Relaxation study of cement based grouting material using nuclear magnetic resonance

Aiming at actual condition of poor effect of hole sealing for the reason of poor cement paste fluidity in the process of coal mine gas drainage,by adding a water reducing agent,cement paste for hole sealing was produced.The changes of initial distribution,weighted average values and total relaxation signal intensity of transverse relaxation time(T 2) of water in pure cement paste and water reducing agent added cement paste were studied with low field proton nuclear magnetic resonance(NMR).The results show that there are four peaks in T2 distribution curves of cement paste:the first peak is related to the bound water in flocculation,the second and the third peaks are related to the water in flocculation,water reducing agent makes it extending towards the long relaxation time,increasing its liquidity,and the fourth peak is related to the free water.By using weighted average values of T2 and total relaxation signal intensity,hydration process of cement pastes could be roughly divided into four stages:the initial period,reaction period,accelerated period and steady period.By analyzing the periods,it makes sure that the grouting process should be completed in the reaction period in the site,and the drainage process should be started in the steady period.The results have great guiding significance to the hole sealing and methane drainage.

Three dimensional structure prediction and proton nuclear magnetic resonance analysis of toxic pesticides in human blood plasma

The purpose of this study was to investigate the nuclear magnetic resonance （NMR） assignments of hydrolyzed products extracted from human blood plasma. The correlations between chemical, functional and structural prop- erties of highly toxic pesticides were investigated using the PreADME analysis. We observed that toxic pesticides possessed higher molecular weight and, more hydrogen bond donors and acceptors when compared with less toxic pesticides. The occurrence of functional groups and structural properties was analyzed using ~H-NMR. The ~H- NMR spectra of the phosphomethoxy class of pesticides were characterized by methyl resonances at 3.7-3.9 ppm （8） with the coupling constants of 11-16 Hz （Je-cns）. In phosphoethoxy pesticides, the methyl resonance was about 1.4 ppm （8） with the coupling constant of 10 Hz （Je-cH2） and the methylene resonances was 4.2-4.4 ppm （8） with the coupling constant of 0.8 Hz （Jp-cH3）, respectively. Our study shows that the values of four parameters such as chemical shift, coupling constant, integration and relaxation time correlated with the concentration of toxic pesticides, and can be used to characterise the proton groups in the molecular structures of toxic pesticides.

A review of nuclear magnetic resonance(NMR) technology applied in the characterization of polymer gels for petroleum reservoir conformance control

Polymer gel systems have been widely applied to control excessive water and improve oil recovery(IOR)in petroleum reservoirs.They are usually divided into two main types,in-situ cross-linked polymer gels,and pre-formed polymer gels.In recent years,nuclear magnetic resonance(NMR) technology has been gradually applied to the research of polymer gel systems due to its unique analysis advantages.This paper is intent to review these works systematically.For in-situ cross-linked polymer gel systems,NMR can be used to characterize the chemical structure changes of the polymer,the cross-linker,and the auxiliary agent in the formulation of the polymer gel systems.Moreover,the gelation time and the gel strength of the in-situ cross-linked polymer gel systems can also be measured by NMR.For pre-formed polymer gels,NMR can be employed to detect the chemical structure of the designed products.Last,the NMR method can evaluate the plugging,water control,and oil improvement performance of the polymer gels in porous media without using dopants.This review can help readers build a more systematic understanding of the application of NMR technology in polymer gel systems for IOR and help re searchers to more deeply study the performance of polymer gel systems.

Study of Polymer Flooding in Heterogeneous Porous Media by Using Nuclear Magnetic Resonance

