高压电脉冲在页岩气开采中的压裂实验研究

基于液电效应原理,采用高压电脉冲放电对模拟岩样及实际砂岩岩样进行了压裂实验研究。脉冲电源最大储能40 kJ/20 kV,放电电流最高可达70 kA。实验结果表明,高压电脉冲能够在岩样中造成非常明显的裂缝,可以在多个方向上造出多条具有一定高度（最大0.32 m）的裂缝,近井筒裂缝无明显的扭曲,裂缝的形态与放电电压、能量及放电次数有关。对模拟岩样压裂后产生的裂缝进行了三维形貌分析,得到裂缝的表面平均粗糙度在0.430~1.075 mm之间,具有一定的导流能力。     

高压电脉冲在页岩气开采中的压裂实验研究

基于液电效应原理,采用高压电脉冲放电对模拟岩样及实际砂岩岩样进行了压裂实验研究。脉冲电源最大储能40 kJ/20 kV,放电电流最高可达70 kA。实验结果表明,高压电脉冲能够在岩样中造成非常明显的裂缝,可以在多个方向上造出多条具有一定高度（最大0.32 m）的裂缝,近井筒裂缝无明显的扭曲,裂缝的形态与放电电压、能量及放电次数有关。对模拟岩样压裂后产生的裂缝进行了三维形貌分析,得到裂缝的表面平均粗糙度在0.430~1.075 mm之间,具有一定的导流能力。     

页岩矿物不同润湿性表征与吸附微观机理

无机矿物作为页岩气吸附的重要载体,其表面性质对甲烷吸附能力有着重要影响,而润湿性作为固体重要表面性质之一,对矿物气体吸附能力的影响不可忽视.文章以蒙脱石和石英作为研究对象,通过对矿物表面甲基化(-CH₃)和羟基化(-OH)处理来改变其润湿性,以探究无机矿物表面润湿性对甲烷吸附能力的影响.采用分子动力学方法研究矿物体系的润湿性,用接触角对润湿性进行定量表征,并构建纳米狭缝,结合巨正则蒙特卡罗方法模拟润湿性改变前后,CH₄在矿物中的吸附变化.研究结果表明,水滴在羟基化矿物表面迅速破裂并铺展在矿物表面,而在甲基化表面铺展程度较小,普遍呈半球形.羟基化蒙脱石和石英表面的润湿接触角分别为12.7°和26.5°,均小于其甲基化表面接触角62.5°和85.7°.甲基化矿物甲烷吸附量均高于其羟基化,气体几乎大都以吸附状态位于孔隙壁面,随着矿物亲水性的减弱,其对甲烷吸附能力增强.     

Trace gas detect based on spectral analysis and harmonic ratio

Optical Review - A novel method of gas concentration calibration for tunable diode laser absorption spectroscopy, in which spectral analysis and harmonic signal intensity ratio measurement are...     

Terahertz-dependent identification of simulated hole shapes in oil gas reservoirs

Detecting holes in oil–gas reservoirs is vital to the evaluation of reservoir potential. The main objective of this study is to demonstrate the feasibility of identifying general micro-hole shapes, including triangular, circular, and square shapes, in oil–gas reservoirs by adopting terahertz time-domain spectroscopy(THz-TDS). We evaluate the THz absorption responses of punched silicon(Si) wafers having micro-holes with sizes of 20 μm–500 μm. Principal component analysis(PCA) is used to establish a model between THz absorbance and hole shapes. The positions of samples in three-dimensional spaces for three principal components are used to determine the differences among diverse hole shapes and the homogeneity of similar shapes. In addition, a new Si wafer with the unknown hole shapes, including triangular, circular, and square, can be qualitatively identified by combining THz-TDS and PCA. Therefore, the combination of THz-TDS with mathematical statistical methods can serve as an effective approach to the rapid identification of micro-hole shapes in oil–gas reservoirs.     

