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Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an improved analytical model is presented to predict the shielding effectiveness (SE) and resonances of an apertured enclosure composed of the material of finite conductivity. In the model, the modified parameters of the rectangular waveguide are introduced to deal with the lossy enclosure with apertures, which can consider the effects of wall loss on the SE. Firstly, according to the circuit theory and electromagnetic topology (EMT) theory, the lossy enclosure is modeled as the circuit model and signal flow graph, respectively. Then, the electric field components at the monitor point can be obtained; hence, the SE can be predicted accurately. Finally, the presented model is utilized to analyze the effects of various parameters and conditions on the SE. The validity of the presented model is verified by the CST through several cases, showing that the lossy enclosure is feasible to damp all the resonant modes. [ABSTRACT FROM AUTHOR]

In a straight-cylinder model in a strong longitudinal magnetic field, the MHD oscillations of a plasma of a finite conductivity are considered in a situation when there is no resonant surface in the plasma on which the component of the perturbation wave vector vanishes along the field. At high conductivity, there are large-scale oscillations with a radial wavelength on the order of the column radius, which in the entire volume differ little from those described by an ideal MHD. It is shown that with a jump in the density and electron temperature on a certain magnetic surface near the wall, another MHD mode may exist along with such oscillations due to the finite conductivity. In this mode, the perturbations are large-scale and almost ideal in most of the plasma volume, but small-scale in the radial coordinate and not ideal in the wall region. [ABSTRACT FROM AUTHOR]

Multi-wing and asymmetrical hydraulic fractures around wellbore are usually observed in hydraulic fracturing and refracturing treatments. Therefore, it is significant for us to study pressure transient analysis. In this paper, by employing Laplace transform and finite cosine Fourier transform, a new semi-analytical model was deviated and solved under condition of constant rate for multi-wing fractured wells (MWFWs) of finite conductivity in hydrocarbon reservoirs with dual-permeability behavior in Laplace domain. Stehfest inversion algorithm can be adopted to obtain wellbore pressure of MWFWs in real domain. The solution of the simplified model in this paper was validated with dual porosity dual-permeability and asymmetrical hydraulic fracture, and results reach a good agreement. Type curve, according to pressure derivative characteristic, can be divided into six regimes (bilinear flow, linear flow, radial flow of natural fractures, cross flow and radial flow of system). The influence of some vital parameters (dimensionless conductivity, storage coefficient, crossflow coefficient, permeability ratio et al.) on dimensionless pressure and its derivative curves were analyzed in details. The presented model can be used to understand pressure transient characteristic of MWFWs in hydrocarbon reservoirs with dual-permeability behavior. • A new welltest mathematical model of multi-wing fractured well in hydrocarbon reservoirs with dual-permeability behavior. • Laplace transform, finite cosine Fourier transform and Stehfest inversion algorithm can be adopted. • The simplified model in this paper was validated and results reach a good agreement. • The influence of some vital parameters on dimensionless pressure and its derivative curves were analyzed in details. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing may induce horizontal fractures in shallow, tectonically active or high-reservoir-pressure formations. Studying the pressure transient behavior of the horizontal fractures can provide insights into the size and shape of the formations as well as their productivities. However, our knowledge about the pressure transient behavior of a horizontal fracture is far from adequate. In this study, a semi-analytical model is proposed to characterize the pressure transient behavior of finite-conductivity horizontal fractures in bounded reservoirs. Specifically, we discretize the horizontal fracture into rectangle plane elements, each of which is treated as a plane source. (In this work, a plane source indicates a rectangle plane, and the oil flows from the matrix to this plane.) The transient flow in the fracture systems can be numerically characterized with the finite difference method, whereas the transient flow in the matrix system can be analytically simulated with the Green function method; as such, the flow behavior in both the fracture and matrix can be modeled. Subsequently, we construct the mathematical model by coupling the finite difference formulations for the fracture system and the analytical functions for the matrix system. This semi-analytical model is arranged into a matrix format and can be readily solved with the Gaussian elimination method. The key features of the proposed approach can be summarized as: it can model an irregular horizontal fracture by discretizing the horizontal fracture into small elements, such that the real fracture configuration can be better captured; the fracture conductivity can be taken into consideration; and the non-uniform influx distribution along the fracture can be modeled to better honor the actual flow behavior from the matrix to the fracture. We also apply the semi-analytical method to analyze the flow regimes of single-phase oil flow from a circular horizontal fracture and an elliptical horizontal fracture in a bounded reservoir; the flow regimes such as wellbore after flow, bilinear flow, formation linear flow, early pseudo-radial flow, late pseudo-radial flow, elliptical flow, and boundary dominated flow can be observed during oil production. In addition, we examine the influences of formation thickness, fracture’s vertical position, fracture conductivity, and wellbore storage on the pressure dynamics of a circular horizontal fracture. It is found that the early pseudo-radial flow results from two different flow scenarios: one is near the edge of the horizontal fracture when the formation thickness is small, while the other one is surrounding the horizontal fracture in the vertical direction when the formation thickness is sufficiently large. The wellbore storage mainly exerts influences on the early production period, and its duration tends to be longer as the fracture conductivity decreases. Furthermore, the flow regimes and pseudo-skin factor are comprehensively investigated for an elliptical horizontal fracture and an irregular-shaped horizontal fracture that may be induced by the stress heterogeneity in the reservoirs. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Geoscience is the property of Natural Gas Geoscience and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper deals with an assessment of the influence of finite conductivity to the current induced along the horizontal grounding electrode. Analysis is performed in frequency and time domain, respectively. Current distribution along the grounding electrode buried in a lossy half-space is determined via analytical solution of the corresponding Pocklington equation in the frequency domain. The corresponding time domain response is obtained by means of Inverse Fast Fourier Transform (IFFT). The electrode is excited via an equivalent current source. Presence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The electrode current is calculated for the case of perfectly conducting (PEC) electrode and for the electrodes made of copper and aluminum. Comparison of results shows no significant discrepancy between these electrodes, justifying the use of a PEC electrode approximation.

