Rayleigh Frequency Research Articles

Enhancing the Performance of PNN-PHT Perovskite Ferroelectric via Configurational Entropy Strategy: Component Design, Electric Properties, and Mechanism Analysis

The traditional approach to designing ferroelectrics through phase boundaries has limitations in regulating polarization configuration and achieving significant performance enhancements. In contrast, the concept of high-entropy materials has emerged as a promising strategy for designing new materials with enhanced properties. Herein, by incorporating the high configurational entropy (Sconfig) strategy, the investigation explored the influence of Sconfig on the electrical properties of PNN-PHT piezoceramics. The results demonstrated that high Sconfig values were highly beneficial in improving the piezoelectric properties and significantly influenced the microstructure and grain size. The increase in Sconfig value was found to be positively correlated with the Rayleigh coefficient (α), dielectric loss (tanδ), and frequency dispersion (γ), while inversely correlated with the coercive electric field (Ec). By exploring the mechanism via Raman and simulation analyses, it was discovered that high Sconfig induces enhanced disorder, increased lattice distortion, and sharp volume changes. This ultimately resulted in a richer phase structure, reducing the potential energy barriers and leading to a lower activation energy (Ea) required for polarization switching. This finding provides novel strategies and directions for the development of high-voltage and high-coercive-field materials, holding promise for designing piezoelectric devices with enhanced power density and precision.

Interaction of acoustic waves with spin waves using a GHz operating GaN/Si SAW device with a Ni/NiFeSi layer between its IDTs.

A two port surface acoustic wave (SAW) device was developed to be used for the control and excitation via spin waves (SW). The structure was manufactured using advanced nanolithography techniques, on GaN/Si, enabling fundamental Rayleigh interdigitated transducer (IDT) resonances in GHz frequency range. The ferromagnetic resonance of the magnetostrictive Ni/NiFeSi layer placed between the IDTs of the SAW device can be tuned to the SAW resonance frequency by magnetic fields. Using structures with finger and interdigit spacing of 170 nm and 100 nm, fundamental Rayleigh IDT resonance frequencies of 6.4 and 10.4 GHz have been obtained. Coupling of SAW to SW was demonstrated through transmission measurements at the fundamental Rayleigh frequencies in a magnetic field, μ0H from -280 to +280 mT, at different angles (θ) between the SAW propagation direction and the magnetic field direction. For the 6.4 GHz resonator a maximum decrease of about 1.2 dB occurred in |S21|, at μ0H = 30 mT and at θ = 45. Time-gated processing of the frequency domain raw data was used to remove the direct electromagnetic cross talk and triple transit effects. Nonreciprocity associated to the coupling was analyzed for the two SAW structures. The quantitative influence of the magnetic field strength on the phase of the transmission parameters is also presented.

Geomechanics Modeling of Strain-Based Pressure Estimates: Insights from Distributed Fiber Optic Strain Measurements

Summary Rayleigh frequency shift distributed strain sensing (RFS-DSS) has been demonstrated as a potential technology for characterizing fracture geometries and optimizing the completion design in unconventional reservoirs. The combination of RFS-DSS strain and pressure gauge measurements has been reported recently in field applications (Dhuldhoya and Friehauf 2022; Haustveit and Haffener 2023) to characterize conductive fracture dimensions and production profiles. Haustveit and Haffener (2023) demonstrated a novel technique that uses RFS-DSS strain change during production, measured from a far-field observation well, to monitor the drain profile of a horizontal multistage well. The strain change and pressure change were strongly related during production, and this relationship was applied to continuously estimate pressure drawdown along the full length of the well. However, the sensitivity or influencing factors of the relationship between strain change and pressure change along the fiber are not yet fully understood. Therefore, the main objective of this study is to investigate the relationship between strain change and pressure change under various fractured reservoir conditions and provide guidelines for better utilizing this novel strain-pressure relationship to estimate conductive fractures and pressure profiles. We use a coupled geomechanics and fluid flow model to simulate the strain and pressure changes in the near-well and far-field regions during stable production and shut-in periods. A linear relationship is used to fit the strain change and pressure change data obtained from both producing and monitoring wells. We analyze the impact of various fracture properties [size and permeability of the stimulated reservoir volume (SRV) around fractures, fracture conductivity, fracture area, and skin factor] on the linear relationship based on the R2 value and fitting error. The relationship between the strain change and pressure change during the stable production obtained by our numerical study is consistent with the field measurements. The slope of strain change vs. pressure change during one day of production is significantly influenced by fracture properties. Overall, the monitoring well shows a stronger linear relationship than the producing well during both stable production and shut-in periods. A better linear relationship between the strain change and pressure change is associated with a larger fracture conductivity or larger fracture spacing scenario on both producing and monitoring wells during the stable production period. The cluster spacing affects the linear relationship between strain and pressure change during rock deformation. When cluster spacing is reduced, the nonlocal effect of deformation becomes more pronounced, resulting in a weaker linear relationship. During the shut-in period, the monitoring well exhibits a stronger linear relationship with a high R2 value and small fitting error compared to the producing well. The linear relationship obtained during the shut-in period is less reliable for the producing well. In cases of homogeneous fractures, where the fracture properties are uniform, the strain change and pressure change are similar, except for two outer fractures. This study provides a better understanding of the relationship between strain change and pressure change measured in the near-well and far-field regions during stable production and shut-in periods. The results of our study also demonstrate the potential for utilizing the RFS-DSS strain measurement to characterize the effective fracture and drainage dimensions.

