MODELLING RUNOFF GENERATION ON SMALL AGRICULTURAL CATCHMENTS: CAN REAL WORLD RUNOFF RESPONSES BE CAPTURED?

This paper focuses on the problem of quantifying real world catchment response using a distributed model and discusses the ability of the model to capture that response. The rainfall–runoff responses of seven small agricultural catchments in the eastern wheatbelt region of south-western Australia are examined. The variability in runoff generation and the factors that contribute to that variability (i.e. rainfall intensity, soil properties and topography) are investigated to determine if their influence can be captured in a mathematical model. The spatially distributed rainfall–runoff model used in this study is based on the TOPMODEL concepts of Beven and Kirkby (1979), and simulates runoff generation by both the infiltration excess and saturation excess mechanisms. Simulations with the model revealed the highly complex nature of catchment response to rainfall events. Runoff generation was highly heterogeneous in both space and time, with the runoff response being governed by the spatial variability of soil properties and topography, and by the temporal variation in rainfall intensity. Although the model proved capable of simulating catchment response for many events, the investigation has demonstrated that not all aspects of the variability associated with agricultural catchments (particularly the effects of land management) can be captured using this relatively simple model. © 1997 by John Wiley & Sons, Ltd     

A GIS‐based variable source area hydrology model

Effective control of nonpoint source pollution from contaminants transported by runoff requires information about the source areas of surface runoff. Variable source hydrology is widely recognized by hydrologists, yet few methods exist for identifying the saturated areas that generate most runoff in humid regions. The Soil Moisture Routing model is a daily water balance model that simulates the hydrology for watersheds with shallow sloping soils. The model combines elevation, soil, and land use data within the geographic information system GRASS, and predicts the spatial distribution of soil moisture, evapotranspiration, saturation‐excess overland flow (i.e., surface runoff), and interflow throughout a watershed. The model was applied to a 170 hectare watershed in the Catskills region of New York State and observed stream flow hydrographs and soil moisture measurements were compared to model predictions. Stream flow prediction during non‐winter periods generally agreed with measured flow resulting in an average r² of 0·73, a standard error of 0·01 m³/s, and an average Nash‐Sutcliffe efficiency R² of 0·62. Soil moisture predictions showed trends similar to observations with errors on the order of the standard error of measurements. The model results were most accurate for non‐winter conditions. The model is currently used for making management decisions for reducing non‐point source pollution from manure spread fields in the Catskill watersheds which supply New York City's drinking water. Copyright © 1999 John Wiley & Sons, Ltd.     

一种缝洞型碳酸盐岩储层胶结指数m计算新方法

碳酸盐岩储集空间类型多样、孔隙结构复杂,具有很强的非均质性,使得传统的阿尔奇公式应用效果不佳,主要原因之一在于胶结指数m的无法准确确定.基于多孔介质理论,在深入分析不同孔隙空间对储层导电贡献外,进一步考虑了孔隙形态对导电性能的影响,尤其是裂缝倾角,进而给出了全新的计算胶结指数m的方法,并深入剖析组成碳酸盐岩复杂孔隙空间的各部分对胶结指数m的影响.认为对于物性较差的缝洞型储层,裂缝倾角对胶结指数m的影响很大,当裂缝角度较小时,裂缝会使胶结指数m变小,而当裂缝角度较大时,裂缝反而会使胶结指数m变大;当储层物性很好时,裂缝倾角的影响则可以忽略.实际应用表明,利用基于裂缝倾角的多孔介质模型得到的胶结指数m所计算的含水饱和度精度相比传统方法有较大提高,且该方法适用于任何类型的储层,具有很好的应用性.     

Effects of pore fluids on quasi-static shear modulus caused by pore-scale interfacial phenomena

It is evident from the laboratory experiments that shear moduli of different porous isotropic rocks may show softening behaviour upon saturation. The shear softening means that the shear modulus of dry samples is higher than of saturated samples. Shear softening was observed both at low (seismic) frequencies and high (ultrasonic) frequencies. Shear softening is stronger at seismic frequencies than at ultrasonic frequencies, where the softening is compensated by hardening due to unrelaxed squirt flow. It contradicts to Gassmann's theory suggesting that the relaxed shear modulus of isotropic rock should not depend upon fluid saturation, provided that no chemical reaction between the solid frame and the pore fluid. Several researchers demonstrated that the shear softening effect is reversible during re-saturation of rock samples, suggesting no permanent chemical reaction between the solid frame and the pore fluid. Therefore, it is extremely difficult to explain this fluid–rock interaction mechanism theoretically, because it does not contradict to the assumptions of Gassmann's theory, but contradicts to its conclusions. We argue that the observed shear softening of partially saturated rocks by different pore fluids is related to pore-scale interfacial phenomena effects, typically neglected by the rock physics models. These interface phenomena effects are dependent on surface tension between immiscible fluids, rock wettability, aperture distribution of microcracks, compressibility of microcracks, porosity of microcracks, elastic properties of rock mineral, fluid saturation, effective stress and wave amplitude. Derived equations allow to estimate effects of pore fluids and saturation on the shear modulus and mechanical strength of rocks.     