We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in rectangular waveguides with finite conductivity walls. The wavenumbers kx and ky in the x and y directions respectively, are obtained as roots of a set of transcendental equations derived by matching the tangential component of the electric field (E) and the magnetic field (H) at the surface of the waveguide walls. The electrical properties of the wall material are determined by the complex permittivity ε, permeability μ, and conductivity σ. We have examined the validity of our model by carrying out measurements on the loss arising from the fundamental TE10 mode near the cutoff frequency. We also found good agreement between our results and those obtained by others including Papadopoulos’ perturbation method across a wide range of frequencies, in particular in the vicinity of cutoff. In the presence of degenerate modes however, our method gives higher losses, which we attribute to the coupling between modes as a result of dispersion.

Shale gas flow is controlled by multiple mechanisms and multi-stage hydraulic fracturing often creates complex fracture geometry. It is very challenging to incorporate various transport mechanisms of shale gas and evaluate production performance of the multiple fractured horizontal well (MFHW) in shale gas reservoirs. This paper presented a new semi-analytical model to study the pressure behavior and production performance of MFHWs with finite conductivity fractures in shale gas reservoirs. Multiple mechanisms were considered, which contained diffusion in kerogen bulk, desorption from the surface of organic matters and clay minerals, slippage flow in matrix pores, transient-state inter-porosity flow and Darcy flow in natural fractures. Finite-conductivity hydraulic fractures, stress sensitivity effect and inclination angles were also taken into account. Line source function, Laplace transformation, perturbation technique, numerical discrete method, Gauss elimination method and Stehfest inversion algorithm were employed to calculate the pressure responses. A field case from Barnett Shale was used to illustrate the validity of this model. Type curves were plotted and flow regimes were identified. A synthetic case was used to study the effects of hydraulic fracture conductivity, inclination angle, permeability modulus, kerogen content, clay minerals content, solubility coefficient, diffusion coefficient, Langmuir pressure and Langmuir volume on well production performance. By performing sensitivity analysis of key factors, we come to some conclusions that hydraulic fracture conductivity has an optimal value for shale gas development; a small inclination angle and a large permeability modulus have a negative effect on well performance while a large Langmuir pressure and Langmuir volume have a positive effect; both clay minerals and organic matters contribute to shale gas production; dissolved gas stored in kerogen bulk should be considered and a larger diffusion coefficient is beneficial for dissolved gas to release. With its rapid computational speed, this semi-analytical approach will serve as an efficient tool to evaluate well productivity and provide critical insights into development optimization of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

