Electromagnetic Tool Research Articles

Signals of electromagnetic tool with toroidal coils in deviated wells (following numerical simulation results)

The study is aimed at analyzing the applicability of the logging tool with toroidal coils in the sections of deviated oil-and-gas wells. We carried out a three-dimensional finite-difference simulation of the electromagnetic signals in geoelectric models of oil-, gas-, oil-water- and water-saturated reservoirs for the entire set of operating modes, frequencies and positions of the receiver toroidal coils. Characteristic features of the signals were revealed depending on the resistivity contrast and reservoir thickness at various well deviation angles.

Effects of formation structure on directional electromagnetic logging while drilling measurements

Directional electromagnetic (EM) logging while drilling (LWD) tools have been widely used in well navigation for its azimuthal sensitivity and deep depth of detection (DOD). In this paper, an efficient 2.5D finite difference method (FDM) associated with non-uniform meshes and parallel computing is applied to evaluate the formation structure effects on the EM tools. The algorithm is validated by comparing the numerical results with analytical/3D FEM solutions in 1D and 2D heterogeneous formations. The effects of complex formation structures, e.g., faults, curved boundaries and unconformities are further analyzed by using the FDM code. Two new curves GPF and GAF are defined by subtracting the geosignals in a 1D layered model from that of a 2D fault model to quantitatively evaluate the fault detection capability. Numerical results show that the EM tools are sensitive to faults, especially the low dip angle ones. The depth of detection to fault reduces from 10.6 m to 4.0 m as the dip angle increases from 15° to 45°. Numerical cases also indicate that the EM tool responses can be affected by the sharp slope curved boundaries, while the effects of the gentle slope (<0.2) boundaries can be neglected. Furthermore, examples in unconformity and oil/water contact formation demonstrate that a 2D structure can affect the signal amplitude significantly.

Effects of Rough Hail Scattering on Polarimetric Variables

We use a commercially available full-wave electromagnetic (EM) tool to model scattering off rough hail. Through modeling various axis ratios and surface roughness, we systematically evaluate their effect on the polarimetric variables used for hail size discrimination. Our results produce the differential reflectivity and the copolar correlation coefficient typically not achieved using forward operators. We compare our results with available information in the literature. The inclusion of the additional shape parameter brings new insights into problems associated with the polarimetric variable for hailstone size gauging. Finally, using dual-polarization weather radars’ (WSR-88Ds’) observations of a hail storm on two opposite sides, we hypothesize that the source of negative differential reflectivity is wet oblate hail in the resonant size range.

A Hybrid Loop-Tree FEBI Method for Low-Frequency Well Logging of 3-D Structures in Layered Media

Electromagnetic simulation plays an essential role in formation conductivity determination by electromagnetic well-logging tools, especially when the nonvertical borehole and invasion zones are present in a layered earth. A hybrid finite-element boundary integral (FEBI) method is suitable for such well-logging simulations. The usage of layered medium Green's functions allows the simulation background to be a planar stratified medium to characterize the earth formation. However, conventional FEBI using the Rao-Wilton-Glisson (RWG) basis function produces inaccurate results due to the low-frequency breakdown of the boundary integral equation solution. The new contribution of this work is to apply the loop-tree (LT) basis functions in the FEBI method to reduce the numerical error at low frequencies. Such an LT-FEBI method can handle all specific requirements of well-logging simulations at low frequencies. A direct solver is applied to make it more efficient to obtain logging curves with multiple source locations. The LT-FEBI simulation results are validated in several numerical examples, including a challenging well-logging model with a deviated borehole and invasion zones in the Oklahoma formation having 28 layers.

