Geochemical Journal, Vol. 40, pp. 227 to 243, 2006 Geochemical evaluation of the hydrocarbon prospects of sedimentary basins in Northern Nigeria N. G. OBAJE,1* D. O. ATTAH,2 S. A. OPELOYE3 and A. MOUMOUNI1 1Department of Geology and Mining, Nasarawa State University, Keffi, Nigeria 2Department of Metallurgical Engineering, Federal Polytechnic, Idah, Nigeria 3Department of Geology, Federal University of Technology, Yola, Nigeria (Received April 25, 2005; Accepted November 9, 2005) 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. Organic geochemical and organic petrologic studies indicate the existence of potential source rocks in the Benue Trough and the Chad Basin, with coal beds constituting major potential source rocks in the whole of the Benue Trough. The generation and production of liquid and gaseous hydrocar- bons from coal beds presently is world-wide indisputable. Although TOC values and liptinite contents are relatively high in the Mid-Niger (Bida) Basin, Tmax values and biomarker data show that hydrocarbons are probably just being generated in the basin and may not yet have been expelled nor migrated in large quantities. Keywords: biomarkers, petroleum, coal, maceral, Benue Trough ing of the South Atlantic (Fig. 2). Commercial hydrocar- INTRODUCTION bon accumulations have recently been discovered in Chad Nigeria’s current national petroleum reserves asset and Sudan within this rift trend. In SW Chad, exploita- (proven) is put at 35 billion barrels of oil. Gas reserve on tion of the Doba discovery (with an estimated reserve of the other hand has been estimated to be about 170 trillion about 1 billion barrels of oil) has caused the construction standard cubic feet. Current production of oil and gas in of a 1070 km-long pipeline through Cameroon to the At- Nigeria comes entirely from the Niger Delta onshore and lantic coast. In the Sudan, some “giant fields” (Unity 1 & offshore. Some exploration campaigns have been under- 2, Kaikang, Heglig, etc.) have been discovered in the taken in sedimentary basins of Northern Nigeria with the Muglad basin (Mohamed et al., 1999). The major source aim to expanding the national exploration and produc- rocks and reservoirs are in the Aptian-Albian-Cenomanian tion base and to thereby add to the proven reserves asset. continental deposits of the Abu Gabra and Bentiu forma- Sedimentary basins of Northern Nigeria comprise the tions, respectively, which are similar and correlatable to Middle and Upper Benue Trough, the southeastern sector the well-developed Bima Sandstone in the Nigerian up- of the Chad Basin, the Mid-Niger (Bida) Basin, and the per Benue trough. In Niger Republic, oil and gas shows Sokoto Basin (Fig. 1). However, these inland basins have have also been encountered in Mesozoic–Cenozoic se- continued to frustrate the efforts of many explorers, prin- quences in the East Niger graben, which is structurally cipally because of the poor knowledge of their geology related to the Benue-Chad-Sudan-Libyan rift complexes and the far distance from existing infrastructure (discov- (Zanguina et al., 1998). ery must be large enough to warrant production invest- Within the sedimentary basins of Northern Nigeria, ments), and for these reasons, many international com- the Nigerian National Petroleum Corporation (NNPC) panies have turned their focus away from frontier onshore through its frontier exploration services arm (NAPIMS) to frontier deep-water and ultra deep-water offshore. has drilled some wells in the Nigerian sector of the Chad The sedimentary basins of Northern Nigeria are one Basin and only gas shows were encountered. The first part of a series of Cretaceous and later rift basins in Cen- well in the Benue Trough region, Kolmani-River-1, drilled tral and West Africa whose origin is related to the open- by Shell Nigeria Exploration and Production Company (SNEPCO) to a depth of about 3000 m in 1999 encoun- tered some 33 billion standard cubic feet of gas and little *Corresponding author (e-mail: [email protected]) oil (that has been the only well drilled by that company Copyright © 2006 by The Geochemical Society of Japan. in that area to date). Two other wells, Kuzari-1 and 227 Fig. 1. Sketch geological map of Nigeria showing the inland basins and sample localities (inset: upper Benue trough magnified). Results from the Anambra Basin not presented in this study. L I B Y A E G Y P T A L G E R I A R E SIRTE D EAST NIGER S E A TERMIT/ BLUE NILE KANEM N I G E R S U D A N C H A D BORNU BAGARRA MELUT BONGOR GONGOLA T N I G E R I A DOBA F I R YOLA E T H I O P I A BENUE N N A O O C. A. R. IC R R MUGLAD NGAOUNDERE F ANZA NIGER E DELTA M TA A S C A E Z A I R E (D.R.C.) K E N Y A 200 Km Major oil discovery Major oil and gas shows Fig. 2. Regional tectonic map of western and central African rifted basins showing the relationship of the Muglad, Doba and East Niger Basins to the Benue Trough/Gongola Basin. Locations of regional shear zones (marked with half-arrow) and major zones extension (complete arrow) are shown. (Adapted from Schull, 1988.) 