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- ItemOpen AccessCalcareous Nannofossil Biozonation Scheme of the Deep Offshore Niger Delta(2015-08-13) Fadiya, Lawrence SuyiA high resolution calcareous nannofossil biostratigraphic study was carried out on eight wells from the deep offshore Niger Delta with the aim of subdividing the sequences penetrated into zones and local subzones. The study is also aimed at identifying new nannofossils species, dating observed condensed sections as well as identifying nannofossil species with acme events. Ditch cuttings from the eight wells (DPW1 – DPW8) obtained from the Niger Delta were logged and composited at 10 metres interval and processed for nannofossil analysis using the modified standard smear technique. The prepared slides were examined with the Olympus Photomicroscope at 1000X and 1500X magnifications under cross polarized and transmitted light. Detailed species identification of all encountered nannofossils was made in eight horizontal sweeps (traverses) in each slide by using relevant bibliographic references. Nannofossils distribution plots were made on the scale of 1:5000 with sample depths on the Y-axis and all nannofossil taxa observed on the X-axis using the Stratabug biostratigraphic software. Zonal subdivision was based on First and Last occurrences of marker species as well as their relative abundance. The abundance and diversity patterns were calibrated with chronostratigraphically important bioevents to date all observed major condensed sections for the sequence stratigraphic interpretation of the studied wells. The results revealed high to moderately diverse and abundant calcareous nannofossils in the eight wells in the area. The zones encountered in this study ranged from the Early Miocene NN1 (CNIa) to Early Pliocene NN13 (CN10c) zones. Four wells – DPW2, DPW4, DPW5 and DPW6 penetrated sediments of Miocene to Early PIiocene age while wells DPW1, DPW3, DPW7 and DPW8 were restricted within the Miocene age. Five major zones NN1, NN2, NN4, NN5 and NN11 were subdivided into subzones. The acme events of Discoaster pentaradiatus, D. quinqueramus, D. berggrenii, D. bollii and D. deflandrei were found to be associated with the 5.0 Ma, 5.8 Ma, 7.0 Ma, 9.2 Ma and 16.0 Ma Maximum Flooding Surfaces respectively following the Haq et al.'s Global Sequence Cycle Chart. The Miocene/Pliocene boundary was easily inferred from the consistent occurrence of Ceratolithus acutus and C. armatus (5.2 Ma) in the Niger Delta deepwater. Two new nannofossils species – Calcidiscus sp. 1 and Calcidiscus sp. 2 of the Late Miocene age were identified in the studied wells. A dearth of nannofossils spanning a period of approximately 5 Million years between 10.9 Ma – 15.6 Ma was observed within the Middle Miocene Serravalian age of the deep offshore Niger Delta. It was concluded that the zonation scheme used in the study had further helped to subdivide the deep offshore Niger Delta Miocene - Pliocene sequence into easily recognizable biostratigraphic units.
- ItemOpen AccessA Study of Littoral Foraminiferal Fauna of the Sediments Off the Lagos Coast, Southwestern Nigeria(2015-05-08) Olayiwola, Moshood Adegboyega; Odebode, M. O.This study is aimed at documenting, determining the distribution, composition, and diversity pattern, and defining the biotopes and biofacies of foraminiferal fauna with the view to characterizing the littoral environments off the Lagos Coast, Southwestern Nigeria. Twenty grab-samples, supplied by the Nigeria Institute for Oceanography and Marine Research, Lagos, were washed over 2000 μm and 63 μm sieves. The foraminiferal contents were picked, stored in micro-paleontological cellules, and the systematic description carried out. The identified individual foraminiferal taxa were counted and the relative abundance data generated were subjected to diversity index and multivariate analyses. Eighty-three foraminiferal species were recorded. The identified foraminiferal fauna is constituted by 96 % Rotaliina, 2.73 % Miliolina and 1.27 % Textulariina. They belong to 15 super families, 27 families and 41 genera. Rotaliina strongly dominated the inner and middle continental assemblages. Textulariina and Miliolina occur only in the inner continental shelf as rare species. The four most abundant benthic species are Hanzawaia boueana, Cancris auriculus, Florilus boueanum, and Nonion depressulum. They constitute 6.90 %, 4.27 %, 3.68 %, and 3.54 % of the total identified benthic fauna respectively. The most abundant planktic taxa are Globigerinoides rubber, G. trilobus immaturus, G. trilobus trilobus, Neogloboquadrina dutertrei dutertrei, and Globigerina bulloides. These respectively constitute 8.80 %, 6.95 %, 3.06 %, 6.40 %, 9.60 %, and 2.80 % of the total recorded planktic foraminifera. The Planktic / Benthic (P / B) ratio of the foraminiferal species increases from near the shoreline to the middle shelf in the study area. The 11 diversity indices employed indicate a general increase in the diversity indices away from the shore. The samples belong to three. Fisher's (a) diversity index groups. Group A has low diversity value of 4.81 while group B has moderate diversity of 8.07 and group C has relatively high diversity value of 17.36. The samples also belong to three multivariate clusters that are interpreted as biotopes. Biotope A comprises samples LE4 and LE4A. Abundance of Rotaliina and rare occurrence of Textulariina and Miliolina characterize it. Biotope B comprises samples LE3, LEI and LElA and is dominated by Rotaliina but has common occurrence of Textulariina and Miliolina species. Biotope C consists of samples LE2, LE5 and LE7 and is characterized by abundance of Rotaliina species and very rare occurrences of Textulariina and Miliolina species. Most of the Benthic and planktic species identified are "warm-water" tolerant. The only "cold to temperate-water" forms recorded are the benthic species of Cassidulina, Eponides, Lenticulina and Uvigerina, and planktic Globigerinoides bulloides, Globorotalia inflate and G. scitula scitula. The study concluded that all the taxa are normal marine, well-oxygenated inner to middle continental shelf forms. They constitute the foraminiferal fauna characteristic of the shallow marine waters and littoral sediments off the Lagos Coast.