Polymer has been successfully used to enhance crude oil recovery at high water cut stage.However,the application of polymer flooding is limited by the heterogeneity of reservoir.In this work,the role of polymer flooding in heterogeneous reservoir was explored by nuclear magnetic resonance(NMR)spectroscopy.Parallel core displacement experiments were carried out to study polymer flooding in heterogeneous formation.The results showed that the polymer flooding area was related to permeability and pore connectivity.At the end of the water flooding stage,the residual oil was not evenly distributed in porous media.The percent crude oil recovery increased with the increase of pore diameter.Crude oil recovery from cores with larger pores was higher,and water broke through the highly permeable core first.After 0.3 PV polymer injection,the water mobility of the high permeability core decreased.Polymer injection showed a dual effect,an oil displacement effect and a traction effect.The oil displacement effect was responsible for driving out the crude oil in large pores,whereas the traction effect was responsible for driving out residual oil from small pores.After 1 PV polymer injection,the polymer solution channeled through the highly permeable core rapidly.The crude oil in large pores was washed out completely.The NMR water-phase spectrum line of the highly permeable core was much higher than that of the low permeable core.Under different core permeability and porosity,the NMR peak of the crude oil-phase spectrum line indicated that the polymer flooding is mainly effective on pores>40μm.

Mammography combined with breast dynamic contrast-enhanced-magnetic resonance imaging for the diagnosis of early breast cancer

Objective The aim of this study was to investigate the application of mammography combined with breast dynamic contrast-enhanced magnetic resonance imaging(DCE-MRI) for the diagnosis of early breast cancer. Methods Mammography and DCE-MRI were performed for 120 patients with breast cancer(malignant, 102; benign; 18). Results The sensitivity of mammography for early diagnosis of breast cancer was 66.67%, specificity was 77.78%, and accuracy was 68.33%. The sensitivity of MRI for early diagnosis of breast cancer was 94.12%, specificity was 88.89%, and accuracy was 93.33%. However, the sensitivity of mammography combined with DCE-MRI volume imaging with enhanced water signal(VIEWS) scanning for early diagnosis of breast cancer was 97.06%, specificity was 94.44%, and accuracy was 96.67%. Conclusion Mammography combined with DCE-MRI increased the sensitivity, specificity, and accuracy of diagnosing early breast cancer.

Physics and mathematics of magnetic resonance imaging for nanomedicine:An overview

Magnetic resonance imaging(MRI), magnetic resonance angiography(MRA) and magnetic resonance spectroscopy(MRS) are fundamental concepts used in modern medicine to improve health care. These concepts are based on the principle of nuclear magnetic resonance(NMR). Over the years, various laboratories around the world have applied different numerical techniques based on the Bloch NMR equations to solve specific problems in physics, biology, chemistry, engineering and medicine. The ultimate goal of any physician is to obtain maximum physical, biophysical, chemical and biological information on any tissue or cell under examination. This goal can be achieved by solving the Bloch NMR flow equations analytically. In this review, we present the basic principle of NMR/MRI in a way that can be easily understood by any researcher who needs an NMR concept to solve a specific medical problems. After a very brief history of the subject, a second order, non homogeneous, time-dependent differential equation derived from the Bloch NMR equation is presented. This equation has the basic intrinsic properties of MRI, MRA and MRS that can be extracted by means of classical and quantum mechanics for possible application in nanomedicine.

Measuring Transverse Relaxation Time of Xenon Atoms Based on Single Beam of Laser in Nuclear Magnetic Resonance Gyroscope

Nuclear magnetic resonance gyroscope (NMRG) has the characteristics of high precision and miniaturization, and is one of the main applications of quantum technology in the field of navigation. The transverse relaxation time (T_(2)) of the xenon nuclear spin in the atomic cell of the NMRG directly affects the angular random walk of the gyro. Accurate and rapid measurement of T_(2) is conducive to further improvement of gyroscope. At present, for the measurement of T_(2), the schemes of two orthogonal lasers for pumping and detecting are usually used. By applying two fast-switching orthogonal static magnetic fields and a single beam of circularly polarized laser with corresponding wavelength to pump the atomic cell, the xenon nuclear macroscopic magnetic moment Larmor precession is generated. The cesium atoms parametric magnetometer in cell is formed to detect the free induction decay signal generated by nuclear spin precession of xenon atoms. The measurement of T_(2) by a single laser simplifies the measurement equipment compared with traditional method with two lasers. The experimental results show that the T_(2) of xenon atoms is more than 10 s, and the effects of temperature are studied, which lay the foundation for the subsequent improvement of gyro performance.

