A decomposition method of nuclear magnetic resonance T2 spectrum for identifying fluid properties

Based on analysis of NMR T2 spectral characteristics,a new method for identifying fluid properties by decomposing T2 spectrum through signal analysis has been proposed.Because T2 spectrum satisfies lognormal distribution on transverse relaxation time axis,the T2 spectrum can be decomposed into 2 to 5 independent component spectra by fitting the T2 spectrum with Gauss functions.By analyzing the free relaxation response characteristics of crude oil and formation water,the dynamic response characteristics of the core mutual drive between oil and water,the petrophysical significance of each component spectrum is clarified.T2 spectrum can be decomposed into clay bound water component spectrum,capillary bound fluid component spectrum,micropores fluid component spectrum and macropores fluid component spectrum.According to the nature of crude oil in the target area,the distribution range of T2 component spectral peaks of oil-bearing reservoir is 165-500 ms on T2 time axis.This range can be used to accurately identify fluid properties.This method has high adaptability in identifying complex oil and water layers in low porosity and permeability reservoirs.

Study on algorithms of low SNR inversion of T_2 spectrum in NMR

The method of regularization factor selection determines stability and accuracy of the regularization method. A formula of regularization factor was proposed by analyzing the relationship between the improved SVD and regularization method. The improved SVD algorithm and regularization method could adapt to low SNR. The regularization method is better than the improved SVD in the case that SNR is below 30 and the improved SVD is better than the regularization method when SNR is higher than 30. The regularization method with the regularization factor proposed in this paper can be better applied into low SNR （5〈SNR） NMR logging. The numerical simulations and real NMR data process results indicated that the improved SVD algorithm and regularization method could adapt to the low signal to noise ratio and reduce the amount of computation greatly. These algorithms can be applied in NMR logging.

利用NMR T2谱分布研究储层岩石孔隙分形结构

利用NMR T_2谱分布进行储层岩石分形结构研究,进而分析岩石物性,是一种分析、评价储层孔隙结构与物性的新方法。在前人研究的基础上,首先,对中—高孔渗储层的分形性质作了进一步的分析;其次,着重讨论了在低孔低渗情况下,利用NMR T_2谱分布研究岩石分形结构这一方法的适用性与准确性;最后,对此方法在中—高孔渗储层与低孔低渗储层中的应用进行了对比分析。对中—高孔渗储层与低孔低渗储层研究均表明:利用NMRT2谱法可以较准确地判断岩石孔隙结构的分形性质与进行分形维数计算;同时应用该方法求取的分形维数可以较好地表征岩石物性,从而为储层特征研究、储层分类等提供参考依据。

银杏种子萌发过程低场核磁T2反演谱解译初探

随着科学技术的发展,低场核磁共振(Low Field Nuclear Magnetic Resonance, LF-NMR)横向弛豫时间(Transverse Relaxation Time, T_2)反演谱检测技术越来越多的被应用于农业,但当前对T_2反演谱的解译尚停留在水分相态分布层面。为探索从物质成分角度对种子T_2反演谱进行解译的新方法,该研究以银杏种子为对象,利用低场核磁共振技术检测并对比银杏鲜种、种子粉末及其主要成分试样的T_2反演谱,分析各信号峰的形成机理,并以此为依据对其在种子萌发过程中的变化进行解译。研究结果表明:淀粉与蛋白质混合试样T_2反演谱的峰T_(21)、T_(22)、T_(23)以及淀粉与油脂混合试样的峰T_(24)在峰顶时间上和种子粉末试样相对应信号峰完全一致;在物质成分及配比完全相同的情况下,种子粉末试样T_2反演谱的峰T_(21)~T24的峰顶时间较鲜种分别相差12.98%、32.21%、13.02%、0%,T_(21)、T_(22)峰比例较鲜种分别偏少41.72%、29.33%,T_(23)峰比例偏多92.26%,T_(24)峰比例偏少91.71%,说明种子组织结构会对其内部水分的弛豫时间和相态分布比例造成一定影响。仅从物质成分角度考虑,种子内水分的弛豫时间主要在淀粉、蛋白质的影响下表现为T_(21)、T_(22)、T_(23),在淀粉和油脂的影响下表现为T_(24)。由此认为峰T_(21)、T_(22)主要为吸附在淀粉和蛋白质上相态不同的结合水的信号,峰T_(23)为主要被淀粉和蛋白质束缚后产生的半结合水的信号,峰T_(24)主要为种子中自由水的信号(少量源自油脂)。此外,种子即将裂壳时将形成T_(2a)(峰顶时间在10 ms左右)、T_(2b)(峰顶时间>1 000 ms)2个新信号峰,可作为预示种子萌发状态即将发生重要变化的"预兆峰"。提出的从化学组分及核磁检测原理角度对银杏种子萌发过程T_2反演谱进行解译的新途径,可为基于LF-NMR方法对种子萌发过程中化学组分变化进行活体分析提供参考。