228 N. G. Obaje et al. Fig. 3. Stratigraphic successions in the Benue Trough, the Nigerian sector of the Chad Basin, the Mid-Niger Basin and the relationship to the Niger Delta. Nasara-1, drilled by Elf Petroleum Nigeria Limited pre-dating the mid-Santonian have been compressionally (TotalFinaElf) in 1999 to a depth of 1666 m and Chevron deformed, faulted, and uplifted in several places. Com- Nigeria Limited (ChevronTexaco) in 2000 to a depth of pressional folding during the mid-Santonian tectonic epi- about 1600 m, respectively, were reportedly dry. sode affected the whole of the Benue Trough and was With this development, it has become necessary to quite intense, producing over 100 anticlines and synclines evaluate the prospectivity of this frontier region, espe- (Benkhelil, 1989). Following mid-Santonian tectonism cially the availability or otherwise of favorable petroleum and magmatism, depositional axis in the Benue Trough systems. At the core of any petroleum system is a good was displaced westward resulting in subsidence of the quality source rock (TOC > 0.5%, HI > 150 mgHC/gTOC, Anambra Basin. The Anambra Basin, therefore, is a part liptinite content > 15%, Tmax ≥ 430°C, Ro 0.5–1.2%, of the lower Benue Trough containing post-deformational biomarker validation). However, other petroleum system sediments of Campano-Maastrichtian to Eocene ages. It elements must include, apart from established source is logical to include the Anambra Basin in the Benue rocks, also reservoir and seal lithologies, establishable Trough, being a related structure that developed after the trapping mechanisms and favorable regional migration compressional stage (Akande and Erdtmann, 1998). The pathways. In this work, we have aimed at evaluating the Benue Trough is subdivided into a Lower, Middle and an source rock qualities of Cretaceous–Tertiary sequences Upper portion (Figs. 1 and 3). Reviews on the geology in the sedimentary basins of Northern Nigeria (excluding and stratigraphic successions in the Benue Trough with the Sokoto Basin at this stage) as an input to the under- details on each formation, bed thicknesses, lateral exten- standing of petroleum system elements in the basins. sions and stratigraphic locations have been given by Carter et al. (1963), Offodile (1976), Petters (1982), Pet- ters and Ekweozor (1982), Obaje (1994) amongst others. REGIONAL GEOLOGIC SETTING Details on the evolution and stratigraphic framework of The Benue Trough of Nigeria is a rift basin in central the Chad Basin have been given in Avbovbo et al. (1986) West Africa that extends NNE-SSW for about 800 km in and Olugbemiro et al. (1997). The Mid-Niger Basin some- length and 150 km in width. The trough contains up to time known as the Bida or Nupe Basin is a NW-SE 6000 m of Cretaceous–Tertiary sediments of which those trending embayment perpendicular to the main axis of Hydrocarbon prospects of sedimentary basins in Northern Nigeria 229 Table 1. Rock Eval pyrolysis results of samples from the Middle Benue Trough and Mid-Niger (Bida) Basin Sample ID Locality Formation TOC S1 S2 S3 Tmax HI* OI** (wt%) (mg/g) (mg/g) (mg/g) (°C) Middle Benue Trough OBIC 6 Jangwa Awgu 17.40 0.41 21.76 5.37 444 125 31 OBIC 5 Jangwa Awgu 75.60 2.60 192.77 2.69 457 255 4 OBIC 4 Jangwa Awgu 76.30 3.04 203.84 2.52 452 267 3 OBIC 3b Jangwa Awgu 26.40 0.84 43.51 1.48 457 165 6 OBIC 3 Jangwa Awgu 79.10 3.16 207.3 2.50 459 262 3 OBIC 2b Jangwa Awgu 70.60 2.27 171.54 2.31 453 243 3 MBJJ 9 Jangwa Awgu 27.00 3.93 41.20 1.65 452 153 6 MBJJ 8 Jangwa Awgu 44.20 0.26 18.42 19.13 441 42 43 MBJJ 7 Jangwa Awgu 43.10 0.19 10.81 18.12 445 25 42 MBJJ 6 Jangwa Awgu 61.10 1.93 83.05 13.60 449 136 22 MBJJ 5 Jangwa Awgu 18.50 0.38 22.18 5.32 444 120 29 MBJJ 4 Jangwa Awgu 23.80 0.72 39.58 1.23 455 166 5 MBJJ 3 Jangwa Awgu 2.69 0.02 1.99 0.30 463 74 11 MBJJ 2 Jangwa Awgu 66.70 4.38 164.29 1.33 452 246 2 MBJJ 1 Jangwa Awgu 17.40 0.08 2.49 12.49 457 14 72 Mid-Niger/Bida Basin AHOK 5 Ahoko/Lokoja Patti 2.74 0.07 2.98 2.30 429 109 84 AHOK 3 Ahoko/Lokoja Patti 2.79 0.06 2.39 2.30 425 86 82 AHOK 2 Ahoko/Lokoja Lokoja 2.39 0.06 1.78 1.92 423 74 80 AHOK 1 Ahoko/Lokoja Lokoja 2.73 0.05 1.71 2.08 421 63 76 *mgHC/gTOC; **mgCO2/gTOC.