On natural modes in moonpools with recesses

The theoretical model of Molin [6] is extended to the case of rectangular moonpools with one or two recesses, as can be found in some drillships. Obtained natural frequencies and modal shapes of the piston and first sloshing modes are compared with experimental results available in literature, with good agreement. An approximation easy to implement is proposed for the natural frequency of the piston mode. Further illustrative results are presented when some geometrical parameters of the moonpool are being varied.     

地面核磁共振方法在大坝安全检测中的试验研究

地面核磁共振方法是一种直接探测地下水信息的地球物理勘查方法,本文将该无损探测技术用于土石坝的渗流安全评估试验。由于探测的核磁共振信号源于地下水中的氢质子,则可以确保核磁共振响应仅与地下水信息有关。利用地面核磁共振方法直接找水的技术优势,探测堤坝的浸润面,以判断堤坝的渗流(漏)隐患,为堤坝尤其是小型病险水库堤坝、易发事故的堤防的病险诊断提供一种便捷、高效和可重复利用的方法。通过NUMISPOLY多道核磁共振探测系统在某原体大坝检测中的试验,得到原体大坝的浸润面,进而对土石坝进行渗流(漏)隐患的评估,该方法为堤坝渗流(漏)隐患探测提供了一种有效而可靠的新方法。      

致密砂岩储层流体参数核磁共振实验研究

利用核磁共振技术对致密砂岩储层岩心流体参数进行研究,简述致密砂岩储层流体参数核磁共振测量原理及计算岩心流体参数方法。实验确定了岩心流体动用参数T2截止值方法,进行了可动流体致密砂岩储层分类评价研究。油田矿场核磁共振测量岩心含油饱和度、可动流体饱和度,并对可动流体饱和度、含油饱和度识别油水层方法进行研究。表明:实验测定红河区块岩心T2截止值为4.06ms,利用致密砂岩储层岩心可动流体等级划分标准,对致密砂岩储层岩心单井及不同层位、多井之间进行储层比较分类评价。油田矿场核磁共振技术测量计算的含油饱和度结果与常规方法测量的含油饱和度结果对比,表明油田矿场核磁测量含油饱和度是可行且可靠的。岩心含油饱和度与可动流体饱和度比值大小可识别油水层。      

肝上皮样血管内皮瘤的CT与MRI特征及病理基础

目的:探讨肝上皮样血管内皮瘤(HEHE)的CT与MRI表现特征及病理基础。资料与方法:回顾性分析经手术治疗且病理证实的HEHE 10例患者资料。结果:10例均主要表现为肝内多发包膜下结节。8例出现“包膜皱缩征”;6例出现“晕环征”;2例出现“棒棒糖征”;8例出现“瘤内血管征”。增强扫描8例表现为动脉期轻中度边缘强化;门脉期及延迟期进一步向心性强化;2例表现为动脉期边缘轻度强化,门脉期及延迟期未见明显变化。结论:肝脏多发包膜下结节,“包膜皱缩征”、“晕环征”、“棒棒糖征”、“瘤内血管征”等表现具有一定的特征性,尤其是“棒棒糖征”或“瘤内血管征”具有一定的特异性,有助于HEHE的诊断及鉴别诊断。      

核磁共振T_2谱奇异值反演改进算法

通过分析最佳奇异值保留个数与信噪比的关系,改进了传统的SVc反演算法,提出了一种新的实现非负约束的迭代方案.数值模拟实验和实际应用表明,改进的奇异值分解算法可以适用于低信噪比(5相似文献   

Improvements in Inversion of Magnetic Resonance Exploration-Water Content, Decay Time, and Resistivity

In this review article, we present recent developments and Improvements in magnetic resonance sounding (MRS), a newly established geophysical exploration method that provides unique information about hydrogeophysical properties due to its direct sensitivity to hydrogen protons and proton dynamics. Starting with the most sophisticated and complete MRS formulation, we give a detailed view on how to solve the equation, i.e., inverting exactly for all model parameters: water content, decay time, and resistivity. Giving a short review of general inversion schemes used in geophysics, the special properties of MRS inversion are evaluated and the development of MRS inversion over recent years is shown. We present the extension of MRS to magnetic resonance tomography (MRT), i.e., the extension to two-dimensional investigations and appropriate inversions. Finally, we address restrictions, limitations, and inconsistencies as well as future developments.     

