Structural mapping and prospects identification in Otio oil field, Niger Delta

This research presents a detailed structural mapping and prospects identification study of the Otio Field located in the Niger Delta. The study integrates 3D seismic data and well logs to delineate subsurface structures and assess the hydrocarbon potential of the field. Five key horizons were evaluated using petrophysical analysis, revealing porosity values ranging from 18 to 27 %, water saturation levels between 20 and 31 %, and Net-To-Gross ratios of 59 to 96 %. Time-depth structure maps were generated for each horizon, allowing for the identification of two prospects, namely the North-Eastern and South-Eastern prospects. The North-Eastern prospect was ranked higher due to its larger estimated hydrocarbon volume, with Sand E2 identified as the most promising reservoir based on volumetric analysis. This study underscores the importance of integrating seismic and petrophysical data for effective exploration and field development, providing a basis for future drilling decisions in the Otio Field. The research method started with the subsurface evaluation of the “Otio Field” integrating well log data from the field and seismic data spanning the field. The databases used for this project are three Dimensional (3D) seismic cube, base map, six well data in LAS format and check shot data for only one well. The results show the identified hydrocarbon bearing zones are Sands D, E1, E2, H and J as interpreted from gamma-ray and resistivity logs. The sand correlation across the field showed uniform sand development from well to well. The checkshot is interpreted as good because of the absence of outliers or spurious values. The plot is a gentle slope that eventually steepens because of com-paction of the underlying units that causes Two-Way Time to decrease. The results from the structural Interpretation, sixteen faults (F1–F16) were interpreted across the field as seen on seismic section. Faults in the field trend in the East-West direction with majority of them dipping north except for faults F4 F6, F7 and F9 dipping south. In the conclusion, the 3D structural analysis of Otio Field in the Niger Delta enhanced understanding of its structural styles and hydrocarbon traps. Eight reservoirs were identified, with five hydro-carbon-bearing sands (D, E1, E2, H, J) mapped, consisting of sands sealed by shales.

1. Obiekezie T.N., Bassey E.E. 3D structural analysis of Otu Field, Niger Delta, Nigeria. Physical Science International Journal. 2015;7(2):114-126. https://doi.org/10.9734/PSIJ/2015/16512.

2. Nyantakyi E.K., Hu W., Borkloe J.K. Integrated 3D seismic and petrophysical analysis for hydrocarbon exploration in the Niger Delta. Petroleum Science and Technology. 2013;31(15):1590-1600.

3. Ophori D.U., Gorring M., Olsen K., Orhua E., Hope J. A preliminary analysis of groundwater chemistry in shallow boreholes, Ughelli, Nigeria. Journal of Environmental Hydrology. 2007;15. Available from: http://www.hydroweb.com/protect/pubs/jeh/jeh2007/ophori.pdf [Accessed 18th February 2025].

4. Doust H., Omatsola E. Niger Delta. In: Edwards J.D., Santogrossi P.A. (eds). Divergent/passive margin basins. American Association of Petroleum Geologists Memoir; 1990, vol. 48, p. 239-248. https://doi.org/10.1306/M48508C4.

5. Owoyemi A.O., Willis B.J. Depositional patterns across syndepositional normal faults, Niger Delta, Nigeria. Journal of Sedimentary Research. 2006;76:346-363. https://doi.org/10.2110/jsr.2006.025.

6. Nton M.E., Adesina A.A. Aspects of structures and depositional environment of sand bodies within Tomboy Field, offshore western Niger Delta, Nigeria. RMZ-materials and geoenvironment. 2009;56(3):284-303.

7. Ibe A.C., Anyanwu C.P. Geoenvironmental assessment of the Niger Delta region. Journal of the Geological Society of Nigeria. 2014;50(2):123-135.

8. Doust H., Omatsola E. Niger Delta. In: Edwards J.D., Santogrossi P.A. (eds). Divergent/passive margin basins. American Association of Petroleum Geologists Memoir; 1989, vol. 48, p. 201-238.

9. Short K.C., Stauble A.J. Outline of geology of Niger Delta. American Association of Petroleum Geologists Bulletin. 1967;51(5):761-779. https://doi.org/10.1306/5D25C0CF-16C1-11D7-8645000102C1865D.

10. Ejedawe J.E. Patterns of incidence of oil and gas in the Niger Delta Basin. Journal of Petroleum Geology. 1981;4(2):167-183.

11. Bilotti F., Shaw J.H. Deep-water Niger Delta fold and thrust belt modeled as a critical-taper wedge: the influence of elevated basal fluid pressure on structural styles. American Association of Petroleum Geologists Bulletin. 2005;89(11):1475-1491. https://doi.org/10.1306/06130505002.

12. Lambert-Aikhionbare D.O. Relationship between diagenesis and pore fluid chemistry in Niger Delta oil-bearing sands. Journal of Petroleum Geology. 1982;4(3):287-298. https://doi.org/10.1111/j.1747-5457.1982.tb00540.x.

13. Evamy B.D., Haremboure J., Kamerling P., Knaap W.A., Molloy F.A., Rowlands P.H. Hydrocarbon habitat of Tertiary Niger Delta. American Association of Petroleum Geologists Bulletin. 1978;62(1):1-39. https://doi.org/10.1306/ C1EA47ED-16C9-11D7-8645000102C1865D.

14. Weber K.J. Sedimentological aspects of oil fields in the Niger Delta. Geologie en Mijnbouw, 1971;50(1):559-576.

15. Corredor F., Shaw J.H., Bilotti F. Structural styles in the deep-water fold and thrust belts of the Niger Delta. American Association of Petroleum Geologists Bulletin. 2005;89(6):753-780. https://doi.org/10.1306/02170504074.

16. Armentrout J.M., Kanschat K.A., Meisling K.E., Steffens G.S. Neogene turbidite systems of the Niger Delta: Seismic examples and analogues for exploration and reservoir characterization. American Association of Petroleum Geologists Bulletin. 2000;84(9):1336-1357.

17. Hooper R.J., Fitzsimmons R.J., Grant N., Vendeville B.C. The role of deformation in controlling depositional patterns in the south-central Niger Delta, West Africa. Journal of Structural Geology. 2002;24(4):847-859. https://doi.org/10.1016/S0191-8141(01)00122-5.

18. Knox G.J., Omatsola E.M. Development of the Cenozoic Niger Delta in terms of the “Escalator Regression” model and impact on hydrocarbon distribution. In: Van Der Linden W.J.M., Cloetingh S.A.P.L., Kaasschieter J.P.K., Van De Graaff W.J.E., Vandenberghe J., Van Der Gun J.A.M. (eds). Coastal Lowlands. Dordrecht: Springer; 1989, p. 181-202. https://doi.org/10.1007/978-94-017-1064-0_12.