页岩气在粗糙纳米孔中吸附和输运的分子模拟

从微观上理解固气表面的吸附和注气驱替原理,有助于完善页岩气开采理论.本文通过运用蒙特卡洛和分子动力学方法,模拟了甲烷在粗糙壁面结构孔隙中的吸附和流动行为.研究结果显示粗糙结构对甲烷的吸附量有显著影响,压力小于20 MPa时,粗糙模型中的吸附量更大.注气驱替时,粗糙模型中二氧化碳的突破时间和甲烷的采收率,相比光滑壁面模型明显增加.这是由于粗糙结构模型的页岩壁面表面积更大,在低压下气体吸附能力更强.矩形粗糙结构页岩模型的选择吸附性强于三角粗糙结构模型和光滑模型.研究阐明了甲烷吸附和驱替的微观机理,为提高页岩气采收率提供了指导.     

Environmental response nanosilica for reducing the pressure of water injection in ultra-low permeability reservoirs

The super-hydrophobic silica nanoparticles are applied to alter the wettability of rock surface from water-wet to oil-wet. The aim of this is to reduce injection pressure so as to enhance water injection efficiency in low permeability reservoirs. Therefore, a new type of environmentally responsive nanosilica (denote as ERS) is modified with organic compound containing hydrophobic groups and “pinning” groups by covalent bond and then covered with a layer of hydrophilic organic compound by chemical adsorption to achieve excellent water dispersibility. Resultant ERS is homogeneously dispersed in water with a size of about 4–8 nm like a micro-emulsion system and can be easily injected into the macro or nano channels of ultra-low permeability reservoirs. The hydrophobic nanosilica core can be released from the aqueous delivery system owing to its strong dependence on the environmental variation from normal condition to injection wells (such as pH and salinity). Then the exposed silica nanoparticles form a thin layer on the surface of narrow pore throat, leading to the wettability from water-wet to oil-wet. More importantly, the two rock cores with different permeability were surface treated with ERS dispersion with a concentration of 2 g/L, exhibit great reduce of water injection pressure by 57.4 and 39.6%, respectively, which shows great potential for exploitation of crude oil from ultra-low permeability reservoirs during water flooding.

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Microwave permeability of metamaterials based on ferromagnetic composites

In this paper, we focus on metamaterials based on ferromagnetic composite combined with an inductive pattern. CoFeSiB amorphous ferromagnetic glass-coated microwires and thin films are involved in the composite. The inductive pattern is a coiling of Copper wire with a varying number of loops. We derived the microwave permeability of the ferromagnetic material inside the inductive pattern through a Landau–Gilbert model of gyromagnetism. In agreement with experimental results, the engineering of resonance frequency of the sample is achieved through the number of loops of the coiling.     

Mixture gas component concentration analysis based on support vector machine and infrared spectrum

A novel quantitative analysis method of multi-component mixture gas concentration based on support vector machine (SVM) and spectroscopy is proposed. Through transformation of the kernel function, the seriously overlapped and nonlinear spectrum data are transformed in high-dimensional space, but the highdimensional data can be processed in the original space. Some factors, such as kernel function, range of the wavelength, and penalty coefficient, are discussed. This method is applied to the quantitative analysis of natural gas components concentration, and the component concentration maximal deviation is 2.28%.     

Enhancement of hydrogen gas permeability in electrically aligned MWCNT-PMMA composite membranes

The multi-walled carbon nanotube (MWCNT) dispersed polymethylmethacrylate (PMMA) composite membranes have been prepared for hydrogen gas permeation application. Composite membranes are characterized by Raman spectroscopy, optical microscopy, X-ray diffraction, electrical measurements and gas permeability measurements. The effect of electric field alignment of MWCNT in PMMA matrix on gas permeation has been studied for hydrogen gas. The permeability measurements indicated that the electrically aligned MWCNT in PMMA has shown almost 2 times higher permeability for hydrogen gas as compare to randomly dispersed MWCNT in PMMA. The enhancement in permeability is explained on the basis of well aligned easy channel provided by MWCNT in electrically aligned sample. The effect of thickness of membrane on the gas permeability also studied and thickness of about 30 μm found to be optimum thickness for fast hydrogen gas permeates.     