矩震级及其计算

简要叙述地震震级概念的提出及其历史发展。文中指出,矩震级M_W是目前量度地震大小最理想的物理量。与传统上使用的其他震级标度相比,矩震级不会饱和,对于所有地震,无论大小、深浅,无论使用远场、近场地震波资料,大地测量和地质资料中的何种资料,均可测量矩震级,并能与熟知的震级标度如面波震级M_S相衔接。矩震级是一个均匀的震级标度,适于震级范围很宽的统计。矩震级是国际地震学界选定的首选震级,负责向公众发布地震信息的部门优先采用的发布的震级。文中介绍了计算矩震级所用的公式,详细解说了具体的计算步骤,分析了由于采用的计算矩震级公式的不同,采取的具体的数值计算步骤的不同引起的问题以及解决这些问题的相关的规定。     

Review Paper: Post-stack 4D seismic time-shifts: Interpretation and evaluation

A review and analysis of post-stack time-lapse time-shifts has been carried out that covers published literature supplemented by in-house datasets available to the authors. Time-shift data are classified into those originating from geomechanical effects and those due to fluid saturation changes. From these data, conclusions are drawn regarding the effectiveness of post-stack time-shifts for overburden and reservoir monitoring purposes. A variety of field examples are shown that display the range and magnitude of variation for each class of application. The underlying physical mechanisms creating these time-shifts are then described, and linked to a series of generic and field-specific rock physics calculations that predict their magnitudes. These calculations serve as a guide for practitioners wishing to utilize this information on their own datasets. Conclusions are drawn regarding the reliability of this attribute for monitoring purposes, and the extent to which further development is required and how it should be reported by authors.     

Estimating gas saturation in a thin layer by using frequency‐dependent amplitude versus offset modelling

Various models have been proposed to link partial gas saturation to seismic attenuation and dispersion, suggesting that the reflection coefficient should be frequency‐dependent in many cases of practical importance. Previous approaches to studying this phenomenon typically have been limited to single‐interface models. Here, we propose a modelling technique that allows us to incorporate frequency‐dependent reflectivity into convolutional modelling. With this modelling framework, seismic data can be synthesised from well logs of velocity, density, porosity, and water saturation. This forward modelling could act as a basis for inversion schemes aimed at recovering gas saturation variations with depth. We present a Bayesian inversion scheme for a simple thin‐layer case and a particular rock physics model and show that, although the method is very sensitive to prior information and constraints, both gas saturation and layer thickness theoretically can be estimated in the case of interfering reflections.     

南海北部荔湾3区块天然气水合物分布特征及目标识别

针对天然气水合物钻探与取样难以解决的水合物矿体空间展布等问题,利用白云-荔湾凹陷高密度分析重新处理的三维地震资料,首先基于模糊数学的多属性融合技术对水合物分布进行刻画;再通过高分辨率速度场对浅层开展高分辨率宽频无井反演技术,提高了水合物层分辨率;最后,利用岩石物理方法及多种模型对水合物饱和度进行定量预测,实现了对5～6m厚水合物层的有效辨别,进而形成了一套适合于孔隙充填型的水合物矿藏目标识别评方法。结果表明:应用该技术可有效对荔湾3水合物富集区第四条带水合物空间刻画,揭示出该区水合物饱和度最高可超40%,同时薄层与厚层水合物具有明显互层分布特征,在水合物矿体刻画及饱和度预测基础上,进一步对该区实施了井位优选,该方法预测的水合物层与实际钻探H1和H2站位吻合较好。这些结果说明常规三维油气地震数据在经过宽频处理后可应用于高分辨率水合物勘探,节约经济成本,同时提高了常规地震在水合物勘探中精度与实用性。     

Effects of periodic saturation on stress–strain relationship of a sandstone mixture

While a crushed sandstone particle mixture, usually used as an engineering fill, is filled along bank of or in a large reservoir, it is subjected to periodic saturation induced by filling-drawdown cycles of reservoir water. The periodic saturation may induce post-construction settlement, and reduce stability of the filled body. In order to evaluate the effects of periodic saturation on stress–strain relationship of the mixture, several triaxial tests are carried out. According to experimental data, the periodic saturation may induce an increment of axial strain (Δε; <0.226%), a decrement of crest of deviator stress (Δ(σ₁?σ₃)_f; <0.192?MPa) and a decrement of angle of shearing resistance (Δφ; <3.70°). With increment of the number of periodic saturation cycles, the variations of the three parameters may be fitted by logarithmic curves. And with increase in the stress level for periodic saturation, the variations of the three parameters may be fitted by straight lines. Three fitting equations to predict the three parameters’ values, and an equation to calculate the settlement induced by the periodic saturation of a large-area filled foundation, are suggested.     

胶州湾秋季文石饱和度分布及控制因素分析

基于2017-10-18航次在胶州湾调查获取的水文、碳化学和叶绿素a(Chl a)等数据与资料,分析了秋季该海域文石饱和度(Ω_arag(现场))的分布状况,探讨了影响其空间分布的主要控制因素。结果显示,秋季航次期间胶州湾表层Ω_arag(现场)为1.85～2.57,平均值为(2.20±0.24);其分布具有较大的空间差异,低值位于湾的西部和东北部(<2.05),高值位于湾口(>2.45),总体上呈现出由湾口向湾顶逐步降低的趋势。除了通过分析Ω_arag(现场)与温度、盐度和Chl a的相关性来定性确定Ω_arag(现场)的主控因素外,我们还通过引入总碱度与溶解无机碳的差值作为Ω_arag(现场)的指征参数,定量确定了影响Ω_arag(现场)空间分布的主要过程及其贡献。研究发现,陆源输入是影响胶州湾秋季Ω_arag(现场)空间分布的最重要因素(>50%),而温度和生物过程的影响相对较小。