Permeability Variation Research Articles

Influences on geothermal circulation in the Okataina Volcanic Centre, New Zealand

The Okataina Volcanic Centre (OVC) in the Taupo Volcanic Zone (TVZ) is New Zealand's most recently active caldera and lava dome complex, erupting 85 km3 of magma equivalent in the past 21 ka. Successive caldera collapses over the past ∼550 kyr have created a complex crustal structure through which fluids now migrate, evidenced by hot springs and several geothermal fields located predominantly around the caldera margins. While recent magnetotelluric (MT) modelling suggests that high-temperature upwelling fluids originate from mid-crustal locations at the margins of an inferred magmatic complex, it is still uncertain to what degree various factors influence these fluid pathways from source to surface. Here, we use heat and fluid flow models to explore the roles that simplified geological structures, topography, and deep, localised heat sources play in determining the locations of upflow at the OVC.To isolate and understand individual processes that modulate fluid flow, we created TOUGH2 heat and fluid flow models that encompass a 35 by 39 km2 area extending beyond the topographic boundaries of the OVC calderas. An average heat input of 700 mW/m2 was set at the base of the models at 5 km depth, either as a uniform hot plate or as discrete zones of higher heat input with locations derived from MT models. The upper boundary of the models followed water table elevation, which is a slightly muted reflection of topography. We constructed a suite of models, ranging from uniform rock properties to more complex permeability variations that correspond to basement/volcanic rocks and large-scale faults inferred from gravity data and surface mapping. Models ran for 50 kyr, the approximate time since the most recent caldera-forming event. Elevated model temperatures were compared with low-resistivity zones from shallow (<500 m) Direct Current (DC) apparent resistivity values and deeper sensing MT resistivity models.Our models suggest that topography and localised basal heat sources are the largest influences on the locations of geothermal upflows. In the western half of the study area, observed upflows beneath Waimangu and Tikitere can be modelled with localised heat sources and topography alone. Upflow under Rotoma to the north-east is not replicated by any of our suite of models, suggesting that unmapped heat sources are important in this area. In the east of the study area, modelled upflow is dominated by present-day topography which is strongly influenced by <25ky Tarawera and Haroharo Volcanic Complexes and < 1ky Tarawera River valley. Our models suggest that strong permeability contrasts associated with large-scale faults would have effects on regional-scale fluid circulation that are not observed in real life, and that the coincidence of OVC topographic boundaries and geothermal systems is due to the boundaries' also being topographic lows rather than fluid conduits.

Modeling and Optimization of Vanadium Flow Batteries Incorporating Variable Permeability and Resistance

The vanadium flow battery employing vanadium element of different valences as the active substances for both sides is a promising device for large-scale energy storage applications. In this paper, a vanadium flow battery dynamic model incorporating the variable vanadium ion permeabilities and cell resistance is proposed, and the cell performance is subsequently analyzed and optimized. The variation of permeability and resistance is tested, and a laboratory flow cell is engaged for simulation. The results demonstrated that: (i) the proposed model behaves a superior prediction precision in comparison with the existing models with constant permeability and resistance; (ii) operated in temperature range of 25 °C and 35 °C is favored to achieve an improved energy efficiency; (iii) low and high operating temperatures are respectively preferred for vanadium flow batteries operated at low and high current densities. Such in-depth analysis can not only be highly beneficial to the operation and optimization of vanadium flow batteries to realize an enhanced performance, but offer a cost-effective modeling method with high accurate prediction precision to understand the characteristic and behavior of vanadium flow batteries within a wide operating temperature as well, thus avoiding large amounts of experimental testing that expends extensive materials and time.

