A. A. Okiwelu

University of Calabar

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E. E. Okwueze

University of Calabar

I. A. Ude

University of Calabar

V. I. Obianwu

University of Calabar

I. B. Osazuwa

Federal University Oye Ekiti

Iosr Journals

Christ University

Atan Obeten Egor

Cross River University of Technology

Emi Ohara

Japanese Red Cross Nagoya Daini Hospital

Chibuike Akpa

Ebonyi State University

I. B. Osazuwa

Federal University of Petroleum Resource Effurun

K. M. Lawal

Ahmadu Bello University

Cooperative Institutions

University of Calabar

King Saud University

Suez University

Vietnam National University, Hanoi

Cross River University of Technology

Ebonyi State University

Federal University of Petroleum Resource Effurun

Ahmadu Bello University

Al-Azhar University

Japanese Red Cross Nagoya Daini Hospital

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Delineation of deep-seated crustal structures from magnetic data in the southeastern part of the Niger Delta basin, Nigeria

Frontiers in Earth Science (2024)

Ohara E. Eze A. A. Okiwelu Stephen E. Ekwok Kamal Abdelrahman Hassan Alzahrani

Regional magnetic data in the southeastern segment of the Nigerian Niger Delta were evaluated with the aim of mapping deep-seated tectonic elements. Enhanced filtering operations and 3D forward modelling were applied on the magnetic data. These geologic features triggered the formation of rollover anticlines and faults that serve as structural traps in the study area. The filtered residual magnetic data revealed geologic structures characterized with NE - SW, N - S, and E - W orientations. The 3-D models detected the faulted crustal blocks, gradient zones, and intra-basement compositional magnetic variations. Furthermore, some prominent horst and graben structures as well as related normal faults characterized with distinct magnetic signatures were observed. Faults of base magnetic (of various compositions) were observed to be the fabricating mechanisms of the magnetic anomalies. Collectively, these structures influenced the patterns of magnetic anomalies with direct effects on the hydrocarbon trapping systems, as well as the pathways and accumulation zones for hydrothermal minerals. On the whole, the interpreted results revealed that the basement surface is rippling. Additionally, the depth result showed sedimentary thicknesses that ranged from 4–10 km. Again, the estimated crustal thickness varied from 14 to 19 km. This study has displayed the capabilities of the magnetic method in mapping the depth and configuration of basement rocks, which are crucial in controlling the formation of structural traps. Identifying these basement structures early helps in understanding the overall geological framework and potential hydrocarbon systems.

Niger delta

Southeastern Nigeria

10.3389/feart.2024.1439199

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Citations (1)

Spherical harmonic representation of the geomagnetic fields in the Nigeria sector of the Niger delta basin

American Journal of Scientific and Industrial Research (2010)

A. A. Okiwelu E. E. Okwueze I. B. Osazuwa

A 0.5 0 x 0.5 0 representation of the geomagnetic elements and their rates of change have been predicted for the Nigeria sector of the Niger Delta basin using the spherical harmonic analysis.The geomagnetic elements computed are the total field (F), horizontal field (H), north component (X), east component (Y), vertical component (Z), declination (D), inclination (I) and their rates of change,

Niger delta

Representation

10.5251/ajsir.2010.1.2.190.202

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Magnetic anomaly patterns, fault-block tectonism and hydrocarbon related structural features in the Niger Delta basin

Figshare (2014)

Iosr Journals A. A. Okiwelu

Niger delta

Anomaly (physics)

Hydrocarbon exploration

Fault block

10.6084/m9.figshare.1179358

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3D Modelling and Basement Tectonics of the Niger Delta Basin from Aeromagnetic Data

InTech eBooks (2012)

