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Karaganda Coal Basin bears the largest undeveloped reserve of coalbed methane (CBM) in Kazakhstan, which lacks water resources for implementing large-volume hydraulic fracturing. Cryogenic fracturing utilizing liquid nitrogen (LN2) has been trialled in fields and is a waterless fracturing technique under intensive research these days. This study aimed to evaluate the cryogenic treatment efficacy of Karaganda coal samples as well as to understand the coal permeability evolution during the thawing period. X-ray fluorescent spectrometry (XRF) and microscope imaging identified the compositional and structural heterogeneities of coal specimens mined from different interlayers. Acoustic emission test, permeability measurement, and microscope imaging comparatively characterized the dry coal structure alteration before and after immersion into LN2. Cryogenic treatment slowed down the S-wave velocity through coal specimens, enhanced permeability by over 65 % after temperature recovery as well as created new fractures, enlarged existing ones, and spalled coal particles. Dynamic permeability evolution against temperature rise during the thawing process has been successfully captured for the first time. Overall, the experimental measurements support that the LN2 cryogenic fracturing technique would be effective in stimulating coalbeds for CBM production in Karaganda Coal Basin.

Based on the tortuous capillary network model, the relationship between anisotropic permeability and rock normal strain, namely the anisotropic dynamic permeability model (ADPM), was derived and established. The model was verified using pore-scale flow simulation. The uniaxial strain process was calculated and the main factors affecting permeability changes in different directions in the deformation process were analyzed. In the process of uniaxial strain during the exploitation of layered oil and gas reservoirs, the effect of effective surface porosity on the permeability in all directions is consistent. With the decrease of effective surface porosity, the sensitivity of permeability to strain increases. The sensitivity of the permeability perpendicular to the direction of compression to the strain decreases with the increase of the tortuosity, while the sensitivity of the permeability in the direction of compression to the strain increases with the increase of the tortuosity. For layered reservoirs with the same initial tortuosity in all directions, the tortuosity plays a decisive role in the relative relationship between the variations of permeability in all directions during pressure drop. When the tortuosity is less than 1.6, the decrease rate of horizontal permeability is higher than that of vertical permeability, while the opposite is true when the tortuosity is greater than 1.6. This phenomenon cannot be represented by traditional dynamic permeability model. After the verification by experimental data of pore-scale simulation, the new model has high fitting accuracy and can effectively characterize the effects of deformation in different directions on the permeability in all directions.

Based on the tortuous capillary network model, the relationship between anisotropic permeability and rock normal strain, namely the anisotropic dynamic permeability model (ADPM), was derived and established. The model was verified using pore-scale flow simulation. The uniaxial strain process was calculated and the main factors affecting permeability changes in different directions in the deformation process were analyzed. In the process of uniaxial strain during the exploitation of layered oil and gas reservoirs, the effect of effective surface porosity on the permeability in all directions is consistent. With the decrease of effective surface porosity, the sensitivity of permeability to strain increases. The sensitivity of the permeability perpendicular to the direction of compression to the strain decreases with the increase of the tortuosity, while the sensitivity of the permeability in the direction of compression to the strain increases with the increase of the tortuosity. For layered reservoirs with the same initial tortuosity in all directions, the tortuosity plays a decisive role in the relative relationship between the variations of permeability in all directions during pressure drop. When the tortuosity is less than 1.6, the decrease rate of horizontal permeability is higher than that of vertical permeability, while the opposite is true when the tortuosity is greater than 1.6. This phenomenon cannot be represented by traditional dynamic permeability model. After the verification by experimental data of pore-scale simulation, the new model has high fitting accuracy and can effectively characterize the effects of deformation in different directions on the permeability in all directions. [ABSTRACT FROM AUTHOR]

Reservoir geologic fluid-bearing granular materials are characterized by multiscale nonuniformity and coupled multiphysical mechanisms, for which conventional poroelastic theory cannot accurately portray wave dispersion and attenuation characteristics. To design a suitable dielectric wave propagation model to characterize the dispersion and attenuation laws of dynamic waves in geologic reservoirs, first, the branching functions of frequency-dependent dynamic permeability and dynamic tortuosity are derived by considering the effects of the geometry and fractal structure of fluid-bearing granular materials on the high-frequency properties of permeability and tortuosity. Second, the stress‒strain relationship of the fluid-particle system is redrawn by the viscoelastic‒plastic constitutive relation, and the dynamic wave propagation model of fluid-containing granular materials at a unified frequency is constructed by an integrated dissipation mechanism including frictional dissipation, internal dissipation, and plastic energy dissipation-wave propagation model based on viscoelastic‒plastic constitutive relation and dynamic permeability (WVPDP model). Finally, the reliability of the WVPDP model is verified by carrying out wave velocity tests on saturated dolomite and sandstone, and the effects of different parameters on the wave velocity dispersion amplitude and attenuation peak are analysed. The results show that the WVPDP model can accurately characterize the dispersion and attenuation of dynamic waves in granular media under uniform high and low frequencies and can invoke different dissipation mechanisms at different excitation frequency intervals, which is shown by the fact that internal dissipation and the plastic mechanism play the main role in the low-frequency interval, and frictional dissipation gradually replaces internal dissipation and plastic dissipation to become the main dissipation mechanism with increasing excitation frequency. Parameters such as fluid viscosity, reference angular frequency and reference quality can have different effects on the dispersion amplitude and transition band range of the fast P-wave and S-wave, the two mechanical response mechanisms in the medium of fluid-containing granular materials. • To reveal the fluid-particle interaction mechanism under dynamic loading. • To propose the viscoelastic‒plastic constitutive relationship for the particles in reservoir geologies. • To establish a dynamic wave propagation model that can portray the energy dissipation. [ABSTRACT FROM AUTHOR]

The sound field in porous media is affected by fluid flow governed by dynamic permeability. This macroscopic quantity is frequency dependent and can be connected with a relevant pore-scale estimation called the stochastic dynamic permeability (SDP) model. To further investigate the characteristics of the SDP model with different variables related to Biot relaxation frequency and envisage its potential applications in borehole acoustics, the influence of microstructures from a pore-scale image on dynamic permeability is studied. Then, the characteristics of dynamic permeability and a borehole Stoneley wave with different parameters are explored by sensitivity analysis. According to the influences of pore fluid parameters including density and viscosity, the velocity dispersion and attenuation of Stoneley waves in oil, gas and water-bearing formations are calculated. The results show that the dynamic permeability is affected by the microstructure of pores and the Biot relaxation frequency parameters have a crucial influence on the attenuation of the borehole Stoneley wave. Meanwhile, the attenuation coefficient can be used to identify the type of pore fluids. This is verified by an application to in situ acoustic logging data. The work provides a relatively comprehensive understanding of the features of the SDP dynamic permeability and indicates an approach to identify pore fluid by using a borehole Stoneley wave. [ABSTRACT FROM AUTHOR]

