Screening and Ranking of Chad Basin for co 2 Sequestration Potential in Nigeria

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1 INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 4, No 1, 2013 Copyright 2010 All rights reserved Integrated Publishing services Research article ISSN Screening and Ranking of Chad Basin for co 2 Sequestration Potential in Nigeria 1 * and N.G Obaje 1 Department of Geology and Mining, Ibrahim Badamosi Babangida University, Lapai, Nigeria yusufishaq73@yahoo.com ABSTRACT Sedimentary basins are suitable to different degrees for CO 2 geological sequestration as a result of various intrinsic and extrinsic characteristics. This paper preliminarily screened and ranked the Chad Basin of Nigeria sector based on Bachu (2003) ranking and screening criteria adapted which includes factors such as tectonic setting, basin size and depth, geology, hydrogeology, hydrocarbon potentials, climate, geothermal, existing resources and industry maturity. For each criterion i (i = 1 5) used for the evaluation of basin suitability, monotonically increasing numerical function f i is assigned, which are continuous or discrete, to describe a value placed on a specific class j for that criterion. The lowest and the highest functions of this functions characterize the worst and best class in terms of suitability for that criterion, i.e. f i,1 = min (f i ), where and f i,n = max (f i ); where ( n = 3, 4 or 5).The criteria relate to either the containment security, the volume of storage capacity achievable, or considering the economic or technological feasibility. The results shows that Chad basin has R k score value of 0.53 against the f i, n = max (f i ) value equal to 1 as highest value of the function characterize the best in terms of suitability for the criterion in which this ranking are based on. Regional screening and ranking of the entire basins are recommended while detailed local site characterisation of the basin is needed to assess its overall suitability for CO 2 sequestration potentials, since countries like Cameroon, Central African Republic, Niger, Chad, and Nigeria shares the basin on regional level Keywords: Screening Chad Basin, Nigeria, CO 2 geological sequestration, Criterion, Ranking and 1. Introduction Global search for economic and viable earthly minerals for energy development; Biomass, Solid minerals, Fossil fuel, Hydrocarbon and the solution to natural and man-made phenomenal affecting the earth; Earth quake, Greenhouse gases by the Geologist, Geophysicist and other Scientist is now a global issue to save the planet. Geoscientist have been looking for way forward for an alternative sources of energy (Renewable Energy) that is safer for about less to non emission of carbon dioxides (CO 2 ), Methane (CH 4 ), and other related greenhouse gases into the atmospheres other than Nuclear Energy that will greatly reduces the measure of continuous raising in temperature of the earth we lived; The Global Warming! As a result of anthropogenic carbon dioxide (CO 2 ) emissions, atmospheric concentrations of CO 2, a major greenhouse gas, have risen from pre-industrial levels of 280 to 360 ppm, primarily as a consequence of fossil fuel combustion for energy production (Bryant 1997). Increasing concentrations of CO 2 affect the Earth atmosphere energy balance, enhancing the natural greenhouse effect and thereby exerting a warming influence at the Earth s surface. Because of uncertainties regarding the Earth s climate system, there is much Submitted on June 2013 published on August

2 public debate over the extent to which increased concentrations of greenhouse gases have caused or will cause climate change, and over potential actions to limit and/or respond to climate change. Planetary cooling forces that are intensified by warmer temperatures and by strengthening of biological processes, which would be enhanced by the same rise in atmospheric CO 2 concentrations, may cancel the predicted climate warming (Idso 2001). Carbon dioxide can be sequestered in geological media by geological (stratigraphic and structural) trapping in depleted oil and gas reservoirs, solubility trapping in reservoir oil and formation water, adsorption trapping in uneconomic coal beds, cavern trapping in salt structures, and by mineral immobilization (Figure 1) (Blunt and others 1993; Gunter and others 1993, 1997; Hendriks and Blok 1993; Dusseault and others 2002). Use of CO 2 in enhanced oil and gas recovery (EOR and EGR; Holtz and others 2001; Koide and Yamazaki 2001) and in enhanced coalbed methane recovery (ECBMR; Gunter and others 