Threshold pressure gradient of fluid flow through multi-porous media in low and extra-low permeability reservoirs     

HongEn Dou  ShiYing Ma  CunYou Zou  ShangLin Yao 《中国科学:地球科学(英文版)》2014,57(11):2808-2818

After analyzing many studies of fluid flow theory of multi-porous media in low and extra-low permeability reservoirs and the numerical simulation of non-Darcy flow, we found that a negative flow rate occurs in the existing non-Darcy flow equation, which is unreasonable. We believe that the existing equation can only be considered as a discriminant to judging Darcy flow or non-Darcy flow, and cannot be taken as a fluid flow governing equation of multi-porous media. Our analysis of the experimental results shows that the threshold pressure gradient (TPG) of low and extra-low permeability reservoirs is excessively high, and does not conform to fluid flow through multi-porous media in the actual reservoir situation. Therefore, we present a reasonable TPG ranging from 0.006 to 0.04 MPa/m at the well depth of 1500 m and oil drainage distance of 500 m. The results of our study also indicate that the non-Darcy flow phenomenon will disappear when the TPG reaches a certain value. In addition, the TPG or non-Darcy flow in low and extra-low permeability reservoirs does not need to be considered in the productivity prediction and reservoir numerical simulation. At present, the black oil model or dual-porous media is suitable for simulating low and extra-low permeability reservoirs.  相似文献   

Quick Response to 2‐MIB Episodes Based on Native Population Odor Sensitivity Evaluation          下载免费PDF全文

Jianwei Yu  Wei An  Min Yang  Junnong Gu  Nan Cao  Youjun Chen 《洁净——土壤、空气、水》2014,42(9):1179-1184

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基于阈值分割与边缘检测的对象轮廓提取方法研究     

陈勇滨  王永丽 《成都信息工程学院学报》2010,(6):246-251

为了提高智能视频监控系统中对象检测算法的检测准确性,实现对检测对象轮廓的准确提取,在分析目前常用于获取对象轮廓形态的对象检测方法不足的基础上,提出了基于阈值分割与边缘检测的对象轮廓提取方法。该方法需要阈值而又不依赖于阈值,选取任一阈值对检测对象进行阈值分割,再结合Sobel边缘检测以及经过定制的边界跟踪算法,实现对检测对象轮廓的提取。经实验得出的轮廓检测结果在不同阈值的条件下都呈现出较好的完整性与一致性。因此,方法具有较好的鲁棒性,实现了对检测对象轮廓的完整提取,提高了对象检测算法的检测准确性。  相似文献   

基于地震目录估计完备震级方法的数值实验   总被引：8，自引：2，他引：6       下载免费PDF全文

黄亦磊  周仕勇  庄建仓 《地球物理学报》2016,59(4):1350-1358

本文将5种估计完备震级(magnitude of completeness,简记为Mc)的方法运用在三个不同模型产生的理论地震目录上,进而对比它们的优缺点.我们发现分段斜率中值分析法MBASS(The Median-based analysis of the segment slope)适用于不完备部分台网探测地震能力随震级变化快及监测能力在时间上存在不均匀性(heterogeneity)的目录中,但是要求目录包含大量的地震事件,而b值稳定法MBS(The Mcby b-value stability approach)则适合用于台网探测地震能力随震级减小衰减慢地震目录,但是比较费时.最大曲率法MAXC(The Maximum Curvature technique)和拟合优度测试法GFT(The Goodness-of-Fit Test)在使用时都低估Mc,需要加调整量.完整性震级范围法EMR(Mcfrom Entire Magnitude Range)则一般给出比较稳定、适中的Mc估计值.这种方法适用在地震数目少,且对地震丢失容忍度比较高的情况.在实践中针对不同性质的地震目录,我们希望这项研究能帮助研究者选择最合适估计完备震级Mc的方法,并指出了一些估计完备震级中应当避免的问题.  相似文献   

Effect of reservoir construction on suspended sediment load in a large river system: thresholds and complex response   总被引：2，自引：0，他引：2  

Jiongxin Xu  Yunxia Yan 《地球表面变化过程与地形》2010,35(14):1666-1673

Dam construction greatly alters the channel boundary of rivers, making the dammed river system a human‐controlled system. Based on hydrometric data in the upper Changjiang River basin, the change in behaviour of sediment transport of some dammed rivers was studied. As a result, some phenomena of threshold and complex response were found. When the coefficient (C_r,a) of actual runoff regulation by reservoirs, defined as the ratio of total capacity of reservoirs to annual runoff input, is smaller than 10%, suspended sediment load at Yichang station, the control station of the Changjiang River, shows a mild decreasing trend. When this coefficient becomes larger than 10%, suspended sediment load decreases sharply. The coefficient of 10% can be regarded as a threshold. The C_r,a of 10% is also a threshold, when the variation of suspended sediment concentration (SSC) with C_r,a at Yichang station is considered. The impacts of reservoir construction can be divided into several stages, including road construction, dam building and closure, water storage and sediment trapping. During these stages, some complex response was identified. At the station below the dam, SSC increases and reaches a maximum, and then declines sharply. This phenomenon was found on the main‐stem and several major tributaries of the upper Changjiang River. In the Minjiang River, where a series of dams were built successively, the response of SSC is more complicated. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

