Department of Geology

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Department of Geology

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Open Access
The Influence of Geological Factors on the Engineering Properties of some Western Nigerian Residual Lateritic Soils as Highway Construction Material.
(Obafemi Awolowo University, 1985) Mesida, Ebenezer Ajibola; Akinmusuru, Joe
The fundamental influence of geology on some geotechnical properties of lateritic soils as highway -construction material within a restricted macroclimatic area of Akure and llesha in the deciduous rain forest belt of South Western Nigeria was investigated. Lateritic soils derived from four major petrological units, namely t'.aarse, P~yrphyrit.ie Granite, Coarse to medium Charnockite, Coarse to medium massive amphibolite, and medium Grained Talc Schist were concentrated upon the different ways in which Geochemistry, Clay Mineralogy, Degree of weathering and Laterization influenced the engineering properties of the sails were examined. The results have conclusively proved that geology is the main factor controlling the geotechnical properties of residual lateritic soils within the restricted climatic environment. A new parameter, termed the water absorption coefficient of lateritic soils was evolved. It is the angular relationship between the 48-hour soaked CBR value of a soil and average percent value of the soils' CBR at Optimum Moisture Content of Modified AASHO acompaction. The mean values of the coefficient in the four soils studied showed discernible relationship to the respective parent rocks. Recommendations for further research include an investigation of the relationship between the shear strength parameters of compacted genetic lateritic soils especially in the triaxial test: and the relationship between the water absorption coefficient and the geophysical resistivity values of similarly compacted genetic lateritic soils. Such subsequent research may eventually provide convenient quantitative engineering parameters which would relate the variations of moisture content, dry density, geophysical resistivity and the triaxial shear strength values in genetic lateritic soils in general.
Open Access
A Comparative Study of Resistivity Sounding Curves from Two Drainage Areas of Kafanchan, Kaduna State
(Obafemi Awolowo University, 1985) Akwuba, Godwin Kingsley; Ako, B. D.
A comparative analysis of resistivity sounding curves obtained from two drainage areas near Kafanchan, Kaduna state, underlain by rocks of the Precambrian basement complex of Nigeria, was carried out. A small part of one of the areas is occupied by the newer basalt. The resistivity investigation was done by the ACME Drillers Limited, Lagos under the auspices of Kaduna State Water Board, Kaduna. The resistivity data was interpreted by curve matching techniques and by the computer based automatic technique. A quantitative comparison of the VES curves from the two areas was done by studying the geoelectric sections and by the use of a numerical method that essentially compared the shapes and magnitudes of the VES curves. In addition, the VES curves were compared qualitatively by studying the curve types, maps of the Dar Zarrouk parameters (transverse unit resistance (T), longitudinal unit conductance, (S) and the coefficient of anisotropy (λ), and maps of the approximate depth to the fresh basement complex. The results obtained showed that characteristics of the VES curves from the two areas are different from each other and that those from the basalt part of the area are particularly different from these from the basement complex part of the two areas. The most probable aquifer layers in the whole area were found to be the weathered zone of the basement complex and the alluvial deposits between the basalt layers. It is suggested that a multi-electrode profiling work be carried out in the area underlain by basalt in the order to map probable buried river channels.
Open Access
Aspects of Organic Geochemistry of Shales Associated with the Nigerian Tar Sands.
(Obafemi Awolowo University, 1985) Adedayo, Babatunde Adebayo; Nwachukwu, J. I.
Ten shale samples from three Geological Consultancy Unit, University of Ife, boreholes (Nos. 19, 20 and 25) drilled within the Ondo State tar sand belt were analysed. Bitumen was extracted from all the samples using a standard Soxhiet apparatus. Organic carbon was determined and kerogen isolated from eight samples. Elemental analysis was also carried out on six samples. Organic carbon ranged from 1.6 - 4.9 wt.% and shows that the shales contain adequate organic carbon for source-rocks. The extractable bitumen (SOM) ranged from 1,293 ppm to 28,432 ppm with the aliphatic, aromatic/ester and nitrogen, sulphur and oxygen containing compounds (NS0's) constituting 4 - 340 ppm, 57 - 788 ppm and 631 - 8,879 ppm, respectively of the SOM. Microscopic examination of the kerogen shows that amorphous, herbaceous and coaly organic matter types constitute 53 - 74%, 16 - 41%, and 6 - 21%, respectively. A plot of the hydrogen/carbon and oxygen/carbon atomic ratios on a Van Krevelen diagram indicates that kerogens are types II and III, and are thermally immature. This shows that the shales associated with the tar sands are not the source for the bitumen in the tar sands
Open Access
Variability in the Geothechnical Properties of an Amphibolite Derived Laterite Soil.
