Browsing by Author "Raji, Wasiu O"
Now showing 1 - 20 of 26
Results Per Page
Sort Options
Item 2D electrical resistivity imaging of tantalite- bearing veins in Kaiama, Nigeria(Taylor and Francis, 2022) Raji, Wasiu O; Bale, Rafiu, BThe utility of the electrical resistivity (ER) method of geophysics for delineating tantalite-rich zones is demonstrated. To avoid negative environmental consequences, the local authority refused the use of trial-and-error method by the artisanal and small-scale miners. 2D ER method was applied to delineate the locations and dimensions of the tantalite-rich zones. Data were acquired along nine profiles in the study area at predetermined locations, after reconnaissance field mapping, using SuperSting R8/IP Earth Resistivity Metre, 84 electrodes, and the full accessories. Each profile was 249 m long with 84 electrodes coupled to the ground at 3 m intervals on a straight line following the dipole–dipole electrode array. Data acquired were processed to obtain tomographic images of the subsurface. The results revealed low resistivity anomalies (1–60 Ωm) corresponding to tantalite-rich quartz veins that intruded into the high-resistive migmatite-gneisses-schist complex. The tantalite-rich zones were located at depths ranging from near-surface to about 45 m, their lengths and thicknesses range from 40 to 220 m and 3 to 32 m, respectively. A pit dug along profile six confirmed the low resistivity structures to be tantalite-rich quartz veins. Findings from the study are useful for economic evaluation of similar deposits, determining the extent of excavation required for mining, and planning land reclamation.Item Application of 2-D resistivity survey to groundwater aquifer delineation in a sedimentary terrain: A case study of south-western Nigeria(European water Resources Association, 2017) Raji, Wasiu O; Aluko, Khadijat, O; Ayolabi, Elijah, AThis study demonstrates an application of two-dimensional resistivity surveys to groundwater exploration in a problematic sedimentary terrain where thick clay layers impedes groundwater aquifer recharge. The objectives of the study are to (i) select locations for citing new boreholes and (ii) investigate causes of the failure of the two boreholes previously drilled in the area. Six profiles of 830 m length each were surveyed to probe the subsurface lithologies and their groundwater potentials. Data acquisition system comprised a Super Sting Resistivity Meter, 84 metallic electrodes, and their accessories. Data acquired from the survey were forward modeled and tomographically inverted, using finite difference techniques. Results of the study revealed the different rock layers beneath the survey lines, their spatial distribution and their resistivities. Two new boreholes, BH3 and BH4, drilled based on the inverted 2-D resistivity images are very productive and have respective yields of 46 l/s and 48 l/s in the dry season. The choice of the locations for the new boreholes was informed by the presence of low resistivity structures interpreted as saturated (wet) sand, good vertical and lateral extents of the saturated sands, the depth of the aquifer in relation to the water table, and the absence of impermeable (sandy clay) cover that could retard groundwater recharge and discharge. The resistivity images of the 2-D survey also show that the failed boreholes – BH1 and BH2 were located on low resistivity structures interpreted as aquifers. But the aquifers have limited vertical and lateral extents, and are adjacent to thick impervious sandy-clay layer. Overall, the study demonstrates the suitability and the superiority of 2D resistivity survey to the traditional 1D – four electrodes survey.Item Assessment of Carbon dioxide storage capacity of Selected aquifers in J field, West Africa.(2022) Raji, Wasiu O; Bello, Omotayo, S.; Adeoye, Taiye, O.A combination of seismic data and petrophysical logs from five wells acquired in ‘J’ Field, Niger Delta, Nigeria, have been analyzed to assess the carbon dioxide (CO2) storage potential of some saline aquifers in ‘J’ field. The study aims to evaluate the volume of CO2 that can be potentially stored in the aquifers and the risk of CO2 leakages in the storage. The sand aquifers were correlated across the five wells to evaluate their thicknesses and lateral extent. Porosity, permeability, formation water resistivity, and net sand thickness were estimated in the different wells. The Horizons corresponding to the top of the aquifers was mapped, and time and depth structured maps were generated for structural analysis and volumetric estimations. The risk of CO2 leakages through sealing layers (cap rocks) was evaluated in terms of caprock integrity and pore pressure sealing mechanism. Results of the study showed that four aquifers, namely, L20, N30, M40, and P50, are laterally extensive across the five wells and have thicknesses that range from 14 to 352 m. The individual CO2 storage capacity of