High Porosity Values Research Articles

Three-dimensional pore connectivity evaluation in a Holocene and Jurassic microbialite buildup

Microbial carbonates have complex pore networks formed by their biological growth framework, which later may be modified by diagenetic alteration. A proper evaluation of the porous media characteristics and their evolution is essential to better characterize microbial carbonate reservoirs. However, conventional methods of fundamental rock characteristic description are insufficient to elucidate the heterogeneity of pore networks and textural shifts. X-ray computed tomography allows a better evaluation of these fundamental characteristics, which, when integrated with stratigraphic analysis, enhances the understanding of the volume and connectivity of pore networks in different microbial textures. A three-dimensional evaluation of a Holocene microbialite from Brazil provides insights about how the primary pore network is related to the textural changes in microbialite successions, which, in ancient deposits, may be reduced or enhanced by diagenesis. Conventional methods such as petrography, carbon and oxygen stable isotope analysis, and laboratory measurements for porosity and permeability were integrated with computed tomography images and three-dimensional rendering to provide a high-resolution history of the evolution of porosity and permeability within this microbialite. The pore network differences are related to microbial textural evolution driven by environmental changes. The depositional textures control petrophysical properties based on fundamental rock characteristics such as structure size, structure packing, and framework fabric. Those fundamental characteristics influence the pore volume and number of pore throats. Large structures, open packing, and chaotic framework fabric result in a better connected pore network, whereas small structures, tight packing, and organized fabric result in less connected pore networks. Comparative pore geometry analysis of the Upper Jurassic Smackover Formation thrombolites shows that their depositional textures also had high primary porosity values. If the microbial textures and petrophysical properties are environmentally controlled, their prediction in the subsurface is made possible by refined depositional models.

Wave damping by a vertical porous structure placed near and away from a rigid vertical wall

Damping of water waves by a vertical porous structure placed at some distance from a vertical wall is investigated within the framework of linear water wave theory. The rectangular porous structure is placed on a small rectangular elevation. An incident wave of small amplitude propagates through the structure – some portion gets reflected back while some portion gets transmitted to a third region bounded vertically by a rigid wall which is considered to be at a distance near the porous structure, and also away from the wall at a large distance as a separate case. Boundary value problems are set up in all three regions and, by using the matching conditions along the vertical boundaries, a system of linear equations is deduced. The roots of the relevant dispersion relation are used in setting up the system of equations. The overall scattering phenomenon is studied with respect to different relevant parameters. The dependence of the coefficients on the thickness (width) of the porous structure is investigated for different numbers of modes and porosity. It is observed that, except for the case when the porous structure is thin, the reflection and transmission coefficients give rise to values as expected. In the case, when the rigid wall is nearer to the structure, the reflection coefficient decreases rapidly for a thin structure and converges for all numbers of evanescent modes afterwards. The transmission coefficient also decreases as the width increases, ultimately converging and vanishing for a wide structure. When the wall is at a large distance away from the structure, the behavior of both the reflection and transmission coefficients remain the same. For both cases of the wall being nearer and away from the structure, higher porosity gives rise to lower reflection coefficients and higher transmission coefficients. However, the transmission coefficients converge and vanish when the porous structure is very wide. We also discuss the energy loss against the width of the porous structure for different values of number of modes and porosity. Irrespective of the positioning of the rigid wall, we observe that for higher values of porosity, energy loss is more pronounced when the structure is not thin, whereas energy loss is same for all numbers of modes. All our observations are supported by graphs. Good agreement of our result with earlier results justifies our model.