In this work, the authors have studied the interaction between electromagnetic fields which are generated by lightning and overhead line in electrical power system. For this study, the authors constructed a system of equations. In which the network topology; with all its elements (linear or not) and wave exciter lightning are taken into account. This analysis is developed in time from the general equations of transmission lines with second members, with consideration of the frequency dependence of the correction terms related to the impedance of a finite conductivity of ground as well as non‐linearities loads. The simulation results presented in this study demonstrate the effectiveness of this analysis for the calculation of induced voltages generated by lightning on a grid of lines. [ABSTRACT FROM AUTHOR]

A new analytical solution of pressure transient analysis is proposed for multistage fracturing horizontal well (MFHW) with finite-conductivity transverse hydraulic fractures in shale gas reservoirs. The effects of absorption, diffusion, viscous flowing, stress sensitivity, flow convergence, skin damage and wellbore storage are simultaneously considered as well in this paper. Laplace transformation, source sink function, perturbation method and superposition principle are, respectively, employed to solve related mathematical models of reservoir system and hydraulic fracture system. And then boundary element method (BEM) is applied to couple reservoir system and hydraulic fracture system. The transient pressure is inverted from Laplace space into real time space with Stehfest numerical inversion algorithm. Based on this new solution, the distribution of transient pseudo-pressure for MFHW with multiple finite-conductivity transverse hydraulic fractures is obtained. Different flowing regimes are identified, and the effects of relevant parameters are analyzed as well. The essence of this paper is considering the effects of transient gas flowing occurrence in finite-conductivity hydraulic fractures with BEM. Compared with some existing models and numerical simulation model of shale gas reservoirs, this proposed new model can provide a relative more accurate analysis of the relevant parameters, especially for the fracture conductivity. In conclusion, this new model provides the relative accurate and comprehensive evaluation results for multistage fracturing horizontal technology. [ABSTRACT FROM AUTHOR]

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Experimental results of investigations of nonreciprocity for surface magnetostatic spin waves (SMSW) in the magnonic crystal created by surface acoustic waves (SAW) in yttrium iron garnet films on a gallium gadolinium garnet substrate as without metallization and with aluminum films with different electrical conductivities (thicknesses) are presented. In structures without metallization, the frequency of magnonic gaps is dependent on mutual directions of propagation of the SAW and SMSW, showing nonreciprocal properties for SMSW in SAW – magnonic crystals even with the symmetrical dispersion characteristic. In metalized SAW – magnonic crystals the shift of the magnonic band gaps frequencies at the inversion of the biasing magnetic field was observed. The frequencies of magnonic band gaps as functions of SAW frequency are presented. Measured dependencies, showing the decrease of magnonic gaps frequency and the expansion of the magnonic band gap width with the decreasing of the metal film conductivity are given. Such nonreciprocal properties of the SAW – magnonic crystals are promising for signal processing in the GHz range. [ABSTRACT FROM AUTHOR]

Finite conductivity, size dependency and surface layer are known as crucial factors that affect the electromechanical response and pull-in instability of micro/nano-electromechanical systems (MEMS/NEMS). However, these effects are yet ignored on modeling the instability of MEMS/NEMS fabricated from functionally graded materials (FGMs). Herein, a modified continuum model is developed to incorporate these effects on the dynamic behavior and electromechanical instability of double-sided FGM NEMS bridge. Using Gurtin–Murdoch model in conjunction with nonlocal Eringen elasticity, the governing equations of the nano-bridges is derived considering the surface layer and size dependency. The Coulomb and Casimir forces are incorporated in the governing equation considering the corrections due to the finite conductivity of FGM (relative permittivity and plasma frequency). The validity of the proposed method is elucidated by comparing the results obtained from the present study with the results reported in the literature. The stability analysis of the nanostructure is conducted by plotting time history and phase portraits. The effects of various parameters including finite conductivity, nonlocal parameter, surface stresses and material characteristics on the dynamic pull-in behavior of the nano-bridges are studied. The obtained results imply a significant impact of the abovementioned corrections on the instability threshold and pull-in parameters of the FGM nanobridge. [ABSTRACT FROM AUTHOR]

