Niger Delta Ecosystems: the ERA Handbook/Resources of the Niger Delta: Minerals
14 RESOURCES OF THE NIGER DELTA: MINERALS
- Mining in the Niger Delta
- Oil Mining in the Niger Delta; the Moral Issue
- Oil Geology and Production
- The National Importance of Oil in Nigeria
- The International Importance of Oil in Nigeria
- Natural Gas
- Soil and Clay
- Periwinkle Shells
14.1 MINING IN THE NIGER DELTA
It is because of oil and gas that the international community is interested in the Niger Delta, but for Local People, sand, soil and clay, periwinkle shells and salt are no less important. However, a number of mineral resources are mined in the Niger Delta but oil is the most important. Important in terms of its international demand, of its value to the Nigerian economy and of the impact that oil mining has upon the human ecology of the area. No one can live in the Niger Delta without becoming aware that oil is the political, economic and environmental issue that eclipses all others. Next to oil, its associate product, gas, is the most important, and likely to become more so in years to come.
The previous chapters have discussed renewable natural resources. If their exploitation is managed properly - so that the ecosystems, which produce them, remain viable - they can be produced indefinitely, be they fish, bushmeat, timber or agricultural produce. Thus, fishermen, hunters, loggers and farmers have an incentive to manage these ecosystems sensibly in order to ensure they continued supply of what they need.
Mineral resources, on the other hand, are non-renewable. Their exploitation is not dependent upon the viability of ecosystems, the degradation of which has little, if any, impact upon their supply. In fact in modern times the commercial exploitation of minerals has shown scant respect for the viability of ecosystems because the short-term maximisation of returns on capital does not take into account the cost of the ecological damage caused by mining. This is a cost borne most heavily by Local People (host communities) and not by the owners of mining companies. For example, large areas of Europe remain scarred by nineteenth century mining activity.
Nonetheless, it would be wrong to assume that mining inevitably has a greater impact than does the exploitation of ecosystems for renewable natural resources. For instance a well-managed oil field can have a much less damaging impact than a large mono-crop plantation. A farm road has no less of an impact than a road serving an oil field.
14.2 OIL MINING IN THE NIGER DELTA: THE MORAL ISSUE
Nigeria has an undemocratic and corrupt political process. The willingness with which mining companies tend to exploit this process, springs from the historical entrenched culture of the Western oil companies in their relationships with third world countries. This oil industry culture is founded on five assumptions:
- that profit maximisation is the only basis upon which a company can be run, so that any expenditure beyond what is required to get out the oil is resisted;
- that a 'deal' can be made with governments only, regardless of the government's legality or morality, and regardless also of the wishes or needs of the Local People;
- that once an arrangement has been made with a government a mining company can do what it likes-in fact, to act as if it is a government agency;
- that the 'market' (i.e. the industrialised world) has a right to have the resources it wants, at the lowest possible price, and regardless of the costs to the Local People who are obliged to play host to mining companies; and
- that 'we', the mining companies, know best and are acting responsibly.
Generally, neither the companies nor the governments with whom they associate, (from both the first and the third worlds) are willing to accept any divergence from this culture which is re-enforced with a mixture of cynical public relations and intimidation. It is fair to say that the adverse impacts of mining upon the lives of host communities (and, for that matter, the extravagant use of mineral resources by the industrialised world) arises more from this immoral culture (this wickedness) than from anything else. Thus, until there is a culture shift by mining companies towards an acceptance of some of the moral responsibility for the injustices that the host communities suffer, mining will continue to be an activity that is at best unwelcomed, and in most cases feared by Local People. This fear is especially the case in countries where governments are able to act with impunity against the interests of their own citizens.
As described in the next chapter, there is no doubt that the oil industry has a significant adverse environmental impact upon the Niger Delta. This not only damages human ecosystems, leading to deprivation and environmental health problems, but it also distorts social conditions. This distortion of social conditions in turn influences political conditions in terms of people's views about their ability to change the society in which they live and the degree to which these views translate into tension between different groups within society.
This does not mean that the oil mining industry is the cause of all the problems in the Niger Delta, but it does mean that conditions are simpley worse than they would be without the industry.
In order to appreciate the impact of that the oil industry has upon the human ecology of the Niger Delta, one requires an understanding not only of the underlying human ecological conditions of the area (the overall aim of this book) but also of the nature of the Nigerian oil industry itself. The following sections aim to bring the reader to such an understanding.