1997; Gale and Freund 2001), and hydrodynamic trapping in deep aquifers (Bachu and others 1994) represent actually forms of CO 2 geological storage with retention times of a few months to potentially millions of years, depending on flow path and processes. In all cases of enhanced recovery of hydrocarbons, CO 2 ultimately breaks through at the producing well and has to be separated and recirculated back into the system, thus reducing the storage and sequestration capacity and efficiency of the operation, notwithstanding the additional CO 2 produced during the separation and compression stages. However, the economic benefits of incremental oil and gas production make EOR, EGR, and ECBMR operations most likely to be implemented first. Only sedimentary basins contain geological media generally suitable for CO 2 storage and/or sequestration: oil and gas reservoirs (geological and solubility trapping), deep sandstone and carbonate aquifers (solubility, hydrodynamic and mineral trapping), coal beds (adsorption storage and trapping), and salt beds and domes (cavern trapping). In addition, these media have both the space (porosity) and injectivity (permeability) necessary for CO 2 injection, and, by and large, have the ability to either prevent or delay for geologically significant periods of time the CO 2 return to the atmosphere. Crystalline and metamorphic rocks, such as granite, on continental shields, are not suitable for CO 2 storage and sequestration because they lack the porosity and permeability needed for CO 2 injection, and because of their fractured nature. Volcanic areas and orogenic belts (mountains) are also unsuitable mainly because they lack capacity and are unsafe. Fortunately and serependitously, sedimentary basins are also where fossil energy resources are found, produced and, by and large, used for power generation (Hitchon and others 1999). In Nigeria, there are seven (7) sedimentary basins; Chad basin, Sokoto basin, Bida Basin, Anambra Basin, Dahomey basin, Niger Delta basin and Benue Trough (Upper, Middle and Lower) all distributed majorly on the inland, while Dahomey and Niger Delta basin are both offshore (Figure 2). Chad basin has the largest basin size and deepest sedimentary piles in Nigeria when looking at the inland basins and Niger Delta basin for offshore respectively. Figure 1: Showing various means of CO 2 sequestration or storage in geological media (after Bachu, 2003) 17

3 1.2 Location and geological setting The Nigerian sector of the Chad Basin, known locally as the Bornu Basin, is one of Nigeria s inland basins occupying the northeastern part of the country. It represents about one-tenth of the total area extent of the Chad Basin, which is a regional large structural depression common to five countries, namely, Cameroon, Central African Republic, Niger, Chad, and Nigeria. The Bornu Basin falls between latitudes 11 0 N and 14 0 N and longitudes 9 0 E and 14 0 E, covering Borno State and parts of Yobe and Jigawa States of Nigeria, figure 2. Figure 2: Generalized geological map of Nigeria showing the location of Chad Basin (after Obaje, 2009) The Chad Basin belongs to the African Phanerozoic sedimentary basins whose origin is related to the dynamic process of plate divergence. Notable exceptions, however, are the deformed basinal sequences of the Paleozoic fold belts of Moroco and Mauritania which resulted from the Hercynian convergent motion and collision of Africa and North America, and the Tindouf and Ougarta basins which are Paleozoic successor basins (Burke, 1976; Petters, 1982). It is an intracratonic inland basin covering a total area of about 2,335,000 km 2 with Niger and Chad Republics sharing more than half of the basin. The basin belongs to a series of Cretaceous and later rift basins in Central and West Africa whose origin is related to the opening of the South Atlantic (Obaje et al., 2004). In Nigeria, other inland basins of the same series include the Anambra Basin, the Benue Trough, the Mid-Niger (or Bida) Basin and the Sokoto Basin. The Nigerian sector of the Chad Basin, known locally as the Bornu Basin represents about one-tenth of the whole basin. It constitutes the southeastern sector of the Chad Basin. 1.3 Lithostratigraphy Geologic outcrops in the Chad Basin are scarce, being blanketed by Quaternary sediments. The rare exposures of the older series of Early Cretaceous are mostly found in the Niger Republic part of the basin. The sedimentary fill in most parts of the basin is made of Late Cenozoic middle Eocene continental sediments and Cretaceous and Tertiary series accumulating preferentially in tectonic rifts. Data gathered from the adjacent basins and 18