The principal focus of this work is on pressure behaviors of a horizontal well intercepted by multiple non-planar fractures. The non-planar fractures can be obtained by combinations of multiple wings with varied non-planar angle (NPA) and length. In theory, the bilinear flow regime, first linear flow, first radial, biradial flow and the pseudo radial flow regime can be identified for coplanar multi-fractured well. However, in practice, the shorter fracture spacing makes the biradial flow absent. The results of our investigation indicated that NPA mainly affects the first linear flow when C fD >1 and the bilinear flow when C fD ≤1. As the NPA increases, the pressure depletion enlarges. However, the impact of NPA on pressure depletion is not linear relation. When NPA<50°, the change of relative derivative pressure (RDPC) is less than 5%. The characteristic straight line corresponding to the flow regimes can be identified approximately. When NPA=70° and 80°, it reaches 10% and 20%, respectively. In this case, the NPA exerts strong influence on the pressure derivative curve and the formation linear flow cannot be observed even at high fracture conductivities. It is shown that for small value of the wellbore storage C D , it will not affect the existence of flow regimes just delay the occurring time of characteristic flow regimes. For bigger value of the C D , the wellbore storage may conceal the early flow regimes and the bilinear flow and first linear flow may be no longer observed. Meanwhile, the effect of NPA on pressure weakens. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have simulated lightning induced voltages above three non-flat terrains with rotational symmetry. [•] The lightning induced voltages obtained over non-flat terrains are greater the inclination angle of the terrain is increased. [•] The inclusion of finite conductivity causes considerable increments of the induced voltage over non-flat terrains. [•] The calculation of lighting induced voltages requires the inclusion of the terrain because the great differences presented compared with the flat ground simulation. [ABSTRACT FROM AUTHOR]

We consider the problem of neutral inclusions for two-dimensional conductivity and anti-plane elasticity. The neutral inclusion, when inserted in a matrix having a uniform field, does not disturb the field outside the inclusion. The inclusion consists of a core and a shell. We show that if the inclusion is neutral to two linearly independent fields, then the core and the shell are confocal ellipses. [ABSTRACT FROM PUBLISHER]

This article presents a defect modeling in eddy current non-destructive testing systems by using a new developed method called coupled electric field. It permits to improve qualitatively several models developed so far by many authors using coupled circuit methods that consider the defect only as loss of material. However, a defect can occur with a finite conductivity such as impurity, small burns and micro-solder. For this reason, this investigation consists of extending the coupled circuit method to the modeling of this kind of defects. The proposed approach consists of firstly considering the defect as an electric conductive volume and secondly changing the state variable presenting the electric current by the electric field one. This procedure permits expressing explicitly the impedance variation caused by the presence of an axi-symmetrical defect according to its characteristics. The comparison between the impedance variations calculated using finite elements method and the proposed one demonstrates a very good concordance. After this validation, the study covers also the influence of the defect shape and position on encircling probe impedance. This method is interesting since it permits a fully characterization of this kind of defects and facilitates the inversion process. Moreover, using a 3D finite element observation, this fast tool of simulation can be adapted for a fast phenomenological modeling of asymmetrical configurations. [ABSTRACT FROM AUTHOR]

The effects of Hall currents on the Rayleigh-Taylor instability of an incompressible, finitely conducting viscoelastic fluid were investigated. It is assumed that the fluid is permeated by a uniform two-dimensional horizontal magnetic field. It is shown that the solution is characterized by a variational principle. Proper solutions were obtained for a semi-infinite fluid in which the density varies exponentially in the vertical direction. The dispersion relation was derived and solved numerically. It was found that Hall currents and finite conductivity have a destabilizing influence, while viscosity and elasticity have a stabilizing influence on the growth rile of the unstable mode of disturbances.

The paper deals with an assessment of the influence of finite conductivity to the current induced along the horizontal grounding electrode. Analysis is performed in frequency and time domain, respectively. Current distribution along the grounding electrode buried in a lossy half-space is determined via analytical solution of the corresponding Pocklington equation in the frequency domain. The corresponding time domain response is obtained by means of Inverse Fast Fourier Transform (IFFT). The electrode is excited via an equivalent current source. Presence of the earth-air interface is taken into account via the simplified reflection coefficient arising from the Modified Image Theory (MIT). The electrode current is calculated for the case of perfectly conducting (PEC) electrode and for the electrodes made of copper and aluminum. Comparison of results shows no significant discrepancy between these electrodes, justifying the use of a PEC electrode approximation. [ABSTRACT FROM AUTHOR]