- ItemOpen AccessComparative Petrophysical Study of Reservoir Sandstones in the "U", "K" And "N" Fields, South-East of the Niger Delta(2015-04-28) Nwigwe, Kingsley UzochukwuThe study identified, correlated and petrophysically evaluated sandstone reservoirs in the "U", "K" and "N" fields situated in the southeastern part of the Niger Delta with a view to identifying common traits that could be used for predicting reservoir quality and thus enhance hydrocarbon recovery. Digital well log data of eight wells from the Niger Delta were analyzed and interpreted using the flow chart for log interpretation as a guide and the 7.6 version of the SMT Kingdom Suite software as a tool. Graphic plots and charts were used to determine and to illustrate the variability of some petrophysical properties (porosity, shale volume, grain size, bulk volume water and relative permeability). In calculating the compaction coefficient and percentage compaction of the sandstones, the Athy and Einsele decompaction equations were used. Sandstones of good reservoir quality were identified in "U", "K" and "N" fields; 19 for the "K" field, one for the "N" field, and two for the "U" field. The reservoirs in the "K" field varied in texture from very fine to coarse grained while those in "N" and "U" fields were fine-grained. A total gas-in-place of about 18.30 million cubic feet and optimal oil-in-place of about 7.39 million barrels were estimated for the "K" field. Values of moveable hydrocarbon index (< 0.7), moveable hydrocarbon saturation (high) and residual hydrocarbon saturation (very low) showed that the hydrocarbons had moved. The sandstones in the study area had percentage compaction values of 29.74 — 47.62 % and compaction coefficient values ranging from 0.0003 — 0.0005 m-1 (0.00009 — 0.0002 ft-1). The studied wells did not penetrate the overpressure zones. A model compaction equation expressed as ØA v = 0.0028Z + 46.55 (for depth in feet) or ØA v = 0.00084Z + 46.55 (for depth in meters) (where porosity, ØA v is in percent and depth, Z, is in feet or meters) was subsequently derived for porosity prediction in the hydrostatically pressured sandstones. Effective porosity values for the reservoirs ranged from 18.0 — 38.0 %, and showed a general decrease with depth. The sand beds showed good correlation within fields and were fairly correlatable across fields. In conclusion, the sandstones of the three fields showed good reservoir qualities but differed in their hydrocarbon saturations. The "K" field appeared to be more of gas field than an oil field.