(Obafemi Awolowo University, 1985) Ogunsanwo, Olufemi; Malomo, S; Akinmusuru, J.O.
Variabilities in the geotechnical properties, over a small area, of soils derived from coarse grained rocks have been widely recorded. Such reports concerning soils derived from fine grained rocks are however sparse. This thesis examines the variability in the geotechnical properties of a laterite soil derived from a fine-grained gneissic amphibolite from the Ile-Ife-Ilesa area of South-western Nigeria. The laterite soil is clayey and highly plastic and belongs to the Itagunmodi soil association. The variability of undisturbed soil samples taken from an area of one square meter has been examined through their shear strength, consolidation and permeability characteristics. A considerable sample to sample variation of the shear strength and consolidation characteristics was recorded. The coefficients of variation recorded for cohesion and angle of internal friction were greater than 50% and 155 respectively under total and effective stress conditions. The overconsolidation ratios for samples of the laterite soil were determined using the Cassagrande and the 'constrained modulus' methods. The coefficients of variation obtained for this parameter via the two methods were in excess of 40%. Although the overall chemistry of the samples remains uniform, mineralogical variations exist in terms of the clay mineral (kaolinite) and goethite contents. Microstructural analyses of the soil show that the soil possesses variable microstructures. The microstructures have been related to variation in the goethite content of the soil. The variability of the geotechnical properties have been attributed to the variable microstructures occuring within the soil as a result of the inconsistent cementation of the soil particles by the non-uniformly distributed goethite. The results emphasize the need for collection of a large volume of data when the geotechnical properties of laterite soils are required.
Open Access
Groundwater Exploration in Parts of Oyo and Ondo States Using Remote Sensing Techniques.
(Obafemi Awolowo University, 1985) Adeyemi, Gabriel Oladapo; Malomo, Siyan
Subsurface water in the basement complex areas is confined to the weathered overburden and the underlying fracture zones. The weathered overburden is only promising where it is thick and fairly sandy. These conditions are not obtained everywhere in the basement complex area. A large amount of groundwater is known to occur within fracture zones in the absence of thick overburden. An attempt was made at the possibility of locating fracture controlled groundwater by means of remote sensing techniques. Side looking airborne radar (SLAR) imagery of scale 1:250,000 sheet No. NB31-4 was studied. Aerial photographs of scale 1:40,000 covering areas around Oke-Mesi and Landsat imagery (Scale 1:1,000,000) of the entire area were also studied. The study area covers the bulk of the basement complex rocks of Ondo State, parts of Oyo State and very minor portions of them in Kwara and Bendel States. Lineaments were visually interpreted using a magnifier and a mirror streoscope. Those interpreted on radar imagery were graphically analysed and statistically treated. Comparison of borehole yields with the interpreted lineaments showed that the boreholes with high yields in the study area are located on the intersection of, or close to, long lineaments. Four of the six boreholes whose yields exceed 6,000 litres per hour were sited on lineaments longer than 5 kilometres. Two of the nine boreholes whose yields fall below 3,000 litres per hour were sited on lineaments whose lengths exceed 5 kilometres. The calculated Spearman Rank Correlation Coefficient of 0.20 also indicates that well yields increase with lineament lengths. This research emphasises the importance of remote sensing techniques in groundwater exploration.
Open Access
Sedimentary Geology of Part of the Southern Benue Trough.
(Obafemi Awolowo University, 1986) Agumanu, Azuwuike Ephraim; Okezie, C.N.