In order to accurately predict the production performance of coalbed methane (CBM) wells and to formulate a reasonable production system, this paper established a coal reservoir permeability model considering the influence of pulverized coal blockage. Then, on the basis of this model, the flow velocity sensitivity (FVS) experimental data of 15 groups of coal samples taken from the Baode Block, Qinshui Basin, Liulin Block, Hancheng Block, and the Huanglong Coalfield were fitted to determine the permeability models for different coal samples. On this basis, this newly established permeability model was incorporated into a previously developed CBM well performance analysis software, and production history matching was carried out on two CBM wells. Finally, the effects of the parameters of pulverized coal blockage on the permeability of coal reservoirs and the production performance of CBM wells were studied by taking the fitting parameters of CBM Well W1 as the reference. And the following research results are obtained. First, this new model considering the influence of pulverized coal blockage can quantitatively describe the variation of coal reservoir permeability with fluid velocity. In addition, this model can be incorporated into a CBM numerical simulation software or a CBM well performance analysis software to apply it in a wide range. Second, the coal reservoir permeability is less affected by pulverized coal blockage in the Baode Block, but this effect shall not be ignored in the Qinshui Basin and the Huanglong Coalfield. Third, the greater the theoretical maximum permeability damage degree (Dmax) and the permeability damage degree index (n) are, the lower the relative flow velocity (v0.5) corresponding to the critical flow velocity of pulverized coal blockage is and the more obvious the effect of pulverized coal blockage on coal reservoir permeability is. Fourth, in order to reduce the adverse effect of pulverized coal blockage on coal reservoir permeability, it is suggested to reduce the production pressure difference appropriately in the process of production, especially in the initial stage of gas production, so as to avoid severe damage to coal reservoir permeability.

The permeability interpretation accuracy of single wells in the Middle East super-thick carbonate reservoir can hardly meet the actual demand of water injection development. Therefore, this study develops an iterative split algorithm to calculate single-well segmental dynamic permeability and SPI (specific production index) based on the dynamic and static well test, PLT (production log test), production test, and logging interpretation data. Moreover, the dynamic permeability classification evaluation index was optimized. The detailed steps are as follows: 1) The liquid supply of a single well is split according to tp PLT. 2) For some production intervals, the log interpretation data are applied to carry out the second iteration splitting of formation coefficient and fluid supply. 3) The proportion of liquid supply in the stratification section is calculated based on the calculation results of steps 1 and step 2. 4) The total formation coefficient of well test interpretation is divided based on the calculation results of step 3. 5) The dynamic permeability and SPI are calculated. The research results show that the dynamic permeability and SPI of a single well are accurate to the scale of one meter from the several original meters to tens of meters, which can better meet the needs of water injection development. In addition, SPI can be used as an essential index for permeability classification evaluation. Taking the Halfaya Oilfield and the Mishrif format reservoir as examples, the low penetration rate of the MB1-2 high penetration rate is 200md and the lower specific production index limit is 0.35 bbl/(d·m·psi), respectively. The dynamic foundation of the high-permeability layer is identified. This method offers a new idea for the title of high-permeability streaks. Moreover, this method can provide the scientific basis for correcting the permeability attribute model, water injection plan optimization, single-well completion cementing scheme, and water coning control, which can be popularized and applied in the same reservoirs.

The existing magneto-optical imaging of weld defects is carried out under a constant magnetic field or alternating magnetic field. The magneto-optical image (MOI) is easy to saturate under a constant magnetic field, resulting in the loss of defect information. It is very difficult to realize magneto-optical imaging of micro-defects under alternating magnetic fields. Therefore, magneto-optical imaging under a combined magnetic field is proposed in this article. Firstly, the effect of dynamic permeability on the law of magnetization of defects is analyzed. Then, through simulation experiments, the magnetic flux leakage law of defect samples under constant magnetic field, alternating magnetic field, and combined magnetic field are analyzed. Finally, the magneto-optical imaging experiment is used to study the imaging law of wire cutting grooves under different magnetic field excitation. The experimental results show that compared with constant magnetic field and alternating magnetic field, the difference of leakage magnetic field under combined magnetic field excitation is more obvious. This shows that using a combined magnetic field for imaging detection can effectively improve the disadvantage that it is difficult to realize an MOI of micro-defects under an alternating magnetic field. [ABSTRACT FROM AUTHOR]

Pulsatile flows of viscoelastic fluids are very important for lab-on-a-chip devices, because most biofluids have viscoelastic character and respond distinctively to different periodic forcing. They are also very important for organ-on-a-chip devices, where the natural mechanical conditions of cells are emulated. The resonance frequency of a fluid refers to a particular pulsatile periodicity of the pressure gradient that maximizes the amplitude of flow velocity. For viscoelastic fluids, this one has been measured experimentally only at macroscales, since fine tuning of rheological properties and system size is needed to observe it at microscales. We study the dynamics of a pulsatile (zero-mean flow) fluid slug formed by a viscoelastic fluid bounded by two air-fluid interfaces, in a microchannel of polymethyl methacrylate. We drive the fluid slug by a single-mode periodic pressure drop, imposed by a piezoactuator. We use three biocompatible polymer solutions of polyethylene oxide as model viscoelastic fluids, and find resonances. We propose a model accounting for surface tension and fluid viscoelasticity that has an excellent agreement with our experimental findings. It also provides an alternative way of measuring relaxation times. We validate the method with parameters reported in the literature for two of the solutions, and estimate the relaxation time for the third one.

Probing the flow permeability of porous media with elastic waves is a formidable challenge, also because the wave‐induced oscillatory motion renders the permeability frequency dependent. Existing theoretical models for such a dynamic permeability assume that the frequency dependence is primarily controlled by a single characteristic length scale of the pore space. However, the fact that in most natural porous media there exists a distinct range of pore sizes is ignored. To overcome this limitation, we develop a dynamic permeability model that explicitly incorporates the pore size distribution. We show that the pore size distribution has a first‐order effect on the dynamic permeability. Since the pore size distribution can be deduced from techniques such as nuclear magnetic resonance, our results indicate the possibility to jointly use remote‐sensing technologies for improved permeability determination and cross‐fertilization of laboratory and in‐field techniques. Plain Language Summary: The flow rate of fluid through a porous material depends on the permeability. When the porous material is excited with elastic waves, there is an oscillatory fluid motion in the pore network. Then the permeability becomes frequency‐dependent, that is, a dynamic permeability. We develop a model for the dynamic permeability in porous materials with a range of pore sizes. We find that the pore sizes and their pore volume fraction have significant influence on the dynamic permeability. This is the first time to make connection between the elastic wave, whose velocity and attenuation are controlled by the dynamic permeability, and the nuclear magnetic resonance technique from which the pore size distribution can be inferred. Key Points: We propose a dynamic permeability model revealing that the pore size distribution has a first‐order effect on the dynamic permeabilityThe effect of wettability on the dynamic permeability is explored by the implementation of the slip boundary conditionThe proposed model builds a connection between signatures of elastic waves and techniques to obtain the pore size distribution such as NMR [ABSTRACT FROM AUTHOR]

