Seismic interpretation and petrophysical evaluation of SH field, Niger Delta

Three out of the 14 hydrocarbon-bearing sands (A, B and I) in the ‘SH’ field onshore Niger Delta which contain bulk of the hydrocarbon reserves in the field were considered as development candidates. Seismic interpretation and petrophysical evaluation of logs of 13 wells were integrated with the aim of verifying and ascertaining the hydrocarbon reserves prior to field development which involves enormous financial commitment. Results show that the field is structurally controlled by sets of northwest–southeast-trending synthetic faults which dip southwest. Hydrocarbon traps at the three sand levels are rollover anticlinal closures that are generally sealed by a major listric fault that demarcated the field into northwest and southeast blocks. The southern fault block is hydrocarbon bearing; wells drilled in the field targeted these closures and encountered a number of stacked hydrocarbon-bearing sand levels. Reservoir-A developed a hanging-wall rollover anticlinal structure sealed by a major listric fault forming a trap with oil–water contact (OWC) of 1222 m TVDSS. Reservoir-B also shows similar structure as reservoir-A, but it is partitioned into two hydrocarbon compartments by a sealing fault; these two compartments have different OWCs. Reservoir-I exhibits similar structure to reservoir-A. The evaluation of the petrophysical characteristics revealed that the reservoirs are of good quality with average net to gross, porosities, water saturation and hydrocarbon saturation ranging from 0.774 to 0.980, 0.220–0.339, 0.133–0.367 and 0.633–0.867, respectively. Variation in the petrophysical parameters and the uncertainty in the reservoir structure of the three reservoirs were considered in calculating range of values of gross rock volume and in-place volume. The study shows oil-in-place volume in the range of 243.83–357.90 MMstb in reservoir-I, whereas reservoir-A contains 148.98–241.14 MMstb, reservoir-B1 31.31–50.36 MMstb and reservoir-B2 67.79–108.98 MMstb of oil. Conclusively, this study has further confirmed the high productivity and commercial viability of the wells within the field of study to be able to adequately compensate for the cost of development

Radiation hazard in soil from Ajaokuta North-central Nigeria

Background: Measurement of the radiation dose distribution is important in assessing the health risk a population and serve as reference in documenting changes to environmental radioactivity in soil due to man-made activities. Materials and Methods: The activity concentration of 238U, 232Th and 40K in soil samples obtained from different locations in Ajaokuta Local Government area was measured using Hyper Pure germanium Detection System (HPGe). Results: The calculated average concentration of the radionuclides ranged from 12 ± 1 Bqkg-1 to 59 ± 2 Bqkg-1 for 238U, 14 ± 1 Bqkg-1 to 78 ± 5 Bqkg-1 for 232Th and 49 ± 2 Bqkg-1 to 1272 ± 23 Bqkg-1 for 40K. In order to evaluate the radiological hazards due to natural radionuclides within Ajaokuta, the absorbed dose rate, gamma index, radium equivalent and excess lifetime cancer risk were estimated. According to measured data from the top soil (0-10 cm), the estimated radium equivalent (Raeq) ranges from 55.7 Bqkg-1 at Steel Complex to 253.3 Bqkg-1 obtained from Forest samples. Conclusion: The mean absorbed dose rate, annual effective dose and gamma radiation index evaluated were 66.2 nGyh-1, 81.2 µSvy-1 and 1.05 respectively which are higher than the recommended limit for normal background radiation. Thus, we conclude that people living in these locations may be exposed to higher radiation

Seismic driven reservoir characterization, offshore Niger Delta, Nigeria

This paper presents the subsurface characterization by applying integrated three dimensional seismic attributes analysis on a 3D seismic dataset from OPO field, within the western Niger Delta basin. The volume attributes aimed at extracting features associated with hydrocarbon presence detection, net pay evaluation and porosity estimation for optima reservoir characterization. Neural network (NN) derived chimney properties prediction attribute was used to evaluate the integrity of the delineated structural traps. Common contour binning was employed for hydrocarbon prospect evaluation, while the Seismic coloured inversion was also applied for net pay evaluation. Amplitude anomalies were used to delineate bright spots and flat spots; good reservoirs in term of their porosity models, and fluid content and contacts (GOC & OWC) were identified in the area through common contour binning, seismic colour inversion and supervised NN classification

Seismic attributes analysis for reservoir characterization; offshore Niger Delta.