L20, M30, N40, and P50 was estimated to be 6.97×1010, 1.48×1010, 7.78×109 and 1.49×1010 tons, respectively. The combined aquifer storage capacity was estimated to be 1.07×1011 tons. The sealing layers have low risk of CO2 leakages. The study concluded that the aquifers have good potential for CO2 storage and low risk of leakages. The study ranked L20 as the best among the four aquifers.Item Attenuation (1/Q) estimation in reflection seismic records(Institute of Physics publishing, 2013) Raji, Wasiu ODespite its numerous potential applications, the lack of a reliable method for determining attenuation (1/Q) in seismic data is an issue when utilizing attenuation for hydrocarbon exploration. In this paper, a new method for measuring attenuation in reflection seismic data is presented. The inversion process involves two key stages: computation of the centroid frequency for the individual signal using a variable window length and fast Fourier transform; and estimation of the difference in the centroid frequency and travel time for paired incident and transmitted signals. The new method introduces a shape factor and a constant which allows several spectral shapes to be used to represent a real seismic signal without altering the mathematical model. Application of the new method to synthetic data shows that it can provide reliable estimates of Q using any of the spectral shapes commonly assumed for real seismic signals. Tested against two published methods of Q measurement, the new method shows less sensitivity to interference from noise and change of frequency bandwidth. The method is also applied to a 3D data set from the Gullfaks field, North Sea, Norway. The trace length is divided into four intervals: AB, BC, CD, and DE. Results show that interval AB has the lowest 1/Q value, and that interval BC has the highest 1/Q value. The values of 1/Q measured in the CDP stack using the new method are consistent with those measured using the classical spectral ratio method.Item Comparison of Six Classical Electrode Arrays of 1D Resistivity Survey for Subsurface Delineation – Field Experiments(University of Ilorin, Nigeria, 2020) Raji, Wasiu O; Ibitoye, Philiphs E; Abiri, Olufunmbi A; Adepoju, Jamiu, A; Abdulkadir, Kamil, ASix classical Traditional Resistivity Survey methods comprising Schlumberger, Wenner, Dipole-dipole, Wenner-Schlumberger, Pole-dipole and Pole-pole arrays were tested for subsurface stratigraphic delineation in a series of field experiments conducted in the basement complex area of Ilorin, North central Nigeria. The aim of the study is to determine the suitability, strength, and weakness of the different array system for subsurface stratigraphic delineation. Interpretations and comparisons of results from the different arrays were based on the lithologic sections obtained from borehole drillers’ logs in the study area. The results of the study showed that some arrays are more reliable for geo-electric layer delineation than others. Wenner-Schlumberger and Schlumberger arrays gave the overall best results in terms of estimating the vertical extent of layers and depth to hard rock (fresh basement rock). Wenner-Schlumberger array proved to be a reasonable alternative to Schlumberger array when strong vertical resolution is needed. Dipole-dipole, pole-dipole, and Wenner arrays consistently underestimate the number of horizontal layers in most of the study locations, thereby suggesting low sensitivity of the methods to vertical resistivity changes. In situations where the four electrodes cannot be situated within the vicinity of the target, results of the study showed also that pole-pole rather than pole-dipole is a better method of resistivity survey. Interestingly, none of the methods is one hundred percent accurate when compared to the borehole lithologic sections. The study recommends Schlumberger and Wenner-Schlumberger methods for high-resolution subsurface delineation in the study area. Descriptions of the field procedure and electrodes arrangement for the six classical arrays are detailed in this paper with the goal of providing guides to non-professional geophysicists like Agriculturists, Civil and Water engineers, and new-comers in the discipline of geosciences who sometimes engage traditional methods of resistivity survey for testing soil and concrete material and citing water-wells /boreholes.Item COVID-19 lockdown and remote attendance teaching in developing countries: A review of some online pedagogical resources(Taylor and Francis, 2022) Raji, Wasiu O; Oloyede, Abdulkareem, A; Faruk, NasirThe Corona Virus 2019 (COVID-19) pandemic has negatively impacted teaching and learning globally, imposing widespread closure of schools from the elementary to tertiary levels. As of 14 April 2020, teaching activities of over 1.75 billion students globally were disrupted in about 200 countries that have implemented full or partial lockdown across the world. At the time of writing, the