Petroleum system analysis of the Khatatba Formation in the Shoushan Basin, north Western Desert, Egypt

The Middle Jurassic Khatatba Formation is an attractive petroleum exploration target in the Shoushan Basin, north Western Desert, Egypt. However, the Khatatba petroleum system with its essential elements and processes has not been assigned yet. This study throws the lights on the complete Khatatba petroleum system in the Shoushan Basin which has been evaluated and collectively named the Khatatba-Khatatba (!) petroleum system. To evaluate the remaining hydrocarbon potential of the Khatatba system, its essential elements were studied, in order to determine the timing of hydrocarbon generation, migration and accumulation. Systematic analysis of the petroleum system of the Khatatba Formation has identified that coaly shales and organic-rich shales are the most important source rocks. These sediments are characterised by high total organic matter content and have good to excellent hydrocarbon generative potential. Kerogen is predominantly types II–III with type III kerogen. The Khatatba source rocks are mature and, at the present time, are within the peak of the oil window with vitrinite reflectance values in the range of 0.81 to 1.08 % Ro. The remaining hydrocarbon potential is anticipated to exist mainly in stratigraphic traps in the Khatatba sandstones which are characterised by fine to coarse grain size, moderate to well sorted. It has good quality reservoir with relatively high porosity and permeability values ranging from 1 to 17 % and 0.05–1,000 mD, respectively. Modelling results indicated that hydrocarbon generation from the Khatatba source rocks began in the Late Cretaceous time and peak of hydrocarbon generation occurred during the end Tertiary time (Neogene). Hydrocarbon primarily migrated from the source rock via fractured pathways created by abnormally high pore pressures resulting from hydrocarbon generation. Hydrocarbon secondarily migrated from active Khatatba source rocks to traps side via vertical migration pathways through faults resulting from Tertiary tectonics during period from end Oligocene to Middle Miocene times.

Characterization of structure of gluten-free breads by using X-ray microtomography

The effects of different gums and gum blends addition on crumb structure of gluten-free breads were studied by X-ray microtomography. The gums used were xanthan, guar, locust bean (LBG), agar, methylcellulose (MC), carboxymethylcellulose (CMC) and hydroxypropylmethylcellulose (HPMC) and the gum blends were xanthan–guar and xanthan–LBG. Porosity, number, average size, aspect ratio and roundness of pores were used as parameters to describe the internal structure of the crumbs. Characteristics of the crumb structure were related to the hardness, cohesiveness and springiness of breads. Gluten-free breads prepared with the addition of MC, agar and no additives had the highest porosity values with the lowest number of pores, which would be indicating a non-uniform crumb structure with large pores. There was a negative correlation between porosity and number of pores (r = −0.90) and a positive correlation between porosity and average size of pores (r = 0.80). Lowest porosity, lowest average pores area and the highest number of pores were observed on gluten-free breads prepared with the addition of xanthan, CMC, xanthan–guar, xanthan–LBG and HPMC. The higher number of smaller pores is associated with a finer crumb structure. Data showed that the hardness values of breads were positively correlated with porosity (r = 0.87) and average area of pores (r = 0.87) and negatively correlated with the number of pores (r = −0.92). On the other hand, cohesiveness and springiness values of breads were negatively correlated with porosity (r = −0.86 and −0.88), average area of pores (r = −0.81 and −0.90) and positively correlated with number of pores (r = 0.89 and 0.88).

Reservoir identification using full stack seismic inversion technique: A case study from Cambay basin oilfields, India

Abstract Full stack seismic data in Cambay basin, India, shows limited contrast between sandstone reservoirs and other lithologies. The seismic inversion result has been used here to convert the seismic reflection data into impedance log at each point and the ratio of every point. Wavelet estimations have been carried out for four wells namely, AM-11, AM-12, AM-13 and AM-14 lying between Sanand and Nawagam oilfields located in the Ahmedabad–Mehsana block of Cambay basin. The combination of P-impedance and compressional wave velocity (Vp) to shear wave velocity (Vs) ratio has been used to delineate the pay sand. Reservoir pay sand in Eocene pay formation has been delineated from these wells. The cross plotting technique between Vp/Vs (from four wells AM-11 to AM-14 under the study area) and P-impedance values has differentiated sand and shale. It is observed that the high P-impedance sand is associated with low porosity (15–18%) values while the low P-impedance sand is associated with relatively high porosity (20–25%) values.