This paper aims to clarify the homogenization results of the fluid–structure interaction in porous structures under the quasi-static and dynamic loading regimes. In the latter case, the acoustic fluctuations yield naturally a linear model which can be introduced in the configuration deformed as the consequence of the steady permanent flow. We consider a Newtonian slightly compressible fluid under the barotropic acoustic approximation. In contrast with usual simplifications, the advection phenomenon of the Navier–Stokes equations is accounted for. The homogenization results are based on the periodic unfolding method combined with the asymptotic expansion technique which provide a straight procedure leading the local problems for corrector functions yielding the effective model parameters and the macroscopic model. We show that the local problems for the solid and fluid parts are decoupled even in the dynamic interactions including the wall shear stress on the periodic interfaces. The dynamic permeability depends on the fluid flow properties including the advection effects associated with an assumed stationary perfusion of the porous structure. [ABSTRACT FROM AUTHOR]

Hydraulic flow, electrical flow and the passage of elastic waves through porous media are all linked by electrokinetic processes. In its simplest form, the passage of elastic waves through the porous medium causes fluid to flow through that medium and that flow gives rise to an electrical streaming potential and electrical counter-current. These processes are frequency-dependent and governed by coupling coefficients which are themselves frequency-dependent. The link between fluid pressure and fluid flow is described by dynamic permeability, which is characterised by the hydraulic coupling coefficient (Chp). The link between fluid pressure and electrical streaming potential is characterised by the streaming potential coefficient (Csp). While the steady-state values of such coefficients are well studied and understood, their frequency dependence is not. Previous work has been confined to unconsolidated and disaggregated materials such as sands, gravels and soils. In this work, we present an apparatus for measuring the hydraulic and streaming potential coefficients of high porosity, high permeability consolidated porous media as a function of frequency. The apparatus operates in the range 1 Hz to 2 kHz with a sample of 10 mm diameter and 5–30 mm in length. The full design and validation of the apparatus are described together with the experimental protocol it uses. Initial data are presented for three samples of Boise sandstone, which present as dispersive media with the critical transition frequency of 918.3 ± 99.4 Hz. The in-phase and in-quadrature components of the measured hydraulic and streaming potential coefficients have been compared to the Debye-type dispersion model as well as theoretical models based on bundles of capillary tubes and porous media. Initial results indicate that the dynamic permeability data present an extremely good fit to the capillary bundle and Debye-type dispersion models, while the streaming potential coefficient presents an extremely good fit to all of the models up to the critical transition frequency, but diverges at higher frequencies. The streaming potential coefficient data are best fitted by the Pride model and its Walker and Glover simplification. Characteristic pore size values calculated from the measured critical transition frequency fell within 1.73% of independent measures of this parameter, while the values calculated directly from the Packard model showed an underestimation by about 12%. [ABSTRACT FROM AUTHOR]

• Proposing a weak magnetization-based dynamic permeability testing method for internal defects in ferromagnetic materials. • Thorough analysis of the detection principle and performance validation through simulations and experiments. • Insightful investigation of key factors affecting detection signal through experiments. • The smaller magnetization (current) than that of conventional magnetic flux leakage testing under a similar detection capability. Magnetic flux leakage (MFL) testing is effective in detecting internal defects in ferromagnetic materials. However, it requires the saturation magnetization of materials, which is not always practicable in complex inspection environments. Therefore, this study presents a novel dynamic permeability testing (DPT) method, in which internal defects will induce dynamic permeability variations on the surface of weakly magnetized ferromagnetic materials, and the variations are then detected by alternating current detection coils with magnetic cores, enabling the identification of internal defects. The principle of DPT is analyzed through simulations, which are subsequently verified by experiments. Furthermore, the effects of excitation frequency, probe lift-off, and defect size on the DPT signal are investigated experimentally. Finally, the comparison with conventional MFL demonstrates that the DPT method can effectively identify the internal defect using a weak magnetization current of 0.1 A (about 0.25 T in the steel plate), whereas MFL requires 0.5 A (about 1.32 T) to achieve a similar detection capability under the same probe lift-off values. This new method has significant practical value, especially in situations where saturation magnetization is not feasible. [ABSTRACT FROM AUTHOR]

A conceptual model of anisotropic and dynamic permeability is developed from hydrogeologic and hydromechanical characterization of a foliated, complexly fractured, crystalline rock aquifer at Gates Pond, Berlin, Massachusetts. Methods of investigation include aquifer‐pumping tests, long‐term hydrologic monitoring, fracture characterization, downhole heat‐pulse flow meter measurements, in situ extensometer testing, and earth tide analysis. A static conceptual model is developed from observations of depth‐dependent and anisotropic permeability that effectively compartmentalizes the aquifer as a function of foliation intensity. Superimposed on the static model is dynamic permeability as a function of hydraulic head in which transient bulk aquifer transmissivity is proportional to changes in hydraulic head due to hydromechanical coupling. The dynamic permeability concept is built on observations that fracture aperture changes as a function of hydraulic head, as measured during in situ extensometer testing of individual fractures, and observed changes in bulk aquifer transmissivity as determined from earth tides during seasonal changes in hydraulic head, with higher transmissivity during periods of high hydraulic head, and lower transmissivity during periods of relatively lower hydraulic head. A final conceptual model is presented that captures both the static and dynamic properties of the aquifer. The workflow presented here demonstrates development of a conceptual framework for building numerical models of complexly fractured, foliated, crystalline rock aquifers that includes both a static model to describe the spatial distribution of permeability as a function of fracture type and foliation intensity and a dynamic model that describes how hydromechanical coupling impacts permeability magnitude as a function of hydraulic head fluctuation. This model captures important geologic controls on permeability magnitude, anisotropy, and transience and therefor offers potentially more reliable history matching and forecasts of different water management strategies, such as resource evaluation, well placement, permeability prediction, and evaluating remediation strategies. [ABSTRACT FROM AUTHOR]

We consider the direct problems for poroelasticity equations. In the low-frequency approximation we prove existence and uniqueness theorems for the solution to a certain mixed problem. In the high-frequency approximation we establish the uniqueness of a weak solution to the mixed problem and its continuous dependence on the data in the cases of bounded and unbounded temporal intervals and for however many spatial variables. [ABSTRACT FROM AUTHOR]