纳米氧化铝改性地面井固井水泥水化机制研究

随着地面井固井技术发展加快,工程现场对于地面井固井水泥浆的早期流动性及凝结性能有了更高的要求。为了提高固井工程注水泥作业的顶替效率,改善固井工程现场作业应用情况,提出了纳米氧化铝颗粒改性固井水泥的方法,利用核磁共振技术对质量分数为0、0.05%、0.10%、0.15%及0.20%的纳米氧化铝改性水泥浆(水灰比为0.44)在不同水化龄期的水化反应变化特征进行了研究,探究了纳米氧化铝改性水泥的水相分布、物理结合水总信号量变化、峰形指数及迁移速率。结果表明:纳米氧化铝改性水泥浆在水化阶段的T2图谱会出现3个弛豫峰,分别对应絮凝结构填充水(0.1~10 ms)、毛细水(10 ms)、自由水(800~1000 ms);其物理结合水总信号随纳米氧化铝质量分数增加而逐步减少,其中质量分数为0.20%的纳米氧化铝改性水泥浆信号量减少速率最快;峰形指数呈现先上升后下降的趋势,当水化反应进行至600 min时,质量分数为0.20%的改性水泥浆变化速率最快,弛豫峰向短弛豫方向移动速率加快;结合迁移速率将纳米氧化铝改性固井水泥水化反应阶段划分,其水化机制分别作用在4个水化时期:①初始水化期(5~60 min),水化速率未发生明显改变;②加速水化期(60~600 min),纳米氧化铝使水泥浆中物理结合水转化为化学结合水所经历时间变短,水化进程加快,达到促进水泥水化的效果;③稳定水化期(600~1200 min),水泥体系趋于稳定;④延缓水化期(1200~1800 min),物理结合水转化为化学结合水速率变慢,水泥水化进程减慢。研究结论得到,纳米氧化铝改性水泥浆水化时期可以划分为4个阶段,分别起到物理填充、加速、稳定、延缓的作用。在加速期,纳米氧化铝促进水泥的早期流动,有利于水泥浆的泵送及流动,在延缓期,纳米氧化铝延缓水泥的进一步水化进程,利于发展早期强度。其中,质量分数为0.20%的纳米氧化铝改性水泥浆对于水泥水化进程影响最大,促进填充水向结合水的转化,在加速水化期间对于水泥浆水化反应加速程度最大,以此作为依据对现场固井水泥的制备及应用提供指导。

基于NMR的非饱和土相对渗透系数快速预测新方法

非饱和土的渗透系数作为研究非饱和土中水分运移的重要参数,直接测量方法原理简明但试样尺寸较大,耗时较长;土-水特征曲线(SWCC)间接预测方法由于需要获取土-水特征曲线,同样较为耗时,工作量较大。为此,结合核磁共振(NMR)理论与渗流理论提出了不同孔径孔隙通道渗透系数与弛豫时间的关系,通过对不同大小孔隙通道渗透系数进行累加,提出了基于核磁共振的饱和/非饱和土渗透系数预测模型和快速预测方法。为验证模型的合理性,以湖南黏土为研究对象,进行了不同初始孔隙比试样脱湿、吸湿过程以及饱和状态下的95次核磁共振试验,获取相应的NMR曲线,采用瞬时剖面法获取不同初始孔隙比试样非饱和相对渗透系数,并与该模型预测值对比。研究发现:利用脱湿、吸湿过程不同含水率下NMR曲线以及饱和状态的NMR曲线均具有较好的预测效果,但基于饱和状态下试样的NMR曲线预测效果相对最好,测量成本和耗时也最小,因此建议采用饱和状态试样NMR曲线直接预测非饱和相对渗透系数。