3D interconnected porous biomimetic scaffolds: In vitro cell response

Bone cell response to 3D bioinspired scaffolds was tested on osteoblast culture supernatants and by means of quantitative polymerase chain reaction (qPCR). Foaming and freeze-drying method was optimized in order to obtain three-dimensional interconnected porous scaffolds of gelatin at different contents of nanocrystalline hydroxyapatite (HA). Addition of a non toxic crosslinking agent during foaming stabilized the scaffolds, as confirmed by the slow and relatively low gelatin release in phosphate buffer up to 28 days. Micro-computed tomography reconstructed images showed porous interconnected structures, with interconnected pores displaying average diameter ranging from about 158 to about 71 μm as the inorganic phase content increases from 0 to 50 wt %. The high values of connectivity (>99%), porosity (> 60%), and percentage of pores with a size in the range 100-300 μm (>50%) were maintained up to 30 wt % HA, whereas higher content provoked a reduction of these parameters, as well as of the average pore size, and a significant increase of the compressive modulus and collapse strength up to 8 ± 1 and 0.9 ± 0.2 MPa, respectively. Osteoblast cultured on the scaffolds showed good adhesion, proliferation and differentiation. The presence of HA promoted ALP activity, TGF-β1, and osteocalcin production, in agreement with the observed upregulation of ALP, OC, Runx2, and TGF-β1 gene in qPCR analysis, indicating that the composite scaffolds enhanced osteoblast activation and extra-cellular matrix mineralization processes.

Development and experimental verification of a mathematical model of lithium ion battery

A model of the lithium ion battery is developed which takes into account intercalation and extraction of lithium ions in the active mass of negative and positive electrodes, the dependences of equilibrium electrode potentials on the concentration of intercalated lithium, the ion transfer in pores of electrodes and the separator, the kinetics of electrode reactions, and the electric double layer charging. As the active material for the negative electrode, UAMS graphite material is used. Lithium-nickel-cobalt oxide serves as the positive electrode. The porous structure of electrodes is studied by the method of standard contact porosimetry. Sufficiently high porosity values found for both electrodes (50% for anode and 27% for cathode) made it possible to consider the interface as regards the internal pore surface found from porosimetry data rather than as regards their external surface as in the previous studies. A comparison of calculated and experimental discharge curves demonstrates their closeness, which points to the correctness of the model. By the fitting procedure, the coefficients of solid-state diffusion of lithium ions and the rate constants for reactions on both electrodes are found.

Carbonation Coefficients from Concrete Made with High-Absorption Limestone Aggregate

Normal aggregates employed in concrete have absorption levels in the range of 0.2% to 4% for coarse aggregate and 0.2 to 2% for fine aggregate. However, some aggregates have absorption levels above these values. As the porosity of concrete is related to the porosity of both the cement paste and the aggregate and the carbonation rate is a function, among other things, of the porosity of the material, there is concern about the effect of this high porosity material in achieving good quality concrete from the durability point of view. Thus, the objective of this investigation was to study the carbonation rates of concrete specimens made with high-absorption limestone aggregate. Four different water/cement ratios were used, and cylindrical concrete specimens were exposed to accelerated carbonation. High porosity values were obtained for concrete specimens beyond the expected limits for durable concrete. However, carbonation coefficients related to normal quality concrete were obtained for the lowest water/cement ratio employed suggesting that durable concrete may be obtained with this material despite the high porosity.