Abstract Non-symmetric upward and downward pressure diffusion from the point of intrusion is a common phenomenon in fluid-triggered seismicity. In most studies, a stress and pressure dependent permeability is applied resulting in a depth-dependency. An alternative source of non-symmetric diffusion are variations in fluid properties with depth due to temperature or salinity gradients causing buoyancy and affecting hydraulic diffusivity. We evaluate these processes to identify to what extent each may result in non-symmetric diffusion. We find that over short time scales of a couple days, stress-dependent permeability has the strongest influence on non-symmetric diffusion processes, while temperature effects become more important over longer time scales of months. Salinity plays only a very minor role. We verify these findings by applying our model to the 2008 West-Bohemian swarm, which is most likely triggered by degassing CO 2 from the mantle. As the first swarm phase lasts thirty days with high pressure intrusion for approximately 7 days, we verify that asymmetric diffusion is dominated by the mechanical and hydraulic state of the system. Although density and viscosity of supercritical CO 2 vary strongly in the pressure and temperature range present, due to the small amount of intruding fluid, the temperature and buoyancy effect is limited. Hence, we require unrealistic permeability gradients with depth to explain the asymmetric vertical pressure diffusion observed. We introduce an increased permeability based on fracture (re-)activation as contributor to intensify asymmetric diffusion and reducing the necessity of exaggerated permeability gradients. We conclude, that for short-term events up to 50 days simulations of realistic seismic cloud behavior will require constraints with respect to depth-variations of the hydraulic parameters and should consider increased permeability due to fracture (re-)activation. Long-term simulations over months require a sophisticated coupling of heat and fluid flow in combination with an adequate equation of state for the fluid phase. Highlights • Non-symmetric vertical pressure diffusion is common in fluid-triggered seismicity. • To match observations, unrealistic strong permeability gradients would be required. • Influence of temperature is significant for long time intrusions over months. • Salinity only plays minor role. • Permeability enhancement through fault reactivation may play major role. [ABSTRACT FROM AUTHOR]

Abstract: Rivers in climatic zones characterized by dry and wet seasons often experience periodic transitions between losing and gaining conditions across the river‐aquifer continuum. Infiltration shifts can stimulate hyporheic microbial biomass growth and cycling of riverine carbon and nitrogen leading to major exports of biogenic CO2 and N2 to rivers. In this study, we develop and test a numerical model that simulates biological‐physical feedback in the hyporheic zone. We used the model to explore different initial conditions in terms of dissolved organic carbon availability, sediment characteristics, and stochastic variability in aerobic and anaerobic conditions from water table fluctuations. Our results show that while highly losing rivers have greater hyporheic CO2 and N2 production, gaining rivers allowed the greatest fraction of CO2 and N2 production to return to the river. Hyporheic aerobic respiration and denitrification contributed 0.1–2 g/m2/d of CO2 and 0.01–0.2 g/m2/d of N2; however, the suite of potential microbial behaviors varied greatly among sediment characteristics. We found that losing rivers that consistently lacked an exit pathway can store up to 100% of the entering C/N as subsurface biomass and dissolved gas. Our results demonstrate the importance of subsurface feedbacks whereby microbes and hydrology jointly control fate of C and N and are strongly linked to wet‐season control of initial sediment conditions and hydrologic control of seepage direction. These results provide a new understanding of hydrobiological and sediment‐based controls on hyporheic zone respiration, including a new explanation for the occurrence of anoxic microzones and large denitrification rates in gravelly riverbeds. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical model of the dynamics of liquid flow in an angular accelerometer comprising a porous transducer in a circular tube of liquid. Wave speed and dynamic permeability of the transducer are considered to describe the relation between angular acceleration and the differential pressure on the transducer. The permeability and streaming potential coupling coefficient of the transducer are determined in the experiments, and special prototypes are utilized to validate the theoretical model in both the frequency and time domains. The model is applied to analyze the influence of structural parameters on the frequency response and the transient response of the fluidic system. It is shown that the radius of the circular tube and the wave speed affect the low frequency gain, as well as the bandwidth of the sensor. The hydrodynamic resistance of the transducer and the cross-section radius of the circular tube can be used to control the transient performance. The proposed model provides the basic techniques to achieve the optimization of the angular accelerometer together with the methodology to control the wave speed and the hydrodynamic resistance of the transducer. [ABSTRACT FROM AUTHOR]

Stress waves contain useful information about the properties of porous materials; they can be recovered through different non-destructive testing methods such as crosswell, vertical seismic profile, borehole logging as well as sonic tests. In all these methods, it is crucial to assess the effects of frequency on wave attributes including velocity and intrinsic attenuation. The dependency of permeability on frequency which is known as dynamic permeability and its effects on wave attributes of compressional waves are investigated in the present paper. Utilizing the dispersion relation derived for compressional waves, it is shown how the velocity and intrinsic attenuation of waves propagated in water saturated sand may be influenced by dynamic permeability. In low frequency range (viscous dominated flow regime), the dynamic permeability behaves like Darcy steady-state permeability and its effects on wave attributes are negligible. However, deviations from Darcy permeability start to occur at higher frequencies. Therefore, it is important to know how dynamic permeability controls the behavior of wave velocity and intrinsic attenuation in relatively high frequencies. For example, it is demonstrated that neglecting dynamic permeability results in overestimation of velocities of fast and slow waves in high frequency ranges (inertia dominated flow regime).

Clarifying the hydrate dissociation behavior, microstructure evolution, and corresponding seepage property evolution of hydrate reservoirs is essential for dissert area prediction, single-well production ability evaluation and the development of reasonable exploitation strategies. In this study, depressurizing dissociation was conducted on a hydrate-bearing sandy specimen using X-ray CT under triaxial stress, and the results show that hydrate dissociation first starts from the hydrate-gas interface preferentially, and then, some cavities would be formed among the patchy clusters. Later, when the hydrate particle dissociates to a sufficiently small size, the dissociated water gathers on the surface of the hydrate, wrapping the hydrate in the water phase, which prevents contact between the hydrate and gas phases. Additionally, obvious subsidence was observed after hydrate dissociation even the isotropic stress is 1 MPa. In addition, there is a linear relationship between the volume and area for each hydrate particle, while it is the intercept not the slope depends on the hydrate saturation. With decreasing hydrate saturation, the pore system characteristics would vary significantly. Correspondingly, the dynamic permeability of the hydrate-bearing sediment exponentially increases with decreasing hydrate saturation and is anisotropic due to the inhomogeneity of hydrate dissociation, and it could be predicted via electrical conductivity. • Interfaces consisting of different phase determine the hydrate dissocation order locally. • Hydrate surface area is linear with its volume under dimensionless condition. • The permeability of the dissociating hydrate-bearing sediment presents anisotropic, and a prediction model was proposed. [ABSTRACT FROM AUTHOR]

We report our detailed investigation of the electrical tuning of the ferromagnetic resonance frequency and frequency linewidth in multiferroic heterostructures consisting of FeCo thin films grown onto [Pb(MgNb) O]-[PbTiO] (PMN-PT) substrates with NiFe underlayers. Our study shows that the electrical tuning range of both ferromagnetic resonance frequency and frequency linewidth in this FeCo/PMN-PT heterostructure can be very large. Specifically, the resonance frequency can be tuned from 1.8 GHz to 10.3 GHz, and the frequency linewidth can be changed from 1.6 GHz to 7.3 GHz. The electrical tuning of these microwave properties is discussed in conjunction with the result from the static magnetic characterization and is explained based on the strain-driven magnetoelectric heterostructured effect. [ABSTRACT FROM AUTHOR]

