Sunny C . Ezeh

Miocene deposits in the eastern portion of the Greater Ughelli, Central Swamp and Coastal Swamp depobelts contain well-developed brackish-water trace fossil assemblages. Twelve ichnogenera have been identified, namely: Asterosoma, Bergaueria, Chondrites, Gyrolithes, Thalassinoides, Lockeia, Palaeophycus, ?Conichnus, Planolites, Siphonichnus, Skolithos and Diplocraterion. In addition, common non-descript, passively filled burrows and fugichnia (escape structures) have also been observed. The above-mentioned ichnogenera and associated non-descript structures can be arranged into six distinct and recurring ichnoassociations within the Greater Ughelli, Central Swamp and Coastal Swamp depobelts. Each ichnoassociation is comprised of a group of trace fossils which collectively reflect specific environmental conditions during deposition of these Miocene strata. All trace fossil assemblages illustrate deposition in nearshore, restricted settings. Ichnological and sedimentological criteria w...

Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamm...

The Paleogene sediments located in Ogbunike shows a linear northwest-southeast trending features located between kilometre 11.3 and 14.5 along Enugu-Onitsha expressway and belong to the Anambra basin. Sedimentological examination of the exposed three outcrops show that the area comprises five lithofacies association-The mudrock facies association, lower sandstone facies association, middle sandstone facies association, bioturbated sandstone facies association and the upper sandstone facies association. The sedimentological analyses indicate a high energy, wave dominated and fluvial to shallow marine environment. The lithofacies associations indicate vertically stacked fluvially-tidally influenced and shoreface superimposed on five depositional cycles. The textural analysis of the cross-bedded sandstones reflects a fluvially dissected shallow environment with tidal imprints. Paleocurrrent analysis indicates a radial pattern or fan-shaped which imply fluvial and rose diagram shows that the provenance is northwest while the current flow is in the southeasterly direction. The palynological analysis from fourteen samples of coaly and fossiliferrous mudstone shows similarity of result in terms of paleogeography. The recovered palynomorph assemblage indicate marine-(Acritarchs and dinoflogallates-Apectodinium lyperacanthun, Xenicodinium lubricum, Eisenackia Crassitabulata and Homotryblium Tinuispinosum) and lower percentage of pollen and spores (Eg Buttinia andreevi, Retidiporites magdalenensis, Echimonocolpites, Echitriporites trianguliformis, and Critaeturites cristatus) which indicate freshwater environment. The presence of pteridophytes also suggests a humid environment of deposition. This give the impression that the environment is marine with influenced of continental detritus. This study indicates that marginal marine connection probably occurred in Anambra, Gongola and Bida basin during the paleogene time. Regionally, this idea support that there exist connection between the Mediterranean in the Palaeogene and the Gulf of Guinea.

This work detailed on trace fossil atlas and description, ichnofacies, and the application to interpretation of various depositional environments (brackish-water through fully marine facies). Trace fossils morphology, occurrence, variations and ichnoassociation are compared to other forms from other basins across the world. It is the result of an in-depth research on over 3000 feet of cores from the Miocene reservoirs within the depositional belts of Niger Delta basin. It will be a useful tool for students, experts and academia working either in the Niger Delta basin or in similar siliciclastic reservoirs from other basins of the world.

Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mudstones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamm...

Often analyses of depositional environments from sparse data result in poor interpretation, especially in multipartite depositional settings such as the Niger Delta. For instance, differentiating channel sandstones, heteroliths and mud-stones within proximal environments from those of distal facies is difficult if interpretations rely solely on well log signatures. Therefore, in order to achieve an effective and efficient interpretation of the depositional conditions of a given unit, integrated tools must be applied such as matching core descriptions with wireline log signature. In the present paper cores of three wells from the Coastal Swamp depositional belt of the Niger Delta are examined in order to achieve full understanding of the depositional environments. The well sections comprise cross-bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were laid down in wave, river and tidal processes. Interpretations were made from each data set comprising gamma ray logs, described sedimentological cores showing sedimentary features and ichnological characteristics; these were integrated to define the depositional settings. Some portions from one of the well sections reveal a blocky gamma ray well log signature instead of a coarsening-upward trend that characteris-es a shoreface setting while in other wells the signatures for heteroliths at some sections are bell blocky in shaped rather than serrated. Besides, heteroliths and mudstones within the proximal facies and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on sedimentology and ichnology of cores from these facies was used to correct these inconsistencies. It follows that depositional environment interpretation (especially in multifarious depositional environments such as the Niger Delta) should ideally be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.