The Cretaceous sediments of the southern Benue Trough, comprising the Abakaliki Shale, the Ebonyi Formation (new name), the Eze A1- Formation, the Awgu Formation (all pre-Santonian) and the Enugu Formation (post-Santonian) totaling about 5,000m thick, were studied. The pre-Santonian deposits are arkosie wacke sandstones and shales with abundant illite, smectite/ illite and chlorite. Illite and chlorite increase with depth of burial with corresponding decrease in smectite and smectite/illite. A depth of burial of approximately 3,500m - 4,000m is suggested for the Abakaliki Shale. The post-Sautonian elastics are quartz arenite with higher ZTR-maturity index while the shales have abundant kaolinite. The carbonates studied are chlorozoan oolitic grainstones, wackestone-packstone and mudstone-wackestone referrable to facies belts 6-8 of Wilson (1975). Pyroclastic extrusives contributed both to the smectite development and sandstone (diagenesis). Cross-beddings, paleochannels, interference ripple marks and evaporite aminite suggest lower Clow regime of denositi of the azimuth direction of the cross-beds provides evidence for west and southwest paleocurrent dime tien that were variable during the Coniacian. There was a corresponding stable pa l euslope throughout the pre-Coniacian and the post-Santonian time. A paleohigh (the Cameroun Basement Complex and the Oban massif) persisted east of the southern Benue throughout the period of deposition and steadily supplied detritus to the sub-basin. The environments of deposition range from restricted shallow marine (Abakaliki Shale) at the base through transitional (Ebonyi Formation), shallow marine (Eze Aku and Awgu Formations) and fluvial to paralic (Enugu Formation) at the top. Warm, humid tropical climate and probably locally short-lived arid conditions characterised the sub-basin during the Cretaceous.
Open Access
Biostratigraphy and Paleoenvironmental Analysis of Strata Penetrated by Igbomoturu-I-Well, Niger Delta.
(Obafemi Awolowo University, 1986) Oboh, Francisca Emiede; Salami, M. B.
Palynological investigations were carried out on the subsurface strata of the Igbomotoru-l-Well in the Niger Delta. A lithostratigraphical interpretation of the Well resulted in the delineation of four informal nits referred to as P, P, C and I these units show lithologic characters of the Benin and Agbada Formations. The studied interval (1,123-3,583 metres) was assigned an Upper Miocene age on the basis of its palynological assemblage. These diagnostic forms were Crassoretitriletes anraadshooveni, Peregrinipollis nigericus, Zonocostites ramonaee and Multiareolites formosus. Of the 207 recognised palynomorph species representing 45 spore and 162 pollen species, only 11 were selected for biostratigraphical interpretation. This was as a result of the poor and irregular distribution of the species, many of which were usually corroded. The selected forms included the earlier named species and Pachydermite diederixi, Polypodiaceicsporites sp., Magnastritites howardi, Clavamcnocolpites sp. and Fetitricolpites sp.]. Systematic descriptions were attempted for 50 species whose morphological features were clearly discernible. Three palynological zones which were from top to bottom were established. These zones are: Fereorinipollis nioericus Zone; Petitricolpites Sp.l Zone; Clavamonocolpites Sp. Zone. These zones are subdivisions of the Crassoretitriletes vanraadshocveri zone previously named by earlier workers in the area. Environmental interpretation based on the palynomorph assemblage and lithological characters indicated a transitional depositional environment. However, the relative abundance of Zonocostites ramonae at some intervals within the studied section pointed to a dominantly mangrove swamp environment.
Open Access
Geological Interpretation of Aeromagnetic Data over Abakaliki Area.
(Obafemi Awolowo University, 1986) Bassey, Frances Asuquo; Roy, A.
Data on two aeromagnetic sheets, 303 and 304, of Abakaliki and Bansara area of the Lower Benue Valley of Nigeria have been interpreted geologically. The interpretation has two aspects: (i) Mapping of boundaries between sedimentary and igneous metamorphic rock units, and (ii ) Quantitative interpretation of individual anomalies, suggesting possible source rocks and giving their plan locations, depths, sizes and orientations. Three lithologic boundaries have been mapped aeromagnetically - one for Basement Complex and two for basalts. The Basement Complex boundary thus determined confirms the boundary given on the existing geological map of the area. The two basalt boundaries, however, are substantially different from those shown on the geological map and cover considerably larger areas. It is possible that in the geological past, the two basalt bodies were one and what we see today are the remnants of weathering and denudation of a vastly more extensive basalt formation that came up as extrusive and/or intrusive sills. Five individual magnetic anomalies have been identified and interpreted quantitatively.