duration of the current pandemic cannot be ascertained. Therefore, the teaching and learning process should also adapt to the new normal, which includes suitable social distancing, self isolation and other disruptive guidelines outlined by the World Health Organization. Thus, more than ever, COVID-19 has now emphasized the necessity to embrace different and flexible methods of teaching and, by extension, learning. Therefore, e-teaching and e-learning have emerged as complementary solutions that reduce disruption to educational activities. Despite having a solution in online teaching to reduce the effect of COVID-19 on education, it’s noteworthy that the solution is not available to every educator, learner and school, especially in developing countries. In developing countries, especially across Africa, lack of awareness of the existing online teaching resources and their suitability for remote attendance teaching and lack of skill sets required for using the resources are the issues impeding online teaching. This paper reviews and evaluates twenty-two (22) remote attendance teaching resources, their special features and system requirements. The technical requirements, suitability, and limitations of each application are considered. The implementation challenges of using the resources are discussed, and some solutions are recommended.Item Direct Current Resistivity and Very Low Frequency Electromagnetic Studies For Groundwater Development In A Basement Complex Area of Nigeria,(Faculty of pure and applied Science, Ladoke Akintola University of Science and Technology, LAUTECH, Ogbomosho, 2014) Raji, Wasiu O; Abubakar, Hussain, O.; Bayode, SItem Elastic Velocity Models of A Stratigraphically Complex Carbonate Reservoir, Midland Basin.(Nigerian Minning and Geoscience Society, 207) Raji, Wasiu OCrosswell seismic survey was conducted in a section of midland basin to study a carbonate reservoir of the Wolfcamp formation previously identified on surface seismic data by subtle amplitude and travel-time anomalies. Because the surface seismic data has insufficient resolution to reveal the full geometry of the reservoir and the stratifications around it, crosswell seismic survey having resolution ten-times the surface seismic data was conducted across two wells in the area. The crosswell data was processed for P and S waves travel-time. A finite frequency based optimsed velocity inversion method (OVIM) was applied to image the velocity structure of the reservoir environment after validating the OVIM using synthetic geological model of ‘rainbow’ field. Results of synthetic study gave high resolution complex velocity model comprising horizontal beds and a vertical fracture bearing striking similarities with the true models. The P and S velocity tomograms inverted for the carbonate reservoir show consistent structures that correlate with the well logs from the two well in the area. The velocity tomograms identified the reservoir interval as a low velocity structure adjacent to and overlain by high velocity tight silliciclastic units. The reservoir is delineated as a ~70 m thick stratigraphic trap. Velocity variation within the reservoir interval suggests the presence of facies characterized by variable porosity. The observations in the inverted velocity image are supported by well B velocity log. According to the velocity tomogram, the main pay zone is about 32 m thick extending laterally from well B to the middle of the two wells. Overall, the study demonstrates the enormous potentials of crosswell seismic tomography to address reservoir delineation and characterisation problem usefully.Item Enhanced seismic Q-Compensation: Algorithm Formulation and Synthetic Application(Faculty of Sciences, University of Ilorin, 2013) Raji, Wasiu OItem Fault detection using dip-sterred multi-trace similarity extraction techniques: Case study of using offshore Niger Delata 3D seismic Data(Spain Geophysical Press and Spain Association of Geophysicists, 2014) Jubrin, Babangida; Raji, Wasiu OSee the full paper as attachedItem Geophysical Investigation of Basement Rock Structures around a proposed Dam Site,(Adamawa Stete University, 2017) Raji, Wasiu O; Adeoye, Taiye, O; Ibrahim, K. O.A combination of carefully selected geophysical surveys comprising very low frequency electromagnetic (VLF-EM) and electrical resistivity (VES) methods was employed to study the basement rock structures in a proposed dam site within University of Ilorin campus. Data acquired in the survey were processed to inverted subsurface geological model, 2D conductivity structures and geo-electric cross-sections for the area. The results were interpreted to delineate the subsurface rock and structure, the number of geo-electric layers, and to select a suitable area for the construction of dam extension. The four geo-electric layers delineated correspond to lateritic top-soil layer, weathered rock layer, fractured rock layer, and the fresh basement