Hepatic Steatosis Detection Using Differential Effective Permittivity

Hepatic steatosis is a disorder with high prevalence among obese people. Traditional imaging modalities are more common in hepatic steatosis diagnosis, but they are not suitable for monitoring or treatment evaluation. This study aims at developing a new technique suitable for electromagnetic (EM) tool in the microwave band to differentiate steatotic from nonsteatotic liver. A differential permittivity estimation method for hepatic steatosis detection is proposed. First, the effective permittivity of the right side of the torso is estimated based on the phase difference of EM waves traveling along symmetric paths within the torso. Then, permittivity modeling and statistical frequency selection are performed to model the estimated values and to extract reliable frequency samples. Finally, the percentage of the difference between the permittivity of the left and right sides of the torso is calculated over the selected samples. The effectiveness of the proposed method is validated using simulated signals and phantom measurements. The analyzed results reveal higher contrast between the average permittivity of the left and right sides of the torso for cases with hepatic steatosis (average contrast of 29.2%) compared to those with healthy liver (average contrast of 7.9%). The proposed method can differentiate between steatotic and nonsteatotic liver. It is suitable for clinical applications due to its robustness to unwanted noise and interferences, as well as errors in placement of sensors. The results verify the potential of EM devices, which could overcome shortcomings of traditional imaging techniques by being safe, cost-effective, and portable.

MIMO Interference Channels Assisted by Reconfigurable Intelligent Surfaces: Mutual Coupling Aware Sum-Rate Optimization Based on a Mutual Impedance Channel Model

We study a multi-user multiple-input multiple-output interference network in the presence of multiple reconfigurable intelligent surfaces (RISs). The entire system is described by using a circuit-based model for the transmitters, receivers, and RISs. This is obtained by leveraging the electromagnetic tool of mutual impedances, which accounts for the signal propagation and the mutual coupling among closely-spaced scattering elements. An iterative and provably convergent optimization algorithm that maximizes the sum-rate of RIS-assisted multi-user interference channels is introduced. Numerical results show that the sum-rate is enhanced if the mutual coupling among the RIS elements is accounted for at the optimization stage.

Electromagnetic Insights Into Path Loss Modelling of IRS-Assisted SISO Links: Method-Of-Moment Based Analysis

In this paper, we demonstrate the usefulness of MoM (Method-of-Moments) based methods in efficient path-loss modelling for SISO (single-input single-output) communication links assisted by IRS (Intelligent Reflecting Surfaces). Being a full-wave computational electromagnetic tool, MoM is better equipped compared to high-frequency asymptotic methods like PO (Physical Optics), to handle the crucial electromagnetic (EM) effects like: mutual coupling between IRS unit-cells or interactions with spherical wave-front in antenna near-field. Furthermore, in terms of computational speed, accuracy and reproducibility, the MoM-based MATLAB Antenna Toolbox is significantly advantageous to emulate IRS-assisted wireless channels, as compared to the in-house FDTD (finite-difference time-domain) techniques. We consider a SISO system of two half-wavelength dipoles, and use a rectangular array of circular loops loaded with lumped circuit components as IRS. The lumped circuit loading enables us to control the reactance of individual unit-cells, resulting in alteration of IRS reflection coefficient and consequent changes in channel characteristics. Using numerous numerical simulations, we highlight the impacts of various IRS-parameters like: electrical size and number of unit-cells, distance of IRS from the transmitter/receiver as well as mutual coupling, on the path-loss models (both sub-6 GHz and mm-wave).

Signals of electromagnetic tool with toroidal coils in highly deviated wells

The research is aimed at expanding the applicability of the logging tool with toroidal coils from vertical to highly deviated wells. Its electromagnetic signals are computed with a three-dimensional finite-difference simulation algorithm on the computing resources of the Siberian Supercomputer Center of SB RAS, which is accompanied by a multi-aspect numerical analysis of the signals. We consider a wide range of geoelectric models with various resistivity contrasts: those of oil-, gas- and water-saturated reservoirs having a different number of horizontal boundaries and varying thicknesses, including the case of fine layering.

EMX: Overcoming Silicon Chip EM Simulation Challenges for Passive Circuit Analysis and Model Development

Silicon-chips present several challenges for traditional electromagnetic (EM) tools. In this paper we review how the Cadence EMX Planar 3D Solver has been designed to overcome these issues. Specifically, we discuss necessary features for PDK support: meshing requirements, solver options, and ease-of-use enhancements in the Cadence Virtuoso design environment. EMX can be used as part of scalable model generation process for a variety of typical components, for example inductors, transformers and baluns. These scalable models can then be used for synthesis of optimal components that meet the user-supplied specifications.

