Geosciences-Scholarly Publications

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Open Access
Application of geoelectrical and chemical methods for groundwater assessment in Isheri-North, Ogun state, Nigeria
(Journal of Science and Technology (Ghana), 2015) Adeoti, L; Bello, M.A; Olatinsu, O.B; Adiat, K.A.N
Geoelectrical investigation and chemical analyses were carried out at Isheri North area of Ogun State in order to assess the groundwater quality at shallow depth and its deep potential zone for groundwater development. The study area has been selected for investigation due to infiltration of the polluted Ogun River. Forty-three (43) Schlumberger Vertical Electrical Soundings (VES) and chemical analyses of water samples from one hand dug well and two shallow boreholes in the study area were carried out. Four to five geoelectric layers which correspond to top soil, clayey sand, sandy clay, clay and sand were delineated. The longitudinal conductance values (0.02 - 0.106mhos) of the topsoil in the area reveal its poor to weak protective capacity, thus exposing the underlying clayey sand to contamination as reflected from its resistivity values ranging from 4.8-15.1Ωm. This low resistivity zone at shallow depth (3 – 26m), occasioned by infiltration, was further ascertained by high values of conductivity, turbidity, total hardness, TDS, Cl, Fe, and Mn ions in the analyzed water samples taken at depth ranges from 9 – 16m. The results of the analyzed water samples from this shallow zone are beyond international standards for drinking water. The underlying clay resistivity values ranged between 1.9 - 6.1Ωm and thickness varied from 50.8 - 100.5m. This acts as the seal for the underlying aquifer (sand layer). The resistivity of the sand layer varied from 91.7-159Ωm with a depth interval of 101.7-109.4m and 73.4-82.3m in VES 1 and VES 14 respectively. This constitutes the deep aquifer units in the study area. The longitudinal conductance values of the overburden above the profound aquifer units varied between 10.5-33.0 mhos and are indicative of very good to excellent protective capacity rating. Thus, the underlying deep aquifer units are well protected from being contaminated.
Open Access
Application of Three Electrical Resistivity Arrays to Evaluate Resolution Capacity of Fractured Zones at Apatara Farms, Iwo, Osun State, Nigeria
(Journal of Applied Sciences and Environmental Management, 2017) Adeoti, L; Afolabi, O.S; Ojo, A; Ishola, S.K
The study applied three different electrical resistivity arrays (Wenner, dipole-dipole, and Pole-dipole) based on their resolution capacity to delineate fractured zones at Apatara Farm in Iwo, Osun State, Nigeria. Theoretical apparent resistivity data were computed for each model and contaminated with 5% Gaussian noise as a further concession to real field conditions. The simulated results revealed that the Wenner array gave the least error in trying to reconstruct the true model when the fractured zone is placed near the subsurface. However, when the fractured zone is placed at a depth beyond 5 m, the Dipole-Dipole array gave a better resolution than Pole-Dipole and Wenner array in decreasing order of resolution. The study further revealed that the Wenner array is less susceptible to edge effect at shallow depth while Dipole-dipole is more susceptible to edge effect at deeper depth followed by the Pole-dipole array. 2D electrical resistivity field measurements were carried out to confirm the results of the numerical simulation in the same field using the same parameters. The inverted resistivity images showed that the fractured zones are well delineated by the Dipole-dipole and Pole-dipole arrays but poorly resolved by the Wenner array. The study has demonstrated the usefulness of numerical modelling for imaging of fractured zone necessary for hydrogeological purpose and through modelling, the user has unlimited power to image or simulate a real-world scenario seamlessly before carrying out the actual field survey.