Open Access
Interpretation of Total Field Aeromagnetic Data over Kainji South East Area.
(Obafemi Awolowo University, 1986) Illo, Oliver Amechi; Olorunniwo, M. A.
The total field aeromagnetic data over Kainji South - East have been studied to delineate the basement structural features in the form of profile sections and isobaths maps. Geological appraisal of the area indicates that the main lithological unit is a sedimentary unit generally grouped as the Bida sandstone overlying the basement complex. Several methods of aeromagnetic total field interpretation have been described in the literature. In this work, the Smellie's (1967) approximation method using elementary magnetic sources with its specialization to low magnetic latitude Barker (1975) and the Peters (1949) slope method have been utilized to determine the depths of the main magnetic units in the area. A number of the anomalies in this area were also modeled with two dimensional prismatic bodies (Vacquier et al, 1951) to determine structural regularity, estimates of susceptibilities and depths to magnetic sources. Depth results obtained show remarkable agreement in all techniques used. The results show that the thickness of the sedimentary cover in this part of the middle Niger basin ranges between 1.0 to 2.90km. The main trend in basement relief in this area is Southwest - Northeast.
Open Access
The Geochemistry of the Alluvial Topaz associated with the Jurassic kwandonkaya Granites in North-East Jos, Nigeria.
(Obafemi Awolowo University, 1986) Ajayi, Abiola Olanrewaju; Thorbercke, G.
Occurrences of topaz, associated with cassiterite mineralization within the Jurassic younger granite complex in Nigeria has been mentioned by several authors. This project reports the result of an integrated study of the geology, geochemistry, mineralogy and petrogenetic setting of the alluvial topaz found occurring within the kwandonkaya younger granite complex. The kwandonkaya granites which field mapping and petrographic studies show to be biotite-granites with slight textural variation most probably bear the euhedral topaz crystals in miarolitic cavities which inundate them. Two major varieties of topaz are found they are the 'colourless' and 'blue' types. Inclusions occurring within the crystals are mainly rutile rods and two phase fluid inclusions containing water and a gas. The associated minerals are cassiterite, quartz of four varieties, pottassic feldspars, flourite, micas and plagioclase. Magmatism in the complex was largely restricted to the pneumatolytic phase. A suggested geochemical prospecting method involves using the number of the miqrolitic cavities per unit area, this takes into account that a higher density is associated with greater mineralization hence a consequent enrichment of surrounding placers with gemstones and economic metals.
Open Access
Computer Modelling and Detectability Assessment of the Transition Zone in the Basement Complex Terrain of Southwest Nigeria
(2015-03-25) Ademilua, Oladimeji Lawrence
The main objective of this research was to theoretically model a basement profile containing the transition zone with varying thicknesses and resistivities as a means of assessing the detectability of this zone. This was because the zone has the tendency to be suppressed on the Vertical Electrical Sounding (VES) curve due to its intermediate resistivity and often thin thickness. A research approach that involved the development of a forward modelling computer software had been adopted for generating theoretical Schlumberger VES curves for a typical basement complex profile containing the transition zone while varying its thicknesses and resistivities. An inversion software was also developed to serve as a useful tool in the subsequent interpretation of Schlumberger VES data. The forward modelling software was tested for accuracy by comparing the resistivity curves generated through it with those obtained from two pre-existing software, RESIST 1.0 and WGeoSoft/WinSev. 5.1. The accuracy of the inversion software was also tested using existing VES data with corresponding borehole logs. The results from the accuracy tests showed that BABRES 1.0 had 99.9% accuracy while the depth prediction efficiency of BABRES 2.0 ranged between 87.7% and 99.2%, with an average of 94.0%, thereby showing that the two software were highly reliable. From the series of four-layer HA-type model curves generated by variously keeping the resistivities of the topsoil, weathered layer, transition zone and basement bedrock constant at 500 ohm-m, 150 ohm-m, 300 ohm-m, 1000 ohm-m with thicknesses of lm for topsoil, 10 m for the weathered layer, and varying the thickness of the transition zone between 2 m and 50 m, it was observed that the transition zone became detectable with a thickness ratio (between it and the overlying layers) greater than or equal to 0.73. Similar model study involving the KHA-type model curves with the topsoil, lateritic layer, weathered layer, transition zone and basement bedrock resistivities at 200 ohm-m, 750 ohm-m, 150 ohm-m, 250 ohm-m and 10000 ohm-m respectively and thicknesses of 1 m for topsoil, 2.5 m for the lateritic layer, 10 m for the weathered layer, while the transition zone thickness was varied between 5 m and 80 m, showed that the zone became detectable at thickness ratio greater than or equal to 1.11. It was discovered that the resistivity ratios (between it and immediate overlying layer) permitting detectability ranged between 1.67 to 3.67 for the HA-type, and 1.67 to 4.33 for the KHA-type curves. Below these ranges the zone became undetectable. These resistivity ratio limits were valid only when the minimum thickness ratio was obtained. It was concluded that the basement transition zones were only detectable within certain limits of thickness and resistivity ratios.