Broadband Circuit-Oriented Electromagnetic Modeling for Power Electronics: 3-D PEEC Solver vs. RLCG-Solver

Broadband electromagnetic (EM) modeling increases in importance for virtual prototyping of advanced power electronics systems (PES), enabling a more accurate prediction of fast switching converter operation and its impact on energy conversion efficiency and EM interference. With the aim to predict and reduce an adverse impact of parasitics on the dynamic performance of fast switching power semiconductor devices, the circuit-oriented EM modeling based on the extraction of equivalent lumped R-L-C-G circuits is frequently selected over the Finite Element Method (FEM)-based EM modeling, mainly due to its lower computational complexity. With requirements for more accurate virtual prototyping of fast-switching PES, the modeling accuracy of the equivalent-RLCG-circuit-based EM modeling has to be re-evaluated. In the literature, the equivalent-RLCG-circuit-based EM techniques are frequently misinterpreted as the quasi-static (QS) 3-D Partial Element Equivalent Circuit (PEEC) method, and the observed inaccuracies of modeling HF effects are attributed to the QS field assumption. This paper presents a comprehensive analysis on the differences between the QS 3-D PEEC-based and the equivalent-RLCG-circuit-based EM modeling for simulating the dynamics of fast switching power devices. Using two modeling examples of fast switching power MOSFETs, a 3-D PEEC solver developed in-house and the well-known equivalent-RLCG-circuit-based EM modeling tool, ANSYS Q3D, are compared to the full-wave 3-D FEM-based EM tool, ANSYS HFSS. It is shown that the QS 3-D PEEC method can model the fast switching transients more accurately than Q3D. Accordingly, the accuracy of equivalent-RLCG-circuit-based modeling approaches in the HF range is rather related to the approximations made on modeling electric-field induced effects than to the QS field assumption.

Modeling extra-deep electromagnetic logs using a deep neural network

Modern geosteering is heavily dependent on real-time interpretation of deep electromagnetic (EM) measurements. We have developed a methodology to construct a deep neural network (DNN) model trained to reproduce a full set of extra-deep EM logs consisting of 22 measurements per logging position. The model is trained in a 1D layered environment consisting of up to seven layers with different resistivity values. A commercial simulator provided by a tool vendor is used to generate a training data set. The data set size is limited because the simulator provided by the vendor is optimized for sequential execution. Therefore, we design a training data set that embraces the geologic rules and geosteering specifics supported by the forward model. We use this data set to produce an EM simulator based on a DNN without access to the proprietary information about the EM tool configuration or the original simulator source code. Despite using a relatively small training set size, the resulting DNN forward model is quite accurate for the considered examples: a multilayer synthetic case and a section of a published historical operation from the Goliat field. The observed average evaluation time of 0.15 ms per logging position makes it also suitable for future use as part of evaluation-hungry statistical and/or Monte Carlo inversion algorithms within geosteering workflows.

A simple equivalent circuit model of photoconductive dipole antenna for the study of Terahertz intensity modulation

In this paper, a simple equivalent circuit model has been proposed for Ti–Au photoconductive dipole antenna to analyse its intensity modulation and radiation characteristics. The photocurrent and the terahertz emission intensity obtained using the proposed circuit model is verified using numerical method. Further, the equivalent circuit model is integrated with an electromagnetic tool to analyse its radiation characteristics and the photoconductive antenna is found to provide a directivity of 5.89 dBi at 1.58 THz. Intensity modulation of terahertz radiation is analysed using the equivalent circuit model by applying a bias voltage in the form of pulses. The modulated photocurrent output would produce the corresponding emission intensity which can be used for terahertz data transmission.