Ferrofluid Lubrication of Rotating Curved Rough Porous Circular Plates and Effect of Bearing’s Deformation

This investigation deals with Ferrofluid-based squeeze film performance in rotating curved transversely rough porous circular plates taking bearing deformation into consideration. The results suggest that the transverse surface roughness induces an adverse effect on the performance characteristics, while the magnetic fluid lubricant results in an improved performance. It is found that the combined effect of rotation and deformation causes significantly reduced load carrying capacity. This reduction in load carrying capacity comes at a critical phase when higher values of porosity and standard deviation are involved. However, it is revealed that the adverse effect of porosity, deformation and standard deviation can be compensated up to some extent by the positive effect of magnetic fluid lubricant in the case of negatively skewed roughness by properly choosing curvature parameters. To compensate, the rotational inertia needs to have smaller values.

RESERVOIR CHARACTERISTICS OF THE ALBIAN UPPER QAMCHUQA FORMATION CARBONATES, TAQ TAQ OILFIELD, KURDISTAN, IRAQ

The Albian Upper Qamchuqa Formation in NE Iraq is part of an extensive dolomitized carbonate platform developed during the Barremian – Albian over the passive continental margin of NE Arabia. Recent drilling at the Taq Taq oilfield in Kurdistan has renewed interest in this formation as a reservoir unit. In this paper, the reservoir and petrophysical characteristics of the Upper Qamchuqa Formation at Taq Taq are described using data from wireline logs, cores and thin‐sections from four wells.At Taq Taq oilfield, the Qamchuqa Formation can be divided on the basis of lithology into two units: an upper Dolomite Unit and a lower Limestone Unit. The Dolomite Unit is 140–190 m thick and is dominated by massive dolomites and dolomitic limestones. High porosity values (up to 26%, estimated from well logs) were recorded in intervals comprising fine to medium crystalline planar‐e to planar‐s type dolomite which were frequently oil stained. Pore types include microvugs, moulds, fractures, stylolites and intercrystalline porosity. The Limestone Unit is 72–55 m thick and is composed mainly of bioturbated bioclastic limestones with minor dolomites. A wide range of carbonate facies are present and are dominated by foraminiferal wacke‐packstones and rudist packstones.Wireline log data was used to characterize the reservoir quality of the Qamchuqa Formation at Taq Taq. Four porosity units were recognized. The upper porosity units has the best reservoir quality with average porosities of 15 %, compared to the second unit (7.5%), the third unit (7%) and the fourth unit (4%).Different cut‐off values were estimated, and related petrophysical parameters were evaluated and were used to subdivide the reservoir succession into three reservoir units. The uppermost of these units was found to have the best reservoir characteristics and represents the upper part of the Dolomite Unit. It has a thickness of 31–43.5 m with 25–41 m of net pay and 82% oil saturation. Flow in this unit is dual, dominated by fracture flow superimposed on matrix flow.

Seismic sedimentology study in the high-resolution sequence framework—a case study of platform margin reef-beach system of Changxing formation, Upper Permian, Yuanba Area, Northeast Sichuan Basin, China

The Yuanba (元坝) area is considered another potential large-scale reef-bank gas field following the Puguang (普光) field. However, there are lots of difficulties on the spatial and temporal distribution of reef-beach and the detailed prediction of the effective reservoir in the sequence stratigraphic framework. In this paper, based on the seismic data, well, log and core, we conduct a high-resolution sequence division and build an isochronal sequence stratigraphic framework for the Changxing (长兴) Formation by the methods of wavelet transformation, FMI, etc.. Then, the corresponding relationship among the lithologic facies, logging facies, seismic facies, seismic attribute facies and reservoir of Changxing Formation were established through well-seismic calibration and geological-geophysical modeling. Furthermore, detailed study on the spatial and temporal distribution of microfacies of the reef-beach was carried out by means of seismic attribute extraction. Meanwhile, combined with impedance inversion, the spatial distribution of porosity of reef-beach reservoir was predicted. The results show that the revolution of the reef-beach system contains three stages which are initial bioclastic bank establishment stage, reef development stage and exposure stage. Also, porosity inversion shows that the region with high value of porosity is located in the reef cap, fore reef and back reef.