Open Access
Construction of a Geophysical Resistivity Meter and Application in Site Characterization
(2015-03-27) Afolabi, Olusegun Matthew
An automatic polarity reversing, short circuit protected adjustable output voltage resistivity meter (code named AFORE), was designed and constructed from locally available electronic and electrical materials. This was with the aim of building a resistivity meter that would be cheap and comparable both in quality and suitability with imported resistivity meter and whose circuitry would be understood and could be easily maintained. A high voltage (up to 748 V AC peak to peak), low frequency (< 0.57 Hz) power supply unit was designed and constructed from multivibrator, high current, voltage switching, transformation and automatic polarity reversing circuits. The noise in the two output signals of the multivibrator was filtered with two inverting buffers. The gate and drain to ground voltages of the four high current MOSFET enhanced BJT switches were protected with zener diodes from the transformer spikes. All the outputs of multiple secondary tappings transformer were connected to rotary switch and each selected output voltage was filtered from high voltage spikes with an ac capacitor. The oscillated low and filtered transformed high voltage AC outputs were monitored on oscilloscope to a consistent mains frequency. The output voltage from the transformer was rectified with a bridge rectifier and filtered from AC ripples with electrolytic capacitor. The output current was buffered with zener diode protected avalanche switching MOSFET. Excessive current was limited with two linear switching transistors and two 5 W resistors. The output voltage was reversed automatically and controlled with two multivibrator circuits varied in two modes to allow for the measurements of electrical resistivity (ER) and induced polarization (IP). Circuit for Spontaneous Potential (SP) measurement or removal in ER mode was constructed from a voltage divider network. The constructed resistivity meter was tested and compared with imported ABEM, OMEGA. R50 Soil Test and PASI 16 g1 resistivity meters in geophysical site investigations. The comparative field tests showed that the Vertical Electrical Sounding (VES) curves derived from AFORE resistivity meter and the other imported resistivity meters correlated very well. The inverted double dipole resistivity data from ABEM and AFORE resistivity meters identified similar positions of low resistivity seepage zone and a metallic bleeding pipe along the Opa dam embankment located in Obafemi Awolowo University (OAU) IIe-Ife southwestern Nigeria. The Natural History Museum borehole test site in OAU showed that the interpretation results of AFORE resistivity meter derived VES data compared well (83-97 %) with the borehole lithological log-derived depths. Its geoelectric section compared satisfactorily (85-100 %) with that of the other resistivity meter derived data. AFORE resistivity meter has a weight of 7.5 kg and could be used at an ambient temperature ranging from -15 to 40 0C. The cost of constructing the equipment was about 0.125 million (M) Naira, as against the market values of 2.3 M, 1.4 M, 2.5 M, 2.35 M and 2.1 M Naira for imported PASI 16 gl, OMEGA, ABEM SAS 300C, SYSCAL PRO and Soil Test resistivity meters respectively. It was concluded that AFORE resistivity meter worked satisfactorily well and could be used for teaching, academic research and professional practice.