A. A. Okiwelu I. A. Ude

Magnetic anomalies are a result of two things: a lateral contrast in rock composition (lithology) or a lateral contrast in rock structure [6], [7].Where there is no contrast in magnetization no anomaly is produced.The magnetization could be due to normal induction in the Earth's field or due to remanent magnetization.For accurate modeling and interpretation of magnetic data it is important to recognize and incorporate the remanent component where they exist.Magnetic anomaly transformation/enhancement provides the opportunity to unravel the basement structure and lithology.Such information is not readily available from the total intensity data sets especially if they are of low resolution.Our objective in this study is to demonstrate the relationship between basement framework, magnetic expression and hydrocarbon prospect in the Niger Delta basin using 3-D modelling and enhancement data sets.In the Tertiary Niger Delta basin exploration (seismic) for hydrocarbon is confined to the sedimentary section despite the fact that basement structure analysis has been used in locating hydrocarbon targets in other sedimentary basins of the world.We show that the geodynamics of the deep basement are important phenomena to the explorationist and could be an important factor that can directly lead to the risk assessment of specific prospect sites in hydrocarbon exploration.Specifically, we demonstrate that basement structure in the offshore Niger Delta have control on oil and gas discoveries even though the basement is known to be beyond drillable depths.It is not possible to prove basement control neither with subsurface mapping, as few wells penetrate basement, nor with seismic, as the basement reflector is not always mappable; residual aeromagnetics is the principal technique used in mapping basement and it is generally applied only to outline the basement fault block pattern [8].[9] used aeromagnetic data to show that axis of hydrocarbon pool in Alberta basin is coincident with the strike of the basement sourced magnetic signals.[10] reported the relationship between tectonic evolution and hydrocarbon in the foreland of the Longmen Mountains and showed that superimposed orogenic movement and related migration of sedimentary basins controlled the generation, migration, accumulation and disappearance of hydrocarbons.[11] reported three-sets of traps from geophysical and geological data in offshore United Arab Emirate of which one is basement related.

Niger delta

Basement

10.5772/48158

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Citations (10)

Determination of Nigerian Geoid Undulations from Spherical Harmonic Analysis

Applied Physics Research (2011)

A. A. Okiwelu E. E. Okwueze Ikechi Ude

Geoid undulation has been determined for Nigeria in order to demonstrate its relationship with topography and the dynamic structure of the Earth’s interior. Spherical harmonic expansion using the Earth Gravitational Model 2008 (EGM2008) referenced to the WGS84 (World Geodetic System 1984) with coefficients extending to degree 2190 and order 2159 was found suitable for the determination of geoid undulation. The results from the analysis show that the Nigerian geoid undulations are positive and show overall good correlation with topography. The internal origin of the geoid undulation is attributed to excess mass beneath the ellipsoid. This internal mass distribution extend deep into the mantle. The highest geoid undulations are centered over the North central region of Nigeria with relatively lower values confined to the Nigerian sedimentary basins. The lowest geoid undulation values are within the oceanic areas.

10.5539/apr.v3n1p8

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Isolation of Residuals Determined from Polynomial Fitting to Gravity Data of Calabar Flank, Southeastern Nigeria.

A. A. Okiwelu I. B. Osazuwa K. M. Lawal

The first degree polynomial order is fitted to the Bouguer gravity anomaly data to produce the first residual gravity anomaly map of Calabar Flank. The residual gravity data was computed by subtracting the regional trend from the Bouguer gravity field. The regional trend in the flank is the first degree surface fit and represents anomaly of long wavelength while the residual component have their origin from short wavelength sources (shallow sources). This quantitative approach is advantageous over the wavelength filtering methods. The result of this low order fitting shows that the residual gravity field is characterized by positive and negative gravity anomalies. This is consistent with the geologic setting and tectonics of the Calabar Flank. (Keywords: Bouguer gravity anomaly data, Calabar Flank, gravity field)

Flank

Anomaly (physics)

Free-air gravity anomaly

Density contrast

Source

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Citations (6)

Determination of sediments thickness in part of Lower Benue Trough, Nigeria, from the residualization of aeromagnetic data: Implication for diversification of the Nigerian economy

Applied Journal of Physical Science (2020)

O. P. Akpan A. A. Okiwelu E. E. Okwueze

Aeromagnetic data were used in the study to determine the sediment thickness in the Lower Benue Trough. To achieve the objectives of the study, geophysical techniques were employed to analyze four aeromagnetic maps on a scale of 1:100,000, covering parts of the Lower Benue Trough. These include map merging, polynomial fitting, directional derivatives and forward modeling. Nine (9) profiles were modeled to determine sediment thickness, presence of possible intrusives and the subtle structural features and their trend within the study area. Results from this study revealed the existence of many intrusives which were majorly granite and basalt rocks which suggests complex tectonic events which accompanied the evolution of the Benue Trough. Lineament orientation revealed is majorly NE-SW direction and other directions were NW-SE, E-W and N-S. A sedimentary thickness ranging from 7 to 10 km were suggested by a 3D forward modeling, and this estimated depth did not coincide with an average of 5 km suggested by earlier researchers. Huge variations within the basement complex are however induced by the presence of horst structures as well as graben and this is profound within the depocenters where sedimentary pile is thicker. Magnetic sources within the sediment in Abakiliki, Udi and Nkalagu areas have potentials for hydrocarbon accumulation due to the thickness of the sediments in these parts of the study area. However, Bansara area reveals the presence of lots of intrusives, indicating high geothermal regimes that may not be favourable for hydrocarbon accumulation but have high potentials for solid mineral resources. Therefore, the Bansara area is recommended for organised and formal solid mineral exploration, which can apparently diversified the economy of Nigeria.