• An analytical method for accurately distinguishing mechanical behavior stages was proposed. • The effects of T-P on mechanical behavior and K were discussed. • The change of internal energy of coal in the process of deformation was analyzed. The mechanical behavior and permeability (K) of coal reservoirs are important research directions in the development of coalbed methane recovery. In this study, the raw coal was collected from the Baode block, China. The pseudo-triaxial tests examined the coal mechanical behavior and K under high temperature-pressure (T-P) conditions. We proposed a new micro-slope method to accurately distinguish the deformation stages of coal under high T-P conditions. The whole deformation process is divided into five stages, and the dynamic permeability is divided into six stages. The results show that the K is closely related to the deformation stage and exhibits a U-shaped change with the axial strain, and its minimum value occurs at the end of the elastic deformation. The T and P control the evolution of coal mechanical behavior and K. The peak stress (σ max) and peak strain (ε max) decrease with the T but increase with the P. The initial permeability (K 0) decreases with the increase in P and T in the 10–30 MPa and 30–80 °C range, respectively. On the other side, the minimum permeability (K min) is least affected by the T and P. The kinetic properties of energy dissipation show that, the T and P control the dynamic changes of K by affecting the energy at different stages inside the coal. This study provides a reference for understanding the mechanical behavior of deep coal reservoirs. [ABSTRACT FROM AUTHOR]

Coal reservoir permeability, which changes constantly during the exploitation process, is a key factor for determining the production effects and ultimate recovery of coalbed methane (CBM) wells. To calculate the dynamic permeability more accurately, we reviewed the controlling mechanism of coal reservoir permeability and then established three mathematic permeability change models considering the effective stress, matrix shrinkage and gas slippage respectively. Relation between the production data and permeability by adopting the material balance theory was established and then a production data-based theoretical model for calculating the permeability change during the drainage process was derived. Seventeen wells from the Fanzhuang–Zhengzhuang block in the southern Qinshui Basin of China were employed for a case study. The calculated results clearly reflect the dynamic permeability change. The dynamic permeability curves can be divided into “decline type”, “rebound type” and “rising type”. Furthermore, the impacts of pressure drop, daily gas production, and final pressure on permeability change were analyzed. The results show that the rate of permeability change induced by effective stress had a significant positive linear correlation with the pressure drops. A quadratic relationship existed between the rate of permeability change induced by matrix shrinkage and daily gas production rate. The lower final pressure will give rise to the faster permeability change that induced by gas slippage, which indicates a typically exponential relationship. [ABSTRACT FROM AUTHOR]

Porosity waves are a mechanism by which fluid generated by devolatilization and melting, or trapped during sedimentation, may be expelled from ductile rocks. The waves correspond to a steady-state solution to the coupled hydraulic and rheologic equations that govern flow of the fluid through the matrix and matrix deformation. This work presents an intuitive analytical formulation of this solution in one dimension that is general with respect to the constitutive relations used to define the viscous matrix rheology and permeability. This generality allows for the effects of nonlinear viscous matrix rheology and disaggregation. The solution combines the porosity dependence of the rheology and permeability in a single hydromechanical potential as a function of material properties and wave velocity. With the ansatz that there is a local balance between fluid production and transport, the solution permits prediction of the dynamic variations in permeability and pressure necessary to accommodate fluid production. The solution is used to construct a phase diagram that defines the conditions for smooth pervasive flow, wave-propagated flow, and matrix fluidization (disaggregation). The viscous porosity wave mechanism requires negative effective pressure to open the porosity in the leading half of a wave. In nature, negative effective pressure may induce hydrofracture, resulting in a viscoplastic compaction rheology. The tubelike porosity waves that form in such a rheology channelize fluid expulsion and are predicted by geometric argumentation from the one-dimensional viscous solitary wave solution. [ABSTRACT FROM AUTHOR]

The dynamical response of saturated porous media to transient stresses is complex because of the coupling between the solid and fluid phases. Over the last three decades, theoretical models have emerged and they predict that the transient response of porous media to pore-pressure fluctuations depends only on a single dimensionless number. This single parameter represents the ratio of the forcing frequency to a characteristic frequency of the medium. Although theoretical models for the frequency dependence of the effective permeability of the medium have successfully predicted the response of porous media at high frequency observed in laboratory and numerical experiments, they rely on assumptions that limit their applicability to homogeneous media and narrow pore-size distributions. We use pore-scale flow simulations with four different porous media topologies to study the effect of pore geometry and pore-size distribution on the dynamic response to transient pore-pressure forcing. We find a good agreement with published theoretical work for all but one medium that exhibits the broadest pore-size distribution and therefore the largest degree of pore-scale heterogeneity. Our results suggest the presence of a resonance peak at high frequency where the discharge, and therefore the effective permeability, is significantly amplified compared to their value around the resonant frequency. We suggest two interpretations to explain resonance. At the continuum scale, a finite speed of pore-pressure propagation during transients requires the addition of a correction term to Darcy's law. We derive a hyperbolic mass conservation equation that admits resonance under certain conditions. This model can explain the peak observed for one medium but fails to explain the absence of resonance displayed by the three other media. The second interpretation, motivated by the different pore-size distribution for the texture where resonance is observed, calls for pore-scale processes and heterogeneous pore-pressure distribution among primary and secondary flow pathways. [ABSTRACT FROM AUTHOR]

We prove the uniqueness and continuous dependence on the data of a weak solution to a problem for poroelastic waves with fractional derivatives both in unbounded and bounded time intervals and in all space dimensions. [ABSTRACT FROM AUTHOR]

• Analyzed the effects of different exploitation methods, including step-wise depressurization and combined method, on CH 4 gas production behaviors. • Proposed a novel NMR-based method for quantitively characterizing the overall wettability evolution of hydrate bearing sediment. • Proposed a modified Tokyo model coupled with the wettability term and improved the permeability prediction accuracy by 9.75% • Concluded the control mechanism of hydrate pore habits coupled with wettability of hydrate bearing mixing system on flow seepage behavior. The commercial and sustainable exploitation of NGH reservoir requires a comprehensive understanding of gas production behaviors and seepage-wettability evolutions during hydrate dissociation process in hydrate bearing sediments. In this paper, the in-situ real-time CH 4 hydrate dissociation process in sand pack was acquired with the aid of NMR technique. The results showed that the step-wise depressurization method could effectively prevent the ice generation and/or secondary hydrate formation phenomenon during NGH exploitation. When the pore pressure reached the hydrate dissociation surging point, the CH 4 hydrate dissociation rate would enter a surge stage. Then, the hydrate dissociation rate of simple step-wise depressurization method kept steady for a relatively long time, while the hydrate dissociation rate of combined method showed a pressure-sensitive feature. And the optimum final CH 4 recovery ratio of 92.85% was obtained in Case 7 with the finer step-wise depressurization combined method. The comparison between measured gas effective permeability and prediction value indicated that the accuracy of current widely used permeability prediction models was limited due to lacking consideration of wettability evolutions of hydrate bearing sediments. In this study, a novel NMR-based approach for quantitatively characterizing the overall wettability evolution of hydrate bearing sediments was proposed. It was found out that the hydrophilicity of hydrate bearing mixing system increased with the decrease of hydrate saturation during the dissociation process. And a modified Tokyo model coupled with wettability term was proposed to increase the normalized permeability prediction accuracy by 9.75%, which indicated the flow seepage behavior was governed by the coupling effect of hydrate pore habits and wettability of hydrate bearing sediments. [ABSTRACT FROM AUTHOR]

