Papers by Ndifreke I. Udosen
Results in earth sciences, Jul 1, 2024
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Discover geoscience, Jun 11, 2024
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Water practice and technology, May 14, 2024
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Results in earth sciences, Dec 1, 2024
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Water practice and technology, Jan 31, 2024
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Research Square (Research Square), Oct 16, 2023
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Research Square (Research Square), Oct 24, 2023
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Geomechanics and geophysics for geo-energy and geo-resources, Jul 5, 2018
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Modeling Earth Systems and Environment, 2018
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Modeling Earth Systems and Environment, 2018
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Modeling Earth Systems and Environment, 2018
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Journal of Coastal Conservation, 2017
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73rd EAGE Conference and Exhibition incorporating SPE EUROPEC 2011, 2011
We present a new 3D gravity-inversion approach that retrieves the geometry of an isolated geologi... more We present a new 3D gravity-inversion approach that retrieves the geometry of an isolated geologic source with density contrast and depth of the top known. We approximate the source by an ensemble of vertically juxtaposed 3D right prisms whose horizontal cross-sections are described by polygons and thicknesses are fixed. The polygon vertices of each prism are described by polar coordinates with an unknown origin within the prism. Our method estimates the horizontal Cartesian coordinates of the unknown origin and the radii of the vertices of each polygon. To obtain stable estimates we impose constraints on the source shape. The estimated solution, despite being stable and fitting the data, will depend on the maximum depth assumed for the set of 3D prisms. We also propose a new criterion to determine the optimum depth-to-bottom estimate of the source based on the curve of the estimated total-anomalous mass versus estimated data-misfit measure for the range of different tentative maximum depths considered. Applications to both synthetic and field data show that our method obtains stable solutions that recover the geometry of the 3D source and fit the data, even in the case of a complex simulated body with variable dips and strikes.
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London 2013, 75th eage conference en exhibition incorporating SPE Europec, 2013
We describe the automated search for optimal electrode locations for a 2D resistivity tomography ... more We describe the automated search for optimal electrode locations for a 2D resistivity tomography problem within a meta inverse framework. The framework is incorporated into a forward solver developed for simulating synthetic resistance data, and an inverse solver developed for reconstructing the resistivity distribution. Numerical results obtained from applying these schemes to search for a circular high resistance anomaly are presented. These results show that the meta inverse framework is successful in finding the optimal electrode array locations at which best reconstructions of the resistivity distribution can be obtained.
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London 2013, 75th eage conference en exhibition incorporating SPE Europec, 2013
We describe the design and application of new forward and inverse solvers developed for simulatin... more We describe the design and application of new forward and inverse solvers developed for simulating synthetic resistance data and reconstructing the resistivity distribution of the subsurface in electrical resistivity tomography. The forward solver is based on the finite integration technique; the inverse solver is a domain search algorithm. These solvers were developed as necessary forward and inversion modelling tools to enable the optimisation of electrode positions in resistivity imaging to be explored. Numerical results from implementing these solvers show that they are successful for simulating and reconstructing the resistivity distribution in electrical resistivity tomography.
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Water Practice & Technology
Groundwater contamination is of global concern. The study area (Ikot Ekpene–Obot Akara Local Gove... more Groundwater contamination is of global concern. The study area (Ikot Ekpene–Obot Akara Local Government Areas) continues to experience a swift increase in human population and associated economic activities, leading to the generation of more waste. The fundamental goal of this work is therefore to weigh up the groundwater standard through hydrogeochemical investigation of groundwater samples and the susceptibility potential of the economically exploited aquifer units in the area. The results of the electrical geo-sounding data acquired at 28 locations in the area reveal three to four lithological successions comprising fine/coarse sands and gravels amid patches of thin clay interbeddings at several places. The primary aquifer is the third layer, which is between 10.5 and 101.5 m deep with resistivity values between 359.4 and 2,472.8 Ωm. The hydrogeochemical evaluation of groundwater samples in the area shows that the measured physicochemical parameters are well within the World Heal...
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Geophysical techniques were employed to evaluate the extent of a major coastal aquifer's vulnerab... more Geophysical techniques were employed to evaluate the extent of a major coastal aquifer's vulnerability to near-surface and subsurface contamination with the use of GOD and AVI vulnerability models in Akwa Ibom State, Southern-eastern Nigeria. The study area is strongly dependent on groundwater resources, hence it was important to evaluate the extent of aquifer vulnerability. Interpretations of the resistivity inversion models, constrained by well information, indicated the presence of three lithological layers (motley top soil, fine sand, and coarse sand). The resistivities of the first layer were generally larger than those of the underlying subsurface layers, indicating the percolation of contaminant material into the surrounding aquifer.
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Fracture characteristics were quantified at a site underlain by limestone bedrock in Spaunton Moo... more Fracture characteristics were quantified at a site underlain by limestone bedrock in Spaunton Moors, North Yorkshire, England, with the use of electrical resistivity tomography and azimuthal square arrays. The electrical resistivity tomography survey was conducted to generate a two-dimensional picture of the subsurface. The azimuthal square array survey was conducted to characterize electrical anisotropy due to similarly oriented fractures within the Coralline limestone. Values of fracture strike obtained from graphical analysis of the square array data corresponded with values obtained from geological mapping of the quarry face. On the square array polar plots, the fracture zone was where resistivity was lowest. Secondary porosity was estimated to range between 20 and 27%. This range of values was interpreted to be a result of foliation. The azimuthal inhomogeneity ratio, computed to estimate the severity of lateral resistivity variations on the site, had a value averaging 0.7. This implies that the effects of lateral resistivity variations are not very severe. Electrical anisotropy observed on the study location is due to the presence of fractures. The lateral variations in resistivity are due to lithological heterogeneities within the bedrock. Square array detected anisotropic behavior within the bedrock in spite of overburden effects. The azimuthal square array technique is therefore useful for characterizing fractures and for quantifying anisotropy within the bedrock to generate results consistent with that obtained from geological mapping of existent outcrops.
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Evidently, sedimentary basins have a large potential for groundwater. However, the main issue has... more Evidently, sedimentary basins have a large potential for groundwater. However, the main issue has been the aquifer system's susceptibility to contamination coming from both anthropogenic and natural sources. This research was designed with the intention of valorizing the unique
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has been of a serious concern in recent times. Consequently, this study's major goal is to evalua... more has been of a serious concern in recent times. Consequently, this study's major goal is to evaluate groundwater potentiality and quality in the LGAs via the use of the electrical resistivity technique and geochemical analysis of borehole water samples to map out the zones for the optimum location of boreholes in the area. The results of the Vertical Electrical Soundings (VES) performed at 28 locations in the area show that the lithological succession comprises sands and gravels with minor clay interbeddings at a number of locations. The main aquifer units in the area are found at depths of between 2.1 and 30.2 m, with resistivity values ranging from 40.6 to 2648.1 Ohms-metres. The generated groundwater potentiality map indicates that 89 % of the investigated area has high groundwater potential while 7 % and 4 % have low and moderate potentials respectively. The contamination level in the groundwater is shown to be very low or insignificant. Policymakers in the LGAs can use these insights to effectively manage and utilize groundwater to meet the needs of the masses.
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Papers by Ndifreke I. Udosen