Cut-off frequency of magnetostrictive materials based on permeability spectra

The loss behavior and cut-off frequency of TbDyFe alloy and TbDyFe/epoxy composite have been investigated by measuring their permeability spectra. The loss factor of TbDyFe alloy increases exponentially as the frequency goes up, while it is almost unchanged for the TbDyFe/epoxy composite. The loss factor value for the TbDyFe composite is only 4.3% of that for the monolithic TbDyFe alloy at high frequency of 10 kHz under the peak magnetic induction of 10 mT. The cut-off frequency of TbDyFe/epoxy composite is 6800 kHz, 3 orders of magnitude larger than that of TbDyFe alloy. The cut-off frequency is found to be the ferromagnetic resonance frequency and can be calculated from Snoek's law.     

基于电流变液的可调谐负磁导率材料

通过把负磁导率材料SRR阵列置于高性能电流变液中,研究了电极加载方式、电流变液浓度、电流变液类型以及电场强度等因素对浸入电流变液中的SRR阵列谐振频率的影响. 实验表明,电极加载方式对SRR阵列的磁响应有重要的影响;在容器盒中充满电流变液之后SRR阵列的谐振频率往低频发生了移动,并且可以通过改变外加电场强度来调节,最大的调节范围为130MHz. 数值计算结果表明SRR阵列的有效磁导率在谐振频率附近为负值,并且有效磁导率为负的频率范围也可以通过改变外加电场强度来调节. 关键词： 负磁导率材料 谐振频率 电流变液     

Molecular mechanism of adsorption/desorption hysteresis: dynamics of shale gas in nanopores

Understanding the adsorption and desorption behavior of methane has received considerable attention since it is one of the crucial aspects of the exploitation of shale gas. Unexpectedly, obvious hysteresis is observed from the ideally reversible physical sorption of methane in some experiments. However, the underlying mechanism still remains an open problem. In this study, Monte Carlo (MC) and molecular dynamics (MD) simulations are carried out to explore the molecular mechanisms of adsorption/desorption hysteresis. First, a detailed analysis about the capillary condensation of methane in micropores is presented. The influence of pore width, surface strength, and temperature on the hysteresis loop is further investigated. It is found that a disappearance of hysteresis occurs above a temperature threshold. Combined with the phase diagram of methane, we explicitly point out that capillary condensation is inapplicable for the hysteresis of shale gas under normal temperature conditions. Second, a new mechanism, variation of pore throat size, is proposed and studied. For methane to pass through the throat, a certain energy is required due to the repulsive interaction. The required energy increases with shrinkage of the throat, such that the originally adsorbed methane cannot escape through the narrowed throat. These trapped methane molecules account for the hysteresis. Furthermore, the hysteresis loop is found to increase with the increasing pressure and decreasing temperature. We suggest that the variation of pore throat size can explain the adsorption/desorption hysteresis of shale gas. Our conclusions and findings are of great significance for guiding the efficient exploitation of shale gas.     

利用斯通利波评价中孔低渗地层渗透率*

南中国海东部海域白云深水地区储层孔渗关系复杂,存在中高孔高渗、低孔低渗、中孔低渗等多种类型储层,出现储层间孔隙度相近、渗透率相差一到两个数量级的现象。岩心分析表明渗透率的主控因素是溶蚀孔隙发育和胶结物充填,给常规渗透率评价方法带来挑战。斯通利波对井中流体和孔隙流体之间的压力传递敏感,其幅度衰减和时间延迟可以反映储层流体的渗滤作用,能有效地进行地层渗透率的反演。利用斯通利波评价白云深水地区因孔喉连通性造成的渗透率差异问题,取得了良好的效果。     