Performance Evaluation of Fractal Wavelet Packet Transform on Wireless Communication Systems

The performance of the phase shift keying (PSK) modulation technique over additive white Gaussian noise (AWGN) and multipath propagation channels generally becomes worse for higher-order modes. Therefore, a new modulation technique should be provided in order to have a system that is capable of transmitting data with higher efficiency while maintaining better performance at the same time. This paper presents the development of a fractal wavelet packet transform incorporated within the M-ary PSK system, namely M-ary PSK orthogonal wavelet division multiplexing (OWDM), which is proposed to obtain high performance of modulation in terms of spectrum efficiency and bandwidth resources intended for wireless communication systems. To demonstrate performance improvement over a Rayleigh frequency selective fading channel and in the presence of AWGN noise, the proposed system was evaluated and compared to the basic modulation system and M-ary PSK employing orthogonal frequency division multiplexing (OFDM). The performance results show that M-ary PSK OWDM had better performance in comparison with M-ary PSK OFDM and the conventional system. By utilizing 16 subcarriers, QPSK OWDM achieved bit error rate performance improvement from 1.5 × 10-3 to 1 × 10-4 for Eb/N0 of 20 dB with efficient bandwidth.

Research and application of Rayleigh wave imaging based on the Born–Jordan time‐frequency distribution

AbstractCurrently, the horizontal resolution of Rayleigh wave exploration is low. In this study, we propose the Born–Jordan time‐frequency distribution to analyse Rayleigh waves. The seismic signal was filtered with a wavelet transform for denoising, and the Rayleigh wave was separated in the time domain. Using the Born–Jordan time‐frequency distribution, the time waveform of each frequency comprising the Rayleigh wave from every seismic channel was obtained, and the time difference of the Rayleigh wave with the same frequency was calculated, based on which the dispersion curve between the two channels was obtained. Combined with the multichannel Rayleigh wave dispersion curve, phase velocity and frequency imaging under the seismic arrangement were obtained. Applying this method to detect abnormal geological bodies in engineering investigations showed that hard geologic bodies, such as comcrete rocks, have high velocity and frequency, whereas weak ones have low velocity and frequency. This strategy facilitated the detection of fractured zones, underground goafs and obstacles during pipe‐jacking construction near the surface.

Investigation of Effective Fracture Height Using Strain Responses in a Vertical Monitoring Well during a Well Interference Test