An improved apparent permeability model considering full pore pressure range, variable intrinsic permeability and slippage coefficient

An improved apparent permeability model considering full pore pressure range, variable intrinsic permeability and slippage coefficient

3D Simulations of gas injection on callovo-oxfordian claystone assuming spatial heterogeneity and anisotropy

A series of gas injection tests on Callovo-Oxfordian (COx) claystone from the Bure underground research laboratory (URL) in France were carried out at the British Geological Survey (BGS). The tests were performed using a triaxial apparatus specifically designed to capture small volumetric strains induced by the injected gas flow and consequent material dilatancy. The long-duration experiments were monitored throughout. Measurements also included pressure, stresses (axial and radial stresses prescribed for each test stage), rate of gas inflow, gas outflow volume as well as pore-pressures observed at various points of the sample. A coupled hydro-gas-mechanical 3D numerical model has been developed to simulate the tests. Initial permeability is assumed heterogeneous throughout the specimen and embedded fractures are incorporated in the formulation. Gas pressure-induced deformations during the test lead to variations of permeability due to changes in matrix porosity and, especially, fracture aperture as well as fracture orientation due to material anisotropy. A programme of sensitivity analyses involving the variation of different aspects and parameters of the model contributes to a better understanding of the phenomena and highlights its complexity. The model is able to reproduce the observed behaviour of the tests.

Pore-scale study of mineral dissolution in heterogeneous structures and deep learning prediction of permeability

Reactive transport processes in porous media with dissolution of solid structures are widely encountered in scientific and engineering problems. In the present work, the reactive transport processes in heterogeneous porous structures generated by Monte Carlo stochastic movement are simulated by using the lattice Boltzmann method. Six dissolution patterns are identified under different Peclet and Damkohler numbers, including uniform pattern, hybrid pattern, compact pattern, conical pattern, dominant pattern, and ramified pattern. Particularly, when Peclet and Damkohler numbers are larger than 1, the increase in the heterogeneity rises the chance of preferential channel flow in the porous medium and thus intensifies the wormhole phenomena, leading to higher permeability. The pore-scale results also show that compared with the specific surface area, the permeability is more sensitive to the alteration of the structural heterogeneity, and it is challenging to propose a general formula between permeability and porosity under different reactive transport conditions and structural heterogeneity. Thus, deep neural network is employed to predict the permeability–porosity relationship. The average value of mean absolute percentage error of prediction of 12 additional permeability–porosity curves is 6.89%, indicating the promising potential of using deep learning for predicting the complicated variations of permeability in heterogeneous porous media with dissolution of solid structures.

Permeability evolution of coal subjected to triaxial compression based on in-situ nuclear magnetic resonance

A knowledge of permeability evolution with stress is important for the enhancement of coalbed methane production . In this study, a series of compaction-permeability tests with in-situ nuclear magnetic resonance (NMR) measurement were conducted by using a designed NMR testing system equipped with a loading device. Based on the NMR results, the permeability variation mechanism is investigated during the complete stress-strain process. The stress damage and its influence on permeability are analyzed. Experimental results illustrate that the permeability curve shows a slow decrease first, followed by a stable change, then a slow increase, and finally a sharp rise during the complete stress-strain process. Permeability evolution is closely related to coal pores. Adsorption pores have little contribution to the coal permeability while seepage pores contribute over 99% to the permeability. The permeability growth is found to lag behind the coal pores growth due to the poor connection of new pores. With the increase of damage, coal permeability increases nonlinearly. A power function can be used to describe the relationship for the tested samples.

Nonlinear consolidation analysis of multilayered soil with coupled vertical-radial drainage using the spectral method

The nonlinear variation of soil compressibility and permeability with void ratio (i.e., e-log σ′ and e-log k) has been included in the consolidation theory to accurately predict the behavior of soft soil stabilized by vertical drains. However, most current nonlinear consolidation models incorporating the coupled radial-vertical flow are based on some simplified assumptions, while including some features such as the complex implementation of multilayered computations, time-dependent loading and stress distribution with depth. This study hence introduces a novel approach where the spectral method is used to analyze the nonlinear consolidation behavior of multilayered soil associated with coupled vertical-radial drainage. In addition, time- and depth-dependent stress and soil properties at each soil layer are incorporated into the proposed model. Subsequently, the solution is verified against experimental and field data with comparison to previous analytical solutions. The results show greater accuracy of the proposed method in predicting in-situ soil behavior. A parametric study based on the proposed solution indicates that the ratio between the compression and permeability indices (ω = Cc/Ck) has a great impact on the consolidation rate, i.e., the greater the ω, the smaller the consolidation rate. Increasing the load increment ratio and the absolute difference between unity and ω (i.e., |ω − 1|) can exacerbate prediction error if the conventional simplified methods are used.