Effect of subsurface hydrological properties on velocity and attenuation of compressional and shear wave in fluid-saturated viscoelastic porous media

Summary Over the past years there has been a growing interest in the use of seismic waves to gain required information about the Earth’s subsurface. Despite all achievements, the problem of accurately linking field measurement of seismic attributes to subsurface hydrological properties such as porosity and intrinsic permeability is still ambiguous. The goal of the present paper is to provide a comprehensive study on the effect of subsurface hydrological properties on seismic attributes such as wave attenuation and velocity. This is achieved by using dispersion relations obtained from equations of wave motion that are derived from Biot’s theory of poroelasticity. Since the attenuation predicted from Biot’s theory is only due to relative motion of the solid and fluid phases, viscoelasticity effects are introduced to consider the attenuation caused by grain to grain contact. The dispersion relations for body waves including fast wave, slow wave and shear wave are valid in both low and high frequency ranges where viscous and inertia effects are dominant, respectively. Numerical simulations are performed on sand samples over a wide range of frequencies (1 Hz to 1 MHz). For samples with constant porosity, but different intrinsic permeabilities, it is demonstrated that the velocity of slow wave is higher for the more permeable sample over the full frequency range. The velocity of fast wave and shear wave is higher for the more permeable sample, but the difference is significant only at intermediate frequencies (10–100,000 Hz). However, the corresponding peak velocity and attenuation of each of the wave modes are almost equal for different intrinsic permeability values and, therefore, independent of intrinsic permeability. Another series of numerical simulations are carried out on sand samples with different porosity values. It is shown that the most porous sand has higher slow wave and shear wave velocity, but lower fast wave velocity. Also, the peak attenuation of fast wave and shear wave gets larger as sand porosity increases, but slow wave behavior is opposite. Remarkable result is that all wave modes become more dispersive when porosity increases. Thus, neglecting the dependence of wave velocity on frequency can lead to significant miscalculation of wave velocity for sand samples with high porosity values.

Assessing the accuracy of volume averaging effective diffusivity estimates with Brownian dynamics simulations

The volume averaging method (VAM) is widely used for estimating the effective diffusivity for solute transport in constrained geometries (e.g., porous media). Comparisons with experimental results for different geometric configurations have indicated that the VAM can provide accurate results over a wide range of porous media configurations. This work uses Brownian dynamics simulations (BDS) to estimate effective diffusivities for constrained geometries and to assess the accuracy of estimations from the VAM. For simple microscale geometric configurations, both isotropic and non-isotropic, it was found that the results predictions of effective diffusivity from VAM agree well with results from the BDS for high porosity values. However, some discrepancies are found for low porosity values, which were attributed to a smoothing effect of the VAM closure problem in the vicinity of very small apertures.

Investigation of wicking, wetting and drying properties of acrylic knitted fabrics

In this study, it was aimed to investigate the relationship between different knitted structures and some thermo-physiological comfort parameters. Wetting, wicking and drying properties of single jersey, 1 × 1 rib, 2 × 2 rib and interlock knitted fabrics made out of acrylic yarns were studied and experimental wicking height, wicking weight, transfer wicking ratio, contact angle and WER (water evaporation rate) values were measured. Samples were produced in two different tightness values to obtain slack and tight fabrics for all structures. Some comfort-related parameters were correlated with structural parameters of fabrics such as fabric tightness factor, thickness, porosity, loop length and pore size etc. The statistical analysis results indicate that the effect of the knitted structure is significant for wicking height, wicking weight, contact angle values, transfer wicking ratios and WER values. Wicking height increases depending on knitted structures namely, single jersey, 1 × 1 rib, interlock and 2 × 2 rib, respectively. Slack fabrics have longer loop lengths with higher porosity values and higher pore sizes for all knitted structures. Slack structures of 2 × 2 rib, 1 × 1 rib, interlock and single jersey knits have higher transfer wicking ratios when compared with their tight structures. WER is inversely related with fabric thickness. It decreased with an increase of thickness due to increase of compactness and decrease of air space. All tight knitted structures have higher contact angles than their slack forms due to compactness of the surface.