Summary Understanding and characterizing the effective hydraulic fracture height are critical for optimizing completion design and well performance in unconventional reservoirs. Rayleigh frequency shift distributed strain sensing (RFS-DSS) data provide crucial information about the fracture geometry by measuring the strain change along the fiber. Recently, the strain data from the vertical monitoring well [VMW; Boxwood 5 Pilot Hole (B5PH)] at Hydraulic Fracture Test Site 2 (HFTS-2) was collected during a well interference test conducted on two neighboring horizontal wells [Boxwood 3H (B3H) and Boxwood 4H (B4H)] in September 2020. However, this data set was overlooked and not comprehensively analyzed. Consequently, the valuable information that this data may provide remains unexplored. The objective of this study is to determine how to interpret this vertical strain data and assess its potential to provide insights into the effective fracture height generated in the horizontal wells. To understand the measured strain data, we have developed a coupled fluid flow and geomechanics model to simulate the vertical strain responses observed during production and the well interference test. The characteristics of the strain responses are thoroughly analyzed to establish guidelines for identifying the upper and lower tips of the effective fracture in different fracture geometry scenarios. In addition, field-measured data are examined, and a history-matching process is conducted by comparing the numerical matching results with the observed data to identify the effective fracture height. Furthermore, the pressure gauge data are analyzed and compared with the strain data results to further validate the findings. The study has demonstrated that vertical strain measurements obtained from a VMW can be used to determine the effective fracture height. Large strain responses, characterized by both negative and positive peaks, are observed near the tips of the effective fractures. The upper and lower tips of the effective fracture can be identified by examining the locations of zero-strain change. The magnitude of strain response is affected by the distance between the fracture and the fiber. It is worth noting that the locations where the absolute value of the derivative of fracture conductivity changes abruptly correspond to the positions of the fracture tips. Furthermore, we study and history match the field-measured vertical strain change in HFTS-2 data sets. The pressure gauge data are analyzed to further validate our findings. The effective fracture height determined from the strain measurements falls within the range of 11,360–11,616 ft, which is consistent with the values obtained from pressure gauges (11,360–11,635 ft). Specifically, for B4H, the effective fracture height was determined to be 256 ft at a distance of 330 ft away at the time of data acquisition. Overall, the strain measurements provide valuable, time-dependent insights into the effective fracture height and the active drainage interval.

Distributed magnetic field sensor using nickel-acrylate composite coated silica optical fiber

This paper reports on the development and characterization of a distributed magnetic field sensor utilizing magnetostrictive material and the Rayleigh backscattered signal in optical fiber. The sensor consists of a single-mode fiber (SMF) coated with nickel-acrylate (Ni-Acryl) composite, fabricated using the conventional fiber drawing method. The surface morphology and the coating thickness of the Ni-Acryl were analysed using SEM. The sensor is capable of measuring variations in the strain of the fiber as the external magnetic field strength changes, with a spatial resolution of 20 cm. The experimental results revealed a linear relationship between magnetic field strength and Rayleigh frequency shift, with an average sensitivity of 22.85 MHz/mT. The magnetostrictive strain of the Ni-Acryl composite coated fiber is measured to be 36.4 με in response to the 245 mT applied magnetic field. This study highlights the potential of the developed sensor to be utilized in magnetic field sensing applications, particularly for remote sensing applications in a harsh environment.

Fiber-Optic Strain Measurements Aid Fracture Characterization

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 3864861, “Geomechanics Modeling of Strain-Based Pressure Estimates: Insights From Distributed Fiber-Optic Strain Measurements,” by Wei Ma and Kan Wu, Texas A&M University, and Ge Jin, Colorado School of Mines. The paper has not been peer reviewed. _ The combination of Rayleigh frequency shift distributed strain sensing (RFS-DSS) and pressure-gauge measurements has been reported recently in field applications. The main objective of the study detailed in the complete paper is to investigate the relationship between strain change and pressure change under various fractured reservoir conditions and provide guidelines for better using this novel strain/pressure relationship to estimate conductive fractures and pressure profiles. Introduction With a spatial resolution of 20 cm and a sensitivity of less than 1 με, RFS-DSS can measure mechanical strain changes along the fiber with higher accuracy and sensitivity than low-frequency distributed acoustic sensing measurements. The field applications of RFS-DSS have improved the understanding of near-well and far-field fracture characteristics and the relationship between stimulation and production in unconventional reservoirs. Although some numerical modeling works have been conducted to study the mechanisms of RFS-DSS data sets, the sensitivity, or influencing factors, of the relationship between strain change and pressure change along the fiber are still unclear. In this work, the authors use a coupled geomechanics and fluid-flow simulator to simulate the strain change and pressure change measured along the producing and monitoring wells during both stable production and shut-in periods. Methodology A 3D multilayer reservoir model with dimensions of 300×400×55.82 m was created using Permian Basin data sets. The reservoir was discretized into 553×129×5 gridblocks. To ensure accurate simulation of field RFS-DSS measurements, the mesh was refined around the fracture and wellbore. The fracture width was set to be the same as the RFS-DSS spatial resolution (0.2 m), and the grid size was set to 5 m except for the refined region. As shown in Fig. 1, the reservoir had 11 perforation clusters along the producing well and the monitoring well was 65 m away from the producing well. A fiber cable was installed on both wells to measure the RFS-DSS data set. The producing well was operated for 240 days before being shut in for 4 days, followed by a 1-day reopening and then continued production for 1 year. The pressure decline was 30–40 psi during the 1-day stable production period. Note that the moment after producing 239 days was taken as the reference time to calculate the strain change during the 1-day production (239–240 days) and the moment after 240 days as the reference time to calculate the strain change during the shut-in period (240–244 days).

