Investigation of Time-Lapse Changes with DAS Borehole Data at the Brady Geothermal Field Using Deconvolution Interferometry

Distributed acoustic sensing (DAS) has great potential for monitoring natural-resource reservoirs and borehole conditions. However, the large volume of data and complicated wavefield add challenges to processing and interpretation. In this study, we demonstrate that seismic interferometry based on deconvolution is a convenient tool for analyzing this complicated wavefield. We also show the limitation of this technique, in that it still requires good coupling to extract the signal of interest. We extract coherent waves from the observation of a borehole DAS system at the Brady geothermal field in Nevada. The extracted waves are cable or casing ringing that reverberate within a depth interval. These ringing phenomena are frequently observed in the vertical borehole DAS data. The deconvolution method allows us to examine the wavefield at different boundary conditions and separate the direct waves and the multiples. With these benefits, we can interpret the wavefields using a simple 1D string model and monitor its temporal changes. The velocity of this wave varies with depth, observation time, temperature, and pressure. We find the velocity is sensitive to disturbances in the borehole related to increasing operation intensity. The velocity decreases with rising temperature. The reverberation can be decomposed into distinct vibration modes in the spectrum. We find that the wave is dispersive and the fundamental mode propagates with a large velocity. This interferometry method can be useful for monitoring borehole conditions or reservoir property changes using densely-sampled DAS data.

Study and quantitative assessment of the structural inhomogeneities parameters of composite materials

The possibility of determining the size of the delamination region and the depth of its location in non-metallic multilayer weakly conductive materials using a unique pulsed eddy-current equipment by scanning the sample and registering the region of increasing amplitude of the differential signal has been practically confirmed. The nonstationary thermal and holographic interferometry method is used to obtain information on the shape and size of the bundles. For experimental testing, samples were used made of carbon fiber composite materials with artificially created defects in the structure of the material in the form of delaminations of various sizes and shapes.

Tribofilm Formation of Simulated Gear Contact Along the Line of Action

In this paper, an experimental simulation method was used for evaluating the tribofilm formation in rolling/sliding contact at different points in the line of action. A ball-on-disc test method was employed by which the pressure and slide to roll ratio of gear contact could be simulated. In order to reach a general conclusion, four different oils and two surface roughness were involved in the experiments. The tribofilm evolution was captured using spacer layer interferometry method, and the correlation of tribofilm with the location at the line of action was studied. Results showed that there is a threshold pressure for the tribofilm formation around which the tribofilm growth rate is maximum. Above this threshold pressure, the tribofilm formation is not stable, and the wear is dominant. Below this threshold pressure, the tribofilm growth rate rises by increasing the pressure and the gear contact is safely protected by a stable tribofilm. Graphic Abstract

Phase Equilibrium and Interdiffusion in Blends of Polystyrene with Polyacrylates

The solubility and interdiffusion of polystyrene (PS) with polymethyl acrylate (PMA), polyethyl acrylate (PEA), polybutyl acrylate (PBA), and polyethylhexyl acrylate (PEHA) have been studied by the optical interferometry method. Phase state diagrams are plotted. It is shown that they are characterized by the upper critical solution temperatures (UCST), which are localized in the temperature range above 450 K. Pair interaction parameters and their temperature dependences are determined and analyzed. Extrapolation of the temperature dependence of the interaction parameter was used to construct the dome of binodal curves and determine the spinodal curves in the framework of the Flory–Huggins theory. The diffusion coefficients of polystyrene into polyacrylates and polyacrylates into polystyrene are calculated. The dependences of the interdiffusion coefficients on the concentration, temperature, polystyrene molecular weight, and the number of carbons in the side chain of polyacrylate are analyzed. The numerical values of the interdiffusion coefficients of PS-1 into polyacrylates at 433 K change as −8.5 → −6.7 → −6.4 in the homologous series PMA → PEA → PBA. The coefficients of friction are calculated and the effect of change in the matrix structure on the diffusion of polystyrene in them is estimated.

История развития методов и интерференционных приборов для измерения малой разности оптических фаз (обзор)

Methods of interferometry, which are used to measure very small phase differences, are considered. in fundamental and applied problems. It is shown that the first improvements in interferometric methods for measuring small phase differences for recording various physical phenomena in the second half of the XIX - early XX centuries. carried out by I.A. Fizeau, A.A. Michelson, E. Morley, Lord Rayleigh, D.C. Miller and J.M. Sagnac. It was also shown that the most sensitive method of modulation interferometry was created in the period 1949-1952. Soviet radiophysicists A.A. Andronov, I.L. Berstein and G.S. Gorelik. It is noted that the modulation interferometry method could be implemented even in 1914 with a photocell on an external photoelectric effect, or in 1923 with a photocell on internal photoelectric effect (photodiode). However, then professional opticians used traditional methods for measuring small phase differences, and radiophysics as a science was just beginning its formation. It is shown that the methods of electrical and photoelectric harmonic analysis developed in late XIX - early XX centuries could find successful application in interferometry, but by that time, when they could find practical use, they were almost completely forgotten.