A. P. Aizebeokhai

Geoelectrical resistivity data sets for subsurface characterisation and aquifer delineation in Iyesi, southwestern Nigeria

This article consists of geoelectrical resistivity data sets for thirty (30) vertical electrical sounding (VES) and four (4) traverses of 2D electrical resistivity imaging (ERI) collected within Iyesi, Ota, southwestern Nigeria for about five (5) weeks between December, 2016 and January, 2017 using an ABEM Terrameter (SAS1000/4000). The observed apparent resistivity data sets for the VES were processed using WinResist to obtain geoelectric layer parameters while those of the 2D ERI were processed with RES2DINV to obtain 2D inverse model resistivity images. The geoelectric parameters for the VES and the inverse models for the 2D ERI were integrated to characterise the subsurface and delineate the underlying aquifer units.

Evaluation of optimal reservoir prospectivity using acoustic-impedance model inversion: A case study of an offshore field, western Niger Delta, Nigeria

Abstract The evaluation of economic potential of any hydrocarbon field involves the understanding of the reservoir lithofacies and porosity variations. This in turns contributes immensely towards subsequent reservoir management and field development. In this study, integrated 3D seismic data and well log data were employed to assess the quality and prospectivity of the delineated reservoirs (H1–H5) within the OPO field, western Niger Delta using a model-based seismic inversion technique. The model inversion results revealed four distinct sedimentary packages based on the subsurface acoustic impedance properties and shale contents. Low acoustic impedance model values were associated with the delineated hydrocarbon bearing units, denoting their high porosity and good quality. Application of model-based inverted velocity, density and acoustic impedance properties on the generated time slices of reservoirs also revealed a regional fault and prospects within the field.

Measurements of radioactivity levels in part of OtaSouthwestern Nigeria: Implications for radiological hazardsindices and excess lifetime cancer-risks

Super SPEC RS-125 radiation detector with large 2.0 x 2.0 NaI crystal and linear nenergy ranging from 0.80 MeV to 1.2 MeV was used to measure the activities of primordial nnuclides and the radiation dose exposures rate in Iyana-Iyesi, Ota, southwestern Nigeria. The nmeasured activities vary from 17±0.02 Bqkg-1 to 30.49 ±0.01 Bqkg-1, 50.01 ±0.16 Bqkg-1 to n158.49±0.17 Bqkg-1, and 406.9±0.42 Bqkg-1 to 1275.48±0.82 Bqkg-1 for 238U, 232Th and 40K nrespectively. The acquired gamma radiation dose rate range from 138.696 ±2.06 (nGyh-1) to n350.103±7.21 (nGyh-1) with mean value of 148.22 (nGyh-1), almost three times higher than the nrecommended safe limit of 55 (nGyh-1). The measured activities and radiation dose rate were nengaged to estimate the annual outdoor effective dose, gamma index, excess lifetime cancer nrisks and annual gonadal dose equivalent. It was observed from all the estimated parameters, nthose values in the study area are well above the recommended safe limit for normal nbackground radiation. This suggest that the dwellers and those using the excavated ngeomaterials from this area for construction purposes are exposed to very high radiation from nnatural radionuclides. Further research to evaluate the mineralogy and geochemistry of the clay ndeposits in the area is highly recommended

The use of geological-based geophysical surveys for groundwater distribution in crystalline basement terrain, SW Nigeria

This research involves the subsurface geological characterization for groundwater potential assessment within the campus of the Polytechnic of Ibadan, southwestern Nigeria. The study is directed towards groundwater resources exploration, development and management in the campus. Five 2D resistivity imaging traverses were conducted using nWenner array in addition to five VES surveys using Schlumberger array that provide layering information and geoelectrical parameters. Three geologic layers delineated from the 2D resistivity inversion models include predominantly clayey sand/ sandy clay top soil (overburden), partly weathered or fractured basement and fresh basement. Their inverse model resistivity values ranges 6.68 – 98.6uf057m , 68.0 – 929 uf057m and uf0b3 2252 uf057m with bottom depths ranges 3.8 – 6.4 m and 6.4 – 10 m respectively. 1D model inversion from VES results also delineate three lithologies classifying both topsoil and some part of the partly weathered basement as overburden with resistivity and thickness range 483 – 1746.9 uf057m , 1.1 – 1.8 m; npartly weathered or fractured basement 60.3 – 93.5 uf057m , 8.4 -12.9 m and fresh basement 984.6 – 2078.9 uf057m . The saturated portion of the partly weathered or fractured basement at depth will favour groundwater exploration and development in this area, while the relatively shallow overburden thickness would serve as the protective layer and recharge for the fractures.

Geoelectrical resistivity data set for characterising crystalline basement aquifers in Basiri, Ado-Ekiti, southwestern Nigeria

This article consists of data sets for thirty (30) vertical electrical sounding (VES) and four (4) traverses of 2D electrical resistivity imaging (ERI) collected within, Ado-Ekiti, southwestern Nigeria using an ABEM Terrameter (SAS 1000/4000) system. Win-Resist computer program was used to process the apparent resistivity data sets for the VES to determine the geoelectric layers and their respective parameters (resistivity and thickness). The observed data sets for the 2D ERI were processed using RES2DINV software to obtain 2D inverse model resistivity distribution of the subsurface. The resistivity soundings and the 2D ERI were combined to delineate and characterise the crystalline basement features associated with basement aquifers.

Electrical resistivity imaging (ERI) data for characterising crystalline basement structures in Abeokuta, southwestern Nigeria

This article consists of data sets for five (5) traverses of 2D electrical resistivity imaging (ERI) collected in Abeokuta, southwestern Nigeria. ABEM Terrameter (SAS1000/4000) system and dipole-dipole array were used for the data collection. RES2DINV computer program was used to invert the observed apparent resistivity data to obtain 2D inverse model images of resistivity distribution of the subsurface. The 2D resistivity images were used to characterise the subsurface and delineate the crystalline basement features of hydrological importance in the area.