Petrophysical and Capillary Properties of Compacted Salt

This paper reports experimental results that demonstrate petrophysical and capillary characteristics of compacted salt. The measured data include porosity, gas permeability, pore size distribution, specific surface area, and gas-brine breakthrough and capillary pressure. Salt samples employed in the experiments were prepared by compacting sodium chloride granulates at high stresses for several hours. They represent an intermediate consolidation stage of crushed salt under in-situ conditions. The porosity and permeability of compacted salt showed similar trends to those expected in backfilled regions of waste repositories excavated in salt rock. The correlation between the measured porosity and permeability seems to be independent of the compaction parameters for the range examined in this study. The correlation also shows a different behaviour from that of rock salt. The data of all petrophysical properties show that the pore structure of compacted salt can be better characterized by fracture permeability models rather than capillary bundle ones. Simple creep tests, conducted on the fully-brine-saturated compacted salt samples, yielded similar strain rates to those obtained by a steady-state mechanical model developed from the tests on fully brine-saturated granular salt. A modified procedure is proposed for the evaluation of restored-state capillary pressure data influenced by the material creep. The characteristic parameters for the capillary behaviour of compacted salt are determined by matching the Brooks-Corey and van Genuchten models with the measured data. The Leverett functions determined with different methods agree well.     

Investigation on Fracture Properties of Single-Flawed Tunnel Model Under Medium-to-Low-Speed Impacts

Dynamic fractures occur frequently in geophysical processes and engineering applications.It is thus essential to study crack and failure behaviors,such as crack time-to-initiation,crack growth rate and arrest period under dynamic loading.In this study,impact experiments were implemented by utilizing the single-flawed tunnel specimens under drop-hammer impacts.Four brittle materials,i.e.,green sandstone,red sandstone,black sandstone and polymethyl methacrylate,were selected to make single-flawed tunnel specimens.Strain gauges and crack extension gauges were employed to measure the crack extension parameters.The properties of crack growth rate,crack time-to-initiation and arrest period of these four brittle materials were discussed and analyzed.The corresponding numerical simulation was performed by using the commercial software AUTODYN.The numerical results of crack growth rate and crack time-to-initiation agreed with the impact test results.The commercial software ABAQUS was applied to compute the dynamic stress intensity factors.The results show that both the dynamic initiation fracture toughness and the crack growth rate increase with the elastic moduli of these four types of brittle materials under the same loading conditions,whereas the crack time-to-initiation decreases with the increase in elastic moduli of the brittle materials under the same loading conditions.     

Long-term Petrophysical Investigations on Geothermal Reservoir Rocks at Simulated In Situ Conditions

In the course of stimulation and fluid production, the chemical fluid–rock equilibrium of a geothermal reservoir may become disturbed by either temperature changes and/or an alteration of the fluid chemistry. Consequently, dissolution and precipitation reactions might be induced that result in permeability damage. In connection with the field investigations at a deep geothermal doublet, complementary laboratory-based research is performed to address these effects. The reservoir is located at a depth of 4100 to 4200 m near Groß Schönebeck within the Northeast German Basin, 50 km north of Berlin, Germany. Within the reservoir horizon, an effective pressure of approximately 45 MPa and a temperature of 150°C are encountered. Furthermore, the Lower Permian (Rotliegend) reservoir rock is saturated with a highly saline Ca–Na–Cl type formation fluid (TDS ≈ 255 g/l). Under these conditions we performed two sets of long-term flow-through experiments. The pore fluid used during the first and the second experiment was a 0.1 molar NaCl-solution and a synthetic Ca–Na–Cl type fluid with the specifications as above, respectively. The maximum run duration was 186 days. In detail, we experimentally addressed: (1) the effect of long-term flow on rock permeability in connection with possible changes in fluid chemistry and saturation; (2) the occurrence and consequences of baryte precipitation; and (3) potential precipitations related to oxygen-rich well water invasion during water-frac stimulation. In all substudies petrophysical experiments related to the evolution of rock permeability and electrical conductivity were complemented with microstructural investigations and a chemical fluid analysis. We also report the technical challenges encountered when corrosive fluids are used in long-term in situ petrophysical experiments. After it was assured that experimental artifacts can be excluded, it is demonstrated that the sample permeability remained approximately constant within margins of  ±50 % for nearly six months. Furthermore, an effect of baryte precipitation on the rock permeability was not observed. Finally, the fluid exchange procedure did not alter the rock transport properties. The results of the chemical fluid analysis are in support of these observations. In both experiments the electrical conductivity of the samples remained unchanged for a given fluid composition and constant p-T conditions. This emphasizes its valuable complementary character in determining changes in rock transport properties during long-term flow-through experiments when the risk of experimental artifacts is high.     