Mapping Complex Injectite Bodies With Multiwell Electromagnetic 3D Inversion Data

Electromagnetic (EM) inversion processing of ultradeep resistivity data has advanced from one dimensional (1D) to three dimensional (3D). These advances have helped improve the geological complexity that can be imaged and provide additional reservoir information. The large depth of investigation (DOI) of ultradeep LWD EM tools means that distant boundaries might not be detected by any other sensor in the tool string, making it difficult to verify the results. As inversion results represent a model of the subsurface resistivity distribution and not a direct measurement, it is important to have high confidence in the results. Directly comparing the component data measured by the tool to the modeled component data from the inversion across multiple frequencies provides confidence in the resultant model where the data have a close fit. However, as measurement sensitivities decrease with distance, there is potential for non-uniqueness, generating a model that is geologically unrealistic. Increased confidence can be achieved with independent verification of the model. This paper details results from a trilateral well in an injectite reservoir wherein the sand distribution was expected to be complex. The 1D inversions showed the vertical distribution of the sand, but the results were sometimes distorted by lateral resistivity variations. The 3D inversion of the data allowed the lateral resistivity variations to be resolved. These results can be corroborated by direct comparison with azimuthal resistivity images. Additionally, the laterals all diverged from the same main bore and remained close together initially in an area containing major sand injectites. The 3D inversions from two of the wells overlap and define similarly shaped structures, providing confidence in the 3D inversion model. In complex geobodies, such as the injectites described, significant lateral variation in the reservoir distribution is expected, which is not captured by 1D inversion. Understanding the shape of these structures and their potential connectivity using 3D inversion provides a major increase in reservoir understanding that is critical to completion design.

3D FV Simulation of the Orthogonal Azimuth Electromagnetic Tool Response Logging While Drilling with Multi Annular Grooves Using Potentials

In this paper, we use the 3D cylindrical finite volume (3D FV) method to simulate the Orthogonal Azimuth Electromagnetic Tool (OAEMT) responses Logging While Drilling (LWD) according to the special structure of the OAEMT with multi annular grooves. The algorithm allows the solution of the 3D Maxwell’s equation in inhomogeneous media with arbitrary conductivity and magnetic permeability distributions. For improvement of the computational efficiency and the modeling accuracy of the responses of OAEMT with annular grooves filled with ferrite material on steel mandrel in a completely anisotropic media, several techniques are applied: 1) a 3-D cylindrical irregular grid to avoid stair-casing discretization errors in the transmitter, receiver, and mandrel geometries; 2)the electric field continuation to approximate the perfectly electric conducting (PEC) boundary condition for enhancement of the discrete accuracy of the Helmholtz equations on the surface of steel mandrel; 3)the standardization technique to determine the equivalent conductivity and permeability in a non-uniform element; 4) PARDISO direct solver to solve the discrete equation as far as possible for increase of solution stability. We validate the 3D FV results against the numerical mode matching method. The comparisons show very good agreement. Results from 3-D borehole problems in several complex formation conditions involving eccentric tools and dipping beds are given to demonstrate the robustness of the method.

Hot Electron Plasmon-Resonant Grating Structures for Enhanced Photochemistry: A Theoretical Study

Metallic grating structures have been shown to provide an effective platform for generating hot electrons and driving electrochemical reactions. Here, we present a systematic theoretical study of the surface plasmon resonance in different corrugated metallic grating structures using computational electromagnetic tools (i.e., the finite difference time domain (FDTD) method). We identify the corrugation parameters that produce maximum resonant field enhancement at commonly used wavelengths for photocatalytic applications (633 nm and 785 nm) in different material systems, including Ag, Au, Cu, Al, and Pt. The absorption spectra of each grating structure have been fitted with the analytical equation obtained from Coupled Mode Theory. We then extracted the absorptive and radiative loss rates. The field enhancement can be maximized by matching the absorption and radiation losses via tuning the geometric parameters. We could improve the average field enhancement of 633 nm and 785 nm modes by a factor of 1.8× and 3.8× for Ag, 1.4× and 3.6× for Au, and 1.2× and 2.6× for Cu. The optimum structures are found to be shallower for Ag, Au, and Cu; deeper for Pt; and to almost remain the same for Al. The gratings become flat for all the metals for increasing the average field enhancement. Overall, Ag and Au were found to be the best in terms of overall field enhancement while Pt had the worst performance.