高倍数水驱砂岩中原油黏度、岩心润湿性时变规律核磁共振实验

根据模拟原油黏度与横向弛豫时间谱几何平均值的变化关系,建立了模拟原油黏度预测模型,并结合高倍数水驱核磁共振(NMR)实验实现了孔隙介质中模拟原油黏度的时变规律定量表征;基于核磁共振弛豫理论推导出新的NMR润湿性指数计算公式,结合砂岩岩心高倍数水驱实验,定量表征了水驱过程岩石润湿性的时变规律。研究表明:岩心中剩余油黏度与过水倍数正相关,过水倍数较低时剩余油黏度升高速度较快,过水倍数较高时剩余油黏度升高速度趋缓。剩余油黏度的变化与储层非均质性相关,储层均质性越强,剩余油中重质组分含量越高,黏度越高。注水后储层润湿性将发生改变,亲油储层向亲水储层转变,亲水储层则亲水性更强,且改变程度随过水倍数增加而增强。原油黏度的时变性与润湿性的时变性具有很高的关联性,原油的黏度变化不可忽略,考虑模拟原油黏度变化时计算得到NMR润湿性指数与测试Amott(自吸法)润湿性指数更具有一致性,更加符合储层润湿性时变规律。

超临界CO_(2)作用下无烟煤孔隙结构演化时间效应规律

CO_(2)地质封存技术是实现减排和废弃矿井资源再利用的有效技术之一,但煤层孔隙结构在CO_(2)注入后的变化具有时间效应,其演化规律将直接影响CO_(2)地质封存潜力。为了探索作用时间增加后煤层孔隙结构变化的真实情况,提高CO_(2)地质封存量计算精度,通过对重庆市南桐矿区无烟煤进行超临界CO_(2)吸附实验、低温氮气吸附实验、X射线衍射测试、核磁共振测试、扫描电镜测试等实验,研究了不同超临界CO_(2)作用时间对该区域内煤样孔隙结构的演化规律。研究结果表明:①超临界CO_(2)作用后煤样孔隙度的变化主要发生在7 d内,处理7 d后煤样孔隙度增加了3.20%,7~14 d内煤样孔隙度仅增加了0.05%;②随作用时间增加,煤样孔隙的比表面积增加但变化量逐渐减小,7 d内日均增长19.74%~24.50%,7~14 d内日均增长2.37%~4.60%,其变化规律近似呈对数函数关系;③超临界CO_(2)与煤产生的化学反应引起矿物质的溶解,增大了煤体的表面粗糙度,表征煤样粗糙度的分形维数随着作用时间的增加持续增大;④超临界CO_(2)作用后能有效改变煤样的孔隙度及表面形貌,为CO_(2)吸附提供了更多吸附点位,超临界CO_(2)对孔隙结构的改造效果在7 d内比较明显。结论认为,超临界CO_(2)作用下无烟煤孔隙结构的变化随作用时间增加最终会趋于稳定,研究结果可为无烟煤储层CO_(2)地质封存潜力评价提供理论指导。

Detection of rice seed vigor by low-field nuclear magnetic resonance

A new method to predict the seed vigor of rice was developed to control adulteration during the seed trading process and to address the deficiencies of traditional manual detection methods.Low-field nuclear magnetic resonance(LF-NMR)technique was used to detect the vigor of rice seeds.Four varieties(Beijing-1,Qianchonglang-2,Yanfeng-47 and Shennong-265)of rice seeds from the Rice Research Institute of Shenyang Agricultural University were chosen for the experiment.The transverse relaxation time T_(2),T_(21) and T_(22) were observed in the experiment.The peak start time of free water(transverse relaxation time T_(22)),signal amplitude of bound water(transverse relaxation time T_(21)),and moisture content decreased with the decrease in the vigor of the seeds.There were no obvious trends observed for the top of the peak and the end point of the transverse relaxation time T_(22).In addition,the start,top,and end time of the peak(transverse relaxation time T_(21)),and the signal amplitude of bound water showed no consistent changes.The results indicated that LF-NMR could be used as a method to distinguish the vigor of rice seeds rapidly.This study provided theoretical basis and technical support for the rapid detection of rice seed vigor.

连续波核磁共振实验中外扫描测量法的改进

本文对连续波核磁共振实验中外扫描法测横向弛豫时间误差的主要来源进行了分析,对系统误差的大小进行了定量估算.在此基础上,对外扫描法中横向弛豫时间的测量提出了相应的改进措施,通过计算确定了共振信号半高宽测量时共振信号应在的位置.结果表明,外扫描法测量中,通过x方向的相位调节把共振信号移到偏离中心适当距离的位置上来测量其半高宽,可有效降低非线性扫描电压引起的系统误差.此外,通过对误差大小及共振信号测量位置的计算,能加深学生对横向弛豫时间及外扫描测量法原理的理解.