Theoretical analysis of entropy production in exothermic/endothermic reactive magnetized nanofluid flow through curved porous space with variable permeability and porosity

In current analysis, flow of magnetized nanofluids in porous curved stretchable surface with variable characteristics has been inspected by imposing the thermal radiation, and activation energy. The exothermic/endothermic reactive effect is included along with Buongiorno nanofluid model to investigate the thermal performance more extensively. The Lorentz force characteristics that cause the interaction of magnetic field with nanoliquid motion is further investigated. Additionally, production of entropy in the porous curved system because of irreversible process has been considered here. The modeled systems for considered model are firstly transformed into ODEs via appropriate variables and then computed by employing NDSolve technique using tool of Mathematica. Flow fields variation against relevant variables is inspected via tables and sketches. The key outcome of analysis is that, the entropy rate upsurges for higher local inertia parameter, radiation variable and Brinkman number.

Large and Nonlinear Permeability Amplification with Polymeric Additives in Hydrogel Membranes

Hydrogels which are hydrophilic and porous materials have recently emerged as promising systems for filtration applications. In our study, we prepare hydrogel membranes by the photopolymerization of a mixture of poly (ethylene glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300 000 g.mol-1 in the presence of a photoinitiator. We find that this addition of free PEG chains induces a large and non-linear increase of the water permeability. Indeed, by changing the content of PEG chains added, we obtain variations of the hydrogel water permeability over two orders of magnitude. The highest water permeability values are obtained for the membranes when the PEG concentration is equal to its critical overlap concentration C*. Moreover, we find that the flow rate of water through the membranes varies non-linearly with the pressure. We relate this result to the deformability of the membranes as the applied pressure leads to a compression of the pores. This study provides new perspectives for the design of flexible hydrogel membranes with controlled permeability and their application in water treatment and bioseparation.

Upscaling unsaturated flows in vertically heterogeneous porous layers

Characterising interfacial and unsaturated flows in heterogeneous porous layers is of both fundamental and practical interest. Under the assumption of vertical gravitational–capillary equilibrium, we present a theoretical model to describe one-dimensional flows in a porous layer with vertical variations in average pore size, porosity, intrinsic permeability and capillary pressure jump between invading and displaced fluids. The model leads to asymptotic solutions for the saturation distribution and outer envelope of the invading fluid, and for the background pressure drop across the porous layer. Eight dimensionless parameters are recognised after appropriate non-dimensionalisation of the governing equations, the influence of which is demonstrated through a series of example calculations. In particular, four asymptotic regimes are identified, representing unconfined sharp-interface flows, confined sharp-interface flows, unconfined unsaturated flows and confined unsaturated flows. Finally, in the context of flow upscaling, analytical solutions are derived for the effective relative permeability curves on the basis of exact solutions of the saturation field and interface shape, shedding light on the subtle influence of competition between injection/pumping and gravitational forces, wetting and capillary effects, viscosity contrast between the invading and displaced fluids and vertical heterogeneity of the porous layer.

Gas permeability variation during methane hydrate dissociation by depressurization in marine sediments

Accurate acquisition of permeability change in hydrate-bearing sediments (HBSs) is the key to predicting reservoirs' multiphase fluids distribution and production capacity. Hydrate saturation and effective stress present significant effects on reservoir permeability. Thus, the influence of hydrate saturation and effective stress on gas permeability change of remolded core during decompression was studied. The results showed that effective stress compression and hydrate decomposition determine the flow channel structure within hydrate sediments. Under unconsolidated and low effective stress(σ' = 1.2 MPa) conditions, the gas permeability increased gradually as the decomposition of hydrate, and the magnitude of permeability variation before and after decomposition increased with increasing hydrate saturation, indicating that the effect of hydrate saturation on permeability dynamic change dominated at low effective stresses. When σ′ was increased to 3.2 MPa and 5.2 MPa, the results were contrary, indicating that the effective stress variation on gas permeability dynamic change dominated at higher effective stresses. In addition, it was found that compression led to higher heat transfer efficiency in high-saturation samples. When hydrate saturation was increased from 23.37% to 48.7%, the effect of increasing effective stress on gas production changed from inhibition to facilitation.