Analysis and modeling of petrophysical parameters of the Main Dolomite formation on the basis of well logging and seismic data

The Main Dolomite is one of the most prospective hydrocarbon reservoir formations in Poland. The goal was to determine the Main Dolomite zonation in selected part of carbonate platform sedimentation area and also to analyze the influence of cementation factor on water saturation by well logging and seismic data integration. Well logging interpretation quantitatively characterized petrophysical parameters. Seismic inversion presented the distribution of the parameters at vertical and horizontal scales. Basic statistical calculations of petrophysical parameters, 2D crossplots and seismic inversion were made. The central part of the Main Dolomite interval indicated the best reservoir properties. High porosity values and low P-wave velocity, low bulk density and low water saturation values were observed in the analyzed zone. Mudlogging confirmed the occurrence of gas. Determination of hydrocarbon saturation in carbonates is a challenge for well logging interpretation and geophysical interpretation. The cementation factor is one of the main coefficients in petrophysics which strongly affect water saturation. Adopting the wrong value of this parameter causes serious error in the coefficient of the water saturation value. In the paper, water saturation was modeled using the Borai equation and Shell formula. By using the computed water saturation and fluid substitution method theoretical velocities of P-waves and S-waves (also P-wave/S-wave velocity ratio) were calculated. Results of the comprehensive interpretation of logs are the basis for lithology determination but P-wave and S-wave velocity can also serve as a source information about lithology. In reservoir rocks VP/VS ratio may also work as a confirmation of gas saturation.

Electrochemical Performance of Polyvinyl Alcohol Nano-fiber based Nonwoven Separator for Lithium ion Battery

Micro porous nonwoven as separator for lithium ion battery has been developed using electrospun polyvinyl alcohol (PVA) nano-fibers with diameter of around 250 nm. The PVA nonwoven showed higher porosity, lower Gurley value and better wettability in an electrolyte solution than polyolefin micro porous membrane separator. The nonwoven was electrochemically stable in the voltage range of 3 to 4.5 V vs. Li+/Li on a cyclic voltammetry measurement. In spite of its high porosity and low Gurley value, any internal short circuit was not observed for cell using it during charge-discharge test. The cell also showed better cycle stability and rate capability than that using a polyolefin one, which could be attributed to low Gurley value, high porosity and better wettability of the PVA nonwoven.

Prediction of lithofacies and reservoir quality using well logs, Late Cretaceous Williams Fork Formation, Mamm Creek field, Piceance Basin, Colorado

Understanding the controls and distribution of reservoir quality is important for the economic success of tight-gas reservoirs in which diagenesis interacts with primary depositional variations in environment and texture to exert a strong control on pore networks, rock mechanical properties, and natural fractures. In the Upper Cretaceous Williams Fork Formation of the Piceance Basin, framework grain composition is a major control on compaction and the occurrence of authigenic phases. Alteration of volcanic grains in the upper Williams Fork led to grain-coating clay precipitation. Ferroan dolomite cement is found only in the deeper marine-influenced intervals in which dolostone fragments are present. This study shows that careful petrographic assessment of lithofacies heterogeneity can be upscaled by correlation with log properties to yield tools for field-scale reservoir quality prediction. Twelve lithofacies are identified based on sand-grain populations, cement types, and clay matrix content. Sandstones of the highest reservoir quality are those with grain-coating clays that inhibit quartz cementation; these sandstones can be identified based on high-density porosity log values. Sandstones with the poorest reservoir qualities are tightly cemented with carbonate and quartz cement or are rich in clay matrix. Carbonate-cemented intervals are identified by low-density porosity. Clay matrix–rich samples have high gamma-ray and low-density porosity values. The presence of abundant potassium feldspar in the upper intervals results in high gamma-ray readings even in the clean (clay matrix–free) sandstone.