Under oscillatory Stokes flow, dynamic permeability of assemblage of soft spherical particles is derived. For the bed of soft particles, the fluid-particle system is represented as an assemblage of uniform permeable spheres fixed in space. Each sphere, with a surrounding envelope of fluid, is uncoupled from the system and considered separately. This model is popularly known as cell model. Oscillatory Stokes equations are employed inside the fluid envelope, and oscillatory Brinkman equations are used inside the porous region. Four known boundary conditions namely: Happel's, Kuwabara's, Kvashnin's, and Cunningham's are considered on the outer boundary and results are compared. The behavior of dynamic permeability is analyzed with various parameters such as Darcy number ( Da), frequency parameter ( ϖ), porosity ( φ), and viscosity ratio ( δ). Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We analyze the effect that the geometrical place of anastomosis in the circulatory tree has on blood flow. We introduce an idealized model that consists of a symmetric network for the arterial and venous vascular trees. We consider that the network contains a viscoelastic fluid with the rheological characteristics of blood, and analyze the network hydrodynamic response to a time-dependent periodic pressure gradient. This response is a measurement of the resistance to flow: the larger the response, the smaller the resistance to flow. We find that for networks whose vessels have the same radius and length, the outer the level of the branching tree in which anastomosis occurs, the larger the network response. Moreover, when anastomosis is incorporated in the form of bypasses that bridge vessels at different bifurcation levels, the further apart are the levels bridged by the bypass, the larger the response is. Furthermore, we apply the model to the available information for the dog circulatory system and find that the effect that anastomosis causes at different bifurcation levels is strongly determined by the structure of the underlying network without anastomosis. We rationalize our results by introducing two idealized models and approximated analytical expressions that allow us to argue that, to a large extent, the response of the network with anastomosis is determined locally. We have also considered the influence of the myogenic effect. This one has a large quantitative impact on the network response. However, the qualitative behavior of the network response with anastomosis is the same with or without consideration of the myogenic effect. That is, it depends on the structure that the underlying vessel network has in a small neighborhood around the place where anastomosis occurs. This implies that whenever there is an underlying tree-like network in an in vivo vasculature, our model is able to interpret the anastomotic effect. [Copyright &y& Elsevier]

Abstract: A Fast Fourier Transform (FFT) based method for computing the dynamic permeability of periodic porous media is presented. The flow is described by the linearized Navier–Stokes equations in the presence of an oscillatory pressure gradient across the domain. The method of resolution uses an iterative scheme and exact expressions for the dynamic Green’s tensor in Fourier space. The accuracy of the approach is assessed through comparisons with an exact solution, in the case of the flow in a cylindrical tube, and with available numerical data provided in the literature for the case of a flow through regular arrays of spheres or ellipsoids. [Copyright &y& Elsevier]

Dynamic permeability is relevant to textile applications subjected to fluid/gas flow under high pressure, such as automotive airbags, wearable airbags and parachute fabrics. Dynamic permeability can be determined when a porous medium is tested under transient pressure conditions. This paper utilizes a reliable approach to measure and characterize dynamic permeability for woven fabrics. The experimental principle is based on the ideal gas law and the non-linear Forchheimer equation. Compared with static permeability measured under a constant low pressure, the dynamic permeability is an intrinsic property determined by change of fabric geometry and structure due to a high-pressure load. The pressure-induced deformation is identified, including effects on fiber and yarn arrangement, yarn porosity and fabric thickness. The level of deformation is a function of the number of fabric layers and initial pressure drop. The experimental results show that the dynamic permeability is higher than the static permeability for loose fabric, while it is lower for tight fabrics. For tight fabric, more fabric layers and a lower initial pressure can reduce the difference between the static and the dynamic permeability. Analytical models are used to explain and predict both static and dynamic permeability. [ABSTRACT FROM PUBLISHER]

Abstract: Thin films of FeCoHfN were fabricated by co-sputtering technique with the deposition angles varied. Their dynamic magnetic properties were characterized and discussed in conjunction with an analysis based on Landau–Lifshitz–Gilbert equation. High ferromagnetic resonance frequency beyond 6GHz was achieved by adjusting the deposition angle. A discrepancy between static and magnetic anisotropy was observed and discussed within the framework of Hoffmann''s ripple theory. Also, the variations of frequency linewidth, damping factor, and permeability with the change of deposition angle were presented and discussed. [Copyright &y& Elsevier]

Abstract: The ability of a highly compressible porous layer (HCPL), imbibed with a Newtonian liquid, to dissipate energy is underlined in recent papers related to ex-poro-hydrodynamic (XPHD) lubrication. The total absorption of energy of a squeeze/impact is due to the hydrodynamic forces generated within the HCPL. Mostly all XPHD processes take place in dynamic conditions, therefore it is essential to know if the permeability determined at constant thickness is adequate for such processes. For this reason, squeeze at constant velocity and impact tests were performed on HCPLs completely saturated with Newtonian liquids, thus the variation of dynamic permeability was determined. [Copyright &y& Elsevier]

Abstract: Static and dynamic magnetic properties of exchange-biased FeCo/MnIr multilayers were systematically investigated. A huge increased ferromagnetic resonance frequency up to 10GHz was observed in the case of thin MnIr layers being possibly interpreted as the contribution of the rotatable anisotropy. The rotatable anisotropy as well as the resonance frequency and frequency linewidth can be tuned by changing the thickness of MnIr layer. The correlation between the variation of rotatable anisotropy and enhancement of coercivity and magnetic damping is discussed. [Copyright &y& Elsevier]

Abstract: This paper presents the feasibility of the application of two commercial nanofiltration (NF) membranes (Desal5 DK and NF-270) in the removal of metal ions from an acidic leachate solution generated from a contaminated soil using H2SO4 as a soil washing agent. The experimental results of soil washing indicated that H2SO4 is highly effective in removing metal ions from contaminated soil. Following this process, the treatment of this acidic solution by nanofiltration membranes showed good metal ion rejection (between 62% to 100%) where divalent ions were better rejected than monovalent ions. For characterization purposes, the membrane experiments were conducted using K2SO4 solutions at different pHs. Membrane performance criteria were evaluated according to membrane permeability and ionic retention in the tank and permeate, taking into account different operating conditions such as pressures, flow rate and pH. These results demonstrated the effectiveness and feasibility of the application of nanofiltration treatments in the cleaning-up of contaminated water residues generated during soil washing processes. [Copyright &y& Elsevier]