4 boreholes indicate that the Bornu Basin is made up of five stratigraphic units that include the Bima Sandstone at the bottom, the Gongila Formation, the Fika Shale, the Keri Keri and Chad Formations. In most cases the Chad Formation lies directly unconformably on the Fika Shale Figure 3. Figure 3: Idealized N-S stratigraphic cross-section the Benue Trough and the relationship to Niger Delta and Chad Basin (vertical scale exaggerated; erosion and uplift not considered) (after Obaje, 2009) 2.1 Methodology for basin-scale screening and ranking of co 2 geological storage potential A preliminary local scale screening and ranking process (Chad basin; Nigeria sector) is used to establish the potential of the basin for CO 2 geological storage potential before detailed site characterisation will be carried out. Sedimentary basins can be screened and ranked as to their overall suitability for CO 2 storage, based on geological, geographical and industrial characteristics. This study has adapted screening and ranking criteria developed by Bachu (2003), which includes factors such as tectonic setting, basin size and depth, geology, hydrogeology, geothermal regimes, hydrocarbon potential, maturity, on/off shore, climate and accessibility among others. Table 1 documents the criteria that were used to assess the basin-scale suitability of Chad basin studied for geological storage of CO 2. For each criterion, the classes are arranged from least favorable to most favorable left-to-right across the table. The criteria relate to either the containment security, the volume of storage capacity achievable, or consider the economic or technological feasibility. The present-day tectonic setting of a basin gives an indication as to the likely tectonic stability of the region, which is an important consideration for containment risk (i.e. tectonically-active areas, such as subduction zones, are the least favorable due to their increased susceptibility to natural earthquake risk and attendant fault seal failure). The basin size and depth reflects the possible storage capacity achievable, as the larger and deeper the 19

5 basin is, the greater the likelihood of having laterally extensive reservoir and seal pairings, possibly in more than one stratigraphic interval. Table 1: Criteria for Sedimentary basins for CO2 geological sequestration (after Bachus, 2003) The depth of the sedimentary fill of the basin is also relevant to the phase state of the CO 2 (i.e. depths greater than ~800 m result in dense supercritical CO 2 and hence significantly increased storage capacity) and also impacts on the likely economic feasibility, as the greater the depth to the injection target the larger the associated costs of drilling. The stratigraphy of the area is reviewed to identify possible geological formation that may provide reservoir and seal pairs. The reservoir-seal pair criteria (geology) are a qualitative assumption about the likely abundance, lateral extent, thickness and depth of possible reservoir-seal horizons. While, faulting intensity as component of geology view both containment and capacity issue. The more extensively fractured that an area is, the greater the risk for containment breaches, and the lower the likely storage volume achievable due to the need to inject within individual fault blocks. The geothermal conditions of the basin has an impact on the storage capacity, as within colder basins; more CO 2 can be contained within the same unit volume of rock due to the increased density of the CO 2, while verse- verse in warm basin. The hydrocarbon potential of a region gives an indication of the suitability of the area for CO2 storage, on the assumption that if the rocks are suitable for containing and storing oil and gas, then it is likely that they are also suitable for storing CO 2. Maturity of the extractive industries in the region reflects the likely database available that is the more developed an area is the greater amounts of data available for CO 2 storage assessment. The climate of the region affects the likely surface temperatures (and hence the geothermal conditions) and likewise, accessibility and infrastructure reflect the variability in condition in terms of getting the captured anthropogenic CO 2 from source to point of sequestration. 20