Effect of 2D Image Resolution on 3D Stochastic Reconstruction and Developing Petrophysical Trend

Multi-resolution digital rock physics (DRP) makes it possible to up-scale petrophysical properties from micron size to core sample size using two-dimensional (2D) thin section images. Resolution of 3D images and sample size are challenging problems in DRP where high-resolution images are acquired from small samples using inefficient and expensive micro-CT facilities. Three-dimensional stochastic reconstruction is an alternative approach to overcome these challenges. In this paper, we use multi-resolution images and investigate effect of 2D image resolution on 3D stochastic reconstruction and development of petrophysical trends for our two sandstone and carbonate original representative volume elements (RVEs). The proposed method includes three steps. In the first step, the spatial resolution of our original RVEs is decreased synthetically. In the second step, stochastic RVEs are realized for each resolution using two perpendicular images, correlation functions, and phase recovery algorithm. In the reconstruction method, a full set of two-point correlation functions (TPCFs) is extracted from two perpendicular 2D images. Then TPCF vectors are decomposed and averaged to realize 3D stochastic RVEs. In the third step, petrophysical properties like relative and absolute permeability as well as porosity and formation factor are computed. The output is used to develop trends for petrophysical properties in different resolutions. Experimental results illustrate that the proposed method can be used to predict petrophysical properties and reconstruct 3D RVEs for resolutions unavailable in the acquired 2D or 3D data.     

A new Apparatus for Long-term Petrophysical Investigations on Geothermal Reservoir Rocks at Simulated In-situ Conditions

We present a new apparatus capable of maintaining in-situ conditions pertinent to deep geothermal reservoirs over periods of months while in the same time allowing a variety of continuous petrophysical investigations. Two identical devices have been set up at the GFZ-Potsdam. Lithostatic overburden- and hydrostatic pore pressures of up to 100 and 50 MPa, respectively can be simulated. In addition in-situ temperature requirements of up to 200°C can be met. The use of corrosion resistant parts throughout the pore pressure system allows investigations with highly saline formation fluids. Rock permeability, electrical conductivity as well as compressional- and shear-wave velocities can be measured simultaneously and the pore fluid can be sampled under pressure for further chemical analysis. Scientifically, the usage of the device focuses on risk potentials in exploration and exploitation of deep geothermal reservoirs. Particularly, the investigations address possible effects of fluid-rock interactions on the transport properties of a reservoir host rock.     

Impacts of the Cell-Free and Cell-to-Cell Infection Modes on Viral Dynamics

Virus can disseminate between uninfected target cells via two modes, namely, the diffusion-limited cell-free viral spread and the direct cell-to-cell transfer using virological synapses. To examine how these two viral infection modes impact the viral dynamics, in this paper, we propose and analyze a general viral infection model that incorporates these two viral infection modes. The model also includes nonlinear target-cell dynamics, infinitely distributed intracellular delays, nonlinear incidences, and concentration-dependent clearance rates. It is shown that the numbers of secondly infected cells through the cell-free infection mode and the cell-to-cell infection mode both contribute to the basic reproduction number. Under some reasonable assumptions, the model exhibits a global threshold dynamics: the infection is cleared out if the basic reproduction number is less than one and the infection persists if the basic reproduction number is larger than one. Two specific examples are provided to illustrate that our theoretical results cover and improve some existing ones. When the underlying assumptions are not satisfied, oscillations via global Hopf bifurcation can be observed. A brief simulation of two-parameter bifurcation analysis is given to explore the joint impacts on viral dynamics for the interplay between nonlinear target-cell dynamics and intracellular delays.     

