Geotechnical Considerations for Foundation Design in Parts of Yenagoa, Bayelsa State, Niger Delta Nigeria (Published)
This research was to determine geotechnical properties of the subsoils in some part of Yenagoa and environs to obtain proper foundation design parameters, six towns in Yenagoa local government area, Bayelsa state was investigated. Six geotechnical boreholes was drilled and laboratory studies of soils samples were obtained from 0-20.25m deep. Subsurface soil profiles were delineated followed by determination of their index and mechanical properties, including Atterberg limits, particle sizes distribution, undrained shear strength, shear box test and consolidation coefficient. The general soil profile consists of (from top to bottom), , upper Silty clay horizon (0.0-5.25m thickness) soft to firm for Yenagoa study areas, Medium silty clay horizon (0.75 to 1.5m thickness) soft to firm Yenagoa study areas, low clayey sand horizon (0.75 to 1.5m thickness) soft Yenagoa study areas, peaty clay (1.0m thickness between 3.0-4.0m) soft Igbogene Yenagoa, upper sand horizon (3.0m thickness) silty sand Etegwe town Yenagoa, lower sand horizon (13.5 to 18.0m) silty sand to fine to medium and medium coarse appear in all the boreholes in Yenagoa. Yenagoa sub-soil show clay of high plasticity, silt of intermediate to high plasticity (CH, MI and MH) according to unified soil classification system from the results it shows that pad foundation is more economical in the study areas. Raft foundation is more economical in the six towns study areas of Yenagoa with Allowable bearing capacity of the upper clay layer ranges from 23-128KN/m2 In view of the significant variations in the stratification and engineering geological index properties of the soil in the six towns in Yenagoa while geotechnical data of one location cannot be used as a basis for design of foundation in a nearby land. Axial load carrying capacity for 305, 306mm, 356, 360mm, 406mm, 600and 610mm diameter for bore pile and tubular driven steel cased piles respectively were calculated for all the studies areas. Where high rise building is required in the various study areas. The study shows that the frequent causes of building collapse in Yenagoa are as a result of inadequate geotechnical investigations of the subsoil, poor quality materials, and poor work supervision.
Keywords: Bayelsa State, Niger-Delta, Yenagoa, foundation design, geotechnical consideration
Facies Analysis and Paleoenvironmental Reconstruction of Well X, Onshore Niger Delta, Nigeria (Published)
Biofacies and lithofacies analysis of one hundred and ninety-two (192) ditch cutting rock samples from well x, onshore Niger Delta was carried out for the purpose of the paleoenvironmental reconstruction of the rock succession. The objectives were to identify the lithofacies units and species of foraminifera and to use both quantitave and qualitative foraminiferal assemblage to recognise the benthonic foraminiferal biofacies and integrate both results for delineation of paleobathymetric and paleoenvironmental settings of sediments penetrated by well x interval studied. The rock samples were prepared through wet-sieve analysis with 63µm mesh sieve size, and subsequently through dry-sieve analysis with 250µm and 500µm mesh sieve sizes. The prepared rock samples were analyzed to generate data for sedimentological grain-size analysis and foraminifera biofacies assemblages. The grain-size analysis provided lithofacies associations, sand/shale ratio and sorting/gradational profile for the studied intervals of well-x while the micropaleontological analysis identified a total of ninety-three (93) well preserved foraminiferal species from which three (3) biofacies associations were delineated. The biofacies include: Ammonia beccarii, Ammonia beccarii/Bolivina scalprata miocenica, and Haplophragmoides compressa/ Valvulina flexilis biofacies indicating Shallow Inner Neritic, Inner- Middle Neritic, and Outer Neritic – Upper Bathyal paleoenvironment respectively. The result of the sand/shale ratio and lithofacies associations indicated penetration into the Agbada Formation of the Niger delta and deposition within shallow to deep marine paleoenvironmental settings, predominantly as channels, intercalated with overbank and distal bar/bay deposits. Synthesis of the biofacies and lithofacies indicated stratigraphic development between coastal deltaic and upper bathyal paleowater depths.