6 2.1.1 Fundamental of Screening and Ranking Sedimentary Basins According to Bachus, 2003; there are no large-scale operations for the geological sequestration or storage of CO 2, and whatever operations exist, they were driven by other considerations, such as increasing oil production, avoiding a carbon tax, or complying with regulations regarding sulfur emissions. However, if CO 2 geological sequestration or storages are to be implemented on a large scale, then there is need for a systematic, quantitative analysis of sedimentary basins in terms of their suitability to serve as enhanced CO 2 sinks. A method for such a quantitative analysis based on parametric normalization and ranking, is proposed here, which can be further developed or adapted to more specific conditions. For each criterion i ( i = 1, 5) in Table 1 for evaluating a basin suitability, monotonically increasing numerical function F i is assigned, which can be continuous or discrete, to describe a value placed on a specific class j for that criterion. The lowest and the highest functions of this function characterize the worst and best class in terms of suitability for that criterion, i.e. F i, 1 = min (F i ), where and F i, n = max (F i ), where ( n = 3, 4 or 5). If the classes have a relatively equal importance assigned o them, then a linear function is probably the best for F i. If the increasing value (or importance) is placed on increasingly favorable classes, then geometric or exponential function are probably better. Table 2 presents the numerical values assigned here to the various classes for the criteria in Table 1. For any sedimentary basin k that is evaluated in terms of its general suitability for CO 2 sequestration or storage, the corresponding class j for each criterion i s identified as in Table 1, resulting in a corresponding score F i, j as in Table 2, because the function f i has different ranges of values for each criterion, making comparison and manipulation difficult, the individual scores F i, j are normalized according to Such that P i = 0 for the least favorable class and P i = 1 for the most favorable class for all the criteria i = 1, 15. As a result of this process, each sedimentary basin k being evaluated is characterized by individual scores P k i. The effect of parameterization and normalization is that it transforms various basin characteristics, which have differing meanings and importance, into dimensionless variables that vary between 0 and 1. These can subsequently be added to produce a general score R k, used in basin ranking, which is calculated using: Where W i are weighting function that satisfy the condition: 21

7 Table 2: Scores and weight assigned to criteria and classes for accessing sedimentary basins in terms of their suitability for CO 2 sequestration in geological media (after Bachus, 2003) The weights w 1 assigned in this study to the various suitability criteria are shown in Table 2. The number of criteria (currently 15), the functions F i (i=1,..15) and weights w i the can be changed and/or adapted to changing conditions and priorities. Using this methodology, sedimentary basins, or parts thereof, within a given jurisdiction or geographic region can be assessed and ranked in terms of their suitability for the geological sequestration or storage of CO 2. This ranking can be then used in making decisions for the large-scale implementation of such operations Screening and Ranking Chad Basin (Nigeria sector) The Chad basin was evaluated against criteria for assessing sedimentary basins for CO 2 geological sequestration Table 1 adapted from Bachu (2003). Table 3 shows summarises the results of the screening criteria for the basin studied. A brief discussion of some of the key features of each basin is presented below. 3.1 Criterion potential evaluation Injecting carbon dioxide, generally in supercritical form, directly into underground geological formations like oil and gas fields, saline formations, unmineable coal seams, and saline-filled basalt formations have been suggested as storage sites. Various types of physical trapping; structural: anticline and fault; stratigraphic: unconformity and change in type of rock, or a particular formation thinning out, highly impermeable rock, geochemical trapping mechanisms would prevent the CO 2 from escaping to the surface. Sedimentary basins are considered suitable targets for storing large volumes of CO 2, having characteristics that favour effective storage over hundreds of thousands to millions of years (geological time periods), as demonstrated by the widespread existence of natural CO 2 accumulations as occurred in Colorado Plateau and Rocky Mountain region of the USA ( IPCC 2005 ) as well as hydrocarbons trapped in reservoirs. 22