Improving the Estimations of Petrophysical Transport Behavior of Carbonate Rocks Using a Dual Pore Network Approach Combined with Computed Microtomography

Due to the intricate structure of carbonate rocks, relationships between porosity or saturation and petrophysical transport properties classically used for reservoir estimation and recovery strategies are either very complex or nonexistent. Thus, further understanding of the influence of the rock structure on the petrophysical transport properties becomes relevant. We therefore present a Dual Pore Network approach (D-PNM) applied to???-CT images of bimodal porous media. The major advantage of this method lies in the fact that it takes into account the real architecture of the connected macropore network as well as the microporosity unresolved by???-CT imaging. Whereas governing equations are solved in each individual macropore, transport behavior of microporosity is simulated by average quantities. Thus, D-PNM is particularly suited for the investigation of carbonate rocks, characterized by broad pore size distributions. We describe the principles of the image acquisition and network extraction procedure and the governing equations of D-PNM. The model is tested on three carbonate samples, two outcrop, and one reservoir carbonate. Calculated petrophysical transport properties are compared to experimental data and we show that D-PNM correctly reproduces conventional as well as unconventional electrical transport behavior. A major restriction of D-PNM is the requirement of a connected macropore network, that is, especially in the case of carbonates, not always available. Solutions to that are presented.     

Impacts of biomass-burning on aerosol properties of a severe haze event over Shanghai

Anthropogenic aerosols have significant impacts on the environment and human health in the Yangtze River Delta region,one of the most densely populated regions in the world.A biomass-burning plume swept across this area(Shanghai) in May 2009,leading to changes in the physical and optical properties of aerosols,which were investigated using ground-based remote sensing and in situ measurements via comparisons with dust pollution and background conditions.Experiments show that the biomass-burning plume led to an increase in the average aerosol optical depth(AOD) at 500 nm from 0.73 to 1.00(37%higher),an absorption Angstrom exponent(AAE) of 1.48,and an increase in the Angstrom exponent(α) up to 1.53.Furthermore,local dust aerosols derived from road dust and/or construction dust also led to higher values of AOD(2.68) and AAE(2.16),and a daily average value of α of 1.05.For the biomass-burning plume,the aerosol particles exhibited significant variations in short-wavelength spectra.The single scattering albedo at 670 nm decreased remarkably under the influence of the biomass-burning plume,indicating the significant absorptive ability of the biomass-burning pollution and higher ratio of absorption aerosols within the plume.Under the effects of the biomass-burning,the volume concentration of fine-mode aerosols increased significantly and the PM-fine/PM-coarse volume concentration ratio reached 12.33.This relatively large change in fine-mode particles indicates that biomass-burning has a greater impact on fine-mode aerosols than on coarse-mode aerosols.     

Impacts of biomass-burning on aerosol properties of a severe haze event over Shanghai

Anthropogenic aerosols have significant impacts on the environment and human health in the Yangtze River Delta region, one of the most densely populated regions in the world. A biomass-burning plume swept across this area (Shanghai) in May 2009, leading to changes in the physical and optical properties of aerosols, which were investigated using ground-based remote sensing and in situ measurements via comparisons with dust pollution and background conditions. Experiments show that the biomass-burning plume led to an increase in the average aerosol optical depth (AOD) at 500 nm from 0.73 to 1.00 (37% higher), an absorption Angstrom exponent (AAE) of 1.48, and an increase in the Angstrom exponent (α) up to 1.53. Furthermore, local dust aerosols derived from road dust and/or construction dust also led to higher values of AOD (2.68) and AAE (2.16), and a daily average value of α of 1.05. For the biomass-burning plume, the aerosol particles exhibited significant variations in short-wavelength spectra. The single scattering albedo at 670 nm decreased remarkably under the influence of the biomass-burning plume, indicating the significant absorptive ability of the biomass-burning pollution and higher ratio of absorption aerosols within the plume. Under the effects of the biomass-burning, the volume concentration of fine-mode aerosols increased significantly and the PM-fine/PM-coarse volume concentration ratio reached 12.33. This relatively large change in fine-mode particles indicates that biomass-burning has a greater impact on fine-mode aerosols than on coarse-mode aerosols.     

