Groundwater Prospecting and Exploration in a Low Potential Hard Rock Aquifer: Case Study from Ogbomoso North, South-western Nigeria

Very Low Frequency Electromagnetic (VLF-EM) and Electrical Resistivity methods has been employed to unravel the localized nature of groundwater occurrence in Ogbomoso North, southwestern Nigeria. This was aimed at addressing the growing demand for groundwater use in the area underlain by migmatite gneiss with minor intrusions of pegmatite and quartz veins. Nine profiles comprising five VLF-EM and four electrical resistivity profiles were conducted parallel to the two major azimuths in the area.  The anomalous zones identified on the profiles were further investigated by twelve Vertical Electrical Soundings (VES). Lithologic logs from three boreholes were also used to ground truth the geophysical findings. Quantitative interpretation of VES data showed that the Geoelectrical Succession comprise three to five layer earth models. The aquifer units are localized comprising weathered layer and fractured basement. The lowest yield of 280.6LPH was obtained from well bored on VES point having three-layer earth models made up of resistive-conductive-resistive geoelectric succession. Well bored on VES points having more than three-layer earth models and comprising alternating band of resistive-conductive geoelectric succession have more yield ranging between 520.8LPH and 590.4LPH.  Furthermore, there was strong correlation between geoelectric succession and lithologic sections obtained from the drill cuttings of the bored wells. Keywords: Groundwater Exploration, Geophysical Methods, Lithology Logs, Fractured Basement, Crystalline Rocks

Estimating Geo-Mechanical Strength of Reservoir Rocks from Well Logs for Safety Limits in Sand-Free Production

Hydrocarbon exploration and exploitation does not only require the knowledge of hydrocarbon in-place, however, mechanical competency of the reservoir rock must also be known. The direct method of inferring S- and P-wave velocities from seismic data usually has limitation of poor resolution because of the uncertainty in seismic inversion which may also affect other derivatives. An analytical method is presented with the possibility of predicting shear wave velocity from wireline log data where S-wave sonic logs do not exist. By estimating S-wave velocity, formation geo-mechanical properties can be calculated using P-wave sonic and density logs with appropriate equations. Elastic constants such as Poisson Ratio, Young’s, Shear and Bulk moduli which are the parameters for characterizing rock mechanical properties were estimated and used to predict the mechanical competency of the formation for hydrocarbon exploration. Well planning demands knowledge of these geo-mechanical properties which can be used to estimate the pressures required to initiate a fracture into a formation for the safety of the personnel and equipment, in particular minimizing the associated risks. In this paper, firstly we investigate the possibility to predict the shear velocity from well logs, and then Elastic moduli calculated from the log data can therefore be used effectively in predicting safety limits in sand-free production from friable sandstones. The results of this study shows that the combined modulus of strength (K) and the shear modulus (S) to compressibility (c) ratio (S/c) for the formation are relatively low. The average value of K is lower than the threshold value indicating the minimum value at which fluids may be produced safely at any rate but falls within the range which generally represents a condition in which the problem of sand production should not arise below a certain optimum flow rate. Average value of S/c ratio is lower but tends towards acceptable range. Keywords: Mechanical competency, predicting shear wave velocity, elastic constants, well planning, combined modulus of strength, shear modulus to compressibility ratio

Geophysical investigation of abandoned back-filled railway line: implication on adjacent buildings

A geophysical investigation was carried out on a back-filled segment of an abandoned railway route at Okebadan Estate, Ibadan using electrical resistivity imaging. The study is aimed at depicting the cause(s) of settlement that led to building foundation failure. Five profile lines were established during the study and the apparent resistivity values obtained from the traverse were plotted against the mid-point of electrode separation using least-squares inversion algorithm. Pockets of low resistivity region were obtained from the inverted sections with resistivity values ranging from 77 Ω-m to ˂400 Ω-m. The suspected back-filled earth materials were suspected to be clay and clayey sand. Results indicated that materials used in back filling the abandoned rail route were not well compacted. Consequently, the structural failure of buildings along this abandoned route was attributed to differential settlements of clays and clayey sands on which they were erected.Keywords: Backfill, Foundation, Resistivity, Settlemen

Integrated Geophysical Investigation in Delineating Extent of Pollution Caused by Poultry Waste at Ilora Area, Southwestern Nigeria