In this paper we have described some commonly utilized seismic attributes that are of complementary value to the information acquire through traditional methods of seismic interpretation. Seismic attributes extraction and analyses have proven to offer new information and insights into structural and stratigraphic mapping interpretations. They further assist greatly in delineation of hydrocarbon leads and prospects which subsequently help to reduce exploration and development risk

Experimental evaluation of soil petrophysical attributes: Implications for sustainable agriculture

Agriculture is man’s major supplier of his needs, particularly his primary need which is food. Soil is a major component for sustainable agriculture production needs to be studied and understood. Soil’s characteristics determine the type of crop that would grow and the nature of the yield of the crop. The area of study is Covenant University farmland, where twenty soil samples from the farm were collected and petrophysical parameters such as conductivity and salinity were analysed on each soil sample

Geogenic radiological impact assessment of soil samples collected from parts of Sagamu Southwestern Nigeria

This study is an assessment of the radionuclide concentration level and radiological hazards in soils from Sagamu, Ogun state Nigeria. Soil samples collected from 15 locations were analysed using a 76 x 76 mm Sodium Iodide [NaI (TI)] detector crystal. The estimated average absorbed dose rates, annual effective dose, gamma radiation index and excess lifetime cancer risk of the soil samples were 42.07 nGy/h, 51.59 μSvy-1 0.66and 0.181μSvy-1 respectively. Mean radium equivalent activity of 95.4 Bq/Kg was also obtained for the soil samples. The average soil radionuclides activity concentrations in the area of study were within the worldwide range; although at some locations higher values of 226Ra and 232Th activity concentration were observed. The results of the estimated radiological parameters in this study are lower than the International Commission on Radiological Protection (ICRP) maximum permitted limit. Hence, they have no significant radiological health impacts on the environment and the populace

Geostatistical exploration of dataset assessing the heavy metal contamination in Ewekoro limestone, Southwestern Nigeria

The dataset for this article contains geostatistical analysis of heavy metals contamination from limestone samples collected from Ewekoro Formation in the eastern Dahomey basin, Ogun State Nigeria. The samples were manually collected and analysed using Microwave Plasma Atomic Absorption Spectrometer (MPAS). Analysis of the twenty different samples showed different levels of heavy metals concentration. The analysed nine elements are Arsenic, Mercury, Cadmium, Cobalt, Chromium, Nickel, Lead, Vanadium and Zinc. Descriptive statistics was used to explore the heavy metal concentrations individually. Pearson, Kendall tau and Spearman rho correlation coefficients was used to establish the relationships among the elements and the analysis of variance showed that there is a significant difference in the mean distribution of the heavy metals concentration within and between the groups of the 20 samples analysed. The dataset can provide insights into the health implications of the contaminants especially when the mean concentration levels of the heavy metals are compared with recommended regulatory limit concentration

Geoelectrical characterisation of basement aquifers: the case of Iberekodo, southwestern Nigeria

Basement aquifers, which occur within the weathered and fractured zones of crystalline bedrocks, are important groundwater resources in tropical and subtropical regions. The development of basement aquifers is complex owing to their high spatial variability. Geophysical techniques are used to obtain information about the hydrologic characteristics of the weathered and fractured zones of the crystalline basement rocks, which relates to the occurrence of groundwater in the zones. The spatial distributions of these hydrologic characteristics are then used to map the spatial variability of the basement aquifers. Thus, knowledge of the spatial variability of basement aquifers is useful in siting wells and boreholes for optimal and perennial yield. Geoelectrical resistivity is one of the most widely used geophysical methods for assessing the spatial variability of the weathered and fractured zones in groundwater exploration efforts in basement complex terrains. The presented study focuses on combining vertical electrical sounding with two-dimensional (2D) geoelectrical resistivity imaging to characterise the weathered and fractured zones in a crystalline basement complex terrain in southwestern Nigeria. The basement aquifer was delineated, and the nature, extent and spatial variability of the delineated basement aquifer were assessed based on the spatial variability of the weathered and fractured zones. The study shows that a multiple-gradient array for 2D resistivity imaging is sensitive to vertical and near-surface stratigraphic features, which have hydrological implications. The integration of resistivity sounding with 2D geoelectrical resistivity imaging is efficient and enhances near-surface characterisation in basement complex terrain

Multiple-gradient array for near-surface electrical resistivity tomography

The use of most conventional arrays for near-surface electrical resistivity tomography (ERT) surveys is usually cumbersome, time consuming and labour intensive. Thus, data acquisition teams are often tempted to reduce the data density with a view of speeding up field operation and minimizing the survey cost. This tends to significantly degrade the quality and resolution of the resulting resistivity images. In this presentation, multiple-gradient array, a non-conventional electrode configuration, has been used to conduct rapid and cost effective near-surface ERT without compromising the data density