Scaling laws for natural convection boundary layer of a Pr > 1 fluid on a vertical solid surface subject to a sinusoidal temperature in a linearly-stratified ambient fluid

The understanding of the transient behavior of natural convection boundary layer (NCBL) on a heated vertical solid surface under various heating conditions is of fundamental significance and application importance. In this study, scalings for the parameters representing the behavior of unsteady NCBL flow of a linearly-stratified Pr > 1 fluid on a semi-infinite vertical solid surface heated with a time-varying sinusoidal temperature at different development stages are developed with a scaling analysis, in terms of Ra, Pr, s, and fn, which are the Rayleigh number, Prandtl number, stratification number, and frequency of the sinusoidal temperature, respectively. These scalings are validated and quantified with a series of numerical simulations over wide ranges of Ra, Pr, s, and fn. The frequency of the fluctuations experienced by the NCBL behavior at the transitional stage, due to the stratification of the ambient fluid, is also analyzed, and it is shown that the previously obtained scaling for the unsteady NCBL case with the constant heat flux heating condition is basically applicable for the current case, Ra and fn have additional effects as well due to the time-varying nature of the applied temperature.

ResNet-WGAN-Based End-to-End Learning for IoV Communication With Unknown Channels

An end-to-end learning framework is proposed to optimize each module jointly in the communication system. Recently, Convolutional Neural Network (CNN) and conditional Generative Adversarial Network (cGAN) are used for end-to-end learning. However, deeper network layers will degrade the effect of CNN. cGAN suffers from unstable training and lacks generative diversity. In this paper, we propose the end-to-end learning based on Deep Residual Network (ResNet) and Wasserstein GAN (WGAN) for communication with unknown channels (ResNet-WGAN). First, ResNet is applied to solve the problem of network degradation to extract deeper data features. Second, for unknown channels, WGAN with conditional information is used to fit the channel effect to improve training stability and generative diversity. Finally, we present the simulation results of the ResNet-WGAN under additive white Gaussian noise (AWGN) channel, Rayleigh fading channel and frequency selective channel. The results demonstrate that the ResNet-WGAN reduces the communication Bit Error Rate (BER) and Block Error Rate (BLER). In particular, this paper applies ResNet-WGAN to the Internet of Vehicles (IoV) communication, and the results demonstrate that ResNet-WGAN is more effective.

Natural convection of a Cattaneo–Christov fluid bounded by Cattaneo thick walls with finite thermal conductivity

In order to compare with experimental conditions, it is important to use realistic boundary conditions. In this paper the linear natural convection of a Cattaneo–Christov fluid bounded by two Cattaneo thick horizontal walls with finite thermal conductivity is investigated. In this sense, fluid and walls present heat flux relaxation times. Of particular interest is to find the codimension two points where stationary and oscillatory convection compete to be the first to appear in convection. The specific case where the fluid heat flux satisfies a Cattaneo–Christov constitutive equation and the walls satisfy the usual Fourier constitutive equations is also investigated for the first time. The reason is that the more realistic wall to fluid thicknesses ratio d and thermal conductivities ratio X have not been used before in this problem as part of the main parameters. The critical Rayleigh number, wavenumber and frequency of oscillation are plotted against logX for fixed d and different magnitudes of the relaxation times of the fluid and the walls. The curves of criticality of oscillatory convection have a maximum (stabilizes) in the middle range of logX, close to the codimension-two point, that is, to the intersection with the curve of criticality of stationary convection. In contrast, the curves of criticality of oscillatory convection decrease (destabilize) with an increase of the relaxation time of the fluid. It is revealed that the wall relaxation time stabilizes oscillatory convection even more in the middle range of logX.

