No abstract

Palynofacies analyses of the strata penetrated by Ida-4 wells were carried out with the aim of studying the stratigraphic sequence penetrated by the well in order to establish palynostratigraphic zones, relative age and the paleoenvironment of deposition. Fifty ditch cutting samples within the interval of 2179-3523 m were analyzed. The acid methods of sample preparation for palynofacies analyses were followed. The result of the analyses yielded low to abundant occurrences of pollen and spores with an abundance of small, medium and large sizes of palynomacerals 1 and 2, few occurrences of palynomacerals 3 and 4. The lithology consists of the alternation of shale and sandstone units with few intercalations of argillaceous sandstone units, indicating that the studied interval belongs to the Agbada Formation. The studied intervals were dated to the middle Miocene to late Miocene, based on the recovered age diagnostic marker species such as Zonocostatites ramonae, Multiareolites formosus, Verrutricolporites rotundiporus, Crassoretitriletes vanraadshoveni and Racemonocolpites hians. Two interval range palynostratigraphic zones: Multiareolites formosus-Zonocostatites ramonae, Verrutricolporites rotundiporus-Crassoretitriletes vanraadshoveni and a taxon range zone: Ainipollinite verus zone were proposed. Paleoenvironmental interpretation was based on the palynofacies association and the lithology which revealed that the stratigraphic interval studied was deposited in the Coastal-deltaic (marginal marine) environments.

Palynological analysis was carried out on twenty (20) ditch cutting samples from a section (1284.73-1496.57 m) of the Amansiodo-1 well, Anambra Basin, southeastern Nigeria with the aim of determining the age, biozone, and depositional environment of the sediments within the depth interval. The laboratory techniques of digesting sediments in hydrochloric and hydrofluoric acids for silicates and carbonates removal were followed to process the samples for the recovery of palynomorphs. Fifty two (52) palynomorph specimens were recovered. An assemblage zone of Echitriporites trianguliformis Zone has been established. The section was dated to the upper Maastrichtian due to the occurrences of age diagnostic marker species such as: Cingulatisporites ornatus, Distaverrusporites simplex, Proteacidites sigalii, Dinogymnium cf auclaense, Echitriporites trianguliformis and Retidiporites magdalensis. Based on the palynomorph marine index and environmental indicator flora, the section was inferred to be deposited in marine to brackish (coastal) environments with little influence of fresh water.

Ditch cuttings (69 samples) from a section of Awaizombe-1well located in the Northern Depobelt of the eastern Niger Delta Basin were used for this study. The lithology of the studied interval 1373–1812 m (439 m thick) consists of fissile grey shale and mudstone units. The scid method of sample preparation for palynormorphs’ recovery was adopted. Analysis recorded a well-preserved and diverse assemblage of palynomorphs, rich in pollen, spores and dinoflagellate cysts (dinocysts). First and last occurrences of marker and age diagnostic species were used for palynostratigraphic interpretation. Four palynostratigraphic interval range zones were established: Psilatriporites sp.–Racemonocolpites hians Zone; early Oligocene (Rupelian age), Praedapollis africanus–Doualaidites laevigatus Zone; late Eocene (Priabonian age), middle Eocene (Lutetian and Bartonian ages), Doualaidites laevigatus–Praedapollis flexibilies Zone; and early Eocene (Ypresian age), Verrucatosporites usmensis–Retitricolpites ituensis Zone. The first downhole occurrence of D. laevigatus at the 1482 m marks the late Eocene/early Oligocene boundary. Established zones are useful for inter and intra basins correlation. Lithology and age of the studied section are suggestive of the lower Agbada Formation. Palaeoenvironmental interpretations using diagnostic species revealed two environments: brackish and inner neritic to upper bathyal (0–600 m) under relatively warm-water marine condition indicated by thermophilic dinocyst taxa, such as Lingulodinium machaerophorum, Polysphaeridium zoharyi and Homotryblium spp. The lithology and these types of environments are good sites for hydrocarbon generation.

Sequence stratigraphic analysis was carried out on well BB-3, deep offshore, Niger Delta Basin, Nigeria. This is done in order to delineate sequence stratigraphic surfaces using vertical sequence of depositional environment. Palynological analysis was carried out on 82 ditch cutting samples from well BB-3 using the standard acid technique in order to zone the well. Open hole geophysical log data was also provided for the studied interval 10700–15600 ft belonging to the Agbada Formation. Lithologically, the section varies from alternation of sand and shale units with carbonaceous debris, mica flakes, ferruginised materials and glauconite at some interval as accessory minerals. Biozonation included three taxon range biozones in BB-3 well, the proposed palynological biozones are Belskipollis elegans, Crassoretitriletes vanraadshooveni, Pachydermites diederixi biozones which are correlatable with the pantropical zones. Samples from the section are dated early Miocene to middle Miocene age based on the independent palynological evidences. The deduced paleoenvironments of the strata penetrated by the well range from outer neritic through bathyal to abyssal. The successions were broken into Highstand Systems Tracts (HST), Lowstand Systems Tracts (LST) and Transgressive Systems Tracts (TST) and chronostratigraphic surfaces such as Maximum Flooding Surface (MFS), Sequence Boundary (SB) and Transgressive Surface (TS). Three HST, three LST, three TST, two MFS and three SB were recognised. The MFS and SB were dated 15.9 Ma, 15.0 Ma and 16.7 Ma, 15.5 Ma, 13.1 Ma respectively by correlation of the established pollen zones with the Niger delta Cenozoic chronostratigraphic chart. The sandstone and shale units of the Systems Tracts are potential hydrocarbon reservoirs and seal rocks respectively.