Spatial variation of permeability and consolidation behaviors of soil using ordinary kriging method

The present study is aimed at finding out spatial distribution of permeability characteristic of soil using ordinary kriging method at any location using the data from a few boreholes at NIT (National Institute of Technology) Patna Bihta campus. Kriging is also popularly known as BLUE (i. e. Best Linear Unbiased Estimator) which can be used to interpolate the data obtained from a few locations to get an estimate of any parameter at other locations throughout the study area. In the present work, soil samples collected from eight boreholes have been tested to obtain various geotechnical properties including liquid limit (LL), plastic limit (PL), plasticity index (IP), coefficient of volume compressibility (mv) etc. These values have been used as inputs in an Ordinary Kriging model to calculate coefficient of consolidation (Cv) and coefficient of permeability (k) throughout the NIT Patna, Bihta campus and build contour plots of (Cv) and (k) over the NIT Patna campus to show their spatial variation. The novelty of the current work lies in the first time proposed method for developing the spatial distribution of(Cv) and(k). Markov correlation matrix has been used to develop the correlation behavior of the parameters considering different values of correlation length. In the present study, it is found that the coefficient of consolidation Cv of soil ranges 10−8 (m2/sec). The Kriged values of k are in the range of 10−11 to 10−10 (m/s). Finally, semi-variogram have been shown to display the auto-correlation of the measured data points and cross-validation of data set which establish that the Kriged data are reasonably correlated. Also, various error estimators such as Mean Error, Root Mean Square Error, Average Standard Error, Root Mean Square Standard Error, Mean Standard Error have been calculated using the Kriged data points over the entire area and, it is found that the error level in the predicted Kriged data are reasonably small.

Outcrop scale mixing enhanced by permeability variations: the role of stationary and travelling waves of high saturation indices

AbstractTo study the ore mineralization at the outcrop scale we merge an advection–diffusion simulation with the geochemical software iphreeqc to model the mixing of two realistic fluids. We simulate the infiltration of a metal-rich fluid into a rock that is saturated with pore fluid. We test the feedback effects with a number of scenarios based on an outcrop-scale 5 × 5 m model consisting of two high-permeable vertical faults within a low-permeable host rock that lead into a permeable layer. The hot metal-rich fluid enters the model through the faults from below. We solve the advection–diffusion equation for 12 chemical species and temperature, and use iphreeqc to determine the resulting properties of local fluid domains as well as related saturation indices for minerals. The faults in the model act as pathways for the metal-rich fluid, with the infiltrating fluid displacing the pore fluid. Mixing in the model takes place as a function of advection along permeable faults coupled with diffusion of chemical species at the interface between two fluids, while heat diffusion is fast enough (103 times faster) to equilibrate temperature. Simulations show a high saturation index of mixing-derived minerals such as barite at the interface between the two fluids as a result of fluid mixing. Fast fluid pathways (i.e. faults) show travelling waves of high saturation indices of barite, while low-permeability zones such as fault walls and areas below less permeable layers experience stationary waves of high saturation indices. Our results show that, depending on the dominant transport process (advection or diffusion), mineralization will localize next to permeability contrasts in zones where local diffusion dominates.