Open Access
Application of uphole seismic refraction survey for subsurface investigation: a case study of Liso Field, Niger Delta, Nigeria
(World Applied Sciences Journal, 2013) Adeoti, L; Ishola, K.S; Adesanya, O; Olodu, U; Bello, M.A
In this paper, an uphole refraction survey was carried out at the location of LISO Field in Niger Delta Nigeria in order to determine/estimate the thickness and velocities of the strata with a view to ascertaining the suitability of these layers for seismic reflection data acquisition and engineering structures. A hole drilled to a depth below the weathered layer contained hydrophones positioned at specific depths and dynamite charge as source of seismic energy. The uphole data were acquired using OYO McSeis seismograph. The time- distance plot obtained using IXsexsegy software was used for picking the first breaks arrivals of the signals. The depth of the weathered layer was obtained from these plots. The upsphere software was used to obtain the velocity of the different layers. The cuttings collected during the borehole drilling reveal sand, clay and gravel in which the sand sequence vary in sizes. Analyses of well-log show that the area of study is a two-layer model and the near surface geology is comparatively stable and inhomogeneous with moderate velocity contrast. The average thickness of the weathered layer to the top of the consolidated layer is 4.8m with an average velocity of 466m/s. The weathering thickness ranges from 2.9-8.9m and the velocity ranging from 362m/s to 689m/s. The consolidated layer velocities ranges from 1642m/s to 1884m/s with an average of 1746m/s sufficient enough to support engineering structures. In order to correct for weathering or statics a datum of about 6m deep would be required as this will eliminate the effect of the weathered layer on any proposed engineering structure to be developed in the area or its environs. This will also be suitable for the acquisition of good quality seismic data in the area. Also, mathematical linear regression models were generated relating the velocities of the layers and depth of the weathered layer which could be used for the prediction of one parameter in the absence of others provided they are within the same geologic environment.
Open Access
Effect of flood analysis on the foundation investigation using integrated approach
(Society of Exploration Geophysicists, 2015) Adeoti, L; Odunuga, S; Adegbola, R.B; Oladele, S
The effect of flood analysis on the foundation investigation of the proposed Gas-Fired Power Plant in Badagry, Lagos, Nigeria was carried out using geophysical, geotechnical and geographical information system (GIS) methods. The subsurface information was obtained by using two electrode arrays for the resistivity data acquisition. Geotechnical data were obtained through two boreholes via percursion drilling within the study area. The integration of geophysical and geotechnical data reveals that the subsoil materials comprises fibrous peat, organic silty clay, clayey sand, sandy clay and sand. The analysis of the subsoil conditions via geotechnical data shows the feasibility of foundation around 25 m via piling while the safe grade elevation has been worked out to be 6.672 m for 100yrs return period via GIS approach. Thus, in order to avoid adverse effect of flood on the proposed structure, the safe grade elevation value has to be added to the foundation floor.
Open Access
EXPLORING THE LINKAGES BETWEEN GEOPHYSICAL AND GEOTECHNICAL PROSPECTION TO DETECT FOUNDATION FAILURE OF BUILDINGS IN A WETLAND AREA OF LAGOS, SOUTHWESTERN NIGERIA
(Nigerian Research Journal of Engineering and Environmental Sciences, 2018) Adeoti, L; Opene-Odili, P.N; Oyedele, K.F; Oyeniran, T.A; Ishola, K.S; Ayuk, M.A
The geophysical and geotechnical methods were used to characterize the sub surface geologic units with a view to establishing the causes of foundation failure at Oyadiran Estate, Yaba, Lagos, Southwestern Nigeria. 2–D Electrical Resistivity Imaging, Vertical Electrical Sounding (VES) and Multichannel Analysis of Surface Wave (MASW) were acquired within the study area. Also, a Standard Penetration Testing (SPT) boring was acquired to constrain the geophysical methods. The results of 2–D resistivity and 1-D geoelectric sections delineated four to five geologic units. These correspond to topsoil, clay/peat, sandy clay, clayey sand and sand based on resistivity contrast ranging from 0.25 – 226 Ωm. The 2–D resistivity sections emphasized the lateral and vertical extents of the subsurface geological information. The MASW results revealed similar geologic units based on shear wave velocity discrimination except in a few cases which might be due to subsurface dip of the earth materials. An analysis of a typical geotechnical borehole has assisted to classify sand into loose, medium dense and dense based on SPT N-values and clay into very soft arising from cohesion (cu) value. This study has established that the clay materials with resistivity in the interval of 0.25 – 27 Ωm, Vs values 60 – 80 m/s2 and Cu of 12 -15 kN/ m2could be responsible for the foundation failure. Hence, the integration of 2–D Electrical Resistivity Imaging, VES and MASW complemented with a SPT boring has assisted to reduce this uncertainty by identifying the anomalous zones for detailed and cost effective geotechnical investigation.