河流地貌系统的过程响应模型实验   总被引：6，自引：0，他引：6  

金德生 《地理研究》1990,9(2):20-28

本文讨论了河流地貌系统的过程响应模型的基本原理、设计步骤、模型砂料配制以及实验数据的系统分析,并给出了设计实例和某些分析成果。  相似文献   

用简化脉冲耦合神经网络对图像进行二值分割   总被引：3，自引：0，他引：3  

陈进  龚健雅  刘兴权 《测绘信息与工程》2005,30(1):38-40

结合图像二值分割的特点,对脉冲耦合神经网络算法进行了一定的简化和改进,通过将其应用到航空遥感影像的二值分割中,发现其具有良好的分割效果,特别是在具有强噪声和阴影影响的影像分割中更显示其优于传统的算法。  相似文献   

A study of slope stability prediction using neural networks   总被引：5，自引：0，他引：5  

M. G. Sakellariou  M. D. Ferentinou 《Geotechnical and Geological Engineering》2005,23(4):419-445

The determination of the non-linear behaviour of multivariate dynamic systems often presents a challenging and demanding problem. Slope stability estimation is an engineering problem that involves several parameters. The impact of these parameters on the stability of slopes is investigated through the use of computational tools called neural networks. A number of networks of threshold logic unit were tested, with adjustable weights. The computational method for the training process was a back-propagation learning algorithm. In this paper, the input data for slope stability estimation consist of values of geotechnical and geometrical input parameters. As an output, the network estimates the factor of safety (FS) that can be modelled as a function approximation problem, or the stability status (S) that can be modelled either as a function approximation problem or as a classification model. The performance of the network is measured and the results are compared to those obtained by means of standard analytical methods. Furthermore, the relative importance of the parameters is studied using the method of the partitioning of weights and compared to the results obtained through the use of Index Information Theory.  相似文献   

Sand grain threshold, in relation to bed 'stress history': an experimental study     

D. PAPHITIS  M. B. COLLINS 《Sedimentology》2005,52(4):827-838

Besides particle size, density and shape, the erodibility of a sediment bed depends also upon the exposure to prethreshold velocities in the overlying flow. Such flow effectively rearranges the grains (at and below the bed surface), causing them to become more resistant to subsequent erosion. The effects of the ‘stress history’, leading up to the critical condition for sediment movement, are investigated for unidirectional flows generated in a recirculating laboratory flume. The sediment beds investigated consisted of cohesionless quartz sand grains, with mean grain diameters of 0·194 mm (fine sand), 0·387 mm (medium sand) and 0·774 mm (coarse sand), with narrow particle-size distributions. The critical (threshold) shear velocity (target value) for the three beds was established, within 2·5 min of increasing the flow from zero velocity. The subsequent experiments were performed under prethreshold velocities at 70% (for 5, 10, 20, 40 and 80 min exposure duration), 80% (for 5, 10, 20, 40 and 80 min exposure duration), 90 and 95% (for 5, 10, 20, 40, 80 and 120 min exposure duration) of the target value. Following exposure to these different prethreshold conditions, the flow was increased then to reach actual critical conditions, within a period of 2·5 min. The critical condition for the initiation of sediment movement was established using visual observation (supplemented by video recordings), according to the Yalin criterion. The results show that if the exposure duration to prethreshold velocities remains constant, then the critical shear velocity increases with increasing prethreshold velocity. Likewise, if the prethreshold velocity remains constant, then the critical shear velocity increases with increasing exposure duration. In some circumstances, the critical shear velocity was found to increase by as much as 27%. An empirical formula is proposed to account for the exposure correction to be applied to the critical shear velocities of sand-sized sediment beds; this is prior to their inclusion into bedload transport formulae, for an improved prediction of the magnitude and nature of transport.  相似文献   

极端异常气象资料的综合性质量控制与分析   总被引：24，自引：1，他引：24       下载免费PDF全文

任芝花  刘小宁  杨文霞 《气象学报》2005,63(4):526-533

在传统的气象资料质量控制技术中,通常利用统计方法设置控制界限,对于界限以外的资料作为可疑值被标注或作为错误值而被剔除。文中以中国1971~2000年700多基准基本站中,气温极端事件———青海托托河站1985年10月~1986年3月的极端异常月平均气温为例,介绍了极端异常气象资料的综合性质量控制方法。通过综合性质量控制与分析,即参考Metadata、邻近站检验、不同观测项目间的一致性检查,均证明托托河站1985年10月~1986年3月极端异常月平均气温资料是正确的。从而说明,利用界限控制检查出的所谓错误资料,虽然在统计学意义上很难出现,但是它有可能反映了异常极端的天气气候事件,是正确的。因此,对于极端异常的气象资料,应进一步通过综合性质量控制,分析该资料正确与否,从而保留极端天气气候事件的事实。文中最后介绍了中国1971~2000年700多基准基本站极端异常月平均气温资料的综合性质量检查结果。  相似文献