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Geostatistical modeling of porosity data in ‘oba’ field, onshore Niger Delta

Abstract

A geostatistical approach was used to model porosity of OBA field in onshore area of Niger Delta using simulation technique. The objective is to understand the spatial distribution of porosity and characterize the degree of heterogeneity of underlying formation. Porosity data from twenty-two wells were loaded into SGeMS software. Univariate statistical analysis, experimental semivariogram and Sequential Gaussian Simulation (SGS) were applied on the data. The data was close to normal approximation of Gaussian based of the results of univariate statistics. However, to construct and model horizontal and vertical semivariograms, the data was log-normalized to reduce the coefficient of variation and to get good fit of the model. Parametric semivariogram model shows the range of 72–6480 m, nugget effect of 0.006 and sills of 0.0095, 0.0099 and 0.0111. Six realizations were generated using SGS algorithm and the results suggest that any one of the realizations can independently represents the true picture of the subsurface geology within the study area. Ranking of realizations shows realization 6 as the best and realization 2 as the lowest. This model could be used as an initial condition for simulation of flow.

Open access
Soil corrosivity and aquifer protective capacity of overburden units in Ado-Ekiti, southwestern Nigeria

Abstract

Vertical electrical sounding, well inventory and physicochemical analysis were conducted to evaluate soil corrosivity and aquifer protective capacity of overburden units in the basement complex terrain of Ado-Ekiti, southwestern Nigeria. The topsoil is composed of slightly corrosive materials at the eastern, southern and northeastern flanks and the central portion with resistivity values ranging from 60 to 180 m. Moderately corrosive/slightly corrosive materials (with resistivity values of 10 < ρ < 60 m) constitute the second layer around the eastern, southern and north-eastern flanks. Pockets of areas in the northwestern, southeastern, eastern and central parts of the metropolis are practically non-corrosive with resistivity values in excess of 200 m. Zones of good, moderate, weak and poor overburden protective capacity were delineated, with longitudinal conductance (S) values of 0.7 < S < 4.9, 0.2 < S < 0.69, 0.1 < S < 0.19 and S < 0.1 mhos, respectively. On a regional consideration, 23.31%, 18.80% and 57.9% of the study area is characterised by overburden materials of poor, weak and moderate protective capacity, respectively. Only 6.02% of the area indicates good overburden protective capacity.

Open access
Stochastic – advantages and uncertainties for subsurface geological mapping and volumetric or probability calculation

Abstract

Stochastic, especially simulation, occasionally could be found in different geological calculations, mostly as the most advanced mapping method. Its main attribute is description of uncertainties that are inherent not only to any geological mapping dataset but also to any volumetric or probability calculation. Here are presented uncertainties in all three cases – mapping, volume calculation and probability calculation – and reasons why and when to use stochastic in them. The stochastic, and consequently simulation, is a recommended tool in case of a low number of data (<15 inputs) or large dataset (>40 inputs), but in both cases, the descriptive statistics needs to be known and is reliable. Almost the same could be applied in volumetric calculation, but the success of stochastic in probability calculation depends on large datasets, with 15 or more inputs.

Open access
Thermal conductivity of rocks and geothermal water

Abstract

In this article, the possibilities of use of geothermal energy in relation to the geothermal gradient and aquifer yield are described. Calculations represent information on potential geothermal water reserves that are not affected by cold return water inflow from the reinjection well after a certain period of production time. The calculations apply for continuous production of geothermal water from the aquifer without significant pumping breaks.

Open access
The effect of protective atmosphere on decarburisation of the heat-treated surface of steel

Abstract

In heat-treating furnaces, many different types of protective atmospheres are used. This article researches the effect of protective atmospheres on the quality of the surface layer of bolts during the process of heating to reach the temperature of hardening. For this research, we produced specimens that were annealed in the furnace with two different types of protective atmosphere, i.e. in atmospheres of endothermic gas and nitrogen. After hardening and tempering, we measured the hardness of the specimens and investigated the microstructure. We measured the hardness profile from the surface to the inside of the product. We found that the hardness of the surface of the tested product was lower while using protective atmosphere of nitrogen due to the occurrence of ferrite. The depth of the decarburised layer in this atmosphere reached up to 70 mm, where predominantly there was a microstructure of ferrite on the surface, and then, with depth, an increasingly mixed microstructure of ferrite and martensite was found. The depth of the decarburised layer for sample treated in endothermic gas was minimal (i.e. 10 mm) on the surface.

