Experimental Study on Fracturing Fracture Deformation Mechanism of Shale Reservoir

After large-scale sand fracturing of horizontal wells in shale gas reservoir, fracturing fractures will deform in the production process. However, fracture deformation will lead to the decrease in fracture conductivity and then cause the decrease of gas well productivity. Therefore, in order to evaluate the fracturing fracture deformation mechanism of shale reservoirs, the shale proppant-supported fracture deformation evaluation experiments were carried out under different proppant types, particle sizes, sanding concentrations, and closure pressure conditions, respectively, and the variation curves of fracture width was calculated by a stereomicroscope under different experimental conditions. Then based on the experimental results, the fracture sensitivity factors and fracture deformation mechanism were analyzed, and the deformation mechanisms of fracturing fractures affected by proppant embedding and crushing were studied emphatically. The analysis results of fracture sensitivity factors indicate that the larger the particle size and hardness of proppant, the lower the sand concentration, proppant embedded on the shale rock surface. Moreover, the deeper the proppant is embedded, the faster the fracture conductivity decreases. In addition, the greater the closure pressure, the more serious is the proppant embedment, and the faster the fracture width decreases. The analysis results of fracture deformation mechanism show that, on the on hand, under variable closure pressure, the proppant with larger hardness and larger particle size is used for fracturing, and the proppant embedded in the fracture surface is the main cause of fracture deformation. However, if only the sand concentration of the proppant in the fracture is changed, the fracture deformation is jointly dominated by the embedding and crushing of the proppant. On the other hand, under constant closure pressure, the main mechanism of fracture deformation is that the proppant is embedded into the fracture surface when the closure pressure is low, but if the closure pressure is high, the main mechanism of fracture deformation is the crushing and compaction of proppant.

Sensitivity analysis for automotive EMC measurements using quasistatic Darwin model

Purpose The purpose of this paper is performing a global sensitivity analysis for automotive electromagnetic compatibility (EMC) measurements related to the CISPR 25 setup in order to examine the effect of the setup uncertainties on the resonance phenomenon. Design/methodology/approach An integral equation formulation is combined with Darwin model and special Green’s functions to model the configuration. The method of Sobol’ indices is used to gain sensitivity factors enhanced with a polynomial chaos metamodel. Findings The proposed model resulted in by orders of magnitude lower number of degrees of freedom and runtime compared to popular numerical methods, e.g. finite element method. The result of the sensitivity study is in good agreement with the underlying physical phenomena and improves the understanding of the resonances. Practical implications The fast model supplemented by the sensitivity factors can be used in EMC design and optimization. Originality/value The proposed method is original in the sense of combining a polynomial chaos metamodel with a low-cost integral equation model to reduce the computational demand for the sensitivity study.

Compositional in situ analysis of dusty material stemming from Saturn’s main rings

<p>During the final mission phase, the Cassini spacecraft travelled through the gap between Saturn and its innermost D ring. One goal of these highly inclined orbits was sampling the dust population, mostly made of impact ejecta from the main rings, in the vicinity of the planet. These in situ measurements were primarily carried out by the Cosmic Dust Analyzer (CDA) onboard the spacecraft, which provided time-of-flight mass spectra of individual ice and dust grains, mostly between about 10 and 50 nm in size. Here we present an update on the composition of the silicate dust fraction stemming from Saturn’s main rings, which makes up about 30 % of the observed particles with water ice being the remaining fraction [1].</p> <p>Elemental analysis of the silicate spectra was performed using an updated deconvolution method, based on a technique originally applied to the interpretation of CDA interstellar dust measurements [2]. Neighboring spectral peaks due to mineral-forming ions such as Mg<sup>+</sup>, Al<sup>+</sup> and Si<sup>+</sup> are often unresolvable, because of CDA’s relatively low (m/dm = 20–50) mass resolution [3]. Therefore, application of a deconvolution technique is required to disentangle the peak interferences and derive valuable compositional information. The robustness of the applied method has been tested and optimized through comparison with an independent automated fit algorithm. In order to calculate elemental abundances within the particles, the derived ion abundances were combined with experimentally-determined relative sensitivity factors (RSFs) [4]. To provide context to the measured element ratios, we compared them with a variety of space-relevant materials. We find an overlap with chondritic material for Mg/Si and Fe/Mg ratios. The observed range within the element ratios, however, indicates the contribution of a variety of minerals such as olivine, plagioclase or pyroxenes. Although our results agree with realistic mineral compositions, the calculated abundances of Al<sup>+</sup> ions are still relatively uncertain and can be seen as an upper limit.</p> <p>Additionally, we present the results of a dynamical model, which allow us to derive the likely source region within the main rings of individually detected silicate grains. We find the C and B rings to be the most likely sources of the vast majority of grains with the D ring being only a minor source. Currently an analysis of compositional diversity between the different ring segments is under way.</p> <p> </p> <p><strong>References</strong></p> <p>[1] H.-W. Hsu et al. (2018) In situ collection of dust grains falling from Saturn’s rings into its atmosphere. Science 362.</p> <p>[2] N. Altobelli et al. (2016) Flux and composition of interstellar dust at Saturn from Cassini’s Cosmic Dust Analyzer. Science 352, 312–318.</p> <p>[3] R. Srama et al. (2004) The Cassini Cosmic Dust Analyzer. Space Science Reviews 114, 465–518.</p> <p>[4] K. Fiege et al. (2014) Calibration of relative sensitivity factors for impact ionization detectors with high-velocity silicate microparticles. Icarus 241, 336–345.</p>

Sensitivity factors of aircraft mass for the conceptual design

Purpose The purpose of this work is to further develop the methodology for calculating the aircraft take-off mass and its main functional components for the conceptual analysis and synthesis of new projects. Design/methodology/approach The method is based on the assessment of changes in the take-off gross mass (TOGM) of the already developed project or already existing a basic version of the aircraft when making local mass changes for its modification or for the numerical researches to create a more advanced project. The method is based on the “sensitivity factors of mass” (SFM) of aircraft, which represents the ratio of TOGM to initial (local) mass changes of its main functional components. The method of analytical refined calculation of SFM for the initial mass change and the main aerodynamic characteristics is given. Findings In comparison with the long-known method based on weight (mass) growth factors, which were considered constant, this method takes into account the dependence from the value of the initial local mass change and its functional purpose. Practical implications This method allows the designer to calculate more strictly the final changes in the TOGM on the initial stages of conceptual design when finding new project solutions. Numerical calculations are given on the example of passenger aircraft. The dependence of SFM and TOGM and its functional masses on the value of the initial change of the structure mass are shown. This method is used in the educational process at the college of Aerospace Engineering in the Aircraft Design department. Originality/value The considered method based on SFM is simple and convenient and more accurate for conducting project research on many project parameters when analyzing and synthesizing a new project.