Assessing Geological Deformation Across Spatial and Temporal Scales Using Distributed Fiber Optic Sensing

Summary This work presents a conceptual framework for assessing geological deformation using distributed fiber-optic sensing (DFOS) that is applicable to several common sources of strain encountered during the reservoir life cycle. Common applications include strain associated with seismic and aseismic fault motion, natural and hydraulic fracture dilation and closure, and poroelastic strain evolution during injection and production. We briefly review common geological sources of strain observed in reservoir settings, then discuss the main fiber-based techniques for recording strain with attention to key deformation characteristics at different spatial and temporal resolutions. The relationships between common acquisition parameters, such as spatial resolution, data sampling rate, ability to measure relative and absolute strain, and a priori knowledge of geological strain including geomechanical models, and the availability of baseline measurements are discussed. Finally, a few examples are shown from experimental studies at the Aramco Research Center in Houston, Texas, USA. The facilities host a shallow vertical well instrumented with fiber as well as a surface fiber network embedded in a cement pad. We highlight several data sets acquired using Brillouin and Rayleigh frequency shift (BFS and RFS), low-frequency distributed acoustic sensing (LF-DAS), and DAS interrogation techniques, with a focus on concepts helpful for interpreting field strain. Using these insights as a conceptual framework for assessing geological deformation leads to more informed decisions when planning DFOS acquisitions and interpreting associated strain data.

A use-case efficient DFrFT-based index modulated-OFDM system in the presence of CFO

Index modulated orthogonal frequency division multiplexing (OFDM-IM) only utilizes partial resources to transmit signals according to use case requirement, it leads to higher energy efficiency and spectral efficiency than the classical OFDM. However, in the presence of inter-carrier interference (ICI) due to carrier frequency offset (CFO), the performance of index modulated OFDM system severely deteriorates. To mitigate this issue, a novel discrete fractional Fourier transform (DFrFT) based OFDM-IM scheme over Rayleigh frequency selective fading channel is proposed in this paper. The optimum DFrFT angle (αopt) for this new scheme at various CFO values has been calculated theoretically. Incorporating these estimated αopt, the proposed system achieves a gain of 8 dB over conventional FFT-based OFDM-IM at bit error rate (BER) = 10−3 in a high normalized CFO (ϵ) environment (ϵ=0.2). The system model is also verified for different user applications, i.e., high data rate and low data rate applications. Simulation and analytical results show that the proposed model has a robust and superior performance compared to the conventional FFT-based OFDM-IM, DFrFT-based OFDM, and classical OFDM. Moreover, the proposed DFrFT-OFDM-IM model achieves all these superiorities with the same complexity as the conventional FFT-based OFDM-IM system.

Understanding near-field fiberoptic observations in the context of completion designs, fracturing effectiveness, and drainage characteristics. A case study from the hydraulic fracturing test site (HFTS-2) in Delaware basin

We share a case study from Hydraulic Fracturing Test Site (HFTS) located in the Permian-Delaware Basin in United States. We highlight various distributed acoustic surveys conducted at the site over time which provide insights into cluster level efficiencies and their relationship with perforation efficiencies for test site wells. We use observations from novel Rayleigh frequency shift technique (DSS-RFS) to understand strain change during well shut-in and flow periods as part of pressure interference tests. We have observed a strong relationship between perforation and cluster efficiencies as well as independent far-field observations based on core-through studies which suggest that perforation efficiency is key to optimizing fracture stimulation in horizontal well laterals. Finally, observations from DSS-RFS surveys provide insights into clusters along the wellbore where the drainage or productivity may have been sub-optimal and are likely candidates for re-stimulation or other approaches to be implemented in the future.

Droplet superpropulsion in an energetically constrained insect

Food consumption and waste elimination are vital functions for living systems. Although how feeding impacts animal form and function has been studied for more than a century since Darwin, how its obligate partner, excretion, controls and constrains animal behavior, size, and energetics remains largely unexplored. Here we study millimeter-scale sharpshooter insects (Cicadellidae) that feed exclusively on a plant’s xylem sap, a nutrient-deficit source (95% water). To eliminate their high-volume excreta, these insects exploit droplet superpropulsion, a phenomenon in which an elastic projectile can achieve higher velocity than the underlying actuator through temporal tuning. We combine coupled-oscillator models, computational fluid dynamics, and biophysical experiments to show that these insects temporally tune the frequency of their anal stylus to the Rayleigh frequency of their surface tension-dominated elastic drops as a single-shot resonance mechanism. Our model predicts that for these tiny insects, the superpropulsion of droplets is energetically cheaper than forming jets, enabling them to survive on an extreme energy-constrained xylem-sap diet. The principles and limits of superpropulsion outlined here can inform designs of energy-efficient self-cleaning structures and soft engines to generate ballistic motions.

