1.1 Introduction
Bitumen is a viscous liquid, or a solid consisting essentially of hydrocarbons and their derivatives, and is soluble in carbon disulphide, substantially non-volatile and softens gradually when heated. It occurs naturally on its own or as a by-product of vacuum distillation of crude oil. It is blackish or brownish in colour and possesses water proofing and adhesive properties (Olutoye, 2005). Oil sands formerly known as tar sands are composed of bitumen, mineral matter which includes clay or sand and water (Ako et. al., 2012). The bitumen also referred to as heavy oil constitutes an important energy resource that must be rigorously treated in order to convert it to an upgraded crude oil before it can be used in refineries to produce gasoline and other fuels.
Naturally occurring deposits of bitumen are formed from the remains of ancient, microscopic algae (diatoms) and other once- living things. These remains were deposited in the mud on the bottom of the ocean or lake where the organisms lived. Under the heat (above 50 °C) and pressure of burial deep in the Earth, the remains were transformed into materials such as asphalt/bitumen, kerogen, or petroleum (Gwynn and Hanson, 2007).
As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Research questions, Limitations of the Study and Definition of technical terms.
1.2 Background of Study
Nigeria has a considerable large deposit of bitumen which is found in the Western part of the country (Oboh et al., 2006; Fagbote and Olanipekun, 2012; Ayoade et al., 2014). It has been reported that Nigeria has a reserve of 42.47 billion metric tonnes of bitumen, covering about 120 × 4.3km (Oboh et al., 2006; Ayoade et al., 2014). Although exploration of the Nigerian tar sand oil deposit has not yet commenced, the environment is already battling with the problem of pollution arising from seepages of the natural resource into the surface water and soil in the communities where the resource is found (Adesanya et al., 2014).
The elemental composition of bitumen includes 79-88% Carbon, 7-13% Hydrogen; trace to 3% Nitrogen, 8% Sulphur, 8% Oxygen by weight (UNEP and ZLO, 2004). When the light fractions (paraffin) are lost through natural processes after evolution from organic source materials, the oil becomes heavy, with a high proportion of asphaltic molecules, and with substitution in the carbon network of heteroatoms such as nitrogen, sulfur, and oxygen. Therefore, heavy oil, regardless of source, always contains the heavy fractions (naphthene and aromatic). Most naturally occurring bitumen contains nickel and vanadium in less than 10ppm level (Anja et al., 2009).
Occurrence of the seepage and tar sand deposit over the Okitipupa ridge in the Dahomey basin provided the initial impetus for oil exploration in Nigeria. The significant benefit that may result from the exploitation of this resource (MMSD, 2010) makes its delineation an important concern. The petroleum habitat is almost exclusively the Afowo Formation, a member of the Abeokuta Group. This litho-unit is of Turonian – Maastrichtian age and consists of interbeds of coarse-medium grained sandstones, siltstones and shale deposited in a transitional to marginal marine environment (Akinmosin et. al., 2012).
The economic importance of bitumen is versatile as it is widely used in various applications such as in the construction and maintenance of roads; as a feedstock, in petrochemical industries and as an alternative source of energy.
Omosanya et. al., (2012) have review the bitumen characterization in the eastern part of Dahomey basin which Imeri is part of, they were able to use the Geophysical survey and Sedimentological analysis was carried out on the bitumen seepage at Onikitibi (longitude: 04° 18' 18? E and latitude: 06° 39' 39? N) with a view to elucidate its electrical and lithological characteristic. Electrical resistivity profiling and one vertical electrical sounding along a profile of inter-electrode spacing of 5m-30m, and 1000m were carried out using the Wenner and Schlumberger electrode configuration along the seepage zone. Three samples collected from the exposure were subjected to granulometric analysis in order to determine their particle size distribution and textural characteristics of the deposit.
Odunaike et. al., (2014) have also studied and described the use of two-dimensional electrical imaging technique in defining regions of oil sand deposits and determining the geometry of such deposits in Imeri, South Western Nigeria. Three field survey lines were acquired in different orientations in the study area with one of the lines above the oil sand outcrop observed in the area.
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to utilize electrical resistivity method to map and characterize the bitumen deposit in Imeri area.
1.3 Statement of Problems
Investigation revealed that although exploration of the Nigerian tar sand oil deposit has not yet commenced, the environment is already battling with the problem of pollution arising from seepages of the natural resource into the surface water and soil in the communities where the resource is found (Adesanya et al., 2014).
Until recent years, conventional light crude oil has been abundantly available and has easily met all world demand for this form of energy. By year 2007, however, demand for crude oil worldwide has substantially increased, straining the supply of conventional oil. This has led to consideration of alternative or insufficiently utilized energy sources, among which heavy crude oil and natural bitumen are perhaps the most readily available to supplement short- and long-term needs (Emil D. Attanasi et. al., 2007).