rock. The VLF-EM and resistivity cross-section revealed a series of competent and weak zones. The weak zones are characterized by weathered/fractured rocks, and they correspond to areas of low resistivity anomalies in VES survey and high conductivity anomalies in VLF-EM survey. Competent rock zone corresponds to area of high electrical resistivity anomalies and low conductivities in VLF-EM tomogram. Depth to fresh basement rock in the weak zone ranges from 7.8 – 14.8 m. The competent rock zones correspond to high resistivity anomalies in electrical resistivity cross-section and low conductivity anomalies in VLF-EM tomograms. Depth to fresh basement rock in the competent zone ranges from 3.3 – 6.8 m. the competent zone recommended for the construction of the dam extension.Item Geophysical mapping of contaminant leachate around a reclaimed open dumpsite.(Elsevier, 2017) Raji, Wasiu O; Adeoye, Taiye, OVery low frequency electromagnetic (VLF-EM), 2D Electrical Resistivity Profiling (2D ERP) and Vertical Electrical Sounding (VES) methods of geophysics were deployed to map the extent of leachate contamination in near-surface rocks around a popular reclaimed dumpsite in north central Nigeria. Two years after abandon and waste excavation; the dumpsite was converted to a residential area with over 80 houses under construction. Prior to waste dumping operation, clay-seal was installed at 2 m depth around the dumpsite to prevent leachate from the waste material flowing to the adjoining area. Results from VLF, 2D ERP, and VES show presence of leachate contamination in rocks and soil of the reclaimed dumpsite. Leachate has spread laterally up to a distance of about 1 km on the northern and southern parts of the dumpsite centre, and up to a depth of about 20 m. Compared to the results of similar survey in an area outside the dumpsite, leachate infiltration raised the conductivity signature of the rocks around the dumpsite by about 200%: from 7% to 22%. Both VLF-EM and 2D ERP show the presence of approximate north – south oriented structures/fracture characterised by high conductivity. VES results show the presence of four – five geo-electric layers. Important conclusions from the study are that (i) leachate is still present in the rocks and soil of the reclaimed dumpsite two years after the abandonment and excavation of the waste materials, and (ii) the clay seal installed around the dumpsite could not prevent leachate migration to the adjoining areas.Item Geophysical Studies of Fractures of Basement Rocks at University of Ilorin, South-western Nigeria: An Application to Groundwater Exploration(Nigerian Association of Hydrogeologists, 2007) Olasehinde, Peter, I.; Raji, Wasiu OItem Hydrocarbon Reserve Estimates and Risks Assessment in ‘X’ Ray Field, Niger Delta, Nigeria.(Adamawa State University, 2018) Raji, Wasiu O; Adeoye, Raiye, O; Ibrahim, K. O.Hydrocarbon exploration and production is a high-risk venture. The uncertainties surrounding return on investment is taking a new dimension under the current industry condition. The dwindling nature of crude oil price requires robust assessment of the likelihood of occurrence, the range of possible outcomes, and the threat of loss throughout the life of a hydrocarbon field. Hydrocarbon prospecting in ‘X’ ray field, Niger Delta, Nigeria, revealed two gas prospects inter-bedded in thick shale sequences. Petroleum system elements were evaluated for the two prospects using a set of 3D seismic cube and well logs. Risks associating with each petroleum element were assessed. Result of study shows that the reservoir, trap, and seal are in-place and effective for hydrocarbon accumulation and production. However, organic rich rock that generated the gas accumulation was not found within the field. The absence of source rock within the field indicates high risk for the source and migration path. Average hydrocarbon saturations obtained from the prospects are 0.69, and 0.57 respectively. The estimated gas volumes of 38,620,000,000 BTU(37,892,707 scf)and 1,437,000,000 BTU (1,397,652 scf)for reservoirs 1 and 2 respectively were found to be substantial, to yield positive returns, but continuous charging of the reservoir through the life of the field is a cause for concern. It is presumed that the gas accumulation is generated by a regional source or a source located outside the field under study. To allow well-informed business decision, acquisition and analysis of more data from the neighboring field are recommended.Item Petrophysical Sensitivity of Elastic Modulus and Inverse Quality Factor (1/Q) Analysis in Well Logs,(Akamai University Hawaii, USA, 2014) Raji, Wasiu O; Adeoye, Taiye, OTheoretical studies and laboratory experiments have shown that seismic attenuation (or inverse quality factor, 1/Q) is sensitive to the presence of fluids, degree of saturation, porosity, fault/fracture, and pressure in porous elastically heterogeneous rocks. However, the probable