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<p>The sedimentological and ichnological properties of 60 ft (18.3&#xa0;m) cores of Miocene deposit, together with the stacking patterns of wireline logs correlated across four wells, were analysed to develop a conceptual model of lithofacies variability and depositional environments in a typical Niger Delta basin transgressive systems tract (TST). The study also aimed to identify the factors and processes that controlled the sediment deposition, the sandstone reservoir stacking patterns and systems tracts, and the lithofacies that characterise the depositional environments as well as implications for petroleum production. The backstepping stacking pattern of gamma-ray logs and flooding surfaces in the depth zone of interest indicates TST. Twelve lithofacies were identified from core descriptions, while the lithofacies characteristics or associations of lithofacies resulted in the identification of depositional environments that include transgressive and delta-influenced offshore, transgressive offshore-transition, transgressive shoreface, fluvial channel, and outer, middle, and inner estuaries. The ichnofossil suite in the cores is generally impoverished in abundance, diversity and burrow sizes and sporadically heterogeneous in distribution, indicating brackish-water conditions. Vertical succession of facies shows funnel-shaped morphology as marine facies move landward, typical of estuaries. The moderate abundance of reactivation surfaces and tidal sandbars at the outer estuary, the thick tidalbore and intertidal/overbank deposits at the middle estuary and the tidal ravinement surface at the inner estuary indicate a tide-dominated estuary. The generally fine- to medium-sized sandstone grains and the TST thickness of 95 ft (29&#xa0;m), as well as the compaction-driven subsidence that can be inferred from the growth faults that characterised the study field, suggest that the estuary is not that of an incised valley but that of a delta-plain. The fluvial and estuarine sandstones and the transgressive shoreface sandstone successions are overlain by laterally extensive transgressive shelf mudstone to form a petroleum habitat.</p>

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Sedimentology and ichnology of estuarine reservoir sandstone deposits in a transgressive systems tract, coastal swamp depobelt, Niger Delta Basin, Nigeria

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  • 发表日期：

    2026年7月19日

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  • Raphael Oaikhena Oyanyan,
  • Olugbenga Oluseyi Oshinowo

摘要

The sedimentological and ichnological properties of 60 ft (18.3 m) cores of Miocene deposit, together with the stacking patterns of wireline logs correlated across four wells, were analysed to develop a conceptual model of lithofacies variability and depositional environments in a typical Niger Delta basin transgressive systems tract (TST). The study also aimed to identify the factors and processes that controlled the sediment deposition, the sandstone reservoir stacking patterns and systems tracts, and the lithofacies that characterise the depositional environments as well as implications for petroleum production. The backstepping stacking pattern of gamma-ray logs and flooding surfaces in the depth zone of interest indicates TST. Twelve lithofacies were identified from core descriptions, while the lithofacies characteristics or associations of lithofacies resulted in the identification of depositional environments that include transgressive and delta-influenced offshore, transgressive offshore-transition, transgressive shoreface, fluvial channel, and outer, middle, and inner estuaries. The ichnofossil suite in the cores is generally impoverished in abundance, diversity and burrow sizes and sporadically heterogeneous in distribution, indicating brackish-water conditions. Vertical succession of facies shows funnel-shaped morphology as marine facies move landward, typical of estuaries. The moderate abundance of reactivation surfaces and tidal sandbars at the outer estuary, the thick tidalbore and intertidal/overbank deposits at the middle estuary and the tidal ravinement surface at the inner estuary indicate a tide-dominated estuary. The generally fine- to medium-sized sandstone grains and the TST thickness of 95 ft (29 m), as well as the compaction-driven subsidence that can be inferred from the growth faults that characterised the study field, suggest that the estuary is not that of an incised valley but that of a delta-plain. The fluvial and estuarine sandstones and the transgressive shoreface sandstone successions are overlain by laterally extensive transgressive shelf mudstone to form a petroleum habitat.