Open access
Geotechnical Site Investigation Using S-waves with Implications for Ground Motion Analysis

Abstract

Evaluation results of shear wave attenuation-based ground motion restricted by fracture orientation and rheology, from among those of an extended experimental study, are presented herein. The issues of competence of fractured bedrock dynamically disturbed multilaterally are assessed. Disturbance is primarily modelled by Sh and Sv stimulation, given fracture orientation, while subjected to direct fracture stress regime conditions varying in time. Hence, directionalities of polarisation and stress are taken into consideration simultaneously following simple site-specific non-erodetic approach. Comparison of spectral curves and spectral ratio curves of attenuation with respect to variations of direction and stress emphasise the amplification of the ‘seismic response’ in one direction compared to the other, i.e. vertical vs. horizontal, in terms of weighing possibilities of or predicting structural integrity against failure. The composite analyses of multiple spectral curves not only enable determination of the orientation of the fracture set/s in space but also allow inferring the nature of more amplified response perpendicular to the crack surface compared to that of a response parallel to the crack surface.

Open access
Interpretation of high resolution airborne magnetic data (HRAMD) of Ilesha and its environs, Southwest Nigeria, using Euler deconvolution method

Abstract

Interpretation of high resolution aeromagnetic data of Ilesha and its environs within the basement complex of the geological setting of Southwestern Nigeria was carried out in the study. The study area is delimited by geographic latitudes 7°30′–8°00′N and longitudes 4°30′–5°00′E. This investigation was carried out using Euler deconvolution on filtered digitised total magnetic data (Sheet Number 243) to delineate geological structures within the area under consideration. The digitised airborne magnetic data acquired in 2009 were obtained from the archives of the Nigeria Geological Survey Agency (NGSA). The airborne magnetic data were filtered, processed and enhanced; the resultant data were subjected to qualitative and quantitative magnetic interpretation, geometry and depth weighting analyses across the study area using Euler deconvolution filter control file in Oasis Montag software. Total magnetic intensity distribution in the field ranged from –77.7 to 139.7 nT. Total magnetic field intensities reveal high-magnitude magnetic intensity values (high-amplitude anomaly) and magnetic low intensities (low-amplitude magnetic anomaly) in the area under consideration. The study area is characterised with high intensity correlated with lithological variation in the basement. The sharp contrast is enhanced due to the sharp contrast in magnetic intensity between the magnetic susceptibilities of the crystalline and sedimentary rocks. The reduced-to-equator (RTE) map is characterised by high frequencies, short wavelengths, small size, weak intensity, sharp low amplitude and nearly irregular shaped anomalies, which may due to near-surface sources, such as shallow geologic units and cultural features. Euler deconvolution solution indicates a generally undulating basement, with a depth ranging from −500 to 1000 m. The Euler deconvolution results show that the basement relief is generally gentle and flat, lying within the basement terrain.

Open access
Methodology for preliminary assessment of the radioactivity in natural waters

Abstract

This article presents the results of a preliminary assessment of the radioactivity of natural waters and the isotope analysis of drinking water. It describes the methods for the radiochemical preparation of water samples, which include concentration of uranium isotopes from water samples, extraction from impeding radionuclides and preparation of electrically countable samples. The results of violation of radioactive equilibrium between the isotopes 234U/238U and the several factors affecting this process in water samples have been obtained. It is clear from the obtained result that 234U isotope concentration in groundwater is higher than that in surface water.

Open access
Use of a Combination of Vertical and Horizontal Boreholes in Massive Blasting of Benches in the Surface Quarry Rodež

Abstract

This article deals with the extraction of minerals (limestone/marl/flysch) in the quarry Rodež, which is located in western Slovenia. During the extraction of minerals in a quarry, drilling and blasting of benches are used. The focus of the article is on the analysis of the parameters related to drilling and blasting in surface excavations when using a combination of explosions and introducing horizontal wells along with vertical holes in the bench. On the basis of the analysis of basic parameters through a combination of drilling horizontal wells and charging those with the ammonal + Anfex explosive, analyses of effects of seismic disturbances on potentially affected buildings have also been conducted. The article is connected to and deals exclusively with the basic parameters of drilling and blasting, with the introduction of horizontal drilling and with the analysis of seismic measurements of threatened buildings in accordance with the German standard German Institute for Standardisation (DIN) 4150 during the use of a new method of blasting.

Open access
Asymmetric rolling process

Abstract

Asymmetric rolling is a novel technique used to control both the texture and the grain refinement of metallic materials. The aim of asymmetric rolling is to apply a large shear strain uniformly through the thickness of the plate, by maintaining a high degree of friction between the sheet and the rolls. It can be used to improve the formability of material. One of the advantages of asymmetrical rolling is that the rolling force and torque can be decreased. The methods used for the asymmetric rolling are single roll drive, different work roll speeds, different work roll diameters or different lubricated work roll surfaces.

Open access