough). On the 2nd of February 2019, President Muhammadu Buhari flagged off the drilling of Kolmani River II a site near Barambu, a village in Alkaleri Local Government Area of Bauchi State. The well was drilled to a total depth of about 13,701feet (4,110m), a deeper well compared to Kolmani River I of 3000m depth. The tremendous effort of the current administration has brought the speculation of oil accumulation in the north to an end on 11th October 2019, when the Nigerian National Petroleum Corporation confirmed the discovery of hydrocarbon (oil and gas) deposit in the Gongola basin, rendering the story of whether there is or there is no oil in the North a discussion of the tea joints.
Bima sanstone that was thought to be a potential reservoir is now a proven established reservoir and many other potential reservoirs will sooner or later join scale the speculative line to become established ones. In his review on the Geology and Petroleum potentials of the Benue trough and Anambra basin, Professor M.B Abubakar, the former Director National Center for Petroleum Research and Development (NCPRD) wrote that, At least two potential petroleum systems may be presented in the basins (i.e. Benue trough and Anambra): the Lower Cretaceous petroleum system likely capable of both oil and gas generation and the Upper Cretaceous petroleum system that could be mainly gas-generating.
Sabo Ibrahim Hassan can be reached at firstname.lastname@example.org