The research study focused on the analysis of subsidence and thermal history effects on source rock maturity in the Semliki Basin. The study utilised the back stripping approach and was accomplished using PetroMod Software. The research utilized previous data sets obtained from geochemical reports and final well data reports to generate a basin model of eight (08) Sedimentary Formations ranging in age from Lower Miocene to Pleistocene sediments i.e., Surface, Nyabusozi-Nyakabingo, Nyaburogo, Oluka, Kakara, Kasande, Kisegi and Basement formations. The general trend of subsidence observed is a rapid deepening (13.0 to 11.5 Ma and 3.5 to 2.0 Ma) during the main and later rift phases respectively, followed by an exponential decline in the rate of tectonic subsidence. The maximum heat flow (77.59 mWm？2) at 3.5 Ma corresponds to the Late Pliocene to Pleistocene thus deep burial conditions and represents maximum paleo-temperatures. The medium/dark shales of the Kasande-Kakara formations (2070 - 2100 m and 2480 - 2488 m) are the most prospective source rocks and comprise organic matter (TOC c.2.0%) and an oil-prone Type I/II source rock quality. The source rock maturity plots indicate that the source rock entered the early oil zone at 2.0 Ma whereby the top of the oil generation window is observed with Ro 0.5%, corresponding to the Kasande-Kakara formations at a depth of 2400 - 2500 m. This corresponds to the second subsidence event; however, there was no commencement of oil generation. Though limited by the scope of the data set, this study allowed for a quantification of tectonic subsidence and thermal maturity effects on the identified source rock horizons of the Semliki Basin sediments.
References
[1]
Ingersoll, C. and Azor, A. (2011) Tectonics of Sedimentary Basins. Blackwell Publishing Ltd., 3-43.
[2]
Bostick, N.H. and Foster, J.N. (1975) Comparison of Vitrinite Reflectance in Coal Seams and in Kerogen of Sandstones, Shales, and Limestones in the Same Part of a Sedimentary Section. Centre National de la Recharche Scientifique, 13-25.
[3]
Scheidt, G. and Littke, R. (1989) Comparative Organic Petrology of Interlayered Sandstones, Siltstones, Mudstones and Coals in the Upper Carboniferous Ruhr Basin, Northwest Germany, and Their Thermal History and Methane Generation. GeologischeRundschau, 78, 375-390. https://doi.org/10.1007/bf01988371
[4]
Littke, R., Urai, J.L., Uffmann, A.K. and Risvanis, F. (2012) Reflectance of Dispersed Vitrinite in Palaeozoic Rocks with and without Cleavage: Implications for Burial and Thermal History Modeling in the Devonian of Rursee Area, Northern Rhenish Massif, Germany. InternationalJournalofCoalGeology, 89, 41-50. https://doi.org/10.1016/j.coal.2011.07.006
[5]
Daly, M.C., Chorowicz, J. and Fairhead, J.D. (1989) Rift Basin Evolution in Africa: The Influence of Reactivated Steep Basement Shear Zones. GeologicalSociety, London, SpecialPublications, 44, 309-334. https://doi.org/10.1144/gsl.sp.1989.044.01.17
[6]
Abeinomugisha, D. and Kasande, R. (2013) Tectonic Control on Hydrocarbon Accumulation in the Intracontinental Albertine Graben of the East African Rift System. In: Gao, D.L., Ed., TectonicsandSedimentation, American Association of Petroleum Geologists, 209-228. https://doi.org/10.1306/13351554m1003539
[7]
Mutebi, S., Sen, S., Sserubiri, T., Rudra, A., Ganguli, S.S. and Radwan, A.E. (2021) Geological Characterization of the Miocene-Pliocene Succession in the Semliki Basin, Uganda: Implications for Hydrocarbon Exploration and Drilling in the East African Rift System. NaturalResourcesResearch, 30, 4329-4354. https://doi.org/10.1007/s11053-021-09951-0
[8]
Lukaye, J., Worsley, D., Kiconco, L., Nabbanja, P., Abeinomugisha, D., Amusugut, C., et al. (2016) Developing a Coherent Stratigraphic Scheme of the Albertine Graben-East, Africa. JournalofEarthScienceandEngineering, 6, 264-294. https://doi.org/10.17265/2159-581x/2016.05.004
[9]
Lukaye, J. and Okello, M. (2015) Geochemical Characterization and Correlation of Crude Oils and Potential Source Rocks from the Semliki, Southern Lake Albert and Kaisotonya Basins in the Albertine Graben, Uganda. International Conference and Exhibition, Melbourne, 13-16 September 2015, 557. https://doi.org/10.1190/ice2015-2210807
[10]
H. O. a. G. Limited (2003) Turaco-1 Final Well Report (Geological Section). Report of Heritage Oil & Gas Limited (HOGL).
[11]
H. O. a. G. Limited (2004) Turaco-2 Final Well Report (Geological Section). Report of Heritage Oil & Gas Limited (HOGL).
[12]
Lukaye, J.M. (2009) Biostratigraphy and Palynofacies of Four Exploration Wells from the Albertine Graben, Uganda. AAPG, Article No. 50169.
[13]
Kaye, M.N. (2004) Source Rock Geochemistry Report Turaco-1 Well, Uganda. Aberdeen. Ocean Grove Geoscience Limited.
[14]
Athy, L.F. (1930) Density, Porosity, and Compaction of Sedimentary Rocks. AAPGBulletin, 14, 1-24. https://doi.org/10.1306/3d93289e-16b1-11d7-8645000102c1865d
[15]
Steckler, M.S. and Watts, A.B. (1978) Subsidence of the Atlantic-Type Continental Margin off New York. EarthandPlanetaryScienceLetters, 41, 1-13. https://doi.org/10.1016/0012-821x(78)90036-5
[16]
Fowler, C.M.R. (2004) The Solid Earth: An Introduction to Global Geophysics. 2nd Edition, Cambridge University Press. https://doi.org/10.1017/cbo9780511819643
[17]
Immenhauser, A. (2009) Estimating Palaeo-Water Depth from the Physical Rock Record. Earth-ScienceReviews, 96, 107-139. https://doi.org/10.1016/j.earscirev.2009.06.003
[18]
Scholz, C.A. (1995) Deltas of the Lake Malawi Rift, East Africa: Seismic Expression and Exploration Implications. AAPGBulletin, 79, 1679-1697. https://doi.org/10.1306/7834de54-1721-11d7-8645000102c1865d
[19]
Allen, P.A. and Allen, J.R. (2005) Basin Analysis, Principles and Applications. Blackwell Publishing.
[20]
Sweeney, J.J. and Burnham, A.K. (1990) Evaluation of a Simple Model of Vitrinite Reflectance Based on Chemical Kinetics (1). AAPGBulletin, 74, 1559-1570. https://doi.org/10.1306/0c9b251f-1710-11d7-8645000102c1865d
[21]
Wygrala, B.P. (1989) Integrated Study of an Oil Field in the Southern Po Basin, Northern Italy. Dissertation Thesis, Berichte Kernforschungsanlage Jülich, University of Köln, 217.
[22]
Peters, K.E. (1986) Guidelines for Evaluating Petroleum Source Rock Using Programmed Pyrolysis. AAPGBulletin, 70, 318-329. https://doi.org/10.1306/94885688-1704-11d7-8645000102c1865d
[23]
Tscherny, R.G. (2006) Numerical Simulation of the Thermal Evolution and Basin Development of the Permo-Mesozoic Sudalpins (Dolomites) along the Trans Alp Traverse. Dissertation RWTH Aachen University.