8 The following below nine (9) criterions are evaluated in view of Bachus, 2003 criteria for assessing sedimentary basins for CO 2 geological sequestration (Table 1). Table 3: Results of ranking of the Nigeria sector Chad sedimentary basin in terms of suitability for CO 2 geological sequestration Tectonic Stability The tectonic regime as reviewed in this paper was probably dominated by tensional movement as indicated by the preponderance of high angled normal faults and the scarcity of reverse faults. Majority of the faults in the basin are basement-involved faults; movements along these faults led to high angled faults in the overlying strata. Tectonic pulse was a basin modifying event, which caused folding and basin inversion in the Bornu basins. Folds within the basin are said to be simple and symmetrical with low fold frequencies and amplitudes which increase towards the centre of the basin. Major basement lineaments and faults were produced within the basin during the Pan African crustal consolidation. These revealed truly that the Chad basin of the Nigeria sector is on a stable intracratonic basement rock and not on seismically active region of the continent. The faulting intensity is ranked not extensive and that capacity, containment for CO 2 would be in substantial volume after detail characterisation on the basin Basin Size and Depth Basin size and depth give an estimate of the overall storage volume achievable. The sedimentary basin needs to be deep enough to store CO 2 in a supercritical phase (a depth of approximately 800m is needed for this), while Nigerian sector of the Chad Basin (Borno Basin) covering a total area of 233,500km 2 and over 3,600 m of sediments have been 23

9 deposited. The basin can be termed very large in terms of size and deep when considering the depth as a criteria to estimate the storage volume of the basin Geology As a result of the tectonic tensional movement resulting into the high angled normal faults; low frequencies, amplitudes simple - symmetrical fold within basin, which increases towards the centre of the basin. The basin can be said to be moderately faulted, such that only detail site characterisation would give the extended from the faulted basement rock to extent on overlying sedimentary formations within the basin. Many studies reveal that the natural underground geological formations can provide adequate CO 2 storage for a very long period of time, considering the nature of geologic storage potential. The sedimentary piles in the basin, as related to CO 2 sequestration potentials are reviewed as follows: 3.1.3a Geological Formation: Bima Sandstone The Albian Bima Sandstone lies unconformably on the Precambian Basement. This formation was deposited under continental conditions (fluvial, deltaic, lacustrine) and is made up of coarse to medium grained sandstones, intercalated with carbonaceous clays, shales, and mudstones. It is the deeper part of the aquifer series in the Nigerian sector of the basin and rests unconformably on the basement. The thickness ranges from 300 to 2,000 m and the depth between 2,700 and 4,600 m. This geological formation can be categorize as intermediate with depth range greater than 3500m according to Bachus,2003 basin-scale suitability criteria. At this depth CO 2 can be store at greater depth in its superficial phase, and large volume of the CO 2 would be stored considering the basinal size of the basin. This stable large basinal size and volume, point the basin as having the potential to store large volume of CO 2 over hundreds of thousands to millions of years (geological time) b Reservoir Seal: Fika Shale Turonian Maastrichtian in age, and fully marine blue black Fika shale locally gypsiferous with intercalation of limestones with thicknesses of 430 m, m, 890 m and 840 1,453 m recorded from exploratory wells by Carter et al. (1963), Avbovbo et al. (1986), Okosun (1995) and Olugbemiro et al. (1997), respectively would serves as reservoir seal considering the shale thickness as reviewed for underlying Bima sand stone (Reservoir) to prevent the CO 2 from horizontal and vertical migration at its superficial phase within the basin and on regional base. This can be termed intermediate according to Bachus, 2003 basin-scale suitability criteria and excellent when later proven by detail geophysical site characterisation analyses Hydrogeology Maduabuchi et al. (2006) undertook some groundwater investigations in the Nigerian sector of the Chad Basin and in the process gave some brief descriptions of the geologic and 24