Natural convection of a viscoelastic Cattaneo–Christov fluid bounded by thick walls with finite thermal conductivity

Abstract The linear natural convection of a Maxwell viscoelastic fluid with Cattaneo–Christov heat flux constitutive equation, between two thick walls with finite thermal conductivity is investigated. The viscoelastic fluid and the heat flux have different relaxation times. The main interest is on the curves of criticality for different thicknesses ratio D and thermal conductivities ratio X. In the middle range of log X the curves of criticality stabilize depending on the other parameters of the problem. It is revealed that for some Prandtl numbers the curves of criticality remain higher for small X and lower for large X. However, increasing the Prandtl number this behavior is reversed. It is shown that this has important consequences in the order of the criticality curves when the heat flux relaxation time is increased. Depending on the Prandtl number, an increase of this relaxation time may decrease (destabilize) the curves of criticality until a minimum is reached, after which the curves start to increase (stabilize) again. For two different magnitudes of the viscoelastic relaxation time, the critical Rayleigh number, wavenumber and frequency of oscillation are plotted against log X for different magnitudes of D and the heat flux relaxation time.

Performance Analysis of Wireless Adhoc Networks in Flat Fading and Frequency Selective Fading channels

This research article presents the probability of error analysis in flat fading and frequency selective fading channels for wireless adhoc networks which can aid mobile sustainable networks. Adhoc networks due to their network arrangement which is not fixed and can exhibit mobility its physical layer analysis metric of probability of error needs to be analysed. Information data transmitted from a source node into a wireless channel due to its multipath propagation can limit the performance determined by the metric of probability of error. Wireless channel experiencing flat fading can have Rayleigh distribution, Rician distribution and frequency selective fading channel can be obtained from the power delay profile (PDP). Simulation results are obtained for wireless adhoc networks in matrix laboratory (MATLAB) using binary phase shift keying (BPSK) modulation scheme in flat fading channel and frequency selective fading channels for assessing wireless adhoc networks which also can exhibit similar conditions in mobile networks. The obtained simulation results can provide significant information where 5G and 6G networks are to be deployed and can aid real time implementation.

Error performance analysis of generalized quadrature spatial modulation using H-8QAM

Motivated to enhance the error performance (EP) of generalised complex quadrature spatial modulation (GCQSM) systems, this study proposes a scheme that builds on GCQSM and uses hexagonal quadrature amplitude modulation (H-QAM) constellations which have the advantages of a maximised Euclidean distance with relatively low peak-to-average power ratio, compared to conventional QAM (C-QAM) systems. This in turn, leads to an enhancement of the EP of GCQSM schemes. The proposed scheme utilises a rotated hexagonal 8QAM (H-8QAM) set. Thus, the proposed scheme is herein named; Generalised QSM using H-8QAM (GQSM-H-8QAM). In this study, the EP of the proposed GQSM-H-8QAM scheme is investigated over Rayleigh frequency flat-fading channels with additive white Gaussian noise. Additionally, a theoretical average bit error probability (ABEP) expression of the GQSM-H-8QAM scheme is formulated and validated using Monte Carlo simulations. Compared to simulation results, the ABEP proves to be increasingly tight at high signal-to-noise ratio values. Obtained simulation results also show an improvement in the EP of the GQSM-H-8QAM scheme over various SM schemes like GCQSM, C-QSM and conventional-generalized spatial modulation (C-GSM), at the same spectral efficiency (SE). An improvement in the EP of 0.61 dB with SE of 8 bits/s/Hz is seen in 4times 4 GQSM-H-8QAM over 4times 4 GCQSM using C-8QAM, 2.58 dB over 4times 4 C-QSM-C-64QAM and a gain of 4.85 dB over 4times 4 C-GSM-C-64QAM.

