Geosciences
p-ISSN: 2163-1697 e-ISSN: 2163-1719
2019; 9(1): 18-26
doi:10.5923/j.geo.20190901.03
Okoli Emeka Austin1, Acra Jones Edward2, Ehirim Chukwuemeka Ngozi3, Adewale Dosunmu, Okechukwu Ebuka Agbasi3
1Federal University of Technology, Owerri, Nigeria
2University of Port Harcourt, Nigeria
3Micheal Okpara University of Agriculture, Umudike, Nigeria
Correspondence to: Okechukwu Ebuka Agbasi, Micheal Okpara University of Agriculture, Umudike, Nigeria.
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Copyright © 2019 The Author(s). Published by Scientific & Academic Publishing.
This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/
Three (3) wells from “Sigma Field” and biostratigraphic data of Sigma-25, coastal Swamp Depobelt, Niger Delta were integrated to carry out a sequence stratigraphic analysis of depositional systems in the field and further develop conceptual models in areas not penetrated by wells. The analysis revealed one (1) 3rd order Maximum Flooding Surfaces (MFS) dated 11.5 Ma MFS delineated. The 11.5Ma MFS was identified from bio-stratigraphic analysis of micro-floral and palynological zonation provided for Sigma-25 which dated sediments that penetrated the F9500 zone and P784-750 zone of the Serravallian in the Middle Miocene age on the Niger Delta chronostratigraphic chart. Other candidate Maximum Flooding surfaces dated 10.4 Ma MFS and 9.5 Ma MFS respectively were identified on Sigma-25 using lowest resistivity value and widest separation between density and neutron logs. Four 3rd order depositional sequences bounded by four erosional surfaces interpreted as Sequence Boundaries and dated 12.1, 10.6, 10.35, and 8.5Ma were also delineated. A Transgressive Surface of Erosion (TSE) that mark the onset of marine flooding and turnarounds from progradational facies to retrogradational facies during sequence build-up was delineated in the fourth depositional sequence. The delineated sequences comprised Lowstand Systems Tracts, Transgressive Systems Tracts and High stand Systems Tracts and predominantly reflected a regressive phase. The Low stand Systems Tract (LST) is representative of a delta front process specifically the Distributary Channel fill sediments. Transgressive Systems Tract (TST) consists of retrogradational marine shales deposited during high relative sea levels and when accommodation space was higher than rate of sediment influx. High stand Systems Tracts (HST) consisted of Distributary Mouth bars sands in the first and second depositional sequence displaying generally an aggradational stacking pattern and Fluvial sands in third and fourth depositional sequence displaying generally an aggradational stacking pattern. The depositional model in the field was inferred from Conceptual models generated with the available wells in both strike and dip direction. Sigma field showed a transition from a deltaic environment to a fluvial environment as sea level generally shows a relative fall going upwards across the well section. The sands of LST and HST show good reservoir qualities while the shales of the TSTs could form potential reservoir seals and show source rock potential. The above recognized sequences were deposited within the Non-marine – Inner Neritic paleo-water depths.
Keywords: Unconformities, Progradation, Retrogradational, Aggradational, Paleoenvironments and Reservoir
Cite this paper: Okoli Emeka Austin, Acra Jones Edward, Ehirim Chukwuemeka Ngozi, Adewale Dosunmu, Okechukwu Ebuka Agbasi, Paleoenvironmental Reconstruction of an Onshore Field, Coastal Swamp Depobelt, Niger Delta, Geosciences, Vol. 9 No. 1, 2019, pp. 18-26. doi: 10.5923/j.geo.20190901.03.
Figure 1. Niger Delta Sequence Stratigraphic Column |
Figure 2. Sequence stratigraphic analysis Workflow |
Figure 3. Geophysical well log interpretation |
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Figure 5. Conceptual depositional environment model of Sigma-26 and 30 in strike direction as at 11.5 Ma MFS |
Figure 6. Conceptual depositional environment model as at 11.5 Ma MFS |
Figure 7. Conceptual depositional environment model of Sigma-25 and 30 in dip direction as at 10.4 Ma MFS |
Figure 8. Conceptual depositional environment model in dip direction as at 10.4 Ma MFS |
Figure 9. Conceptual depositional environment model as at 10.4 Ma MFS |
Figure 10. Conceptual depositional environment model as at 10.4 Ma MFS |
Figure 11. Conceptual depositional environment model as at 9.5 Ma MFS |
Figure 12. Conceptual depositional environment model as at 9.5 Ma MFS |