Open Access
Fluid prediction using AVO analysis and forward modelling of deep reservoirs in Faith Field, Niger Delta, Nigeria
(Arabian Journal of Geosciences, 2015) Adeoti, L; Adeleye, K.O; Itsemode, A; Bello, M.A
Amplitude versus offset AVO analysis and forward modelling were used to predict the fluid type and seismic signature in a deep gas reservoir in faith field, Niger Delta. Well A, which identified the major deeper gas bearing reservoir in this field, was used in the modelling to predict what the seismic response would be away from this well at varying thickness and porosity ranges. The entire well was blocked into alternate layers of sand and shale lithotypes; the sands were fluid substituted from its initial in situ condition to 100 % brine saturation, and from the brine case, fluid substituted to 100 % oil and 100 % gas saturations. The elastic properties of these fluid substituted sands were estimated using the Gassmann equations and Batzle and Wang. The results were used in AVO analysis. Seismic forward modelling to determine the seismic wiggle signatures of these sands were also conducted. The variations of pertinent rock properties with depth of burial were also investigated. The results show that sand alpha (interval 10,400–10,650 ft) exhibited a typical class 3 AVO signature. Seismic wiggle response from top of this sand shows a distinct negative trough on the near angle stack and a much larger trough on the far stack. Sand beta (interval 11,700–12,050 ft) exhibited a typical class 2n AVO signature. Sand wedge model response shows increasing amplitudes from tops and bases of these sands as a function of thickness with the limits of seismic resolution shown by the tuning thickness. The gradient-stack plots, Hiltermann’s acoustic impedance (HAI) versus Poisson’s ratio (PR) plots and the AVO models suggest that the hydrocarbon-bearing sands will be distinguishable from sands with 100 % brine saturations. There is significant overlap between oil and gas plots because the oil was modelled as having a high gas oil ratio (GOR) of 3,586. The reservoirs at this level in Faith Field are either condensate or gas bearing. Seismic direct hydrocarbon indicator (DHI) and lithologic delineation are better defined in the shallower sand alpha than the deeper sand beta. These models have shown that any good quality seismic acquired over this prospect would be useful in deriving reservoir properties from seismic (RPFS) for these reservoirs and would be effective in lithologic differentiation or hydrocarbon identification.
Open Access
Geo-electrical investigation of Leachate Impact on Groundwater: A Case Study of Ile-Epo Dumpsite, Lagos, Nigeria.
(Journal of Applied Sciences and Environmental Management., 2011) Adeoti, L; Oladele, S; Ogunlana, F.O
In the past few decades, disposal sites have been filled with household refuse and different kinds of potentially dangerous industrial waste in an uncontrolled manner which poses an enormous risk for the environment, and are the main sources for groundwater contamination. With the aim of assessing impact of leachate on the underlying aquifers by determining and delineating possible leachate infiltration into the aquifer matrix ,Constant Spacing Traversing (CST) was carried out using Wenner array and spacing between 10-60 m along four 160 m – 180 m profiles. The results revealed the aquifer is characterized by low resistivity response generally below 4.5 ohm-m depicting possible contamination of the underlying aquifer from Oke-Odo landfill. The surface of the waste landfill is characterized by differential decomposition of waste as zones of advanced decomposition and fresh waste are reflected as low and high resistivity respectively. The absence of leachate in the aquifer 100 m from the studied area suggests that the leachate has not spread to this area, therefore, safe for groundwater exploitation. This study demonstrated the expeditiousness and effectiveness of the resistivity technique as a tool for geo-environmental mapping of leachate.