Heat treatment and polymer coating effect on Rayleigh scattering based fiber optic temperature measurement

This study experimentally investigates the effect of heat treatment on Rayleigh scattering based distributed single-mode fiber optic temperature measurement. A finite element model was established to investigate the effect of thermal expansion of coatings on the optical fiber core strains and thus, temperature sensitivity before the coatings soften and melt away. A theoretical derivation for the fiber core strains, using Lame equations, was performed to validate the accuracy of the finite element model. It was found that the one-time heat treatment eliminates the hysteresis effect and stabilizes the Rayleigh scattering based fiber optic temperature measurement up to 1000 °C. The typical dual-layer coating effect on the temperature sensitivity of the Rayleigh frequency shift can be neglected at high temperatures in civil engineering application. Numerical parametric studies are performed to design coatings of fiber optic temperature sensors. The present study is promoting distributed fiber optic temperature sensor development and application.

Diagnostic Tool for Unconventionals Evaluates Near-Wellbore Fractures

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 2021-5408, “New Fracture Diagnostic Tool for Unconventionals: High-Resolution Distributed Strain Sensing by Rayleigh Frequency Shift During Production in Hydraulic Fracture Test 2,” by Gustavo A. Ugueto, SPE, Shell; Magdalena Wojtaszek, SPE, Brunei Shell; and Somnath Mondal, Shell, et al. The paper has not been peer reviewed. _ Fiber-optic (FO) monitoring in unconventional reservoirs has proved to be an invaluable diagnostic tool. Unfortunately, gaining detailed understanding of the near-wellbore fracture geometry or cluster or stage productivity through FO has proved to be more difficult. A new FO diagnostic method, distributed strain sensing based on Rayleigh frequency shift (DSS-RFS), provides insights about the characteristics of the near-wellbore-region (NWR) during production. The authors write that this novel FO technique can significantly improve understanding of near-wellbore hydraulic fracture characteristics and the relationships between stimulation and production from unconventional oil and gas wells. Introduction Successful production profiling through distributed acoustics sensing (DAS) has been reported in gas-producing wells. Regrettably, many wells do not generate strong DAS signals while flowing. Recently developed FO production-profiling data-acquisition protocols and work flows rely on collecting signals during short shut-in reopening cycles lasting only a few minutes. Therefore, a need exists to develop new work flows and algorithms using high-fidelity FO data that can be related to the production characteristics of individual perforation clusters (PCs). DSS-RFS Method DSS-RFS uses Rayleigh backscatter in a nonengineered single-mode fiber to measure strain changes along the fiber. When an optical fiber is manufactured, random inhomogeneities of the glass density are created in the fiber core. The random density heterogeneities manifest as a variation of refractive index along the fiber. For a certain laser frequency, the interferences between the Rayleigh backscatters cause irregular but unique amplitude fluctuations in the coherent optical time-domain reflectometer along the fiber length. For each discrete fiber segment, a unique Rayleigh scattering spectrum is obtained by scanning the fiber with a coherent optical time-domain reflectometer with a range of laser frequencies using a tunable-wavelength laser system. This unique Rayleigh scattering spectrum shifts in frequency if the temperature or strain of the fiber section changes. DSS-RFS measures relative strain changes instead of absolute strain along the fiber. However, DSS-RFS has a higher measuring sensitivity than strain measured using Brillouin optical time-domain reflectometry. DSS-RFS has higher spatial resolution than low-frequency DAS. Finally, DSS-RFS does not have the fiber sensing length restrictions of commercially available fiber-Bragg-grating-based DSS systems. First DSS-RFS During Shut-in and Reopening Test In February 2020, DSS-RFS data was acquired at one of the two FO-instrumented wells in Hydraulic Fracture Test Site 2 (HFTS2). The spatial resolution of the measurement was 20 cm, with a time-sampling interval of 150 seconds. The test began after establishing a baseline measurement during normal flowing conditions. The well was shut in for 4 days and opened again in a series of 2-hour shut-in and 1-hour producing cycles. Finally, the well was reopened and DSS-RFS was acquired for approximately 6 hours. This DSS-RFS data allowed for the definition of intervals where extension has occurred corresponding to active clusters with positive strain-change signals, slightly compressed intervals with negative strain-change signals between the clusters, and intervals with inactive clusters. These signals were interpreted to be caused by fracture-aperture changes that, in turn, were caused by pressure increases during shut-in within the fracture network in the NWR.