14.3 OIL GEOLOGY AND PRODUCTION
14.3.1 THE GEOLOGY OF THE NIGER DELTA
As explained in chapter three there have been two Niger Deltas over geological time. The first delta was deposited in tertiary times when the Niger flowed into the tertiary sea, some 60 to 150 million years ago, at least 30m higher than the modern sea. The second delta is made up of deposits left from the lower quaternary era to the present day.
The drop in sea level in quaternary times (commencing about 2 million years ago) caused the Niger to erode a wide flood plain through the tertiary deposits between Yenegoa and Onitsha. The sudden drop from the tertiary to the quaternary deposits is obvious through much of the region, creating two distinct terraces. This is particularly obvious in Port Harcourt at the Bonny River, where a cliff rises thirty feet high above seventy feet of deep water.
This picture is further complicated by what is known as Localised Uplift caused by earth movements. This is why, for instance, the Sombrero River/Ogoni Terrace, at 1518m above sea level, is a few metres higher than the rest of the tertiary terrace.
Because the delta is made up of deposits carried down by the vast Niger/Benue basin it covers a huge area: about 75,000 km² onshore, 75,000 km² offshore on the continental shelf, and about 90,000 km² beyond the continental shelf on what is known as the Guinea Abyssal Plain. This makes a total area of about 240,000 km², only slightly smaller than the entire United Kingdom. The immense weight of the delta (where, at its thickest, the sediments are over 15 km thick) compresses the lower layers (strata) of sediment and also depresses the earth's crust, which periodically subsides as a result. Each time this subsidence occurs, the front (seaward) portion of the delta slumps downwards and forwards creating a fault, introducing sea water (and thus marine conditions) to be brought inshore. Following the subsidence there is a period of stability when fresh riverine deposits are laid over and beyond the older slumped part of the delta, until there is another subsidence.
As a result of these alternating processes, a cross-section of the delta shows an inter-leaving of strata of marine and river sediments. These are roughly horizontal (the older strata altered by compression and subsidence, and by any geological uplift which may occur from time to time), but complicated by obliquely vertical fault lines caused by the slumping of the delta during subsidence.
The areas between the faults are known as Depobelts, which run parallel to the coast, merging at the flanks of the delta where deposition rates are less. Thus the lens shaped depobelts succeed one another in an oceanward direction, becoming older inland, where they are eroded by the modern rivers to provide some of the material for their successors.
It should be remembered that they take place over tens of millions of years.
14.3.2 THE GEOLOGY OF OIL
Oil (and other hydrocarbons associated with it) is formed in the earth when decayed fish, other animals and plants are subjected, over millions of years, to pressure and heating caused by the subsequent deposition of sediments (sedimentation) on seabeds from neighbouring landmasses. Temperatures of between 100 and 150 degrees centigrade are required, which frequently occur between 4 and 10 kilometres below the surface of the Niger Delta. At temperatures above 150 degrees, any oil previously formed is "overcooked" (Cracked) to become Gas.
As the muddy, silty ooze (which geologists call the Source Rock) in which the oil is formed is pressed by successive strata of sedimentation, the oil is squeezed out to accumulate in sandstone strata which are formed from sand deposited by rivers into the sea. The sand is itself turned into rock by the pressure of succeeding sedimentation.
Sandstone is ideal for this purpose because each grain of sand has been rounded by the erosion processes that have carried it from the land mass of which it was once part to be deposited in rivers, lakes or seas. Thus however tightly the grains are crammed together, like marbles in a box, there are still spaces between them. These spaces are called pores and thus porous sandstone is able to hold oil (and gases and other liquids) like a bath-sponge holds water. Where the pores are connected, liquids are able to migrate through the rocks which are Permeable (they can be penetrated by liquids).
The oil in the sandstone sponge is trapped by a stratum of shale which is impervious (cannot be penetrated by liquids and gases), because, unlike sandstones, shales are dominated by clays, the particles of which, being plate shaped, can been forced tightly together without any spaces between them (see figure 6.). The sandstone sponge collects not only oil but also seawater, gas and a variety of associated marine substances such as sulphur and nitrogen compounds.
Spread across horizontal strata of sandstone the oil does not accumulate (we are told) in commercial quantities. However where there are folds or faults, the oil may gather and be trapped in large quantities. This is because oil, being a hydrocarbon, is less dense than water, and thus tends to rise above the water in the sandstone sponge, until it is blocked by a "cap" of impervious shale, as shown in figure 5. Any associated gas, being lighter than both oil and water, sits between the oil and the cap.