Open Access
Geoelectrical investigation of the groundwater potential in Mowe, Ogun State, Nigeria
(British Journal of Applied Science & Technology, 2012) Adeoti, L; Alile, O.M O. M; Uchegbulam, O; Adegbola, R.B
Electrical resistivity survey was carried out to delineate subsurface layers and to determine the ground water potential in the study area. The study was carried out using the ABEM SAS 1000 terrameter which worked on 16 vertical electrical sounding (VES) points within the area. A maximum distance of 550m current electrode spread was adopted for this survey. The result showed the presence of four geoelectric layers with the resistivity of the first layer ranging from 25.54Ωm to 619.45Ωm and thickness of 0.14-9.21m representing topsoil. The second geoelectric layer has resistivity ranging from 20.94Ωm to 706.82Ωm and thickness of 2.58 to 35.36m representing laterite. The third geoelectric layer has resistivity ranging from 12.29Ωm to 598.93Ωm and thickness of 3.33 to 58.06m representing sandy clay. The fourth geoelectric layer has resistivity ranging from 12.1Ωm to 1980.52Ωm and thickness of 11.4 to 45m representing sand. The depth to the aquifers are 13.11m, 55.31m, 6.35m, 50.28m, 51.08m and 28.01m in VES 1, 2, 6, 9, 11 and 16 respectively.
Open Access
Geophysical and geotechnical assessment of a failed canal.
(Society of Exploration Geophysicists, 2015) Adeoti, L; Kehinde, I; Jalekun, A.A; Adegbola, R.B
The integration of geophysical and geotechnical methods was used to assess a failed canal at Ijora Badia, Lagos Nigeria. The subsurface information was obtained by using two electrode arrays for the resistivity data acquisition. Geotechnical data were obtained through four boreholes via percursion drilling within the study area. The integrative approach reveals that the subsoil materials consist of peat, organic silty clay, clayey sand, silty sand, and sand. The study shows that low resistivity values exhibited by soft clay / peat and are possible cause of the collapse. The analysis of the subsoil conditions based on the proposed load of 60 kN/m2 imposed by canal structure on the peaty soil reveals settlement values of 365-843 mm which are too excessive for shallow foundation types. Also lateral and vertical thicknesses of the peat preclude the use of piling and vibroflotation. Thus, ground improvement using chemical grounding is proposed.
Open Access
Geophysical and hydrogeological evaluation of rising groundwater level in the coastal areas of Lagos, Nigeria
(Bulletin of engineering geology and the environment, 2009) Oyedele, K.F; Ayolabi, E.A; Adeoti, L; Adegbola, R.B
The paper reports the change in groundwater level observed in 30 wells in ten locations in southern Nigeria. Borehole data confirmed the electrical resistivity soundings which indicated the presence of topsoil, medium sand, sand, clayey sand and coarse sand. In some cases, there was little apparent change in the rate of groundwater rise, but from the data obtained it can be concluded that in the years 2000–2004 the average yearly rise was 0.3 m while between 2004 and 2007 it rose on average by 0.5 m. This rise in groundwater level has serious implications for both existing structures and the nature of the foundations for future building. The electrical resistivity survey was found to be a helpful tool in detailing the morphology of the groundwater surface and is recommended for ongoing monitoring.
Open Access
Geophysical investigation of saline water intrusion into freshwater aquifers: A case study of Oniru, Lagos State
(Scientific Research and Essays, 2010) Adeoti, L; Alile, O.M; Uchegbulam, O
A total of five electrical imaging lines were measured using the wenner configuration. And a total of twelve VES was carried out within the area of investigation. The lines were aligned almost in a linearly NS azimuths, perpendicular to the ocean. The results were presented as profiles, multi-profiles, maps, pseudo sections and inverted sections. Interpretations of these results involve both qualitative and quantitative deductions from 1D and 2D geoelectric models. WingLink software was utilized for plotting, filtering, modeling and iterations of the resistivity data. From the quantitative interpretation and nearby well log data five distinct layers were identified. The layers are dry and unconsolidated sand, clayey sand, saline sand, saline clay and freshwater sand. The resistivity of the topsoil varies from 3259.59 Ohm-m on VES 2 - 67.04 Ohm-m on VES 12. The resistivity of the freshwater sand varies from 1649.76 Ohm-m on VES 6 - 158.28 Ohm-m on VES 10. The resistivity of the saline layer (saline sand/clay) varies from 2.06 Ohm-m on VES 12 - 39.88 Ohm-m on VES 3. The depth to saline/freshwater interface varies from 12.97 m on VES 8 - 63.01 m on VES 5. The quality of groundwater varies from poor polluted saline water saturated sand/clay through intermediate water quality clayey sand/sand to freshwater sand. The interpreted results show saline water plumes where they occur in different part of the area investigated. The 1D and 2D results correlate to a very high degree indicating saline water intrusion between depth interval of 13 and 64 m in the study area. Two major freshwater aquifers (shallow < 6 m and deep > 60 m) where delineated with most of them occurring unprotected. The results showed the effectiveness and usefulness of electrical resistivity and induced polarization method in mapping saline water intrusion problem in coastal areas.