Classification of different walnut varieties using low-field nuclear magnetic resonance technology and cluster analysis

To classify different walnut varieties based on water and oil content of walnut,and determine their storage conditions,the low-field nuclear magnetic resonance(LFNMR)technology was used to obtain the NMR transverse relaxation time(T 2)of the samples based on the physical and chemical indicators of the walnut quality.The relationship between the relaxation time and phase state of the internal material of the sample was investigated,and the characteristic parameters of the NMR spectrum signals were statistically analyzed using cluster analysis to determine the different walnut varieties,and three different components,as well as their contents,were detected by a LFNMR spectrometer:firmly bound water,weakly bound water,and weakly bound oil.Test results indicated that the oil peak was dominant in the overall signal intensity compared to the water peaks,in which the firmly bound water phase contributed more to the overall water signal between the water peaks.Using the analytic hierarchy process of cluster analysis,21 walnut samples were classified into three different classes,based on the characteristic parameters of the water-content and oil-content spectrum signals.The first class contains four walnut varieties characterized by least water and highest oil contents;the third class contains two walnut varieties,with the highest water content and least oil content;whereas,the second class contains 15 walnut varieties,with both water and oil contents at medium levels.The results showed that LFNMR led to a rapid detection of moisture and oil contents in walnuts,while cluster analysis classified different walnuts varieties based on these parameters.This study also provided the basis for optimizing the storage methods and storage conditions of walnuts.

基于核磁共振信号标定法的致密油藏渗吸实验研究

基于一种新的核磁共振信号标定法开展了致密砂岩岩样的油水渗吸实验,该方法可以根据回归模型将核磁信号总量换算为含油体积,相较常规方法计算更方便、更准确。研究发现渗吸过程可划分为过渡渗吸和稳定渗吸2个阶段,低黏度煤油渗吸样品最佳渗吸时间集中在68 h左右,高黏度致密油渗吸样品最佳渗吸时间集中在188 h左右。渗吸时间充足的情况下,煤油和致密油的最终换油率相差不大,但如果渗吸时间较短,则黏度越大换油率越低。同层位、同黏度的样品具有相似的渗吸动态特征;同层位、高黏油的样品达到稳定渗吸阶段无因次渗吸时间相较低黏油更短。以半径0.5µm作为大、小孔隙的分界线,煤油渗吸样品中半径小于0.5µm的孔隙渗吸换油贡献率平均为83.93%,占据主导地位,原油动用率平均为23.54%;半径大于0.5µm的孔隙渗吸换油贡献率平均为16.07%,相对较少,原油的动用率平均为8.50%,普遍较低,容易形成水锁。致密油渗吸样品在所有孔隙中的渗吸换油贡献率则相对均衡,半径小于0.5µm的孔隙原油动用率平均为14.82%,相对较低;而半径大于0.5µm的孔隙原油动用率平均为29.82%,在焖井过程中普遍会得到有效动用。

在线核磁监测法优化裂缝性页岩油藏赋能渗吸吞吐工艺

赋能渗吸采油可以通过补充地层能量、置换等方式提高原油采收率,目前已成为页岩油藏开发的重要技术。设计合理的赋能渗吸工艺参数,可以更高效地开发页岩油藏。通过4轮次赋能渗吸吞吐实验,利用在线核磁技术分析纳米级原油微观运移特征,优化了裂缝性页岩油藏焖井时间、赋能时机、吞吐轮次等赋能渗吸工艺参数。实验结果表明,首次焖井时间控制在12~15 d即可,随着吞吐轮次的增加,焖井时间应相应减少;吞吐3轮次后对采收率的提升作用不明显,具有明显的有效轮次;压力下降至原始地层压力70%后,继续控压生产效果较差,需及时对地层进行补能,以保证页岩油井高效开发;赋能渗吸时不同液体注入量对采出油量有较大影响,注入量偏少,补充能量不充分,采出效果不佳;但由于储层渗透率极低,补充能量作用半径有限,补能流体量不能无限增加,一般达到压裂裂缝控制体积的0.4 PV左右即可。研究结果可为页岩油藏赋能渗吸工艺参数优选提供技术支撑。