To summarise, five geological conditions are required for the formation of an oil field:
- a source rock (formed by marine deposits);
- a reservoir rock (such as a sandstone sponge);
- a cap rock, to prevent the upward movement of the oil such shale);
- a fault or fold so that the oil is trapped in commercial quantities; and
- time – it takes millions of years for commercially exploitable volumes of oil to accumulate.
The Niger Delta is ideal!
14.3.3 SEISMIC PROSPECTING FOR OIL
When oil companies decide that the basic geological conditions are right (as Shell did in the North-western Niger Delta in 1937) they undertake Seismic surveying in order to identify the composition of the rock strata, and the existence of folds and faults, as potential oil traps.
Seismic prospecting enables energy waves (rather like the shock from the shot of a gun) to be directed into the ground. The return times of the vibration, like an echo, identifies the nature of the rock and its configuration. The vibration is recorded on a microphone called a Geophone.
Thus onshore in the Niger Delta, Seismic prospecting involves laying cables and geophones along previously surveyed receiver lines that are linked by source lines. These lines may be several tens to hundreds of metres apart. The geophones pick up and relay along the cables several shocks set up by Seismogelite explosives shots. There are a number of shots on each source line and each shot consists of in excess of ten kilograms of explosive set in bore holes that are from three to tens of metres deep.
It should be noted that the technology of seismic surveying is a rapidly developing one. For instance, since the late 1980s, oil companies have increasingly used 3Dimensioonal seismic survey instead of the 2-Dimensional processes previously used.
The seismic lines have only to be clear enough to allow sight-lines, safe access, the drilling of the shot-holes (usually by hand with steel tubes that take out a plug of soil) and the laying of the cable. Thus a line that is no more than a metre in width and often less is sufficient, and does not have to be absolutely clear.
Offshore, floating Hydrophones are either hung on cables that are laid on the seabed or towed behind a ship. Energy waves are produced by a compressed air shot, the return vibration being picked up by the hydrophones, indicating the geological conditions.
14.3.4 DRILLING FOR OIL – THE EXPLORATION WELL
If seismic prospecting suggests that there may be commercially exploitable accumulations of hydrocarbons, an exploration well has to be drilled.
Before drilling commences, onshore, the well site is supposed to be sealed. The surface around the well head is covered with concrete and tarmac, around which a drain is dug and a bank built up. The drain is lined with a water-proof impermeable membrane to avoid the contamination of surrounding land from liquids either used in the drilling or escaping from the well. Within the bank, the drain and the concrete surface should be able to contain the equivalent of a few days production.
Boring a well involves using a giant drill. Onshore, the drill equipment is housed within an open steel girder tower called a Derrick, which is about 50m high and mounted upon a platform set about 11m above ground. Within the derrick, a system of pulleys and a wire rope, called a Drilling Line, acts like a crane, from the hook of which is suspended the Drill String.
The Drill String consists of 9m lengths of 25cm diameter, hollow, steel pipes, the lower lengths, called Drill Collars, being the heavier in order to keep the bore hole straight.
In order to drill, a drilling Bit (that 'bites' into the rock or mud strata through which the well is being bored) is screwed into the lowest drill collar and lowered through a Rotary Table mounted on the platform. The rotary table provides the necessary rotation for the drilling string and bit to bore the hole.
Necessary drilling fluids are passed under high pressure down inside the hollow tubes of the drilling string and through jets in the drill bit. The fluids are required to cool and lubricate the bit and to bring debris up the Annulus, which is the space between the drill string and the sides of the borehole. The drilling fluids also prevent the sides of the hole from caving in, and are used to control the pressures within the hole. Drilling fluids can be a simple mixture of water and clay (mud) or combinations of oil and chemicals. Usually, the fluid is stored and mixed on site, and having returned up the annulus, it can be cleaned and used again.
As the well is deepened, more sections of pipe are added to the string. When the well is deep enough sections of protective steel casing pipes are let down as a lining. Down to about 100m the diameter of the well is about 60cms diameter. When drilling has reached this depth the drilling string and bit are withdrawn, a narrower casing put in place and a cement slurry pumped down under high pressure into the annulus between the casing and the well wall to create a lining. Drilling then continues using a smaller bit; the process continues so that the well gets progressively narrower. In the Niger Delta, a typical exploration well might be drilled to 4000 metres below the ground, at which stage it is about 18cms in diameter.