- ItemOpen AccessGeophysical Investigation of Ilesha-Owena Highway Failure, in the Basement Complex Area of Southwestern Nigeria(2015-04-28) Momoh, Odapo LasisiThe aim of this research was to detail the subsurface geoelectric sequence, map the subsurface structural features within the sub-grade soil, delineate the bedrock relief and determine the resistivity type curves that characterize the failed and stable segments of the Ilesha-Owena Highway as a means of establishing the cause(s) of the road pavement failure. The investigation involved the electrical resistivity, magnetic and Very Low Frequency Electromagnetic (VLF-EM) geophysical methods. The electrical resistivity survey utilised the Schlumberger Vertical Electrical Sounding (VES) and dipole-dipole horizontal profiling. Magnetic and VLF-EM measurements were made at 5 m intervals along each of the segments while YES measurements were made at interval of 25 m. The electrical resistivity data were quantitatively interpreted by a computer-iteration technique involving the RESIST and Dippro cm programmes while the KHFILT software was used to process the VLF-EM data which together with the magnetic profiles were qualitatively interpreted. The results showed that the inverted VLF-EM anomaly along the stable road segment mapped a generally resistive subsurface. The magnetic profile along the segm6nt was relatively flat indicating homogeneous subsurface devoid of any major structural feature. Only one fairly conductive zone beneath the failed segments 1 and II respectively, typical of a linear structure, was delineated by the VLF-EM anomaly while two and four magnetic anomalies typical of thin/thick dykes were correspondingly delineated along the two segments. Four major subsurface layers —the lateritic/sandy/sandy clay/clayey sand topsoil; the lateritic layer; the weathered basement and the presumably fresh bedrock were delineated beneath the stable and failed segment II while three subsurface layers- the sandy/sandy clay/clayey sand topsoil, the clayey weathered basement and the presumably fresh bedrock were obtained beneath failed segment I. The geoelectric sections revealed uneven bedrock topography beneath the three segments. The resistivity histogram plot and 2-D resistivity structure showed that the stable segment was characterized by high resistivity laterite to a depth of up to 6 m while the failed segments I and II displayed low resistivity clay and sandy clay topsoil/sub-grade soil. Also narrow deeply weathered zones typical of linear features located within the basement bedrock were delineated beneath failed segments I and II. These features correlated with magnetic derived linear features. It was concluded that the causes of highway pavement failure in a typical basement terrain identified from this study included poor drainage, presence of near surface linear features within the sub-grade soil, clayey nature of topsoil/sub-grade soil below the highway pavement and excessive cut into near surface low resistivity water absorbing clay enriched substratum.
- ItemOpen AccessHydrogeophysical Investigation of Parts of the River Jama'are Floodplain, West Chad Basin, Northeastern Nigeria(2015-04-27) Mohammed, Muraina ZaidThis study aimed at establishing the different subsurface geoelectrical/geological layers, the aquifer units and their hydraulic parameters, the subsurface structures and their influence on the general hydrogeological conditions of River Jama'are floodplain Northeastern Nigeria with a view to providing information for the development of the basin for water supply to Azare township in Bauchi State. The study involved integrated geological, geophysical and hydrogeological investigations. The geological mapping involved direct observations of rock formations. surface landform features and correlation of lithological logs from existing boreholes. The geophysical investigation involved the electrical resistivity method. One hundred and six Schlumberger Vertical Electrical Sounding (VES) stations located at the corners of a 225 x 225 m square grid network were occupied. The inter-electrode spacing (AB/2) was varied from 1 - 225 m. The hydrogeological investigation involved acquisition of borehole lithological logs and pumping test data. The interpretation of the VES data involved partial curve matching and computer iteration technique using Resist software, while the analysis of the pumping test data was carried out using Cooper - Jacob analytical model. Four subsurface geologic layers were identified from the geoelectric sections, aided by borehole lithological logs. These included topsoil, alluvial sand, Chad Formation/weathered basement column and the bedrock. The layer resistivity ranged from 5 - 5706: 69 - 3079: I I -140 and 994 - co ohm-m respectively while the thicknesses of the upper three layers w e r e 0.4 - 6.7; 1.6 - 32.2 and 15.9 - 168.6 m respectively. Four major parallel basement depressions suspected to be regional faults striking approximately NW-SE were delineated. The NW – SE trend correlated with one of the general trends of the regional structures in the Chad Basin. The isopach maps of the topsoil and alluvial sand mirrored a more recent NE-SW trend that correlated with the Tibesti - Cameroon trough. The alluvial sand layer constituted the dominant aquifer unit while the clayey Chad Formation/weathered basement displayed aquitard characteristics. The groundwater yields varied from 2 - 13 litre sec. The pumping test derived transmissivity values varied from 122.7 - 18783.7 m2 day while the hydraulic conductivity varied from 6.7 - 1329.4 m/day. The transmissivity and hydraulic conductivity obtained within the upper 25 - 30 m (142.6 - 18783.7 m2/day and 6.7 - 1329.4 m2 d a y /m) suggested a zone with high recharge and discharge capacities while deeper wells, gave significantly lower values (122.7 - 158.1 m2/day and 5.5 - 11.1 m2/day/m), arising from the effect of thick low permeability clayey Chad formation/weathered basement column. It was concluded from this study that the groundwater potential of the study area was, generally high when the depth of the abstraction boreholes was kept within the upper alluvial deposit or generally not deeper than 25 - 30 m. Deeper boreholes gave characteristically lower groundwater yield due to low transmissivity and hydraulic conductivity of the basal clayey Chad Formation/weathered basement.