Impacts of aerosol chemical compositions on optical properties in urban Beijing,China

The optical properties of aerosols and their chemical composition,including water-soluble ions,organic carbon（OC）,and elemental carbon（EC） in PM_2.5 and PM₁₀,were measured from 26 May to 30 June of 2012 at an urban site in Beijing.The daily average concentrations of PM_2.5 and PM₁₀ were 103.2 and 159.6 μg/m³,respectively.On average,the OC and EC contributed 20.1% and 4.3% ,respectively,to PM_2.5 and 16.3% and3.9% ,respectively,to PM₁₀.Secondary ions(SO₄^2-,NO₃^-,and NH₄⁺) dominated the water-soluble ions and accounted for 57.9% and 62.6% of PM_2.5 and PM₁₀,respectively.The wind dependence of PM_2.5,OC,SO₄^2-,and NO₃^- implied that the pollution sources mainly came from south and southeast of Beijing during the summer.The monthly mean values of the scattering coefficient(σ_sc) and absorption coefficient(σ_ab) at525 nm were 312.9 and 28.7 Mm^-1,respectively,and the mean single-scattering albedo（ω） was 0.85.The wind dependence of σ_sc revealed that this value was mainly influenced by regional transport during the summer,and the relationship between σ_ab and wind indicated that a high σ_ab resulted from the joint effects of local emissions and regional transport.The reconstructed σ_sc that was derived from the revised IMPROVE equation agreed well with the observations.The contribution of different chemical species toσ_sc was investigated under different pollution levels,and it was found that secondary inorganic aerosols accounted for a large part of σ_sc during pollution episodes（35.7% ）,while organic matter was the main contributor to σ_sc under clean conditions（33.6% ）.     

Spectral Response of a Stochastic Oscillator under Impacts

An approximate analytical procedure is presented to estimate theresponse spectrum of an oscillator with elastic impacts under a Gaussian whitenoise excitation. The proposed approach is based on a perturbation analysis ofthe problem and on the use of the stochastic averaging principle. The basicidea is to replace the initial system by a more regular system obtained byapproximating the nonlinear restoring force by a Chebychev polynomial, and thento construct for this regular system two approximations: one for the flowand one for the stationary distribution of the response amplitude. Ananalytical approximation of the response spectrum can then be derived fromthese results. Predictions from this analytical approximation are compared with corresponding digital simulation estimates and with the ones obtained from theconventional equivalent linearization method.     

微机电系统磨损特性研究进展

对微机电系统,尤其是微旋转机械的磨损研究现状进行评述,介绍MEMS及微旋转机械中的各种磨损问题,分析材料和不同工况(表面粗糙度、环境以及载荷)等条件对MEMS及微旋转机械磨损性能的影响,介绍不同形式的磨损模型、分析方法与检测仪器,并对相关领域的研究进展进行展望.     

Random Vibrations with Impacts: A Review

Analytical methods and specific results are presented for random vibrations of systems with lumped parameters and “classical” impacts whereby finite relations between impact/rebound velocities are imposed at the impact instants that are not known in advance but rather governed by the equations of motion. Emphasis is placed on the procedures using special piecewise-linear transformation of state variables that exclude the velocity jumps at impacts or makes them small if impact losses are present. In the former case, exact analyses for stationary probability densities of the response to white-noise excitation are possible, whereas the stochastic averaging method is applied in the latter case. Furthermore, the special case of an isochronous system permits a more profound response analysis, such as predicting the spectral density of the response or subharmonic response to narrow-band excitation. The method of direct energy balance is also illustrated, based on direct application of the stochastic differential equation calculus between impacts. Certain two-degree-of-freedom impacting systems are considered, with application to moored systems, as used in ocean engineering.     

PDMS表面织构润滑特性的研究

利用光刻-复模技术在PDMS表面制作凹坑阵列型表面织构,并采用球-盘式摩擦试验机对具有不同尺寸凹坑阵列的试样进行摩擦试验,研究了软质材料表面织构在混合至流体动压润滑区域的润滑特性.结果表明:对于PDMS材料,凹坑直径是影响摩擦特性的主要因素之一.与无织构试样相比,在低速条件下(0.005m/s)的混合润滑区域较小直径(d=50μm)的织构能够减小摩擦,而较大直径(d=200μm)的织构表现出增大摩擦的效果.在试验范围内凹坑的面积率越大,表面织构的作用越显著.     

泊松比对钢管混凝土拱桥极限承载力的影响

主要研究在几何和材料双非线性影响下,分析大跨度钢管混凝土拱桥钢管内混凝土泊松比变化对桥梁极限承载力的影响.。以某桥为背景,利用ansys程序进行三维有限元仿真分析,在考虑混凝土泊松比变化情况下,逐步改变核心混凝土泊松比直至结构破坏,并与不考虑混凝土泊松比变化的情况相比较,以考察核心混凝土泊松比变化对桥梁极限承载力影响程度,得出在对拱桥的极限承载力分析时,考虑钢管对核心混凝土的套箍作用,可使极限承载力比不考虑混凝土泊松比变化时的计算值高出10%。     

Describing Function Analysis of Systems with Impacts and Backlash

This paper analyzes the dynamical properties of systems with backlashand impact phenomena based on the describing function method. It isshown that this type of nonlinearity can be analyzed in the perspectiveof the fractional calculus theory. The fractional-order dynamics isillustrated using the Nyquist plot and the results are compared withthose of standard models.     