A diagram of an exploration well, figure 7., shows how the progressively narrower Casings fit into one another and are cemented together to create the well.
Finally, a comparatively narrow pipe, known as the Production String, is run below the hydrocarbon producing rock (the sandstone sponge). The last casing and the adjacent part of the production lining is perforated to allow fluids to flow up to the surface. The decision is taken whether to complete the well as a Producer, oil having been struck, or to abandon it as a Dry hole, in which case, the drilling rig and the associated equipment is removed. For a total depth of 4000m, onshore, the operation takes sixty to seventy days.
Where the well is capable of producing, but is to be held for later production, the well head is capped and pressure control valves left in place. This ensures that the formation of any pressures that may build up are contained within the well and that leaks do not occur. The site is regularly monitored.
14.3.5 DIRECTIONAL DRILLING FOR OIL
Wells do not have to be drilled as a straight perpendicular bore. By directional drilling they can be drilled in any direction with angles up to ninety degrees. This is enabled by Motor Drilling whereby the bit is powered by a down-hole motor independently of the drill string which therefore does not have to rotate; and by the use of short-bend tubes with which the angle can be built up. Thus they can be extended from the perpendicular in any direction by up to 10km.
Directional drilling from multiple wells on a single site is now undertaken as a matter of routine in order to minimise the surface 'footprint' of the development phase of an oil field.
14.3.6 OIL PRODUCTION
Where commercial quantities of oil are struck, the exploration well becomes a production well. Here the Production String, being a steel tube of about 12cm diameter, is let down into the well, as shown in figure 7. The end of the tube is perforated to allow any gas, the oil and the water to flow into it. The productive zone of the well is sealed off from the rest of the well by a rubber Packer.
The well head is attached to a Flow Line, which allows the oil and any water and gas (associated with the oil) to flow to a Flow Station. The flow may be assisted on its way by either submersible pumps in the well bore and/or by pump stations along the flowline route.
The flow station receives a mixture of oil, gas and water, so that processing involves three basic steps. These are, in the processing order:
- Gas Processing - whereby the gas (methane, ethane, butane and/or propane) is either flared off, processed (see section 14.6 below) or re-injected into the sandstone sponge.
- Oil Processing - whereby the Crude Oil is separated from the water and the gas, desalted, stabilised and then pumped along the Pipeline to the Oil Terminal.
- Water Processing - whereby the water is re-injected into the sandstone or passed into the local water system.
Re-injection of gas and/or water into the sandstone sponge may be necessary to maintain or enhance the natural pressure in the reservoir, thereby recovering the maximum recovery of hydrocarbons.14.3.7 ABANDONED WELLS
14.4 THE NATIONAL IMPORTANCE OF OIL IN NIGERIA
Oil is very important to the Nigerian economy. Oil revenues provide about 25% of GDP, 90% of foreign exchange earnings and 70% of budgetary expenditure. The government can expect revenues in the order of US$ 20 million a day, even at the depressed prices of the mid 1990s.
Moreover oil will continue to be important to Nigeria in the foreseeable future because other sectors of the economy are unlikely to develop and because the country has enormous reserves. At the end of 1997 Nigeria was reckoned to have proven oil reserves of 15.5 billion barrels (2.11 billion tonnes). Currently the country produces just over 2 million barrels a day (270,000 tonnes) which is about 735 million barrels or 100 million tonnes a year.
Intensive exploration in the Niger Delta and also in the Lake Chad Basin and in Bauchi State is expected to push the reserves up to about 25 billion barrels (3.40 billion tons).
14.5 INTERNATIONAL IMPORTANCE OF NIGERIAN OIL
Nigeria is a very important oil producing country both because of its reserves and because of its current production capacity. In 1996 Nigeria accounted for 3.2% of the world's oil production, being the world's thirteenth largest producer (equal with Kuwait). However Nigeria accounts for about 10% of the world's Light crude oil. Light crudes are valued above other heavier crudes for two reasons: first, they yield larger amounts of light oil products such as benzene, kerosene and propane; and second they contain much lower levels of sulphur, one of major contributors to polluting acid rain. Nigerian Lights consistently out-price other crudes. Thus:
|Dubai (Middle East)||Brent (North Sea)||Nigeria Light|
The major market for Nigerian oil is the United States, taking about 40%, followed by Spain (12-15%), South Korea, India and France, and to a lesser extent Japan, China, Taiwan, the Philippines and Thailand.