Open Access
An innovative technique for estimating water saturation from capillary pressure in clastic reservoirs
(Journal of African Earth Sciences, 2017) Adeoti, L; Ayolabi, E.A; James, L
A major drawback of old resistivity tools is the poor vertical resolution and estimation of hydrocarbon when applying water saturation (Sw) from historical resistivity method. In this study, we have provided an alternative method called saturation height function to estimate hydrocarbon in some clastic reservoirs in the Niger Delta. The saturation height function was derived from pseudo capillary pressure curves generated using modern wells with complete log data. Our method was based on the determination of rock type from log derived porosity-permeability relationship, supported by volume of shale for its classification into different zones. Leverette-J functions were derived for each rock type. Our results show good correlation between Sw from resistivity based method and Sw from pseudo capillary pressure curves in wells with modern log data. The resistivity based model overestimates Sw in some wells while Sw from the pseudo capillary pressure curves validates and predicts more accurate Sw. In addition, the result of Sw from pseudo capillary pressure curves replaces that of resistivity based model in a well where the resistivity equipment failed. The plot of hydrocarbon pore volume (HCPV) from J-function against HCPV from Archie shows that wells with high HCPV have high sand qualities and vice versa. This was further used to predict the geometry of stratigraphic units. The model presented here freshly addresses the gap in the estimation of Sw and is applicable to reservoirs of similar rock type in other frontier basins worldwide.
Open Access
An integrated approach to volume of shale analysis: Niger Delta example, Offrire Field
(World Applied Sciences Journal, 2009) Adeoti, L; Ayolabi, E.A; James, P.L
An integrated approach for the estimation of volume of shale from a suite of logs comprising the gamma ray, neutron-density combination, resistivity, combination of different methods (total) was carried in an Old Niger Delta Field called Orire with a view to ascertaining the reservoir quality and mapping reservoir bodies for further petrophysical analysis. The volume of shale (Vsh) calculation based on naturally occurring gamma ray frequently overestimates shale volume when encounters radioactive sand as sand appears shaly. In this situation, a Vsh calculation from neutron-density data yields a more accurate shale volume but in the presence of gas or light hydrocarbon, this approach is less accurate. The deficiency in this method is now addressed by Vsh calculation from the resistivity data. To avoid overestimation or underestimation of shale volume from any of the methods, the three methods were integrated to obtain Vsh total which finds the minimum value of all the methods. This approach distinguishes properly permeable bed (sand) from non-permeable bed (shale). Also from this method, the depositional environment was easily inferred.
Open Access
Investigation of a Proposed Four Storey Building Sites Using Geophysical and Laboratory Engineering Testing Methods in Lagos, Nigeria.