10 hydrogeologic settings of the Chad Basin. The Precambrian Basement Complex constitutes the bedrock on which sediments ranging in age from Palaeozoic to the Quaternary have been deposited. The Chad Formation is essentially an argillaceous sequence in which minor arenaceous horizons occur. Barber and Jones (1965) named three clearly defined arenaceous horizons in the NE Nigeria of Chad Basin consisting of the upper aquifer and two confined middle and lower aquifers. The upper aquifer consists of Quaternary (lower Pleistocene) alluvial deposits of lake margin origin, alluvial fans or deltaic sediments related to sedimentation around lake Chad covered in many locations by recent sand dunes. The thickness increases considerably from 15 to 100 m north of the lake. The reservoir is composed of interbedded sands, clays, silts and discontinuous sandy clay lenses which give aquifer characteristic ranging from unconfined, semi-confined to confined type. The transmissivity ranges from 0.6 to 8.3 m 2 /day and the aquifer which recharges from rainfall and run-off is mainly used for domestic water supply (hand dug wells and shallow boreholes), vegetable growing and livestock water in (Maduabuchi et al., 2006). The lower Pliocene sequence composed of grey to bluish grey clays varying in thickness from few tens of meters to over 350 m at the edge of the lake separates the middle aquifer from the upper aquifer. The middle aquifer is the most extensively encountered aquifer in the Nigerian sector of the Chad Basin. It lies at a depth between 240 and 380 m and consists of m thick sand beds with interbedded clays and diatomites of Early Pliocene age. The sand fraction consists of moderately coarse to coarser grains of quartz, feldspar, mica and Feoxides. The aquifer geometry has a gentle northeast dip and does not outcrop in the Nigeria sector of the Chad Basin. The average transmissivity is 360 m 2 /day and the hydraulic gradient is 0.015% in the NE direction (Maduabuchi et al., 2006) Geothermal Regime Geothermal regime of sedimentary basin is one of the most important elements to be considered as criteria for suitability assessment of a geological storage; as result of phase behavior and variation of CO 2 properties with temperature, pressure and depth. At normal atmospheric conditions; CO 2 is thermodynamically very stable gas heavier than air and also at temperature greater tan T c = 31.1 o C and pressures greater than P c =7.38 MPa (critical point), CO 2 is in a supercritical state. Bachus, 2003 indicated that basin < 30 o C/km is termed as cold basin and while in Chad Basin, the geothermal gradient falls between 7.6 and 5.90 o C/100m by Kurowska, 2010 reflecting that Chad Basin can be termed one of intracratonic cold basin around the world. In these regards, the basin can said to be favorable for CO 2 storage potential in the area. As of the time of compilation these preliminary results, information regarding hydrostatic variation of pressure is not available Hydrocarbon Potential/Maturity Rocks that are suitable for containing and producing oil and gas are likely to be suitable for storing CO 2. The potential for storing CO 2 will be dependent on the timing of possible hydrocarbon production. If there is a mature oil/gas industry in the area, there will be a larger amount of available information about the site. Most of the hydrocarbon and coal would have 25

11 been discovered and there are likely to be depleted oil and gas reservoirs. Such areas are likely to have good infrastructure such as roads, pipelines and wells. Twenty three wells were drilled. The first well TUMA-1 was spudded on July 27, 1984, of the 23 wells drilled, only two encountered non-commercial gas while the remaining 21 were abandoned as dry wells which led to the temporary suspension of exploration activities before the recent renewed search. On this note, the hydrocarbon potential and maturity can be considered medium for now pending further discoveries are made in the basin Climate Climate affects the surface temperatures, the depth of the water table and the ease of development of storage facilities. The Chad Basin embraces a great range of tropical climates from north to south, although most of these climates tend to be dry. Apart from the far north, most regions are characterized by a cycle of alternating rainy and dry seasons. And this according to Bachus, 2003 screening and ranking; tropical climatic condition of this area is next to the most favorable temperate condition for CO 2 sequestration potential. 