Although the Nigerian National Oil Company (NNPC) controls between 55 and 60% of all the major oil production companies in Nigeria, the companies are actually are operated by foreign oil companies. The industry is dominated by six companies, as follows.
|Nigerian Company||Shareholders||Operator||National Production|
|Shell Development (SPDC)||
|Mobil Producing Nigeria||
|Nigerian Agip Oil||
|Elf Petroleum Nigeria||
|Texaco Overseas (Nigeria) Petroleum||
Other producers include Ashland Oil, Deminex Oil, Pan Ocean Oil, British Gas, Sun Oil, Conoco, British Petroleum, Statoil, Conoil and Dubri Oil.
14.6 NATURAL GAS
14.6.1 NATURAL GAS IN THE NIGER DELTA
After oil the most important mineral found in the Niger Delta is gas.
Natural gas is created either as Biogenic gas or as Thermogenic gas. Biogenic gas arises from the bacterial decay of once living matter (for instance, marsh gas), whilst thermogenic gas arises from the excessive heating of already decayed material including oil. This heating definitely occurs at the depths at which oil is formed, there being no doubt that much of the gas associated with oil is formed by thermogenic processes ('cracking' as described above in sub-section 3.2). Nonetheless, the major component of natural gas is Methane, undoubtedly the product of the bacteria which are the agents of decay. Within professional geological circles, a debate continues about the definite sources of gas.
In addition to methane, natural gas sometimes contains Liquid Petroleum Gases (LPGs), such as propane, butane and pentane. Where LPGs are present the gas is referred to as Wet Natural Gas.
As already explained, most of the natural gas currently produced (and flared off into the atmosphere) in Nigeria is Associated Gas, that is associated with oil. Associated gas is generally, but not always, wet.
Natural gas is also found as Non-associated Gas which arises in three ways:
- where the source rock is gas-prone, i.e. where is made up of a high percentage of deposits derived from plant remains as organic matter, i.e. bio-genic;
- where the rock and/or oil is has been heated to above 150 degrees centigrade so that all the oil has been cracked to become gas, i.e. thermo-genic; or
- where the gas has been able to migrate through permeable rock strata on its own. The non-associated gas fields are shown on map 5 .
Non-associated gas is generally 'dry'; that is, low in LPGs.
In summary, therefore, there are generally four types of natural gas as follows:
|1. BIO-GENIC NATURAL GAS, AS||2. THERMO-GENIC NATURAL GAS AS|
|1A Bio-genic and associated||2A Bio-genic and associated|
|1B Thermo-genic and non-associated||2B Thermo-genic and non-associated|
According to an environmental impact assessment study undertaken for the Nigeria Liquefied Natural Gas project in 1995, Nigerian natural gas can "be roughly described as some:
- 90% methane, with
- 1.5 to 2.0% carbon dioxide,
- 3.9 to 5.3% ethane,
- 1.2 to 3.4% propane and
- 1.4 to 2.4% heavier hydrocarbons."
Also Nigerian natural gas "is lean in Nitrogen (max. 0.3%) and has a low sulphur content (max. 30 mg/m³)". The same survey suggests trace elements in Nigerian natural gas as follows.
|Trace Elements in Nigerian Gas||As mg/m³|
14.6.2 NATURAL GAS AND NIGERIA
Following the former USSR, Iran and Northwest Europe, Nigeria has some of the largest proven reserves of natural gas in the world at about 3 trillion cubic metres, some 2% of world reserves. As with oil, Nigerian natural gas is especially valued because of its low sulphur content.
No one seems to be really sure what is the total Nigerian natural gas production, but it seems to be in the order of 22-25 billion cubic metres a year. Around 18 billion cubic metres of this is associated gas, most of which is flared, although a small amount is re-injected into the sandstone sponge, and even less is sold to electricity generating stations and industrial users. About 3 billion cubic metres per year of non-associated gas is currently tapped for industrial uses.
14.6.3 PROCESSING NATURAL GAS IN NIGERIA
In summary, having spoken to a number of oil industry sources, ERA estimates that natural gas from the Niger Delta is processed at the following rates.
|TYPE OF GAS||ESTIMATED AMOUNT PER YEAR|
|Associated Gas Flared||18 billion m³|
|Associated Gas Re-injected||2 billion m³|
|Associated Gas Used||1.5 billion m³|
|Non-associated Gas Used||1.5 billion m³|
The waste through flaring is prodigious, annually equalling about 45% of the energy requirements of France, the world's fourth largest economy. The obvious solution to the waste would seem to be the development of markets for the desirable low-sulphur gas and/or re-injection into the sandstone sponge until such a market is developed.