(International Journal of Scientific Research in Knowledge, 2014) Oyedele, K.F; Adeoti, L; Oladele, S; Akintunde, K
The spate of engineering structures collapse in Lagos metropolis with its attendant loss of lives and properties has assumed an alarming proportion in recent times. Efforts to mitigate such incidence has necessitated an integrated geophysical and geotechnical investigation of a proposed four storey building sites with a view to determine the suitability of the site for the proposed project. Resistivity investigation, un-drained multi-stage triaxial compression and oedometer consolidation tests were carried out to determine the engineering properties of the subsurface. The results revealed peaty clay to silty sand materials characterized by 35kN/m2 - 75kN/m2 cohesion values, (5°-13°) internal friction, 29.3% - 64.5% natural water content and 1.652 – 1.972 Mg/m3 bulk density. The allowable bearing capacity of 50 kN/m2, volume compressibility from 0.115m2/MN to 0.666 m2/MN, initial void ratio and consolidation coefficient of 0.779 - 1.381 and 2.7 m2/year - 8.3 m2/yearrespectively on the pressure range of 0 to 400 kN/m2 and estimated settlement values of 114 to 273 mm were obtained for the site materials. These results are indicative of soft to stiff clays and presence of sands and silts in the essentially clayey deposit. The study area is thus underlain by extensive zone of ductile and low strength founding materials having medium to high compressibility and settlement value that exceeds the tolerable limit suitable for founding a four storey building and should therefore be avoided. These characteristics preclude the use of conventional shallow foundations, piles or vibro-replacement up to a depth of 30 m.
Open Access
Lithology and fluid prediction from simultaneous seismic inversion over Sandfish field, Niger Delta, Nigeria
(Geosciences Journal, 2017) Adeoti, L; Adesanya, O.Y; Oyedele, K.F; Afinotan, I.P; Adekanle, A
Seismic inversion has been widely practiced in the oil and gas industry because it generates broad bandwidth of impedance data which maximizes vertical resolution and minimizes tuning effects. The lack of accurate prediction of lithology and fluid content of subtle features identified in seismic data acquired over the Sandfish field, Niger Delta, Nigeria necessitated the use of seismic inversion. In this paper, simultaneous seismic inversion is adopted to integrate seismic and well data for quantitative interpretation and uncertainty assessment of the subsurface reservoirs in the Sandfish field. Three Sandfish (Sfn) wells with the required petrophysical logs, check-shot data, high quality 3D seismic data of five angle stacks (6–12°, 12–18°, 18–26°, 26–32°, and 32– 42°) were used for the analysis. A feasibility study including cross-plots of petrophysical and elastic properties from well data was first carried out to establish rock property relationships in the interval of interest. Biot-Gassmann fluid substitution analysis was also used to reveal sensitivity of rock properties to pore-fill type. Low frequency (0–2 Hz) models were generated from interpolation of highcut-filtered P-sonic, S-sonic, and density logs guided by interpreted seismic horizons. The low frequency models were used to broaden the spectrum to estimate elastic volumes. The five partial angle stacks were simultaneously inverted using Jason’s Rock-Trace® inversion software which iterated trial inversions until the model sufficiently matched the seismic data. The inverted P-impedance (ZP), Simpedance (ZS), and density (ρ) were used to derive Poisson’s ratio (σ), volume of sand (Vsand), lambda-rho (λρ), and mu-rho (μρ). The cross-plot of λρ with μρ from well data looks similar to that from inverted results. Sands and shales are discriminated on the basis of sands having low values of μρ. Hydrocarbon-bearing sands are differentiated from water-bearing sands and shales on the basis of having lowest values of λρ. The Biot-Gassmann fluid substitution analysis at reservoir N-01 reveals typical class III amplitude variation with angle (AVA) responses for low-impedance hydrocarbon sands. The lithology and fluid prediction maps extracted from Vsand and σ at the N-01 seismic horizon show variation in lithology and fluid types for the entire volume. The inversion products reveal heterogeneities in the reservoirs away from well control validated by a blind well test. Hence, the study shows that rock-property model from a simultaneous inversion is an effective predictive tool for lithology and fluid types which in turn can guide well placement and predict reservoir development in the field of study.