Abstract: An acidic leachate obtained from a contaminated soil was generated using hydrochloric acid (HCl) as a soil-washing agent and treated by nanofiltration (NF) membranes. This solution was studied in terms of different parameters, such as transmembrane pressures and flow rate, to evaluate membrane permeabilities and ion separation. The experimental results showed that the application of NF membranes is a promising alternative for the removal of metal ions from washing-solutions. For example, both membranes demonstrated a retention capacity higher for multivalent ions such as Al3+, Ca2+, Mg2+ and Mn2+ (between 84 and 100%) compared to monovalent ions such as K+ and Na+ (less than 68%). Additionally, variation in dynamic permeability using the acidic leachate solution due to concentration polarization is presented. Furthermore, the permeation of NaCl–H2O solutions at different feed pH values (5.8, 3.7 and 2.2) was investigated. This study will not only outline a process for treating contaminated soils and waste waters directly but will also offer a new approach to treating industrial residues produced during mining or leather processes. [Copyright &y& Elsevier]

We investigated the dependence of hydraulic properties on the spatial scale of intrinsic and artificial heterogeneity, applying harmonic pore pressure testing to two varieties of Fontainebleau sandstone at various periods and effective pressures. Blocks with porosities of about 5 and 8% were chosen exhibiting a permeability of about 2·10−19 and 1·10−13 m2, respectively. The permeability of the less permeable variety strongly depends on sample size. Artificial heterogeneous rock samples were prepared by stacking pieces of the two sandstone varieties perpendicular and parallel to the main flow direction. The perturbation of the fluid flow owing to the interfaces between pieces of the same variety is controlled by the orientation of and subordinately by the effective stress on the interfaces. Constraints on conduit geometry derived from the effect of interfaces indicate that interconnectivity is more important than pore radius at the lower porosity. The effective permeability of alternating stacks of the two varieties differs tremendously for the two interface orientations; arithmetic and harmonic averages coincide with the effective properties parallel and perpendicular to the main flow, respectively. When the oscillation period is varied two regimes are observed, one with constant permeability at long periods and a second with decreasing permeability for decreasing period at short periods. Order of magnitude considerations of penetration depth suggest that this period dependence may be related to heterogeneity. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is to use Biot’s theory and the Johnson–Koplik–Dashen dynamic permeability model in wave field simulation of a heterogeneous porous medium. The Johnson–Koplik–Dashen dynamic permeability model was originally formulated in the frequency domain. In this paper, the time domain drag force expression of the model is expressed in terms of the shifted fractional derivative of the relative fluid velocity. In contrast to the exponential-type viscous relaxation models, the convolution operator in the Johnson–Koplik–Dashen dynamic permeability model cannot be replaced by memory variables satisfying first-order relaxation differential equations. A new method for calculating the shifted fractional derivative without storing and integrating the entire velocity histories is developed. Using the new method to calculate the fractional derivative, the governing equations for the two-dimensional porous medium are reduced to a system of first-order differential equations for velocities, stresses, pore pressure and the quadrature variables associated with the drag forces. Spatial derivatives involved in the first-order differential equations system are calculated by Fourier pseudospectral method, while the time derivative of the system is discretized by a predictor–corrector method. For the demonstration of our method, some numerical results are presented. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate, at laboratory scale, the behaviour of four different nanofiltration membranes (DS_5, CA, DS_5* and BQ_01) and their efficiency for chromium (III) removal. Principally, a solution of chromium basic sulphate Cr(OH)SO4 (CBS) (33% basicity), utilized in tanning processes, was tested with the different membranes in order to recuperate and concentrate the chromium (III) present in aqueous solutions. Several different transmembrane pressures, flow rates and concentrations were evaluated. In addition, the permeation of NaCl and Cr2(SO4)3·5H2O salts were studied. The results demonstrated acceptable chromium (III) retentions depending on the membrane type, the concentrations used (15.2 and 30.3molm−3) and the operating conditions. The four membranes exhibited different behaviours due to their charge during permeation. The results obtained in this study were analyzed according to the dynamic permeability model. [Copyright &y& Elsevier]

This work is aimed at deriving and at analyzing the dynamic filtration law that describes the acoustics of a gas saturated porous medium, when a wall-slip flow occurs due to low gas pressure. The dynamic filtration law is derived by upscaling the pore-scale description that consists of the equations of linear acoustics and a wall-slip condition on the pore wall. We have shown that the effective dynamic permeability depends on the Knudsen number and can be approximated by the generalized Klinkenberg’s law at low Knudsen numbers. Analysis of these results on a simple geometry proves that this approximation fails at reproducing the macroscopic inertial effects at high pulsations. [Copyright &y& Elsevier]

Experimental investigation of electric field enhanced-nanofiltration (called electro-nanofiltration) is reported for sodium chloride solutions. Electro-nanofiltration performance was quantified under several conditions of concentration, electric potential magnitude and polarity. As reported in Part 1 of this study [1], the membrane evaluated, namely BQ01, displayed a different response with respect to pure water and NaCl solution permeation. In this part the influence of various electric fields on BQ01 performance is reported. The other operating parameters are set up identically as the previous study. Electric field application was found to outshine the increase in effective pore size that was usually observed with BQ01 membranes in the presence of electrolytes (without an electric field). As a result, dynamic permeability decreases when an electric field is applied compared to when no electric field is applied. The evolution of the separation factor and pH regarding concentration, electric potentials and polarity were also reported. [Copyright &y& Elsevier]

Results from an experimental investigation of BQ01 nanofiltration (NF) are reported in this paper aiming at delineating the role of process parameters on BQ01 performances. The data highlight the specific behavior of BQ01 membranes in response to solute type and to variations in solution concentration. Variations in permeability and separation factors due to the presence of electrolytes are recorded. It is demonstrated that the concentration polarization cannot explain the observed variations. To elucidate the mechanisms related to this particular membrane, another approach based on conformational properties of polymer coating (sulfonated polyphenylene oxide, SPPO) is proposed and discussed in relation with characterization results. The hypothesis about mechanisms that are developed in this part will be confronted to a series of NF experiments under the same operating conditions but under electric field (ENF) in part 2 of this study. [Copyright &y& Elsevier]