六种香精化合物核磁共振法纯度定值

建立了核磁共振氢谱法(1HNMR)测定6种香精化合物(香豆素、香兰素、甲基香兰素、乙基香兰素、麦芽酚、乙基麦芽酚)纯度的定值方法。选择合适的溶剂、内标,通过测定样品的定量信号的纵向弛豫时间(T 1)来计算准确定量所需的理论弛豫时间(D 1),比较样品在不同弛豫时间下测得的实际纯度来对D 1进行优化的数据,实验结果显示两种D 1优化方法结果一致。分析样品中每个合适的定量信号所得到的定值结果并找到定值结果差异的原因。最终6种样品的纯度结果分别为99.79%、99.80%、99.78%、99.82%、99.86%、99.53%,扩展不确定度(k=2)分别为0.16%、0.10%、0.22%、0.18%、0.14%、0.14%。其不仅适用于香豆素等香精化合物的含量测定,在弛豫时间及定量峰的确定方面也适用于其他化合物,以确保更精确的定值。

人造板吸水过程的TD-NMR动态研究

利用时域核磁共振(TD-NMR)技术,为研究人造板和水分的关系提供新方法.该文通过研究胶合板(Plywood)、刨花板(Particle board)、中密度纤维板(Medium Density Fiberboard)3种常用人造板吸水过程中水分的自由感应衰减(FID)信号的变化,得出传统称重法得到的吸水率与吸水过程中测得的FID信号高度线性相关,24 h吸水率由大到小依次为胶合板>刨花板>中密度纤维板.通过3种人造板24 h吸水过程中自旋-自旋弛豫时间(T2)大小及分布的实验数据,分析了吸水过程中人造板中水分的状态.实验结果证实了TD-NMR是研究人造板与水分的关系的一个有效手段.

相邻骨科植入物的磁共振射频致热耦合效应作用机理

该文研究了1.5 T/3.0 T磁共振(magnetic resonance imaging,MRI)环境下2个相邻的骨科植入物的射频场相互耦合对射频致热的作用。当患者佩戴多个相邻的植入物时,这些植入物之间的相互作用可能会增加射频致热。采用骨板和骨钉作为例子,通过基于惠更斯原理的数值模拟计算并提取热点位置的入射和散射电场向量的振幅和方向,以分析其他相邻植入物的影响。结果表明,不仅入射场的存在会导致强耦合效应,强散射场也会起作用,通过惠更斯源可以得到器械之间产生的一阶和二阶散射场,如果在一定区域内,一阶和二阶电场项相互叠加,则双植入物系统的射频致热风险会增加。

高温对不同粒径花岗岩剪切特性影响研究

在干热岩水力压裂过程中,高温会弱化热储岩体裂隙壁面强度从而表现出裂隙错动的行为特征,而这种弱化现象与黏聚力和内摩擦角的热变特性相关,因此,了解花岗岩在高温下的力学特性对于干热岩开发过程中热储岩体的稳定性评价具有重要意义。在不同高温条件下进行了粗、细颗粒花岗岩变角剪切试验(45°、55°、65°),分析了高温对不同粒径花岗岩黏聚力和内摩擦角的影响,结合扫描电镜与低场核磁共振试验,进一步研究了热力耦合作用对花岗岩微裂纹与孔隙结构演化规律的影响。研究结果表明:花岗岩的黏聚力随温度升高呈现先增加后降低的趋势,内摩擦角变化规律受温度影响较小,300℃为花岗岩黏聚力发生转化的阈值温度。在温度阈值前,粗颗粒花岗岩黏聚力增幅约为细颗粒花岗岩的5.73倍,温度强化效应对粗颗粒花岗岩影响更为显著。随着温度的升高,花岗岩微裂纹形式由晶内裂纹向沿晶裂纹发展。核磁共振T2谱曲线存在多个间断性峰值,温度升高使粗颗粒花岗岩大孔隙受到压实作用,导致弛豫效应减弱,而热力耦合作用对细颗粒花岗岩大孔隙发展影响有限。该研究结果有望为干热岩热储岩体稳定性评价提供参考。