Open Access
ON THE EFFECTIVENESS OF USING QUANTITATIVE AVO ANALYSIS IN FLUID AND LITHOLOGY DISCRIMINATION IN AN OFFSHORE NIGER
(Ife Journal of Science, 2019) Adeoti, L; Ikoro, C.O; Adesanya, O.Y; Ayuk, M.A; Oyeniran, T.A; Allo, O.J
Quantitative Amplitude Variation with Offset (AVO) analysis of “Jay” Field, offshore Niger Delta, was carried out with a view to properly discriminating fluid and lithology using near, mid and far offset seismic and well data. Seismic and well data were interpreted and analyzed. Synthetic seismogram was generated using density (r) and sonic logs. AVO modeling, seismic AVO attribute analysis and AVO inversion were carried out and the results from well log interpretation using 70-API gamma-ray cut-off, neutron-density over lay and resistivity logs revealed that the field consists of intercalation of sand and shale with typical deltaic depositional environment log signatures. Four identified sand reservoirs (a, b, c and d) with high resistivity values and negative separation in the neutron-density overlay suggested that the field was hydrocarbon bearing probably containing gas or condensate. Two sand reservoirs showed good rock physics results, 'Sand a' at 11,632 ft TVD with 18% porosity (ϕ), 0.25 water saturation (S ), decreasing ratio of compressional wave velocity to shear wave velocity (V /V ) w p Sand Poisson's ratio () relative to the background shale signified AVO response typical of a hydrocarbon bearing sand. 'Sand e' at 5,925 ft TVD, with 30% ϕ, Sw of 1, no change in V /V and relative to the background shale p Simplied that an AVO response was unlikely. Gradient analysis result for the synthetic seismic at the top and base of the two sands agreed with Rutherford's classification scheme for class IV AVO for 'Sand a' and no AVO response for 'Sand e'. AVO attribute analysis and impedance inversion of the seismic volumes confirmed AVO result for the two sands. The study established that AVO technique could be effectively used for fluid and lithology discrimination in the “Jay” Field, Niger Delta.
Open Access
Reservoir fluid determination from angle stacked seismic volumes in ‘Jay’field, Niger Delta, Nigeria.
(Journal of Applied Sciences and Environmental Management, 2018) Adeoti, L; Allo, O.J; Ayolabi, E.A; Akinmosin, A; Oladele, S; Oyeniran, T; Ayuk, M.A
The study was carried out to investigate the dissimilar seismic amplitude responses observed in sandstone reservoirs with the same fluid saturation. This challenge now informed the analysis of different amplitude responses from the ‘Jay’ Field in order to verify the reservoirs fluids around and away from well location based on the integration of Amplitude Variation with Angle (AVA) and seismic inversions. The well log data provided were used to identify hydrocarbon bearing zones and Poisson Ratio analysis. Anomalies from the AVA analysis were investigated using the elastic impedance inversion of the near and far volumes. Crossplots of Lambda-Mu-Rho inversion were produced to relate reservoir incompressibility and rigidity modulus for lithology and fluid determination. Sand E exhibited amplitude increase with angles at well point and also away from well location (red triangle). The approximate elastic impedances of the inverted seismics are almost similar to the log estimates, an indication of good correlation. Integration of incompressibility (Lambda-Rho) and rigidity (Mu-Rho) modulus analyses reveals the presence of gas saturation in reservoir Sand G because low Lambda-Rho coincides with high Mu-Rho from both log estimates and inverted seismics. In the case of Sand D, high Lambda-Rho coincides with high Mu-Rho because it is oil saturated. This study has helped to differentiate the fluids in Sands D and G despite having similar AVA responses. The methods adopted in this work can be useful in hydrocarbon detection from seismic data in fields with similar geological setting.
Open Access
Seismic and petrophysical evidence of abnormal pore pressure in western Niger delta
(Arabian Journal of Geosciences, 2015) Adeoti, L; Olatinsu, O.B; Ishola, K.S; Ogofa, M
A detailed pore pressure evaluation of Tango Field, western Niger Delta, was carried out with the aim of ascertaining depth to overpressure which enables proper well planning and designing in order to reduce cost of exploration and exploitation. The evaluation was carried out using both petrophysical data consisting of sonic, density and resistivity logs obtained in five wells drilled in the area and high resolution-seismic reflection data from which the average and interval velocities were computed. Crossplots were made for well logs data which were fitted with regression curves, and trend lines in order to establish overpressure patterns. Plots of overburden, fracture and hydrostatic gradients with leak off test (LOT), mud weights and modular dynamic tester (MDT) were made to validate the trends established from the crossplots. The results obtained show that normal compaction trends (NCT) were established for all the data used in the analysis and all the wells except well 5 which showed obvious deviations from these trends. Well 5 encountered overpressure at 8,000 ft which was considered earlier than anticipated, hence, it was abandoned. Top of overpressures for wells 2 and 4 were estimated between 9,000 ft and 12, 000 ft respectively. Porosity versus vertical effective stress from the plots confirmed the above depth to overpressure which reveals that the overpressures are primarily generated by disequilibrium compaction.