The dilapidated state of the road networks in the country is also worrisome. Studies have revealed that bitumen, aside from being a vital natural resource for the construction and maintenance of roads, can also be processed and upgraded to yield gasoline.
Beskrovnyi et al., (1975) concluded that three to four times more petroleum was required than the reserves of a natural bitumen for a given deposit. Hence this research work is carried out to isolate the bitumen deposits in Imeri area. There has been an increasing demand for crude oil over the years which may eventually lead to its depletion if alternative means are not provided.
1.4 Aim and Objectives of Study
The aim of the study is to analyze the Reserve Estimate of Imeri Bitumen Deposit using Imeri, Ogun State, Nigeria as a case study. In achieving this aim, the following specific objectives were laid out as follows:
- To delineate the subsurface lithology;
- To map the bitumen deposits in the study area using electrical resistivity method;
- To determine the flow of the bituminous oil in the subsurface;
- To use this reserve in evaluating its commercial viability; and
- To determine the reserve estimate of bitumen deposit in Imeri, Ogun State, South-western Nigeria.
1.5 Research Questions
The study came up with research questions so as to be able to ascertain the above stated objectives. The specific research questions for the study are stated below as follows:
- What is the meaning of bitumen?
- What is its economic viability?
- What is its reserve estimate of bitumen in the area under study?
1.6 Significance of Study
This research work when completed will boost the nation’s economy by preserving our conventional oil reserves while attention is focused on bitumen development, if all the recommendations proposed are implemented.
This study will also be of immense benefit to researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.
1.7 Scope of the Study
The scope of the research is focused on Reserve Estimate of Imeri Bitumen Deposit using Imeri, Ogun State, Nigeria as a case study.
1.8 Limitations of the Study
During the course of this study, many things militated against its completion, some of which are:
- Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
- Research material: availability of research material is a major setback to the scope of the study.
- Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
- Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).
1.9 Geology of the Study Area
The study area is located within the geographical grids of latitude 60 35’ 16.3”N and 60 39’ 40.9”N and longitudes 40 18’ 29.0”E and 40 50’ 20.7”E in Ogun State. It falls within the sedimentary terrain in the Dahomey basin of southwestern, Nigeria. The Dahomey basin is an Atlantic margin basin containing Mesozoic-Cenozoic sedimentary succession reaching a thickness of over 3000m. It extends from southeastern Ghana to the western flank of the Niger Delta. It stratigraphy is classified by various authors into Abeokuta Group, Imo Group, Oshosun Formation, Ilaro Formation and Coastal Plain sands and Alluvium (Jones and Hockey, 1964; Omatsola and Adegoke, 1981 and Agagu, 1985). The Imeri area is underlain by the sediments of the Imo Group. The Benin (Dahomey) Basin constituting part of a system of West African peri-cratonic (margin sag) basin (Klemme 1975; Kingston et. al., 1983) developed during the commencement of the rifting associated with the opening of the Gulf of Guinea, in the early Cretaceous to the Late Jurassic (Burke et. al., 1971; Whiteman, 1982).
The crustal separation, typically preceded by crustal thinning, was accompanied by an extended period of thermally induced basin subsidence through the Middle – Upper Cretaceous to Tertiary times as the South American and the African plates entered a driftphase to accommodate the emerging Atlantic Ocean (Storey, 1995; Mpanda, 1997). The Ghana Ridge, presumably an offset extension of the Romanche Fracture Zone, binds the basin to the west while the Benin Hinge line, a basement escarpment which separates the Okitipupa structure from the Niger Delta basin that binds it to the east. The Benin Hinge Line supposedly defines the continental extension of the Chain Fracture Zone given room for deposition of bitumen inImeri.
All land near or on top of Nigeria’s bitumen belt is likely to be affected by the soil, water, and air pollution associated with extraction. On sites where bitumen is located near the surface, all topsoil would be removed, making farming impossible. Major occupations include subsistence and cash-crop agriculture, fishing, logging, sand mining, and more. All of these industries would be affected by bitumen development (Christina Milos, 2014). “Our people are predominantly farmers and fishermen. They plant cocoa and food crops like cassava. We know that when they start the exploration it will affect our crops. It will affect both cash crops and food crops. It will kill the fishes in the rivers. It will affect our sources of livelihood.” (Ojo et. al.,2004)
1.9.1 Location, Relief, and Climate of the Study Area
The area of study is area is located within the geographical grids of latitude 60 35’ 16.3”N and 60 37’ 13.9”N and longitudes 40 49’ 29.0”E and 40 50’ 20.7”E in Ogun State. It falls within the sedimentary terrain having a plane homogenous topography which can be term as tropical rain forest with tall trees of seasonal cropping ranging from dry to wet season with period of six to five month annually. (Orire et. al., 2007)
The tropical rainfall within the region is heavy which precipitate throughout the year but between 250mm-150mm during the harmattan. The topography of the area is relatively flat plain low land ranging between 14m to 34m above the sea level.