Open Access
Mineralogical and Geochemical Variations in the Regolith of Mokuro-Itagunmodi Area, Ife-Ilesa Schist Belt, Southwestern Nigeria
(2015-04-02) Ajidahun, Emmanuel Jeminiyi
The geochemistry of regolith overlying basement rocks in Mokuro-Itagunmodi area along selected road-cut sections and petrography of the rocks were investigated with a view to determining the mineralogy, major and trace element concentrations and their distribution patterns in relation to the bedrock. Regoliths at four selected locations along Ife- Mokuro – Itagunmodi road were sampled across the regoliths according to the thicknesses of each regoliths. Selected major (Si, Al, Ti, Fe, Mn, Mg, Na and K) and trace (Cr, V, Co, Ni, Cu, Zn, As Pb and Mo) elements were determined in 34 representative regolith samples using the Energy Dispersive X – Ray Fluorescence (ED-XRF) analytical technique. The mineralogical constituents of eight of these samples were also determined using the X-Ray Diffraction (XRD) technique. In addition, petrographic studies of bedrock sample were carried out using the petrographic microscope. The results showed that tremolite-anthophyllite schist and amphibolite constituted mainly the slightly migmatized to non-migmatized metasedimentary and metaigneous rocks of the area. The results further showed that Al2O3 ranged between 23 wt % and 25 wt % whilst Fe2O3 ranged between 22 wt % and 30 wt % in the mottled zone indicating a bauxitic laterite. Significant depletion in SiO2, CaO, Na2O, K20 and MgO was observed whilst Al2O3, Fe2O3, TiO2, MnO, Cr, Co, V and Cu were relatively enriched. The element associations of Cr- Ni- Cu- V- Zn suggested strong maficultramafic influence whilst the strong and significant relationships of Fe and Mn with As, Co, Cu, Ni and Zn ( 'r' = 0.68, 0.91, 0.86, 0.87, 0.86 and 0.50; p < 0.01) resulting from adsorption and co-precipitation in the surficial environments indicated a redistribution of potential pathfinder elements into oxides of Fe and Mn. The XRD analysis results indicated the presence of kaolinite, quartz, chlorite, goethite, rutile, chromite, illite, smectite. and montmorillonite as the major mineral constituents of the regolith. Kaolinite, quartz, chlorite and goethite had mean relative proportions of 35.68 %, 29.95 %, 16.32 % and 12.02 % respectively. In conclusion, the element associations and distribution patterns reflected strong mafic ultramafic influence, however, the effect of heterogenous bedrock could not be ruled out. Furthermore, the clay mineral distribution showed an early stage of weathering in a well drained environment. The relatively high Ni and As enrichment indicated disseminated nickeliferous sulphide and gold mineralization for exploration application.
Open Access
An Evaluation of the Significance of the Accuracy of a Starting Model in Computer-Aided Vertical Electrical Sounding (Yes) Interpretation
(2015-04-17) Bayowa, Oyelowo Gabriel
The aim of this research was to evaluate the degrees of accuracy of the starting model parameters of the conventional partial curve matching, the asymptote/inflection points and the type curve controlled guess techniques of Vertical Electrical Sounding (VES) preliminary interpretation. The study involved both model studies and field data tests. Thirty multilayered (3-5 layers) model Schlumberger VES curves were generated using a forward modeling software (BABRES 1.0) while field Schlumberger VES data were acquired from ten borehole sites located within a basement complex terrain. The theoretically generated and field acquired VES data were interpreted using the three aforementioned interpretation techniques. The interpretation parameters (layer resistivities and thicknesses) from each of the three techniques were used as starting models in the RESIST version 1.0 computer-aided final interpretation. The final interpretation results (resistivities and depths) were compared with the theoretical model parameters while only the depth parameters obtained from the parametric VES curves were compared with the borehole log derived depths. Percentage deviations of the starting model parameters from the actual (model and borehole) layer parameters were analyzed using histograms and frequency curves for error margins inherent in the interpretation techniques. Composite plots of the model depths versus depth parameters obtained from each of the interpretation techniques / borehole logs were used to also evaluate deviations in depths. The results showed that error margins in each of the conventional partial curve matching, asymptotes/inflection points and type curve controlled guess respectively were between ±10%; -30 and +40% and -30 and + 10% in resistivity estimates; ±10%; -10 and +130% and -40 and +100% in depth estimates. The error margins in depth in the field data trial were between -35 and +5% for partial curve matching , -90 and +20% for asymptotes /inflection points and -85 and -10% for type curve controlled guess technique. It was concluded that the partial curve matching interpretation technique gave the most consistently low percentage deviation error margins amongst the three VES preliminary interpretation techniques. There was consistent increase in depth prediction error, with depth, in all the interpretation techniques.
