The study on experimental method of fluid stress sensitivity of low permeability in tight reservoir

According to the industry standard, low permeability and tight reservoir are highly stress-sensitive in laboratory tests. However, this phenomenon has not been effectively confirmed in the field production test. For this reason, a method to measure stress sensitivity by axial loading is proposed. By loading fixed axial stress, the measurement method achieves the effect of equivalent preloading fluid pressure. Meanwhile, the equivalent theoretical curve can be obtained by translating the curve. Through this method, the stress sensitivity of the core with microfracture is studied. According to the results, the stress sensitivity of the cores can be divided into two stages: the first stage is the non-opening stage of microfractures, in which the stress sensitivity is weak; the second stage is the opening stage of microfractures, in which the stress sensitivity increases sharply. When the permeability changes significantly, the corresponding pressure is the microfracture's opening pressure. In addition, if the abscissa of the experimental results corresponds to the field production data, the field stress sensitivity curve of the field reservoir can be obtained. Conventional stress sensitivity test shows that the four cores in the study block exhibit medium to strong stress sensitivity. According to the stress sensitivity curve analysis after curve translation, the stress sensitivity of the reservoir is about 25% in the elastic production stage, which is classified as weak stress sensitivity. This conclusion can effectively support the phenomenon of the unobvious stress sensitivity in the field production of low permeability and tight reservoirs.

Features of the Metallization Influence on Phase Velocities of Acoustic Waves in Piezoelectric Plates

The paper presents an analysis of the influence of the load represented by two metal layers on the change in the phase velocity of the dispersion modes of the elastic Lamb and SH-waves in "Me/ZnO/Me" and "Me/AlN/Me" structures depending on the elastic wave frequency and the ratio of the metal layer to the piezoelectric layer thickness. Aluminum (Al), molybdenum (Mo) and platinum (Pt) are considered as the metal layer materials (Me). Only the elastic Lamb wave modes have localized maxima of the sensitivity curve S for all types of structures. Systems with low values of acoustic impedances for layers and plates materials have maximum values of S for metallization with thin layers, and also have minimal differences in the profiles of the components of the displacement vectors of the elastic wave. Systems with the most different values of acoustic impedances of layers and plates materials have maximum values of S when metallized with thick layers, and also have maximum differences in the profiles of the components of the displacement vectors of the elastic wave. PACS: 43.25.Fe; 43.35.Cg; 77.65.-j

Comparisons of Scotopic/Photopic Ratios Using 2- and 10-Degree Spectral Sensitivity Curves

Despite the fact that a 2-degree spectral sensitivity curve (SSC) is extensively used in scientific research and relevant applications, the choice between the 10-degree or the 2-degree photopic SSCs in practical applications for the calculation of scotopic/photopic ratios (S/P ratios) depends on actual needs. We examined S/P ratios for more than 300 light sources for correlated colour temperatures (CCTs) from 2000 K to 8000 K and blackbody radiant spectra from 10000 K to 45000 K using 2- and 10-degree SSCs. Results showed that the ratio of the S/P values calculated using the 10-degree and 2-degree SSCs was approximately equal to 0.916. The average mesopic luminance difference increased from 0% to 5.7% at a photopic adaptation luminance from 0.005 to 5 cd/m2. For most practical applications, the mesopic luminance values calculated using these two SSCs were different by several percentage units, yet these differences could be neglected. At extremely high CCTs over 10000 K, the mesopic luminance difference may approximate the maximum value of 16%. This work proposes the conversion coefficients for S/P ratios and the transforming mesopic luminance values calculated for 2- and 10-degree SSC systems. These results may help researchers clarify differences between the S/P ratios calculated using different SSCs.

Reanalysis of the Gaia Data Release 2 photometric sensitivity curves using HST/STIS spectrophotometry

Context. The second data release (DR2) from the European Space Agency mission Gaia took place on April 2018. DR2 included photometry for more than 1.3 × 109 sources in the three bands G, GBP, and GRP. Even though the Gaia DR2 photometry is very precise, there are currently three alternative definitions of the sensitivity curves that show significative differences. Aims. The aim of this paper is to improve the quality of the input calibration data to produce new compatible definitions of the G, GBP, and GRP bands and to identify the reasons for the discrepancies between previous definitions. Methods. We have searched the Hubble Space Telescope (HST) archive for Space Telescope Imaging Spectrograph (STIS) spectra with G430L+G750L data obtained with wide apertures and combined them with the CALSPEC library to produce a high quality spectral energy distribution (SED) library of 122 stars with a broad range of colors, including three very red stars. This library defines new sensitivity curves for G, GBP, and GRP using a functional analytical formalism. Results. The new sensitivity curves are significantly better than the two previous attempts we use as a reference, REV (Evans et al. 2018, A&A, 616, A4) and WEI (Weiler 2018, A&A, 616, A17). For G we confirm the existence of a systematic bias in magnitude and correct a color term present in REV. For GBP we confirm the need to define two magnitude ranges with different sensitivity curves and measure the cut between them at Gphot = 10.87 mag with a significant increase in precision. The new curves also fit the data better than either REV or WEI. For GRP, our new sensitivity curve fits the STIS spectra better and the differences with previous attempts reside in a systematic effect between ground-based and HST spectral libraries. Additional evidence from color–color diagrams indicate that the new sensitivity curve is more accurate. Nevertheless, there is still room for improvement in the accuracy of the sensitivity curves because of the current dearth of good-quality red calibrators: adding more to the sample should be a priority before Gaia data release 3 takes place.