Open Access
Seismic refraction and resistivity studies of part of Igbogbo township, south-west Nigeria
(Journal of Scientific Research and Development, 2009) Ayolabi, E.A; Adeoti, L; Oshinlaja, N.A; Adeosun, I.O; Idowu, O.I
Seismic refraction shooting and Electrical resistivity depth sounding have been carried out at Igbogbo (Ikorodu area, Southwest Nigeria) to determine the structural setting of the subsurface materials and groundwater potential. A total of eighteen vertical electrical sounding using the schlumberger array of 500m maximum spread and twenty-seven seismic refraction data using forward and reverse shooting methods of lateral distance 42m along each profile were acquired within the study area. The results indicate the presence of three seismic refraction layers with the first layer having velocity 150-366m/s and thickness 1.0-3.3m, representing topsoil. The second refraction layer is composed of lateritic clay with thickness 4.5-10.5m and velocity 578-878m/s. The third refraction layer consists of sandy clay with velocity 1000- 2500m/s. The delineated refraction layers are characterized by increase in velocity with depth. The geoelectric sounding clearly show that the subsurface layers are characterized by topsoil, laterite, sandy clay, clayey sand, sand and clay with sand acting as aquifer units. The two thick aquifer units mapped are capable of sustainable industrial development in the area. The seismic refraction shooting was able to delineate three layers because of the energy source used which is consistent with the first three layers in geoelectric sounding. To attain deeper depths of penetration using seismic refraction method, a stronger energy source is recommended.
Open Access
Static reservoir modeling using well log and 3-D seismic data in a KN field, offshore Niger Delta, Nigeria
(International Journal of Geosciences, 2014) Adeoti, L; Onyekachi, N; Olatinsu, O; Fatoba, J; Bello, M
This study focuses on the application of 3D static model using 3-D seismic and well log data for proper optimization and development of hydrocarbon potential in KN field of Niger Delta Province. 3D Seismic data were used to generate the input interpreted horizon grids and fault polygons. The horizon which cut across the six wells was used for the analysis and detailed petrophysical analysis was carried out. Structural and property modeling (net to gross, porosity, permeability, water saturation and facies) were distributed stochastically within the constructed 3D grid using Sequential Gaussian Simulation and Sequential Indicator Simulation algorithms. The reservoir structural model show system of different oriented growth faults F1 to F6. Faults 1 and Fault 4 are the major growth faults, dipping towards south-west and are quite extensive. A rollover anticline formed as a result of deformation of the sediments deposited on the downthrown block of fault F1. The other faults (2, 3, 5 and 6) are minor fault (synthetic and antithetic). The trapping mechanism is a fault assisted anticlinal closure. Results from well log analysis and petrophysical models classified sand 9 reservoir as a moderate to good reservoir in terms of facies, with good porosity, permeability, moderate net to gross and low water saturation. The volumetric calculation of modeled sand 9 horizon reveals that the (STOIIP) value at the Downthrown and Ramp segment are 15.7 MMbbl and 3.8 MMbbl respectively. This implies that the mapped horizon indicates hydrocarbon accumulation in economic quantity. This study has also demonstrated the effectiveness of 3-D static modeling technique as a tool for better understanding of spatial distribution of discrete and continuous reservoir properties, hence, has provided a framework for future prediction of reservoir performance and production behavior of sand 9 reservoir. However, more horizontal wells should be drilled to enhance optimization of the reservoir.

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