天然电磁辐射测深技术的应用

天然电磁辐射测深技术是一项利用天然电磁场探测地球介质相对电阻率与介质埋深的地球物理探测技术．此项技术主要探测在天然电磁场作用下在近地表形成的综合电场的垂直分量,根据其频谱的局部变化构制岩层相对电阻率与埋藏深度的直方图,进而对地下岩层的性质和分布特征作出合理的分析和判断．本文主要以探测实例说明本项技术的应用效果及其适用的范围．     

冻融作用下砂岩孔隙结构损伤特征研究

为研究冻融作用下砂岩孔隙结构损伤特征,选取5个岩样进行100次冻融循环试验,并采用核磁共振技术对砂岩孔隙结构进行测试,得到了冻融作用下砂岩的核磁共振弛豫时间T2谱分布、孔隙度等细观结构特征。根据孔隙的孔径分布特征,按孔径尺寸划分为小孔隙、中孔隙、大孔隙3类,并采用扩散双电层理论对不同尺寸孔隙水分布规律进行了分析。结果表明:随着冻融循环次数增加,核磁共振T2分布右移,砂岩的孔隙度增大;同时,水-岩作用导致部分矿物质溶解在孔隙水中,使得孔隙水中离子浓度升高,导致岩石内部产生大量的次生孔隙。随着孔径尺寸的增加,孔隙中的束缚水含量逐渐减少,且小孔隙的束缚水含量远远大于大孔隙;在低温冻结时,自由水先于束缚水结冰,小孔隙束缚水离子浓度的增长幅度小于大孔隙,进而产生了离子浓度差,使得小孔隙中的水分子向大孔隙迁移,造成小孔隙的损伤速率远小于大孔隙。因此,小孔隙在水-岩作用与冻胀压力的作用下不断发育,大孔隙则在冻胀压力下快速扩张、发育,直至岩样发生宏观破坏。     

Full-Sized Pore Structure and Fractal Characteristics of Marine-Continental Transitional Shale: A Case Study in Qinshui Basin,North China

Based on 10 shale samples collected from 4 wells in Qinshui Basin,we investigate the full-sized pore structure and fractal characteristics of Marine-Continental transitional shale by performing organic geochemistry,mineralogical composition,Nitrogen gas adsorption(N_2 adsorption)and Nuclear Magnetic Resonance(NMR)measurements and fractal analysis.Results show that the TOC content of the shale samples is relatively high,with an average value of 2.44wt%,and the thermal evolution is during the mature-over mature stage.The NMR T_2 spectrum can be used to characterize the fullsized pore structure characteristics of shale.By combining N_2 adsorption pore structure parameters and NMR T_2 spectrums,the surface relaxivity of samples are calculated to be between 1.7877 um/s and 5.2272 um/s.On this basis,the T_2 spectrums are converted to full-sized pore volume and surface area distribution curves.The statistics show that the pore volume is mainly provided by mesopore,followed by micropore,and the average percentages are 65.04%and 30.83%respectively;the surface area is mainly provided by micropore,followed by mesopore,and the average percentages are 60.8004%and39.137%respectively;macropore contributes little to pore volume and surface area.The pore structure characteristics of shale have no relationship with TOC,but strong relationships with clay minerals content.NMR fractal dimensions D_(micro) and D_(meso) have strong positive relationships with the N_2 adsorption fractal dimensions D_1 and D_2 respectively,indicating that D_(micro) can be used to characterize the fractal characteristics of pore surface,and D_(meso) can be used to characterize the fractal characteristics of pore structure.The shale surface relaxivity is controlled by multiple factors.The increasing of clay mineral content,pore surface area,pore surface fractal dimension and the decreasing of average pore size,will all lead to the decreasing of shale surface relaxivity.