• Effective stress has cumulative damage effect on gas permeability of muddy core. • Dynamic permeability evolves with effective stress and hydrate saturation. • Intrinsic permeability is the predominant factor for dynamic permeability. • A model used dynamic permeability can predict gas production behaviors well. Methane hydrates with underlying gas are promising for gas production commercially in case of accurate prediction and timely effective measures taken to control dynamic permeability. In a core holder, marine sediments sampled from South China Sea were used to remold hydrate muddy cores. Three consecutive gas production experimental results confirmed that the effective stress has a cumulative negative impact on the reservoir permeability. Thus, a modified Masuda permeability model considering the evolution of effective stress (0.2–5.0 MPa) and hydrate saturation (36.6%–53.1%) was proposed to calculate the dynamic permeability during depressurization. On this basis, dynamic permeability was applied to a mathematical model to study the production characteristics of hydrates with underlying gas. Compared with experimental measurements, the error of underlying gas pressure predicted by the model can be less than 1.92%. Besides, the precise trajectory of the hydrate dissociation front in the core was predicted by the model. The results indicated that the dynamic permeability is dominated by intrinsic permeability, and the effect of hydrate saturation is more significant than that of effective stress. The mathematical model could provide a simple yet practical method for estimating dynamic permeability and predicting gas production performances of hydrate reservoirs with underlying gas. [ABSTRACT FROM AUTHOR]

• Observed the CH 4 hydrate formation and dissociation processes by MRI technique. • Analyzed the effects of water saturation and heterogeneity on CH 4 hydrate formation. • Acquired the dynamic gas permeability variations with the CH 4 hydrate saturation. A clear understanding of methane (CH 4) hydrate pore habits and gas seepage behaviors in hydrate bearing sediments is critical for the exploitation of natural gas hydrate (NGH) reservoir. In this paper, we presented the experimental data of CH 4 hydrate formation and decomposition in sand packs with the aid of magnetic resonance imaging (MRI) technique. The results showed that in homogeneous sand packs CH 4 hydrates preferentially formed in the places where the water saturation was lower than the others, whereas in heterogeneous sand packs, the small grain size parts were the preferred locations for hydrate nucleation and the final hydrate saturation was much higher than the other parts. In this study, the CH 4 hydrate decomposition process was found to consist of three stages, the initiation stage, the rapid decomposition stage and the post-decomposition stage. The relationship between gas permeability and hydrate saturation was obtained by analyzing the MRI scanned images during percolation experiments. The dynamic gas permeability indicated that the hydrate occurrence mode shifted from grain-coating and pore-filling co-existing to grain-coating predominant with the decrease of hydrate saturation. Moreover, the flow obstruction caused by the presence of hydrate barrier and sand migration was much severer in NGH reservoir. [ABSTRACT FROM AUTHOR]

Correlating velocity-gradient relation is crucial for understanding flow behavior of fluid in low-permeability oil reservoirs. Instead of experimental approaches, this paper utilized downhole pressure data analysis for in-situ characterization of nonlinear flow behavior at low velocity. We introduced a dynamic permeability concept, which connects flow equation and nonlinear flow behavior. We then employed pseudo-linear function, piecewise function and continuous function to characterize the nonlinear flow behavior. The transient pressure type curves response ascended in the late-time flow period with consideration of nonlinear flow effect, suggesting that nonlinear flow equations can affect the characteristic of the type curves. The coefficients of approximation function are considered to be model parameters and are determined by downhole pressure analysis. Through our workflow, we can obtain a velocity-gradient relation, describing the nonlinear flow behavior of in-situ fluid. The practicality and efficiency of our new method are illustrated by comprehensive case studies. The in-situ flow behavior in reservoir scale can be characterized by normalizing multiple velocity-gradient curves derived from individual well analysis. Compared with core-flooding experiments, the proposed method is more convenient and economic to characterize flow behaviors in low-permeability oil reservoirs. • This study provides a new approach to characterize nonlinear flow behavior in ultra-low permeability reservoirs. • Our results reflect the fluid flow behavior under formation conditions. • Case studies show a five-step workflow to capture nonlinear flow behavior. [ABSTRACT FROM AUTHOR]

In this paper we analyze the flow of a Maxwell fluid in a rigid porous medium using the method of volume averaging. We first present the local volume averaged momentum equation which contains Darcy-scale elastic effects and undetermined integrals of the spatial deviations of the pressure and velocity. A closure problem is developed in order to determine the spatial deviations and thus obtain a closed form of the momentum equation that contains a time-dependent permeability tensor. To gain some insight into the effects of elasticity on the dynamics of flow in porous media, the entire problem is transformed to the frequency domain through a temporal Fourier transform. This leads to a dynamic generalization of Darcy's law. Analytical results are provided for the case in which the porous medium is modeled as a bundle of capillary tubes, and a scheme is presented to solve the transformed closure problem for a general microstructure. [ABSTRACT FROM AUTHOR]

Wave-induced instantaneous liquefaction is crucial to evaluating the stability of offshore foundations. For the instantaneous liquefaction, most previous studies treated the seabed as an invariant poro-elastic medium and hence led to nonphysical tensile stress in the non-cohesive liquefied zone. In this study, a penalty-like dynamic permeability model is proposed, based on the experimental evidences of permeability increase during soil liquefaction. The nonlinearity induced by the dynamic permeability is solved by an iterative procedure, based on the Newton-Raphson method. The numerical procedure is implemented in an in-house code and compared with analytical solutions under the constant permeability assumption. Numerical observations validate that the proposed dynamic permeability model can alleviate or even eliminate the nonphysical tensile stress in the instantaneously-liquefied zone. In contrast to the constant permeability model, the new model with a dynamic permeability obtains a better agreement with existing cylinder tests under one-dimensional wave loading conditions. For the numerical examples presented, the liquefaction depths predicted by constant permeability can be up to twice of those by the new dynamic permeability model. It is concluded that the conventional model with constant permeability overestimates the liquefaction potential. • A penalty-like dynamic permeability model is presented to numerically analyze the wave-induced instantaneous liquefaction. • The nonlinearity introduced by the dynamic permeability is solved in an in-house code based on the Newton-Raphson method. • The proposed dynamic permeability model can alleviate the nonphysical tensile stress in the instantaneously-liquefied zone. • The conventional model with constant permeability overestimates the liquefaction potential. [ABSTRACT FROM AUTHOR]

• Uniaxial magnetic anisotropy of amorphous FeNiPGd can reach 116Oe. • Magnetic field can improve the surface and dynamic permeability of film. • The ferromagnetic-resonance frequency can achieve 500 MHz under 40 mT. Uniaxial magnetic anisotropy has been induced in multi-element soft magnetic amorphous FeNiPGd thin films, which were fabricated by electroplating with an external magnetic field applied parallel to the plane of the electrode. After the application of the magnetic field, surface morphology of the FeNiPGd layer is improved. The crystal grains are refined, and the number of pores generated on the surface is remarkably reduced. The introduction of external magnetic field can significantly improve the deposition rate and dynamic permeability. And the cutoff frequency can achieve 500 MHz when the applied magnetic field is 40 mT during the deposition process. Specifically, the in-plane anisotropy field of the film was calculated by the area integral method to be approximately 116Oe while the magnetic field is 10 mT, which is obviously higher than that of the binary FeNi material. [ABSTRACT FROM AUTHOR]