The Bornu Basin, which represents a part of the Chad Basin in Nigeria, makes one-tenth of the total area of the Chad Basin that extends to the Republic of Niger, Chad and Cameroun. This basin is a sediment-filled broad depression straddling northeastern Nigeria and adjoining parts of the Republic of Chad. The cumulative thickness of the sedimentary rocks exceeds 3,600 metres. The Nigerian share of the Chad Basin is supposed to be a potential hydrocarbon-producing basin. This is because commercial petroleum accumulations totalling over 120 billion barrels have been discovered in some parts of the basin outside Nigeria (largely in the Republic of Chad) in structurally related contiguous basins. The Gongila Formation (in the Chad Basin) is a transitional sequence between the underlying continental Bima sandstone and the overlying marine Fika shale.
Determining whether the shale beds present in the Gongila Formation are matured enough to generate hydrocarbons, nine wells were used and the petrophysical parameters such as total organic carbon (TOC) and total organic matter (TOM) were calculated for each of the wells. The heat flow history of the basin was calculated by establishing the relationship between the modeled thermal maturity curve and the equivalent observed maturity parameter (vitrinite reflectance). Thereafter this calculated heat flow is used to predict thermal maturity of source rocks and the timing of hydrocarbon generation.
The result obtained reveals that TOC and TOM of shale sequences in each well range from 3.58 to 27.48 wt% and from 1.15 to 8.79 wt%, respectively. Thus, TOC of the Gongila Formation exceeds the kerogen threshold of 0.5 wt% for the generation of hydrocarbons while TOM exceeds the kerogen threshold of 1 wt%. The heat flow was computed from the heat generation and was estimated to range between 33 and 75 mW/m2. The modeled vitrinite reflectance ranges between 0.56 and 0.76%Ro.
It is concluded that the Gongila shale is a potential petroleum source rock. The temperature history is the factor controlling the maturation of organic compounds into fossil fuels. The Gongila Formation’s thermal maturity, assessed on the basis of vitrinite reflectance, indicates that the shale sequences in this formation are within the early oil window and thermally matured for hydrocarbon generation.
1. Genik, G. J. Regional framework, structural and petroleum aspects of rift basins in Niger, Chad and Central African Republic (C.A.R). Tectonophysics, 1992, 213(1), 169–185.
http://dx.doi.org/10.1016/0040-1951(92)90257-7
2. Avbovbo, A. A., Ayoola, E. O., Osahon, G. A. Depositional and structural styles in Chad Basin of Northeastern Nigeria. AAPG Bull., 1986, 70(12), 1787–1798.
3. Carter, J. D., Barber, W., Tait, E. A, Jones, G. P. The geology of parts of Adamawa, Bauchi and Bornu provinces in Northeastern Nigeria. Bull. Geol. Surv. Nigeria, 1963, 30, 1–108.
4. Lijmbach, G. W. M. On the origin of petroleum. In Proc. 9th World Petroleum Congress, Tokyo. Applied Sciences Publisher, London, 1975, 2, 357–369.
5. Tissot, B. P, Welte, D. H. Petroleum Formation and Occurrence: A New Approach to Oil and Gas Exploration. Springer Verlag, Berlin, 1978. 538 p.
6. Schmoker, J. W. Determination of organic-matter content of Appalachian Devonian shales from gamma-ray logs. AAPG Bull., 1981, 65(7), 1285–1298.
7. Meyer, B. L., Nederlof, M. H. Identification of source rocks on wireline logs by density/resistivity and sonic transit time/resistivity crossplots. AAPG Bull., 1984, 68(2), 121–129.
8. Peters, K. E. Guidelines for evaluating petroleum source rock using programmed pyrolysis. AAPG Bull., 1986, 70(3), 318–329.
9. Rybach, L. Amount and significance of radioactive heat sources in sediments. In Collection Colloques et Seminares 44, Thermal Modeling of Sedimentary Basins (Burrus, J., ed). Paris: Paris Editions Technip., 1986, 311–322.
10. Dembicki, H. Jr., Horsfield, B., Ho, T. T. Y. Source rock evaluation by pyrolysis-gas chromatography. AAPG Bull., 1983, 67(7), 1094–1103.
11. Schneider, F., Faure, J. L., Roure, F. Methodology for basin modeling in complex area: examples from Eastern Venezuelan and Canadian Foothills. AAPG Hedberg Conference “Deformation History, Fluid Flow Reconstruction and Reservoir Appraisal in Foreland Fold and Thrust Belts”, 2002.
12. Schneider, F., Devoitine, H., Faille, I., Flaraud, E., Willien, F. Ceres2D: A numerical prototype for HC potential evaluation in complex area. Oil Gas Sci. Technol., 2002, 57(6), 607–619.
http://dx.doi.org/10.2516/ogst:2002041
13. Senftle, J. T., Landis, C. R. Vitrinite reflectance as a tool to assess thermal maturity. In Source and Migration Processes and Evaluation Techniques: AAPG Treatise of Petroleum Geology, Handbook of Petroleum Geology (Merrill, R. K., ed), 1991, 119–125.
14. Cratchley, C. R., Jones, G. P. An interpretation of the geology and gravity anomalies of the Benue valley, Nigeria. Overseas Geological Survey. Geophysical Paper I, 1965, 26.
15. Ajakaiye, D. E., Burke, K. A Bouguer gravity map of Nigeria. Tectonophysics, 1973, 16(1-2), 103–115.
http://dx.doi.org/10.1016/0040-1951(73)90134-0
16. Benkhelil, J. L. Structure et evolution géodynamique du bassin intracontinental de la Benoue (Nigeria). B. Cent. Rech. Expl. 1988, 12(1), 29–128.
17. Fletcher, W. K. Analytical Methods in Geochemical Prospecting. Elsevier Sci. Pub., Amsterdam, 1981. P. 255.
18. Schmoker, J. W., Hester, T. C. Oil generation inferred from formation resistivity Bakken Formation, Williston Basin, North Dakota. In Trans. of the Thirtieth SPWLA Annule Logging Symp., Paper H, 1989.
19. Beardsmore, G. R. The Thermal History of the Browse Basin and its Implications for Petroleum Exploration. Ph.D. dissertation, Monash University, Victoria, Australia, 1996.
20. Bucker, C., Rybach, I. A simple method to determine heat production from gamma logs. Mar. Petrol. Geol., 1996, 13(4), 373–375.
http://dx.doi.org/10.1016/0264-8172(95)00089-5
21. Hunt, J. M. Petroleum Geochemistry and Geology. Freeman and Company, San Francisco, 1979. P. 617.
22. Ritter, U., Zielinski, G. W., Weiss, H. M., Zielinski, R. L. B., Sættem, J. Heat flow in the Vøring Basin, Mid-Norwegian Shelf. Petrol. Geosci., 2004, 10(4), 353–365.
http://dx.doi.org/10.1144/1354-079303-616