Numerical simulations of the synthetic processes and consequences of secondary hydrates during depressurization of a horizontal well in the hydrates production

The depressurization method was implemented through a horizontal well in the production test at Shenhu, the South China Sea in 2020. The numerical model of a layered hydrate reservoir was established based on the in-field data of this test. The gas production rates measured was validated by comparing with the numerical results. The synthesis time, scopes, gas sources and maximum saturations of secondary hydrates were originally clarified by analyzing the data from different monitoring sections, which followed by the sensitivity analyses against the initial permeability of each hydrate-bearing layer. The effect of secondary hydrates on the short-term and long-term productions was quantified. The hydrates were resynthesized extensively above the interface between the natural gas hydrate layer and the mixing layer, which reduced the in-situ permeability and then the well gas production seriously. The areas affected by depressurization were constrained within the mixing layer. The gas sources were supplemented by the primary free gas and the gas decomposed by the hydrates in the upper mixing layer. The vertical extensions of the secondary hydrates were limited to about 5 m due to the lower permeability, while the horizontal distributions were approximately 78 m away from the horizontal well after 3 years. Given that the secondary hydrates were eliminated artificially, the cumulative gas volume produced in the horizontal well was increased by 24% after 3 years. The sensitivity analysis showed that the variations of permeability in the mixing layer had more obvious effects on secondary hydrates. Therefore, the hydraulic fracturing could be used to prevent the resynthesis of hydrates.

Numerical Simulation of Entropy Optimization in Radiative Hybrid Nanofluid Flow in a Variable Features Darcy–Forchheimer Curved Surface

Studies associated with ethylene glycol (EG) have great significance in various engineering sectors because EG is more useful as a cooling agent in various engines. Furthermore, fluid inspection using two distinct nanoparticles has applications in mechanical systems, electronic devices, medical apparatus, and the diagnosis and treatment of disease. Therefore, present comminution explored the entropy production in magnetized hybrid nanomaterials flowing via Darcy–Forchheimer space with varying permeability. Hybrid nano liquid is synthesized by adding cobalt ferrite and gold nanoparticles to ethylene glycol and water. Effects of thermal radiation, Joule heating, heat sources, and an exponential heat source are considered in the energy expression. The assumed problem is modeled in the form of nonlinear PDEs. Such types of problems have mostly occurred in symmetrical phenomena and are applicable in engineering, physics, and applied mathematics. The obtained system is converted to ODEs using suitable substitution transformations. Resultant ODEs are numerically computed with the help of the NDSolve technique using Mathematica software. Their outcomes are displayed through figures and tables. Obtained results reveal that variable permeability and curvature parameters improve the velocity profile, while an exponential heat source (EHS) enhances the thermal effect. It is also observed that entropy optimization improves with the increment in magnetic parameter.

Deformation characteristics and permeability variations induced in the coal matrix induced by thermo-mechanical coupling

ABSTRACT To evaluate the coal deformation characteristics and explore the evolution law of coal permeability under different conditions, the MTS815 and PCI-2 acoustic emission (AE) test systems were applied to conduct the triaxial percolation test under other thermo-mechanical coupling conditions, and the fractal model of coal fractal with integrated stress and temperature was established. The results indicated that the peak stress, strength and deformation parameters of the samples were positively correlated with the confining pressure. The temperature can promote the crack propagation, derivation and new cracks of coal samples. The macrocracks and percolation channels space inside the samples increased with the increase of the thermal-mechanical coupling condition. The AE signal was mainly released in the plastic and peak phases; the growth of confining pressure intensified the aggravation of the internal damage to the coal sample and caused the frequent occurrence of AE signals. The compressive coefficient C f of coal fracture decreased with the addition of average effective stress, and the ruptured coal had the same trend with the increase in pore pressure; the calculated values of the new thermally sensitive model were consistent with the measured values. The applicability of the theoretical mechanism and the data matching were of high credibility.

Nano-scale multicomponent hydrocarbon thermodynamic transport mechanisms in shale oil reservoir