4.1 Discussions The results in Table 3 shows that R k score value of 0.53 against the f i, n = max (f i ) value equal to 1 as highest value of the function characterize the best in terms of suitability for the criterion in which this ranking is based upon. These score values characterize Chad basin to have tropical climatic condition having deposited on a tectonically stable cratonic divergent plates, with very large basin size of 233,500 km 2 and more than 3600 m deep sedimentary piles. The basin is tectonically moderately faulted and possibly fractured by the events, with a moderate geothermal gradient of about 5.9 and 7.6 o C / 100 m, shallow and short flow Hydrogeological systems. The hydrocarbon potential in the basin is ranked for now medium, and the basin is mature on that about 23 wells were drilled into the basin and gas discovered. Ongoing, the basin is under 3D seismic detailed survey prospectivity for oil/gas in commercial quantity. There are no reports or record of neither coal nor salt discovery in the basin this past recent years; and the entire basin can be easily accessed, minor infrastructures are available and with no CO 2 source in the region. By this ranking and screening criteria, the basin can be compared with SW Ontario basin in the Canada s sedimentary basin in terms of its suitability for CO 2 geological storage with R k value of 0.52 as assessed by Bachu, It is not yet possible to predict with confidence storage volumes, sequestration integrity, and fate of injected CO 2 over long periods of time at this local ranking and screening without carrying out regional characterisation of the entire 2,335,000Km 2 basins in other bordered countries. 5.1 Conclusions The geology of the sedimentary basins of Chad basin in the Nigerian sector has been preliminarily screened and ranked to view its potentials for CO 2 sequestration opportunities in the basin. The ranking and screening criteria adapted were developed by Bachu (2003), which includes factors such as tectonic setting, basin size and depth, geology, hydrogeology, 26

12 hydrocarbon potentials, climate, geothermal regimes, existing resources and industry maturity. For each criterion i ( i = 1, 5) in Table 1 for evaluating a basin suitability, monotonically increasing numerical function F i is assigned, which can be continuous or discrete, to describe a value placed on a specific class j for that criterion. The lowest and the highest functions of this function characterize the worst and best class in terms of suitability for that criterion, i.e. F i, 1 = min (F i ), where and F i, n = max (F i ), where ( n = 3, 4 or 5).The criteria relate to either the containment security, the volume of storage capacity achievable, or consider the economic or technological feasibility. The results shows that Chad basin has R k score value of 0.53 against the F i, n = max (F i ) value equal to 1 as highest value of the function characterize the best in terms of suitability for the criterion in which this ranking is based upon. The criterion individual scores P k i for geothermal, geology; fault intensity, and hydrocarbon potentials can in future be subjected to amendment as when further discoveries are made to score the criterion more favorable or better than present ranking score R k value of 0.53.Furthermore, detail site characterisation of the geological storage for it overall suitability for CO 2 sequestration potentials in the basin are needed accentuate its general suitability. 6.1 Recommendations A detailed regional and local site characterisation of geological storages are needed to fully screen and rank the basins for its overall suitability for CO 2 storage potentials in the region, since countries like Cameroon, Central African Republic, Niger, Chad, and Nigeria shares the basin on regional level. The work flow stages for detail of geological storage characterisation on regional base would continue with basin-scale assessment, since this paper have addressed the basin on country/ state scale screening. Geosciences characterisation would be carried out to assess the structural and stratigraphic models; injectivity, containment and capacity of the basin, while the engineering characterisation would look at parameters like; optimum injectivity rate, well design e.t.c; long- term migration, dynamic flow behavior; geochemical reactive transport, geomechanics flow simulations e.t.c Finally, the socio economics characterisation would look into the capital and operating cost of compression, transport and injection cost per tonne of CO 2, quantitative risk assessment, monitoring and verification. 6.2 References 1. Avbovbo A.A, Ayoola EO, Osahon GA (1986) Depositional and structural styles in the Chad Basin of northeastern Nigeria. AAPG Bull 70: Barber W, Jones DC (1965) The Geology and Hydrogeology of the Maiduguri, Borno Province. REC Geological Survey of Nigeria. Pp Burke K (1976) The Chad Basin: an active intra-continental basin. Tectonophysic 36: Bryant E (1997) Climate process and change. Cambridge University Press, Cambridge 27

