River patterns transition of subaqueous distributary channels in delta front and its significances for petroleum geology: an insight from Paleogene Yabus Formation in the Sag A of Melut Basin, South Sudan

Abstract

Subaqueous distributary channel sandbodies within delta fronts are crucial reservoirs in continental petroliferous basins. Understanding the spatiotemporal transition of river patterns in these channels is essential for accurate evaluation and prediction of oil and gas reservoirs, as well as for providing direct evidence of basin evolution. In the Yabus Formation of the Sag A of Melut Basin, a comprehensive analysis involving sequence division, sedimentary characteristics, seismic facies, high-resolution reservoir inversion, and sand body distribution revealed significant insights. During the Yabus Formation deposition, three intermediate base-level cycles were identified, each showing transition phenomena in the river patterns of subaqueous distributary channels within the delta front. Clear identification criteria for different river patterns were established. Braided subaqueous distributary channels exhibited dominant vertical accretion, high sand content, significant sandstone thickness, and continuous-strong amplitude seismic reflections. While the braided-meandering transition pattern showed a combination of vertical and lateral accretion, medium sand content, moderate sandstone thickness, and medium continuous-medium strong amplitude seismic reflections. Meandering subaqueous distributary channels were characterized by lateral accretion, low sand content, minimal sandstone thickness, weak continuous-weak amplitude seismic reflections, and mud-rich inversion features. The primary control factor influencing the transition of river patterns in these channels was identified as the long-term base-level cycle, shaped by paleotopography and sediment supply. Braided subaqueous distributary channels emerged as the main exploration interval for structural prospects, serving as lateral high-speed migration pathways. Dendritic braided and meandering transition intervals were deemed favorable for both structure-lithologic prospects and the expansion of new exploration fields and layers.

Graphical abstract

Keywords

Delta front / Subaqueous distributary channel / River patterns transition / Melut basin in South Sudan

References

[1] BlumM, Marriott S, LeclairS (2009). Fluvial Sedimentology VII: (Special Publication 35 of the IAS). Wiley: 399–424

[2] Chang J, Chen S Y, Wang Q, Pu X G, Yang H Y (2022). Sequence stratigraphy and coal accumulation of shallow water delta systems under low accommodation conditions: a case study from the Lower Permian Shanxi Formation in Bohai Bay region.J Palaeogeogr, 24(2): 361–374

[3] Chen B T, Shi Z S, Ma F L, He W W, Xue L, Ma L, Jia Y R (2018). Creataceous sequence stratigraphic orders and the sedimentary response of sandy beach-bar in Ruman sag, Melut Basin, South Sudan.J Palaeogeogr, 20(6): 1021–1030

[4] Chen B T, Yu X H, Wang L, Shi Z S, Ma L, Xue L, Shi J L, Bai J (2021). Features and control factors of river pattern transition in fluvial deposition and its significance for petroleum geology: an insight from the Jimidi Formation in the Ruman area, Melut Basin, South Sudan.Acta Sediment Sin, 39(2): 424–433

[5] Chen B T, Yu X H, Wang T Q, Ma F L, Li S L, Yang L S (2015). Lithofacies and architectural characteristics of sandy braided river deposits: a case from outcrops of the Middle Jurassic Yungang Formation in the Datong Basin, Shanxi Province.Oil Gas Geol, 36(01): 111–117

[6] Duvall A R, Harbert S A, Upton P, Tucker G E, Flowers R M, Collett C (2020). River patterns reveal two stages of landscape evolution at an oblique convergent margin, Marlborough Fault System, New Zealand.Earth Surface Dynamics, 8(1): 177–194

[7] Dou L R, Xiao K Y, Cheng D S, Shi B Q, Li Z (2007). Petroleum geology of the Melut Basin and the Great Palogue field, Sudan.Mar Pet Geol, 24(3): 129–144

[8] Dou L R, Pan X H, Tian Z J, Xiao K Y, Zhang Z W (2006). Hydrocarbon formation and distribution of rift basins in Sudan-A comparative analysis of them with rift basins in east China.Pet Explor Dev, 33(3): 255–261

[9] Dou L R, Wang J C, Wang R C, Wei X D (2018). The Precambrian basement play in the Central African Rift System.Earth Sci Front, 25(2): 15–23

[10] Dou L R (2005). Formation mechanism and model of oil and gas accumulations in the Melut Basin, Sudan.Bull Mineral Petrol Geochem, 24(1): 50–57

[11] He X J, Zhong J H, Cao M C, Wang Y L, Song G X (2018). The control factors and controlling mechanism of braided river-meandering river at Guantao Formation in northeast of the Dongying Sag.Henan Sci, 36(5): 776–784

[12] Liu B B, Tan C P, Yu X H, Shan X, Li S L (2019). Evolution model of a modern delta fed by a seasonal river in Daihai Lake, north China: determined from ground-penetrating radar and trenches.Front Earth Sci, 13(2): 262–276

[13] Li S L, Ma S P, Zhou L W, Huang X T, Han B, Li H (2022). Main influencing factors of braided-meander transition and coexistence characteristics and implications of ancient fluvial sedimentary environment reconstruction.Earth Sci, 47(4): 1–25

[14] Li S L, Yu X H, Jiang T, Liang X R, Su D X (2017). Meander-braided transition features and abandoned channel patterns in fluvial environment.Acta Sediment Sin, 35(01): 1–9