Trough (economics)

Echelon formation

Horst and graben

Mineral resource classification

Lineament

Horst

Basement

10.31248/ajps2020.031

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Magnetic anomaly patterns, fault-block tectonism and hydrocarbon related structural features in the Niger Delta basin

IOSR Journal of Applied Geology and Geophysic (2014)

A. A. Okiwelu V. I. Obianwu Emi Ohara I. A. Ude

Gridded airborne magnetic data, 3D magnetic forward models in combination with filtered maps and derivative techniques such as analytic signal and directional derivatives were used to reveal basement structure and architecture of the study area in offshore Niger Delta.The generating mechanisms of the magnetic anomalies are boundaries (fault) of basement blocks of different compositions having different physical properties (susceptibilities and remanence) and horst/graben structures with associated normal faults and extensions.The intrabasement sources exhibit anisotropic susceptibilities and depth to basement (sedimentary thickness) is between 4000m to over 10,000m indicating deep depocenters.All these factors combined to influence magnetic anomaly patterns which have implications in hydrocarbon prospect target.The regional structural characteristics of the basement interpreted from the regional magnetic data sets show clear relationship between inferred rift-related basement structures and oil fields.Oil and gas discoveries appear to be located on the flanks of steep/faulted basement and on top of basement structural highs and lows.This study, therefore, is significant in understanding the petroleum system, contributes to basin modelling and can unravel areas of identical structural development in less well-explored sectors of the basin.

Niger delta

Anomaly (physics)

Hydrocarbon exploration

Fault block

10.9790/0990-02113146

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Citations (9)

Alternative models for the interpretation of aeromagnetic data in areas around the

Global Journal of Pure and Applied Sciences (2001)

A. A. Okiwelu

Four interpretational models are recognized in areas around the magnetic equator. They are point pole, line of poles, point dipole and line of dipoles. Point pole models are recognized by adjacent circular contours of magnetic high and low, while line of poles models are identified by elliptical contours of magnetic high and low adjacent to each other. When magnetic contours are simply circular or nearly circular, the source is approximated as point dipole and contours of line of dipole model are always elliptical in shape. A decision between dipolar and monopolar model is made using the shape of magnetic signature. When a magnetic signature has completely dominant low, the correct model will be a dipole. While a magnetic high flanked by low is approximated as point pole/line of pole (monopole). Magnetic signature that does not assume any of these shapes is a pointer to remanent magnetization. The four interpretational models have close relationship with half-width of magnetic anomalies and are therefore valuable for depth determination. The four interpretational models have been employed to analyse aeromagnetic data from crystalline basement and sedimentary areas of Nigeria. Global Journal of Pure and Applied Sciences Volume , No 1 January (2001) pp. 111-116 KEY WORDS: Equator, Model, Dipole, Remanent, Anomaly.

Equivalence point

Line (geometry)

10.4314/gjpas.v7i1.16214

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Strategies for Accurate Determination of Drift Characteristics of Unstable Gravimeter in Tropical, Coastal Environment

Applied Physics Research (2011)

A. A. Okiwelu E. E. Okwueze I. B. Osazuwa

The drift characteristics specific to an unstable gravimeter has been modeled to enhance high quality data that will be useful for gravimetric studies and to determine proper timing of field observations. A pre-field observation was carried out to monitor the tide and thus limiting the relative gravity observation to near-linear time window. Closed loop sequence technique of re-occupying a drift base compatible with the drift characteristics of the Lacoste and Romberg (model G446) and cascade model for the computation of drift were combined to obtain a more reliable data that fulfills the linear drift assumption. Subjecting the modelled drift to descriptive statistics a maximum value (1.6550mGal) and minimum value (- 0.3720mGal) of drift were obtained. This variability in drift values and the disparity between the mean (0.099mGal) and the standard deviation (0.2914mGal) is a pointer to various factors that caused the instrumental drift. Such factors could be attributed to external temperature, age and usage of the gravimeter, mechanical stress and strain in the mechanism as the gravimeter is moved and subjected to vibrations. The low standard error of the mean (0.0196mGal) is a reflection of the validity of the linear drift assumption using the cascade model and the field procedure compatible with the drift characteristics of the gravimeter.

Gravimeter

10.5539/apr.v3n2190

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Citations (2)