An array of technical, geographical and financial factors do not make for an easy solution. Nonetheless efforts are being made to commercially exploit the gas, which point to future scenarios: four examples are given below.
Processing Associated Gas from the Oso Field
A Mobil/NNPC joint venture project plans to start processing associated gas from the Oso Field (see map 5.) in 1998. The field produces about 40 million barrels of oil a year (5.5 million tonnes). Processing will involve separating the LPGs and then re-inject the "purified" methane back into the sandstone sponge.
Processing Associated Gas From the Escravos Fields
A Chevron/NNPC joint venture planned for commencement in 1997 to process about 40% of the gas from the Escravos oil field which is currently flared. This will involve producing 1.6 billion cubic metres of methane annually for use in Nigerian power station or for export to neighbouring countries, and an as yet unknown quantity of LPGs.
Liquefied Natural Gas (LNG)
The most valuable processing option in terms of producing an exportable product, involves piping gas to coastal liquefaction plants for bottling for local use and for export elsewhere. This option is being realised at Oso and Escravos. However the most ambitious project is being undertaken by the Nigeria LNG Ltd, a US$3.8 billion joint venture of NNPC (49%), Shell (26.5%), Elf (15%) and Agip (10.4%). This involves piping natural gas, via a 219km Gas Transmission System from three Gas Treatment Stations to a liquefaction plant at Finima on Bonny Island (see map 3B).
Initially all the gas was to have been non-associated, but international pressure to reduce gas flaring in the Niger Delta induced the SPDC particularly to include associated gas, so that the present project design should be able to use about 10% of the associated gas that is presently flared. Future developments (such as an installation to remove ethane from the associated gas could raise this figure).
The gas treatment stations are at Soku (53.33%), operated by SPDC, at Obrike (23.33%) operated by the Nigerian Agip Oil Company and at Obite (23.33%) operated by Elf Petroleum Nigeria Ltd.
The project should be able to liquefy 8.8 billion m3 of natural gas annually by 1999 producing 5.8 tonnes of LNG. Most of this will be supplied, under 20 year contracts, to Enel of Italy (65%), Enagas of Spain, Gaz de France and Botas of Turkey.
Direct Pipelines from Oil and Gas Fields to Electrcity Generators and insutrial Users
Already the Kolo Creek gas turbine plant and the electricity distribution infrastructure associated with it provides communities along the Kolo and Ekole Creeks with electricity and is a good example of what can be done elsewhere. Also gas will be used to fuel the Aluminium Smelter for Aluminium Smelting Company at Ikot Obassi in Akwa Ibom State and the steel-smelting mill at Ajaokuta.
Although exploited on a much less dramatic scale than oil and gas, sand is the next most important mineral extracted from the Niger Delta. It is used for land reclamation, for making concrete and cement blocks, and as the raw material for glass production at Ughelli. Most comes from riverbeds in the Fresh-water ecozone, and also, to a lesser extent, from the Lowland Equatorial Monsoon and Sand-barrier Island ecozones.
Sand is extracted either industrially by dredgers or by hand. The hand method is confined to shallow waters because the sand is dug off the riverbed and carried to the surface in buckets where it is loaded into canoes.
Sand can be viewed as a locally renewable resource because it is replaced by the rivers which bring it down stream, in its progress towards the sea, where much of it is swept back to form the beach ridges of the Delta coast.
14.8 SOIL AND CLAY
In the LEM ecozone where the soils are deep enough, soil, particularly if it has high clay contents, is dug for building up the foundations of roads, so that Borrow-pits are common sight.
Deposits of Kaolinite clay, found throughout the Niger Delta, are used by women for making clay pots. The Ogoni potters are particularly famous.
14.9 PERIWINKLE SHELLS
Periwinkle shells are a renewable mineral resource used as an especially good calcium aggregate for binding cement to make for concrete. In the Fresh and Brackish-water, and Sand-barrier Island ecozones there is no alternative.
Salt extraction from the Brackish-water ecozones of the Guinea, Ghana and the Benin Republic is extensive, which makes it all the more surprising that so little is extracted in the Niger Delta. It seems that the communities living around the mangrove forest prefer 'native salt' made from the charcoal of Rhizophora racemosa propagules. However, sea salt production occurs at Brass, where seawater is boiled on metal trays.