An integrated VLF-Electromagnetic and Electrical Resistivity survey was carried out in Odo Abata, Ilora area of Southwestern Nigeria in order to investigate the possible extent of groundwater contamination caused by an indiscriminate accumulation of poultry fecal droppings in a seasonal stream. The poultry fecal accumulation solidifies during the dry season and the percolating water plays a significant role in leachate generation and infiltration during the wet season. When in contact with the subsurface aquifer, the leachate forms a plume which diffuses into the pore spaces of aquifer with high rate of infiltration. Field data were collected using ABEM WADI VLF- EM equipment and campus Tigre Terrmeter. A total of eight VLF profiles, four electrical imaging profiles and two VES points were obtained in the vicinity of the study area. Control profiles and VES point were obtained at 500 m away from the study area. Field data were interpreted using KHFFilt program version 1.1a for VLF, Dipro software for electrical imaging and Winresist version 1.0 for VES data. Interpretation of VLF data showed conductive near surface layers and some fractures at depth. Electrical imaging data however revealed a near surface very low resistivity region which is due to the surface fecal accumulation. VES results showed that the overburden is clayey, and the basement is fractured. Depth to basement ranges from 9.3 – 12.8 m. Poultry fecal accumulation with leachate is mostly restricted to the topmost 6 m of the soil and if not controlled, leachate infiltration may reach the shallow basement with time and contaminate the groundwater system of Odo Abata area. Keywords: Very Low Frequency Electromagnetic (VLF-EM), Electrical Resistivity, Contamination, Leachate, Fracture DOI: 10.7176/JEES/9-10-09 Publication date:October 31st 201

Land satellite imagery and integrated geophysical investigations of highway pavement instability in southwestern Nigeria

The high global numbers of road accidents due to bad roads and the failure of other engineering structures have necessitated this study, particularly as road transport accounts for a higher percentage of cargo movement in African countries. The geophysical investigation was carried out on six failed and two stable sections along the Ibadan-Iwo-Osogbo highway to examine the geological factors responsible for highway failure in the area. A Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery of the study area and its environs was acquired and processed for lineaments analyses. Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity methods involving Schlumberger Vertical Electrical Sounding (VES) and 2-D imaging using a dipole-dipole array were utilized. Lineaments were identified across failed localities. Lateral magnetic variations in the near-surface geological materials characterized the study area. The 2-D VLF-EM models generated showed conductive zones corresponding to fractured zones of conductive clay materials within the basement rocks. Subgrade soils below the highway pavement along the failed sections are typical of incompetent clayey and sandy clay/clayey sand formations with resistivity values between 20–475 Ω∙m. In comparison, the subgrade soil beneath the stable sections has moderate to high resistivity values of 196–616 Ω∙m. 2-D resistivity structures across the failed segments identified low resistivity water-absorbing clay and lithological contacts. Water absorbing, clay enriched subgrade soils and the identified near-surface linear conductive features are the major geologic factors, and poor drainage network resulted in the highway failure. Remote sensing and geophysical investigations of the geological sequence and structures underlying the highway should be carried out before construction to effectively complement the routine geotechnical studies to ensure the sustainability of road infrastructure

Fault reactivation potential and associated permeability evolution under changing injection conditions

Acknowledgements The authors wish to acknowledge Adekunle Ajasin University, for granting the lead author a study leave; the African Union for providing the financial support (scholarship) through the Pan African University; and the University of Aberdeen for providing the facilities and enabling environment for a successful research.Peer reviewedPublisher PD

Numerical investigation of the influence of discontinuity orientations on fault permeability evolution and slip displacement

Acknowledgements The authors wish to acknowledge the African Union Commission for providing the financial support through Pan African University; and the University of Aberdeen for providing the facilities and enabling environment for this study. Open access via springer agreementPeer reviewedPublisher PD

Electronic Cash In E-Commerce: Comparative Analysis Of Views Of Hispanic And African-American Business Owners

Based on a survey of 1000 Hispanic and 1000 African-American business owners on the impacts e-commerce and e-cash are expected to have upon business practices, there were significant discrepancies between perceptions of these two groups regarding their ability to track and retain customers and to authenticate the source of e-cash payments.  In addition, while both groups of owners agreed that e-cash will likely replace traditional currency used in commercial transactions between consumers and business, they both are uncertain as to what degree central banks of countries should regulate and how much freedom the private sector should have for developing new forms of e-cash.  Hispanic business owners generally are more receptive to e-commerce viewing it as not making marketing strategies more difficult while African-American owners generally perceive enhanced issues to be resolved