13 5. Blunt M, Fayers FJ, Orr FM (1993) Carbon dioxide in enhanced oil recovery. Energy Convers Manage 34: Bachu S, Gunter WD, Perkins EH (1994) Aquifer disposal of CO2 hydrodynamic and Mineral trapping. Energy Convers Manage 35: Bachu S (2003) Screening and ranking of sedimentary basins for sequestration of CO2 in Geological media in response to Climate Change. Int l J Environmental Geology 44: Carter J D, Barber W, Tait EA, Jones GP (1963) The geology of parts of Adamawa, Bauchi and Borno Provinces in Northeastern Nigeria. Geol Surv Niger Bull 30:108 pp. 9. Dusseault MB, Bachu S, Rothenburg L (2002) Sequestration of CO2 in salt caverns. Paper Canadian International Petroleum Conference. CIM Petroleum Society, Calgary, 11)13 June 10. Furon R (1960) Geologie de l Afrique. Payot, Paris, 400 pp 11. Gunter WD, Perkins EH, McCann TJ (1993) Aquifer disposal of CO2-rich gases: reaction design for added capacity. Energy Convers Manage 34: Gunter WD, Gentzis T, Rottenfusser BA, Richardson RJH (1997) Deep coalbed methane in Alberta, Canada: a fuel resource with the potential of zero greenhouse emissions. Energy Convers Manage 38S:S217 S Gale J, Freund P (2001) Coal-bed methane enhancement with CO2 sequestration worldwide potential. Environ Geosci 8: Jepma 14. Hendriks CA, Blok K (1993) underground storage of carbon dioxide. Energy Convers Manage 34: Hitchon B, Gunter WD, Gentzis T, Bailey RT (1999) Sedimentary basins and greenhouse gases: a serendipitous association. Energy Convers Manage 40: Holtz MH, Nance PK, Finley RJ (2001) Reduction of greenhouse gas emissions through CO2 EOR in Texas. Environ Geosci 8: Idso SB (2001) Carbon-dioxide-induced global warming: a skeptic s view of potential climate change. In: Gerhard L, Harrison WE, Hanson BM (eds) Geological perspectives of global climate change. AAPG Studies in Geology 47, American Association of Petroleum Geologists, Tulsa, pp Koide H, Yamazaki K (2001) Subsurface CO2 disposal with enhanced gas recovery and biogeochemical carbon recycling. Environ Geosci 8: IPCC (2005): Underground geological storage, Chapter 5 of the Intergovernmental Panel on Climate Change Special Report on Carbon Capture and Storage, Geneva, 28

14 Switzerland. Nigeria and Climate Changes: Road to Cop15, Federal Ministry of Environment Pp 14, Accessed 20/08/2011, 5:18pm 20. Kurowska E, S. Krzysztof (2010): Geothermal Exploration in Nigeria; Proceedings World Geothermal Congress 2010 Bali, Indonesia, April Maduabuchi C, Faye S, Maloszewski P (2006) Isotope evidence of paleorecharge and paleoclimate in the deep confined aquifers of the Chad Basin, NE Nigeria. Sci Total Environ 370: Moumouni A, Obaje NG, Chaanda MS, Goki NG (2007) Geochemical evaluation of the hydrocarbon prospects in the Nigerian sector of the Chad Basin, in Petroleum Science Research Progress, Nova Science Publishers NY, pp Moumouni A (2008) Organic geochemical, organic petrological and biostratigraphical evaluation of the hydrocarbon potential of the Nigerian sector of the Chad Basin. Unpublished Ph.D. thesis, Nasarawa State University Keffi, Nigeria, 180pp 24. Obaje NG (1994) Coal petrography, microfossils and paleoenvironments of Cretaceous coal measures in the Middle Benue Trough of Nigeria. Tuebinger Mikropalaeontologische Mitteilungen 11, Okosun EA (1995) A review of the geology of the Bornu Basin. J Mining Geol 31(2), Olugbemiro RO, Ligouis B, Abaa SI (1997) The Cretaceous series in the Chad Basin, NE Nigeria: source rock potential and thermal maturiy. J Petrol Geol 20: Obaje NG, Wehner H, Scheeder G, Abubakar MB, Jauro A (2004) Hydrocarbon prospectivity of Nigeria s inland basins: from the viewpoint of organic geochemistry and organic petrology. AAPG Bull 87: Obaje NG (2009) Geology and Mineral resources of Nigeria: Lecture note in Geosciences accessed 17/5/2010, 6:48PM. 29. Petters SW(1982) CentralWest African Cretaceous-Tertiary benthic foraminifera and stratigraphy. Palaeontographica Abt A 179: Wright JB (1985) Geology and mineral resources of West Africa. George Allen & Unwin, London, 187 pp 31. Younger P.L and others (2010) Water Management Issues in the Underground Gasification of Coal and the Subsequent Use of the Voids for Long-Term Carbon Dioxide Storage. Wolkersdorfer & Freund (Editors) Pp