This work examines ichnological attributes and variability of core samples from four wells (1-4) within the Coastal Swamp and shallow Offshore depobelts in the Niger Delta basin. The cores consist of facies interpreted as mainly shoreface deposits. These deposits are in successions and well-developed. The shoreface successions are divided up into a lower, middle and upper shoreface. The lower shoreface lies within fair weather wave base. The ichnofossils assemblages characteristically represent a diverse and abundant Cruziana ichnofacies. The middle shoreface contains swaly and lesser hummocky cross-stratified sandstones with an ichnofossil assemblage dominated by the Skolithos ichnofacies. The upper shoreface is dominated by planar and trough cross-beddings. Ichnofossils are fairly abundant and consist of deeply penetrating structures of the Skolithos ichnofacies. These facies reveal a wide range of variability, mostly limited to the lower and middle shoreface intervals. This variability appears to be determined by relative storm dominance and the episodic character of associated storm bed deposition. The successions are grouped into three: (1) high energy shorefaces consist entirely of stacked storm beds with moderate bioturbation, (2) moderate energy shorefaces comprises stacked laminated to burrowed intervals, recording recurrent erosive storm bed emplacement, followed by opportunistic colonization, and normally overprinted by resident fair-weather burrowing, and (3) low energy shorefaces ordinarily exhibit intense bioturbation with low preservation of storm beds. Discrimination between lower and middle shoreface deposits is mainly based on the resident fair-weather ichnofossil assemblage; under increased energy settings. In addition, based on storm intensity, relative water depth, storm frequency and shoreline character, the nature of coexistent lower and middle shoreface facies can differ significantly along strike. In some cases, the lower and middle shoreface differentiation was difficult.

Many times, analysis of depositional environments from sparse data results to poor interpretation especially in multipartite depositional setting like the Niger Delta. For instance, discriminating channels sandstones, heteroliths and mudstones within the proximal environment and those of distal facies is difficult if interpretation is made solely on well log signatures. It therefore, entails that in order to achieve an effective and efficient interpretation of the depositional conditions of a given deposit, integrated tools must be applied. This work examines the depositional environments of three wells from the Coastal Swamp depositional belt of the Niger Delta in order to achieve strict understanding of the sediments. The wells comprise cross bedded sandstones, heteroliths (coastal and lower shoreface) and mudstones that were deposited by wave, river and tidal processes. Interpretations were made from each disparate data set comprising gamma ray logs, sedimentological cores showing sedimentary features and ichnological characteristics and integrated to define these depositional settings. Some sections from one of the wells show a blocky gamma ray well log signature instead of fining upward/funnel shape motif that characterise a meandering fluvial point bar system while in other wells the signatures for heteroliths at some sections were blocky-bell shaped in place of serrated/jagged shaped type. Besides, heteroliths and mudstones within the proximal environment and those of distal facies were difficult to distinguish solely on well log signatures. However, interpretation based on the sedimentology (sedimentary structures and textures etc) and ichnology of cores from these facies were used to correct these inconsistencies. It then follows, that depositional environment interpretation (especially in multifarious depositional environment like the Niger Delta) should be made together with other raw data for accuracy and those based solely on well log signatures should be treated with caution.

The importance of trace fossils to production geologist need not to be overemphasised, but recently, as trace fossils application moved from the more obvious to the innocuous, their effects on rock features (bioturbation) that lead to total distortion of the rock has taken a different trend. Some bioturbation (crytobioturbation) has been noticed to cause little destruction on the features of the rock and their distortions on rock rather generate a more homogenised rock property. Crytobioturbation or cryptic bioturbation is generated by a meiofuana that causes a hundred percent (100%) bioturbation effects but do not result to total disruption of the sedimentary features. It could also be by the action of small infauna referred to Macaronichnus tracemaker that preserve imperceptible sedimentary texture by using selective ingestion feeding behaviour or through total removal of sedimentary lamination by burrowing animals in a substrate that otherwise has little lithologic variability.
A total of seven wells from different fields in the Coastal and Central Swamps depobelts of Early – Late Miocene age in the Niger Delta were studied and some sections of one of the wells were cryptically bioturbated. Detailed studies show that they induce a low-contrast, dual porosity flow network to the sedimentary rock, which has implications when applying to resource quality of the porous media. A further study shows that beyond permeability enhancement, they do smoothen out internal heterogeneities that promote uniform permeability distribution.
Thus, it proves that for every facies studies or facies modeling it is essential that these discreet signatures in rock record be put into consideration for better prediction of flow paths (Super Perm) and for efficient application of secondary recovery techniques during the stage of well enhancement

The sedimentological and reservoir characterization of Lokoja sandstone Formation shows that there exist three main lithofacies association- massive conglomeratic sandstone, massive sandstone and clayey-siltstone that were deposited in a fluvial to shallow marine environment. Granulometric studies reveal a dominant of medium grains sandstone with dissection of coarse and fine grains that are moderately to poorly sorted. The skewness indicates mainly negatively skewed with few as symmetrical while the kurtosis shows very platykurtic to platykurtic form. Pebble morphometric analysis suggests compacted bladed and compacted platy to platy with few of elongated forms. Mean sphericity values for the two examined units are 0.64 and 0.68, which indicate dominance influence of both fluvial and beach processes.  Paleocurrent analysis suggests that the sandstones are derived from a southeasterly provenance and transported in a northeastward direction. Grains characteristics also reveal a heterogeneous reservoir with porosity range of 23.4 – 39.1% and permeability of 7 – 25mD which reflect poor inter-connectivity of the heterogeneous reservoir.