Particle size, porosity and temperature effects on char conversion

The effect of particle size, porosity and reactor temperature/reaction rate constant on the progress of a char particle conversion has been investigated numerically by solving the transport equation inside a reacting char particle. Numerical simulations have been conducted for three cases that include two extreme cases and one general case. The two extreme cases correspond to a very large Damkohler number (3.2607 × 10 3) and a very small Damkohler number (0.0042). The third case corresponds to an intermediate value of Damkohler number. For the very large Damkohler number case, concentration profiles of the gasifying agent showed a steep gradient across the particle and the reaction occurred mostly in outer layer of the particle. This behavior corresponds to a diffusion controlled process. For the very small Damkohler number case, gasifying agent concentration was a straight line parallel to the x-axis, with a y-axis value of the surrounding concentration. The reaction occurred homogeneously across the particle and the degree of conversion was only a function in time. This behavior corresponds to a chemically controlled process. The total conversion of the char particle as a function of time has also been calculated for different particle sizes, initial porosity and reaction rate constant. Variation in conversion profiles as a function of time due to variation in initial porosity and reaction rate constant were limited to a certain extent. Very high initial porosity values tend to shift the process towards a chemically controlled one; any further increase in porosity does not have a positive effect on the conversion–time relationship. Very high reaction rate constants tend to shift the process towards diffusion controlled process. Kinetic parameters have been determined experimentally using a chemically controlled process. The obtained parameters have been used in the model to determine the progress of char particle conversion at an increased reactor temperature of 1000 °C. The model has been compared to experimental results at the same temperature (1000 °C). The results showed very good agreement.

Geometric and Hydrodynamic Characteristics of Three-dimensional Saturated Prefractal Porous Media Determined with Lattice Boltzmann Modeling

Fractal and prefractal geometric models have substantial potential for contrib- uting to the analysis of flow and transport in porous media such as soils and reservoir rocks. In this study, geometric and hydrodynamic parameters of saturated 3D mass and pore-solid prefractal porous media were characterized using the lattice Boltzmann model (LBM). The percolation thresholds of the 3D prefractal porous media were inversely correlated with the fraction of micro-pore clusters and estimated as 0.36 and 0.30 for mass and pore-solid pre- fractal porous media, respectively. The intrinsic permeability and the dispersivity of the 3D pore-solid prefractals were larger than those of the 3D mass prefractals, presumably because of the occurrence of larger solid and pore cluster sizes in the former. The intrinsic permeabil- ity and dispersivity of both types of structure increased with increasing porosity, indicating a positive relationship between permeability and dispersivity, which is at odds with laboratory data and current theory. This discrepancy may be related to limitations of the convection dispersion equation at the relatively high porosity values employed in the present study.

Geoelectrical studies for estimating aquifer hydraulic properties in Enugu State, Nigeria

2over eight main geological formations. The thickness, lateral extent and resistivity of the aquiferous layers were determined by the electrical survey. Also, zones of high yield potentials were inferred from the resistivity information. Transmissivity values were inferred using the empirical relationship between hydraulic conductivity and formation factor. Results show highly variable thickness of the main aquifer in the study area. Aggregate longitudinal conductance indicates greater depth of the substratum in the central part of the area, underlain by the Ajali and Nsukka Formations. High values of transmissivity, specific yield and moderate porosity also predominate, thus suggesting thick and prolific aquiferous zone. Lower average values of these parameters were obtained in southwestern and eastern parts underlain by the Imo and Ezeaku/ AwguNdeaboh/ Nkporo Formations, with the eastern part recording the lowest values, except porosity with the highest estimated average value. Maps of various geoelectrical and hydraulic parameters have been produced and the overall results can serve as a useful guide in planning a drilling program in the study area.