Impacts of local dispersion and first-order decay on solute transport in randomly heterogeneous porous media

Stochastic subsurface transport theories either disregard local dispersion or take it to be constant. We offer an alternative Eulerian-Lagrangian formalism to account for both local dispersion and first-order mass removal (due to radioactive decay or biodegradation). It rests on a decomposition of the velocityv into a field-scale componentv , which is defined on the scale of measurement support, and a zero mean sub-field-scale componentv _s , which fluctuates randomly on scales smaller than. Without loss of generality, we work formally with unconditional statistics ofv _s and conditional statistics ofv . We then require that, within this (or other selected) working framework,v _s andv be mutually uncorrelated. This holds whenever the correlation scale ofv is large in comparison to that ofv _s . The formalism leads to an integro-differential equation for the conditional mean total concentration c which includes two dispersion terms, one field-scale and one sub-field-scale. It also leads to explicit expressions for conditional second moments of concentration cc. We solve the former, and evaluate the latter, for mildly fluctuatingv by means of an analytical-numerical method developed earlier by Zhang and Neuman. We present results in two-dimensional flow fields of unconditional (prior) mean uniformv . These show that the relative effect of local dispersion on first and second moments of concentration dies out locally as the corresponding dispersion tensor tends to zero. The effect also diminishes with time and source size. Our results thus do not support claims in the literature that local dispersion must always be accounted for, no matter how small it is. First-order decay reduces dispersion. This effect increases with time. However, these concentration moments c and cc of total concentrationc, which are associated with the scale below, cannot be used to estimate the field-scale concentrationc directly. To do so, a spatial average over the field measurement scale is needed. Nevertheless, our numerical results show that differences between the ensemble moments ofc and those ofc are negligible, especially for nonpoint sources, because the ensemble moments ofc are already smooth enough.     

InSb薄膜的剪切性能研究

InSb薄膜广泛应用于高精度的光电存储、红外探测等技术中.为了提高InSb材料的剪切强度,优化其力学性能,论文对InSb薄膜分别从不同厚度、温度、滑移系取向、孔洞密度等几个方面,对InSb薄膜的剪力响应及其原子构型演变进行分析,以研究其剪切强度和韧性的影响因素.发现厚度较大的薄膜具有更大的弹性模量和极限强度.而温度升高会导致材料的强度极限以及剪切韧性降低.同时还观察到10%孔洞密度下孔洞形状对材料的剪切性能有明显影响而20%孔洞密度下形状不再明显影响材料的剪切性能.此外在不同滑移系取向的研究中发现,滑移系取向对于材料的剪切强度和剪切韧性的影响是不同步的,例如(110)[1-10]滑移系下剪切强度降低而剪切韧性增强.上述结论对于提升InSb材料的剪切性能,合成出具有优异力学性能的InSb光电、磁敏材料具有指导意义.     

离子注入超高分子量聚乙烯的摩擦磨损性能研究

对人工关节软骨材料——超高分子量聚乙烯(UHMWPE)进行O+和C+离子注入改性,采用销-盘式摩擦磨损试验机考察了离子注入UHMWPE试样在血浆润滑条件下同Si3N4陶瓷球对摩时的摩擦磨损性能;用扫描电子显微镜观察分析了注入和未注入试样及其磨痕表面形貌,用红外光谱仪(IR)分析了注入和未注入试样的化学特征.结果表明:经O+和C+离子注入处理的UHMWPE试样表面发生了碳化并形成了类金刚石结构;O+和C+注入处理均有利于增强UHMWPE的耐磨性能,而O+离子注入试样的耐磨性能优于C+离子注入试样,经450keV、5×1015/cm2的O+离子注入试样的耐磨性能最佳;未注入UHMWPE试样在血浆润滑条件下同陶瓷对摩时主要呈现粘着、塑性变形和犁沟特征,而注入UHMWPE试样在相同条件下主要呈现表面硬化层疲劳裂纹萌生、扩展、剥落及磨粒磨损特征.