use of attenuation for reservoir characterization is yet to be tested using well log data. This paper applies the theories of modulus- frequency dispersion to test, theoretically, the sensitivity of P- and S-wave attenuation to the presence of fluids in porous rocks saturated with two or more fluids. Application of the attenuation theory to the analysis of P-wave and S-wave inverse quality factor ( and) in well log data shows that P-wave inverse quality factor is generally higher in hydrocarbon saturated rocks than in brine/water saturated rocks, while the S-wave inverse quality factor does not show direct sensitivity to fluid. A cross plot of the ratio of P-wave and S-wave inverse quality factors, with the ratio of P-wave and S-wave velocities distinguishes gas sand from water sand, and water sand from oil sand. As derived from the analyses, gas sand is characterized by the highest and the lowest ratios; oil sand is characterized by the lowest and the highest ; and water sand is characterized by the and values that plotted between those of the gas and oil sands. The signatures of the bulk modulus, Lame’s first parameter, and compressional modulus show sensitivity to rock fluids. Attenuation analysis in recorded well logs can provide useful guide for hydrocarbon reservoir characterization. (Keywords: Inverse Quality Factor, P-, S- wave, elasticItem Petrophysical Sensitivity of Elastic Modulus and Inverse Quality Factor (1/Q) Analysis in Well Logs,(Akamai University Hawaii, USA, 2014) Raji, Wasiu O; Adeoye, Taiye, OItem Quality Factor (Q) Estimates, Seismic Attenuation and AVO Analysis(Faculty of Science, University of Ilorin, 2010) Raji, Wasiu OItem Reflection Ehancement Processing of Ultra-Shallow Reflection Surveys(Faculty of Physical Sciences, University of Ilorin., 2016) Raji, Wasiu OThe lack of standard procedure for processing shallow reflection seismic data is an impediment to the use of reflection seismic data for near surface applications. The wave field of ultra-shallow reflection data is often complicated by low frequency high amplitude events in the same time window with primary reflections. The standard method for processing exploration-scale seismic data proved unsatisfactory for ultra-shallow reflection seismic data: scaling down the acquisition geometry is inadequate because the frequency bandwidth of the data recorded does not scale up in the same proportion. In this study, data-driven workflow of specialised techniques is used to preserve the low-amplitude energies reflected by shallow geological layers. Surgical top and end muting; cone and polygonal muting; 𝒇−𝒌𝒙 spectral-filtering techniques and careful validation of coherent events, by synthetic modelling, were combined to degrade noise and other non-reflection events. A combination of constant velocity gather, Semblance Plot, and Constant Velocity Stack techniques was applied to obtain the optimum move-out velocity. Applied to an ultra shallow seismic data from Southeast Spain, the workflow improved the signal-to-noise ratio of processed data. The CDP–stacked image constructed for the survey reveals some shallow vertical faults suspected to be associating with the main Carbonera Faults. These faults are comparable to faults projections constructed from a field based geological mapping undertaken many years before the seismic survey.Item Reflections Enhancement Processing For Multi-Component Crosswell Seismic Data.(2016) Raji, Wasiu OItem Review of Electrical and Gravity Methods of Near Surface Exploration for Groundwater.(Nigerian Journal of Technological Development, 2014) Raji, Wasiu OABSTRACT: The theory and practice of electrical and gravity methods of geophysics for groundwater exploration was reviewed with illustrations and data examples. With the goal of reducing cases of borehole/water-well failure attributed to the lack of the knowledge of the methods of geophysics for groundwater exploration and development, the paper reviews the basic concepts, field procedures for data acquisition, data processing, and interpretation as applied to the subject matter. Given a case study of groundwater exploration in University of Ilorin Campus, the three important techniques of electrical method of groundwater exploration are explained and illustrated using field data obtained in a previous study. Interpretation of resistivity data shows that an area measuring low resistivity (high conductivity), having thick pile of unconsolidated rock, and underlain by fracture crystalline is a ‘bright spot’ for citing borehole for groundwater abstraction in a basement complex area. Further to this, gravity method of groundwater exploration was discussed with field data from Wokbedilo community in Ethopia. Bouguer and reduced gravity anomaly results were presented as maps and contours to demonstrate how gravity data can be inverted to map groundwater aquifers and subsurface geological structures during groundwater exploration.