Hydrocarbon mass transport in nanoporous media notably differs from that in traditional micro-scale porous media due to strong solid-fluid interaction in nanoscale confined pore space. Accurate prediction of hydrocarbon thermodynamic transport in nanoporous shale must consider the bound water distribution pattern, fluid occurrence in dual-wet pores (organic and inorganic), thermodynamic phase equilibrium, boundary slippage and rheological property. So far, there is no such a model that incorporates the above mentioned factors into assessing the multicomponent hydrocarbon mass transport in nanoporous shale. In this work, we propose a pore network based multicomponent hydrocarbon mass transport model considering above mentioned factors and the multicomponent hydrocarbon thermodynamic transport mechanisms are elucidated in detail. The bound water film stability and induced capillary condensation are first analyzed according to Kelvin equation and the extended DLVO theory. A thermodynamic phase equilibrium-fluid occurrence coupling model is further developed considering the oil-gas capillary pressure change with oil saturation on pore network model (PNM). The multicomponent hydrocarbon single pore transport model is derived considering boundary slippage, adsorption layer thickness and fluid rheology and is extended to PNM transport simulation. The multicomponent hydrocarbon permeability variations at different pressure, pore size, relative humidity and total organic carbon (TOC) are analyzed in detail. The predicted hydrocarbon flux change with pressure gradient matches well with the previous observed trend in the laboratory experiments. Study results reveal that the multicomponent hydrocarbon exhibits non-linear transport behavior determined by the fluid rheology and the threshold pressure gradient for hydrocarbon starting to flow is mutually controlled by the yield stress and pore size.

Quantification analysis of geometric characteristics of micro crack network on fault rock surface

Faults are common water conduits in coal mines, with variable permeability based upon the extent of cracks along the fault plane. In this study, three samples from a fault were obtained from a mining area in Southwest Shandong, China to determine the geometric characteristics, including crack density, fractal dimension, and crack connectivity. For microstructural analysis of fault rock specimens, scanning electron microscopy (SEM), x-ray diffraction (XRD), and plane-polarized light microscopy tests were used, and the geometric characteristics were calculated. A nonuniformity coefficient that considers the mineral composition is proposed to describe the micro-crack network of fault rocks. The results show that there is a significant positive correlation among three geometric characteristic parameters, and the nonuniformity coefficient is positively correlated with those parameters of the crack network. The crack extension forms of the three fault rock samples are different, which is related to the different fracture toughness of the mineral particles. The optical photomicrographs and SEM images show that crack networks are most developed in the samples with the least clay content. There is a negative correlation between clay content and the geometric parameters of the crack network, which may be related to the friction coefficient of clay.

Heating Rate Effect on Gas Permeability and Pore Structure of Mortar under High Temperature.

This experimental study investigated the effect of heating rate on mortar gas permeability and microstructure. The mortar was heated to three target temperatures (400 °C, 500 °C, and 600 °C) at three heating rates (5 °C/min,10 °C/min, and 15 °C/min). The variations of gas permeability and porosity were measured simultaneously at different confining pressures, and the changes in mortar microstructure were analyzed by NMR and SEM techniques. The results show that the porosity and gas permeability increase with an increase in temperature and heating rate. The gas permeability and porosity continue to decrease as confinement is increased due to a reduction in the pore volume. The microstructure observed by SEM indicates that the high heating rate induces some microcracks at 500 °C and 600 °C. The fractal dimension based on NMR can quantitatively characterize the complexity of the mortar pore structure and shows a quadratic decreasing relationship with gas permeability and porosity.

Description and characteristics of chert nodules in Appollonia Formation, Al Hmmeda road-cut, Al Jabal Al Akhdar, NE Libya

Physical, petrographic and bulk elements analysis of Chert Nodules in Appollonia Formation, Al Hmmeda road-cut were conducted and showed that the origin of these chert by replacement. The suspected siliceous organic matters are of low crystallized silica and were dissolved under the influence of increasing temperature and pH. Most of the chert was localized in the limestone and dolomitic limestone of Appollonia Formation (nodular zone) by percolation of silica-rich solution along microfractures and porous/permeability zones. This local porosity and permeability variations, mostly produced mixing of the diffused digenetic fluids. This process produces the nodular form of the cherts in the Appollonia mudstone facies in the nodular zone, while less marked permeability variations could have produced more regular tabular bodies of chert, which were not observed at least in the studied section. The absence of chert nodules in some adjacent rocks and even at higher elevation in the Appollonia stratigraphic section (nonnodular zone), might reflect effective exhaustion of the silica supply, fewer microfractures condition and perhaps dilution by the marine water of highly reduced silica-rich solution.