Keywords: Niger-Delta, Onshore., biofacies, foraminifera, lithofacies, paleoenvironment
Foraminiferal Biostratigraphy of Well Ad, Western Niger Delta (Published)
Micropaleontological analysis of sixty (62) ditch cuttings rock samples collected from interval, 7800 feet to 12,002 feet of well AD, located offshore western Niger Delta was carried out for the investigation of their age and paleodepositional environment. Standard methods and techniques of foraminiferal sample processing and analysis were followed to disaggregate the microfauna from the rock matrix. The studied interval is predominantly made up of 80 to 100 % sandstone, minor shale and siltstone with variable textural properties. Foraminifera study revealed well preserved and diverse species dominated by the calcareous benthic forms. A total of seventy-four (74) foraminiferal species were recovered among which fifty (52) two are calcareous benthic, six (6) are agglutinating forms while sixteen (16) are planktonic foraminifera. On the basis of the faunal assemblage, abundance and diversity of the important foraminiferal events, four (4) foraminiferal zones (Valvulineria spp, Brizalina mandoroveensis, Hanzawaia concentrica and Lenticulina inornata) were recognised and correlated with F300 and F500 to assign an early to middle Miocene age for the sediments. Paleoenvironmental deductions were based primarily on the richness and diversity of foraminiferal species categories. The presence or absence of planktonic foraminifera aided in deciphering open ocean environments. The dominant biofacies associations recorded within the studied section of Well-AD is the Ammonia beccarii biofacies defined by the rare to common occurrences of Ammonia beccarii, Bolivina scalpratamiocenica, Florilus atlanticus and Epistominella vitrea. Brizalina mandoroveensis species, Lenticulina inornata, Hanzawaia strattoni, Eponides eshira, Cribroelphidium galvestonensis and Hanzawaia concentrica were also in association. The Ammonia beccarii biofacies is indicative of the Shallow/Inner Neritic Paleoenvironment, while the Inner Neritic/Middle Neritic Setting is characterized by top occurrence of Valvulineria spp, a rich continuous occurrence of Epistominella vitrea. The paleoenvironment of the studied section of Well-AD is dominantly inner to middle neritic with concomitant minor incursion of outer neritic setting.
Keywords: Age, Niger-Delta, foraminifera, micropaleontology, neritic, paleoenvironment
Palynomorph Biostratigraphy of VIC 97 Well, Nothern Depo Belt, Niger Delta, Nigeria (Published)
Palynological and sedimentological studies were conducted on sixty ditch cutting rock samples from interval 460 to 4550 feets of VIC-97 well, located at OML 38, Northern Depo-belt, Niger-Delta, to delineate lithofacies units and the age of the rock succession. Standard methods of palynological sample analysis were used to disaggregate the palynomorphs from the rock matrix. Log signatures, sand/shale ratios, textural attributes, and accessory mineal compositions of ditch cutting rock samples were used as lithologic parameters to establish two lithofacies units; the transitional unit having a sand/shale ratio of 80:20 and the continental Unit having a 98:2 ratio ascribed to upper Agbada and Benin formation respectively. Palynological analysis revealed that the retrieved palynomorphs were numerous and reasonably diversified, particularly in the lower portion of the sample interval. Palynological zonation was based on the palynofloral assemblage of important species and their stratigraphic distribution. Thirteen informal biozones were recognised on the basis of their first and last downhole occurences and compared with P 560, P580 and P624 to delineate an early to late Oligocene age for the studied interval.
Keywords: Age, Niger-Delta, lithofacies units, palynomorphs, rock
Benin Flank of the Niger Delta: Quantitative Distribution of Palynomorphs, Palaeoecologic and Palaeoclimatic Interpretation (Published)
This study has reported on the palynomorphs and some associated elements encountered in the Abao Bore hole (BH) of the Maastritchian to the Tertiary of the Benin Flank of Niger Delta in the Southern Nigeria Sedimenatry Basin. Abao BH represented a continuous and complete sequences with total depth of about 3255 feet. The 51 core samples yielded 70 genera and 160 species of dinoflagellates cysts and 43 genera and 60 species of pollen and spores. The various analysis of lithologic formation recognized in the well are in order of succession: Nkporo shale (Maastrtician/Danian) Imo shale (Early Eocene), Ameki Formation (Middle Eocene –Late Eocene/Oligocene) and Ogwashi -Asaba Formation (Miocene) Benin Formation (Miocene/Pliocene). The Palynology analysis also permitted the recognition of 19 dinoflagellate cysts assemblages and 17 pollen/spores assemblages ranging in age from the Maastrticinan to the Miocene. Detailed Paleoenviromental and paleoclimatic interpretation was based on the fact that diversity, abundance and presence of some species reflect either local or regional ecological condition. In general, the paleoclimatic pattern appears to follow the scheme proposed by Van Der Hammen (1957) and there is a close correlation between dominant dinocyst association and pollen/spore percentage in the study area.
Keywords: Benin flank, Niger-Delta, palaeoclimatic interpretation, palaeoecologic, palynomorphs, quantitative distribution
Palynostratigraphy Analysis of the Agbada Formation (Nep-1 Well) Offshore, Eastern Niger-Delta Basin, Nigeria (Published)
Palynological analyses were carried out using 36 composite ditch cutting samples from NEP -1 well, off-shore eastern Niger Delta Nigeria. The interval studied is 1750 meters thick, belonging to the Agbada Formation; lithologically, the section varies from shaly-sand to sandy-shale to shale. Three zonal assemblage schemes have been erected; zone boundaries were placed where significant changes occurred in the abundance of the species, the proposed palynological zones are: Echiperiporites cf. estelae, Psilatricolpites okeizeis and Foeveotricolpites sp. zones; these are correlatable with the pantropical zones. Samples from the section are assigned a late Miocene to early Pliocene age based on the palynological evidences at this site.
Keywords: Agbada, Niger-Delta, Palynomorph, Palynostratigraphy, Stratigraphy