We present a fundamental and accurate approach to compute the attenuation of electromagnetic waves propagating in rectangular waveguides with finite conductivity walls. The wavenumbers kx and ky in the x and y directions respectively, are obtained as roots of a set of transcendental equations derived by matching the tangential component of the electric field (E) and the magnetic field (H) at the surface of the waveguide walls. The electrical properties of the wall material are determined by the complex permittivity ε, permeability μ, and conductivity σ. We have examined the validity of our model by carrying out measurements on the loss arising from the fundamental TE10 mode near the cutoff frequency. We also found good agreement between our results and those obtained by others including Papadopoulos' perturbation method across a wide range of frequencies, in particular in the vicinity of cutoff. In the presence of degenerate modes however, our method gives higher losses, which we attribute to the coupling between modes as a result of dispersion. [ABSTRACT FROM AUTHOR]

The fields at a finite conducting 2-D wedge are studied by means of the surface admittance operator, and compared to the case of a perfect conductor. This technique, applied to a number of numerical examples, allows a thorough investigation of the singular behavior of the fields near the edge, including nonsingular fields such as the longitudinal current distribution. Special attention is devoted to the validity of the quasi-TM approximations, when edge singularities are taken into account. The studied field properties lead to the formulation of an approximative local surface impedance for conductors, and are finally used to show how some differences in the resistive and inductive behavior of conductors with a different geometry are due to edge effects. [ABSTRACT FROM AUTHOR]

The method of lines (MoL) has been applied for analyzing the characteristics of various structures of coplanar transmission lines widely. But in most previous literatures, the metallizations are considered as infinitely thin or PEC(Perfect Electric Conductor). In this paper, the characteristics of coplanar transmission lines (take an example for shielding microstrip lines) with finite conductivity and finite strip thickness are analyzed by MoL and the computation results are shown. [ABSTRACT FROM AUTHOR]

Abstract: This paper extends Tiab''s Direct Synthesis (TDS) technique for interpreting the behavior of the pressure and pressure derivative data of a well intersected by a finite conductivity hydraulic fracture. In this technique log–log plots of pressure and pressure derivative data of a pressure drawdown or pressure buildup test are analyzed without using the type-curve matching or regression procedures. A log–log plot of pressure and pressure derivative versus test time for a fractured well in a closed system may reveal the presence of several straight lines corresponding to different flow regimes; bilinear flow, linear flow, infinite-acting radial flow, and pseudosteady state flow. The slopes and points of intersection of these straight lines are unique and therefore can be used to calculate several well, reservoir and fracture parameters: permeability, skin factor, wellbore storage coefficient, fracture conductivity, half-fracture length, and drainage area. Equations corresponding to the points of intersection are very useful in checking on the parameters obtained from the slopes, when the pressure derivative curve is not smooth. A new equation is derived for calculating (a) the half-fracture length in the absence of the linear flow regime straight line of slope 0.5 such as in the case of low conductivity fracture, (b) the fracture conductivity in the absence of the bi-linear flow line of slope 0.25, and (c) the skin factor in the absence of the infinite acting radial flow line such as in the case of a short test. [Copyright &y& Elsevier]

A two-dimensional coupled problem in electromagneto-thermoelasticity for a thermally and electrically conducting half-space solid whose surface is subjected to a thermal shock is considered. The problem is in the context of the Lord and Shulman's generalized thermoelasticity with one relaxation time. There acts an initial magnetic field parallel to the plane boundary of the half-space. The medium deformed because of thermal shock and due to the application of the magnetic field, there result an induced magnetic and an induced electric field in the medium. The Maxwell's equations are formulated and the electromagneto-thermoelastic coupled governing equations are established. The normal mode analysis is used to obtain the exact expressions for the considered variables. The distributions of the considered variables are represented graphically. From the distributions, it can be found the wave type heat propagation in the medium. This indicates that the generalized heat conduction mechanism is completely different from the classic Fourier's in essence. In generalized thermoelasticity theory heat propagates as a wave with finite velocity instead of infinite velocity in medium. Comparisons are made with the results predicted by the coupled theory for two values of time. [ABSTRACT FROM AUTHOR]