基于改进格子气模型的对向行人流分层现象的随机性研究

在考虑行人视野范围的随机偏走格子气模型基础上, 引入行人对前方开阔区域的移动偏好特性, 提出改进的格子气模型, 对通道内对向行人流进行仿真研究. 模型再现了对向行人流在不同密度下出现的3种演化过程, 发现了行人密度与对向行人流分层现象的形成具有随机性, 以及统计了概率的变化趋势, 同时分析了分层现象形成概率与系统几何尺寸参数、移动强度参数、右行人流比例参数和视野范围参数等的关系. 分析结果表明, 改进的模型能够再现实际低密度下对向行人流不会出现分层现象的特性. 根据分层形成的概率, 可将对向行人流的密度分为5个区间, 不同区间的行人流演化过程各有差异. 模型和分析结果对理解对向行人流的动态演化过程, 提高通道内对向行人流的走行效率有一定帮助.     

玻璃微球壁厚和预充气工艺对气体渗透性能的影响

 以空心玻璃微球为研究对象,利用高压充气系统充气,测量了不同条件下玻璃微球对氘气在室温条件下的气体渗透系数。研究结果表明：微球的壁厚对气体渗透系数影响较大,2 mm以上厚壁球的气体渗透系数约5.0×10^-22 mol·m^-1·s^-1·Pa^-1,而壁厚小于1 mm时,渗透系数约1.56×10^-20 mol·m^-1·s^-1·Pa^-1,两者相差30倍。预充气挑选工艺对微球的气体渗透系数也产生一定影响,对于薄壁空心玻璃微球一次充放气气体渗透系数增加约50％,两次充放气则增大一倍左右。对上述影响因素进行了初步的探讨,气体渗透系数改变的主要原因是玻璃微球表面的结构裂纹、空位和缺陷。     

二维电子气等离激元太赫兹波器件

固态等离激元太赫兹波器件正成为微波毫米波电子器件技术和半导体激光器技术向太赫兹波段发展和融合的重要方向之一。本综述介绍AlGaN/GaN异质结高浓度和高迁移率二维电子气中的等离激元调控、激发及其在太赫兹波探测器、调制器和光源中应用的近期研究进展。通过光栅和太赫兹天线实现自由空间太赫兹波与二维电子气等离激元的耦合,通过太赫兹法布里-珀罗谐振腔进一步调制太赫兹波模式,增强太赫兹波与等离激元的耦合强度。在光栅-谐振腔耦合的二维电子气中验证了场效应栅控的等离激元色散关系,实现了等离激元模式与太赫兹波腔模强耦合产生的等离极化激元模式,演示了太赫兹波的调制和发射。在太赫兹天线耦合二维电子气中实现了等离激元共振与非共振的太赫兹波探测,建立了太赫兹场效应混频探测的物理模型,指导了室温高灵敏度自混频探测器的设计与优化。研究表明,基于非共振等离激元激发可发展形成室温高速高灵敏度的太赫兹探测器及其焦平面阵列技术。然而,固态等离激元的高损耗特性仍是制约基于等离激元共振的高效太赫兹光源和调制器的主要瓶颈。未来的研究重点将围绕高品质因子等离激元谐振腔的构筑,包括固态等离激元物理、等离激元谐振腔边界的调控、新型室温高迁移率二维电子材料的运用和高品质太赫兹谐振腔与等离激元器件的集成等。     

玻璃微球壁厚和预充气工艺对气体渗透性能的影响

以空心玻璃微球为研究对象,利用高压充气系统充气,测量了不同条件下玻璃微球对氘气在室温条件下的气体渗透系数。研究结果表明：微球的壁厚对气体渗透系数影响较大,2 mm以上厚壁球的气体渗透系数约5.0×10-22 mol·m-1·s-1·Pa-1,而壁厚小于1 mm时,渗透系数约1.56×10-20 mol·m-1·s-1·Pa-1,两者相差30倍。预充气挑选工艺对微球的气体渗透系数也产生一定影响,对于薄壁空心玻璃微球一次充放气气体渗透系数增加约50％,两次充放气则增大一倍左右。对上述影响因素进行了初步的探讨,气体渗透系数改变的主要原因是玻璃微球表面的结构裂纹、空位和缺陷。