Open Access
Application of Seismic Attributes to Reservoir Evaluation Over "X" Field, Niger Delta, Nigeria
(2015-04-20) Emofo, Godwin Bonny
The aims of this study on the "X" field in Niger Delta were to identify faults and other subsurface structures, to identify and evaluate the tops and bottoms of sand reservoirs and to correlate seismic attributes with reservoir properties determined from well logs. The study also aimed at investigating the petrophysical characteristics of the reservoirs and at generating time and depth structure maps of the study area. These were done to unravel the subsurface geology and hydrocarbon prospect of the study area. The data used for this study included, Migrated 3-D Seismic section [dip and strike], field check shot-survey, composite well logs and base map of "X" Field sourced from Chevron Nigeria Limited (CNL). The Kingdom Suite Software version 7.6 licensed to Department of Geology, Obafemi Awolowo University, lle-lfe. was used for the interpretation of the data and also for detailed fault mapping and correlation of six wells. Gamma-Ray (GR) and Spontaneous Potential (SP) logs were used to identify sand/ shale sequence. Shallow laterolog (LLS) and deep laterolog (LLD) were used to identify the occurrence of hydrocarbons. Neutron and Compensated Formation Density logs were used to define hydrocarbon type present. The identified hydrocarbon-bearing zones G500 and J400 sands were mapped on the seismic section using time-depth data. Time, depth structure and velocity maps were generated for the interpreted events. Selected computed diagnostic seismic attributes and petrophysical characteristics were analysed. The time and depth structure maps revealed that the dominant trapping mechanism in "X" Field was the growth fault generated rollover anticlines which trend northwest-southeast and northeast-southwest of the downthrown side of the main structure building fault F2. The attribute displays showed that the anomaly was directly on the structural closures, thus supporting the interpretation made from the seismic and well log data. Petrophysical values obtained showed that the identified sands had porosity of 23 % in well-01, 18 % in well-03, 20% in TMB-04, 50 % in TMB-05 and 26 % in TMB-06. Water saturation values (SWA) of 62 % were obtained in TMB-01, 93 % in well-03, 53 % in TMB-04, 65 % in TMB-05 and 98 % in TMB-06 and permeability values obtained were in 1.2 Darcy range. The Oil-In-Place (OOIP) in G500 sand was 391,369,882,209 barrels (502,319,971,914.6 M3) and 2,555 680,724.8 barrels (3,280,194,842.98 M3) in J400 sand. Similarly, Gas-In-Place (OGIP) was 2,458,565,805,694 barrels (3,155,548,656,199.72 M3) in G500 sand and 16,0546,57,047.0 barrels (20, 6060, 18,091.16 M3) for J400 sand. In conclusion, Seismic attributes analysis could be used to predict reservoir rock properties, delineate reservoir bodies in a low net-to-gross ratio formation, which led to optimally selected drilling location of wells. Seismic attributes analysis was found to be cost effective and greatly improved reserve estimates. There was a high probability that new locations identified within the seismic grid in "X" Field were viable prospects.
Open Access
Hydrogeophysical Investigation of Parts of the River Jama'are Floodplain, West Chad Basin, Northeastern Nigeria
(2015-04-27) Mohammed, Muraina Zaid
This 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.
Open Access
Comparative Petrophysical Study of Reservoir Sandstones in the "U", "K" And "N" Fields, South-East of the Niger Delta
(2015-04-28) Nwigwe, Kingsley Uzochukwu
The 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.
Open Access
Geophysical Investigation of Ilesha-Owena Highway Failure, in the Basement Complex Area of Southwestern Nigeria
(2015-04-28) Momoh, Odapo Lasisi
The 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.
Open Access
A 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.
Open Access
Calcareous Nannofossil Biozonation Scheme of the Deep Offshore Niger Delta
(2015-08-13) Fadiya, Lawrence Suyi
A 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.