[15] Li S L, Yu X H, Yang Z H, Dong X M, Zhang T, Zhou Y, Li Y (2015). Fluvial changes and sandbody distribution of Toutunhe Formation in Cainan Area, Junggar Basin.Xinjiang Petrol Geo, 36(6): 660–667

[16] Lu L, Chen S G, Li Z F, Qin Y, Qu Z H, Sheng Y L (2022). Sedimentary evolution and petroleum potential of the Cretaceous to Paleogene in Linhe depression, Hetao Basin.J Palaeogeogr, 24(02): 308–331

[17] MiallA D (1996). The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis, and Petroleum Geology. Berlin: Springer: 66–85

[18] Langat P K, Kumar L, Koech R, Ghosh M K (2020). Characterisation of channel morphological pattern changes and flood corridor dynamics of the tropical Tana River fluvial systems, Kenya.J Afr Earth Sci, 163: 103748

[19] Qiu Y N (1985). River patterns classification in fluvial sedimentology.Pet Explor Dev, 12(2): 72–74

[20] Shi Z S, Wei P S, Wang L, Xue L, Pang W Z, Chen B T, Ma L, Shi J L, Zhao Y J (2021). Formation of the stratigraphic hydrocarbon accumulations of the Upper Yabus Formation in the Northern Sub-basin of the Melut Basin, South Sudan.J Afr Earth Sci, 177: 104166

[21] ShiZ S, ShiB Q, WangL, Shi J L (2018). Sedimentary characteristics and oil and gas exploration of shallow water delta during weak rifting period in faulted lacustrine basin: a case study of Paleogene Yabus Formation in Melut Basin, South Sudan. In: The 15th National Palaeogeography and Sedimentology Conference, 97–98 (in Chinese)

[22] Tan C P, Yu X H, Li S L, Li S L, Chen B T, Shan X, Wang Z X (2014). Discussion on the model of braided river transform to meandering river: as an example of Toutunhe Formation in Southern Junggar Basin.Acta Sediment Sin, 2(3): 450–458

[23] Tang W, Wang Y M, Zhao Z G, Zhong M H, Zhao Y N, Tian J H, Zou M J (2016). A review of fluvial pattern transformation.Geological Review, 62(01): 138–152

[24] Tong X G, Xu Z Q, Shi B Q, Dou L R, Xiao K Y (2006). Petroleum geologic property and reservoir- forming pattern of Melut Basin in Sudan.Acta Petrol Sin, 27(2): 1–10

[25] Wu S H, Ji Y L, Yue D L, Yin S L (2013). Discussion on hierarchical scheme of architectural units in clastic deposits.Geol J China U, 19(01): 12–22

[26] Wang L, Shi B Q, Shi Z S, Zheng F Y, Ma H (2019). Sedimentary characteristics of Paleogene Yabus Formation in shallow-water delta in the northern sag of the Melut Basin, South Sudan.China Petrol Explor, 24(6): 721–729

[27] Woolderink H A G, Cohen K M, Kasse C, Kleinhans M G, Van Balen R T (2021). Patterns in river channel sinuosity of the Meuse, Roer and Rhine rivers in the Lower Rhine Embayment rift-system, are they tectonically forced.Geomorphology, 375: 107550

[28] Yang J, Huang X, Tang Q H (2020). Satellite-derived river width and its spatiotemporal patterns in China during 1990–2015.Remote Sens Environ, 247: 111918

[29] YeX D (2006). Study on Tectonics, Sedimentology and Reservoirs in Melut Basin, Sudan. Beijing: Chinese Academy of Sciences, 64–72 (in Chinese)

[30] Yu P J, Wen J, Tan G M, Shu C W, Li Q, Hu R, Zhang G Y (2020). Experimental study on generalized model of braided river flow structure.Eng J Wuhan U, 53(05): 385–393

[31] Yu X H, Li S L, Tan C P, Qu J H, Zhang C, Zhao C F (2018). Coarse-grained deposits and their reservoir characterizations: a look back to see forward and hot issues.J Palaeogeogr, 20(05): 713–736

[32] YuX H (2008). Clastic Hydrocarbon Reservoirs Sedimentology. Beijing: Petroleum Industry Press, 77–79 (in Chinese)

[33] Yu X H (2012). Existing problems and sedimentogenesis-based methods of reservoir characterization during the middle and later periods of oilfield development.Earth Sci Front, 19(02): 1–14

[34] Yu X H, Li S L, Sun H W (2022). Coupling effect of “Mass-Slope” from source to sink in clastic rock deposition.J Palaeogeogr, 24(6): 1037–1057

[35] Yue X X (2021). Meander-braided transition features and hydrocarbon accumulation characteristics in Neogene Shawan Formation, Chunguang exploration block, Junggar Basin.Petrol Geo Exper, 43(6): 967–975

[36] Zheng R C, Li G H, Chang H L, Li S L, Wang X J, Wang C Y (2015). Sedimentary sequence and paleogeographic characteristics of the Upper Triassic Xujiahe Formation in eastern Sichuan basin.Geo China, 42(4): 1024–1036

[37] Zhu X M, Dong Y L, Liu C, Ye L, Zhang M Z (2021). Major challenges and development in Chinese sedimentological research on petroliferous basins.Earth Sci Front, 28(1): 1–11

Competing interests

The authors declare that they have no competing interests.

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