A 190.3‐dBc/Hz FoM 16‐GHz rotary travelling‐wave oscillator with reliable direction control

This letter presents a rotary travelling-wave oscillator (RTWO) with reliable direction control in a standard 130 nm complementary metal–oxide–semiconductor (CMOS) technology. To achieve low phase noise (PN), and low power consumption, 16-stages customised transmission line segments are designed and simulated on electromagnetic tools. The PN is investigated through modelling the RTWO as multiple standing-wave oscillators. The proposed oscillator achieves 11.2% tuning range, 190.3 dBc/Hz figure-of-merit (FoM) at 1 MHz offset and 192.3 dBc/Hz FoM at 10 MHz offset with 5.8-mW power consumption from 16-GHz carrier.

Analysis of Transmission Line with Distributed Series Voltage Sources Using Green’s Function

In this article, the authors have made an attempt to promote the analysis of transmission lines containing distributed series voltage sources using Green’s function. Authors believe that this tutorial article can enrich a traditional course on transmission line theory due to the following two major value additions. Firstly, it extends the traditional transmission line theory by incorporating distributed voltage sources. Secondly, it acts as an excellent introduction to the concept of Green’s function. In this article, Green’s function for the point series voltage source is systematically derived. The 3D Electro-Magnetic tool is used to validate the analysis. A basic understanding of transmission line theory is a sufficient pre-requisite to dive into this journey.

Designing RF and Microwave Band Pass Filters Using Coupled Resonators

ABSTRACT In this article, the authors have made an attempt to capture the recent developments taking place in the design of band pass filters (BPF) as a tutorial article. The article deals with the design of a reasonably good physical BPF from user specifications, followed by space mapping technique to translate the initial filter into the desired final filter. The authors believe that this tutorial article will benefit both students and engineers alike. A basic understanding of BPF and working knowledge of electromagnetic tool are sufficient pre-requisites to dive into this journey.

Characterization of an electrically conductive proppant for fracture diagnostics

Fracture diagnosis with electromagnetic (EM) and electrical tools requires proppants with high electrical conductivity and mechanical strength. Lab measurements of the electrical and hydraulic conductivity of proppants are critical for selecting the best candidates. Such measurements greatly benefit simulations, field tests, and the ultimate application of such proppants in the field. To that end, a new lab protocol is developed for measuring the electrical and hydraulic conductivity of proppants. The lab setup, which mainly includes a resistivity core holder and a Hassler sleeve core holder, allows for simulation of realistic pressure and temperature conditions when making measurements. Petroleum coke (PC) is proposed as a candidate proppant because of its widespread availability and low cost. Lab measurements show that the effective electrical conductivity of pure PC in a model fracture is approximately 5000 S/m, under a closure stress greater than [Formula: see text] (4000 psi). When PC is mixed with sand, the effective electrical conductivity of the mixture decreases with an increasing weight percentage of sand. Although sand degrades the contact between PC particles, the electrical conductivity stays reasonably high (approximately 1700 S/m) when 50% sand is added. Hydraulic conductivity measurements show that when a fracture is propped with pure PC, the measured fracture conductivity is greater than [Formula: see text] ([Formula: see text]) (dimensionless fracture conductivity greater than 100 for a shale with [Formula: see text] or 100 nD permeability) under a confining pressure of [Formula: see text] (6000 psi). This means that a fracture propped with PC is infinitely conductive in a typical shale formation. When sand is added, the fracture’s hydraulic conductivity becomes even higher, which clearly shows PC’s ability of sustaining high stresses. The proposed protocol provides a robust and effective method that can be generalized for lab testing for other candidate proppants. The data presented clearly show that PC has the potential for field-scale applications in EM hydraulic fracture diagnostics.

Comparison of well integrity logs using ultrasonic tool during workover intervention and innovative electromagnetic tool in rig-less scenario: Colombia case history

Comparison of well integrity logs using ultrasonic tool during workover intervention and innovative electromagnetic tool in rig-less scenario: Colombia case history