核磁共振T2谱最优化反演方法

基于模型构制思想将核磁共振T2谱反演问题转化为求目标函数极小值的最优化问题,建立新的易于实现T2谱非负性约束的优化反演模型,然后利用共轭梯度FR算法解决上述反演问题。将该方法应用于无噪声理论回波数据反演、信噪比SNR=25的理论回波数据反演以及岩心NMR实验数据反演,并与真实谱及实验室国外软件反演结果对比表明,无噪声理论回波数据反演的T2谱与构造谱几乎完全符合;信噪比SNR=25时反演的T2谱和构造谱符合得很好;岩心反演的T2谱与实验室国外软件反演的T2谱符合得很好,谱线光滑连续。利用反演结果计算的核磁孔隙度与实验室氦孔隙度绝对误差为0.65%。

Nuclear magnetic resonance T_2 spectrum:multifractal characteristics and pore structure evaluation

Pore structure characteristics are important to oil and gas exploration in complex low-permeability reservoirs. Using multifractal theory and nuclear magnetic resonance （NMR）, we studied the pore structure of low-permeability sandstone rocks from the 4th Member （Es4） of the Shahejie Formation in the south slope of the Dongying Sag. We used the existing pore structure data from petrophysics, core slices, and mercury injection tests to classify the pore structure into three categories and five subcategories. Then, the T2 spectra of samples with different pore structures were interpolated, and the one- and three-dimensional fractal dimensions and the multifractal spectrum were obtained. Parameters a （intensity of singularity） andf（a） （density of distribution） were extracted from the multifractal spectra. The differences in the three fractal dimensions suggest that the pore structure types correlate with a andf（a）. The results calculated based on the multifractal spectrum is consistent with that of the core slices and mercury injection. Finally, the proposed method was applied to an actual logging profile to evaluate the pore structure of low-permeability sandstone reservoirs.

核磁共振T2谱反演影响因素研究

核磁共振T2谱反演质量决定着核磁共振资料的应用效果。为了提高T2谱反演质量,需要对反演影响因素进行研究。首先对反演影响因素分类,然后利用正反演数值模拟技术对每种影响因素进行数值实验。结果表明,回波采集参数和质量,如回波个数、回波间隔、信噪比对T2谱反演质量影响较大;T2谱反演设置参数,如布点数、布点范围对反演质量影响较小;T2谱形态对反演质量也有较大影响。因此,为提高核磁共振资料的应用效果,除了提高回波信噪比外,还应优化回波采集参数;至于T2谱反演设置参数可以根据具体问题灵活选取。

二维核磁共振D-T2测量数据处理算法及应用

在复杂油水气共存的储层中,一维核磁共振测井仪器测量的回波信号反演出的T2谱会出现谱峰的重叠,导致油气水识别困难。二维核磁共振测井技术通过扩散系数D和横向弛豫时间T2谱的探测,获得D-T2谱,能够对井下流体类型及含量进行更精确的判别与分析。基于二维核磁D-T2数据处理算法软件的研制,利用截取奇异值矩阵的方案进行数值模拟,通过实验室刻度验证,获得了一套可用于井下仪器的后处理算法软件,在渤海某井进行商业井作业,分析结果与地层特征吻合。

核磁共振T2谱反演质量控制方法

为提高核磁共振在石油勘探开发中的应用效果,需要对T2谱反演质量进行控制。基于M-P广义逆反演理论推导回波数据分辨矩阵、T2谱参数分辨矩阵,给出T2谱反演质量控制指标:分辨矩阵的展伸系数、主对角元素最大值、最小值、平均值、极差。计算不同观测模式的反演质量控制指标,选择分辨矩阵接近单位阵的观测模式进行资料采集可以提高T2谱反演质量,从而对反演质量进行控制。数值实验表明,反演质量与质量控制指标具有很好的一致性。因此,该方法可以指导核磁共振测前设计,进行T2谱反演质量控制,为提高核磁共振资料地质应用效果奠定基础。

An unsupervised clustering method for nuclear magnetic resonance transverse relaxation spectrums based on the Gaussian mixture model and its application

To make the quantitative results of nuclear magnetic resonance(NMR) transverse relaxation(T;) spectrums reflect the type and pore structure of reservoir more directly, an unsupervised clustering method was developed to obtain the quantitative pore structure information from the NMR T;spectrums based on the Gaussian mixture model(GMM). Firstly, We conducted the principal component analysis on T;spectrums in order to reduce the dimension data and the dependence of the original variables. Secondly, the dimension-reduced data was fitted using the GMM probability density function, and the model parameters and optimal clustering numbers were obtained according to the expectation-maximization algorithm and the change of the Akaike information criterion. Finally, the T;spectrum features and pore structure types of different clustering groups were analyzed and compared with T;geometric mean and T;arithmetic mean. The effectiveness of the algorithm has been verified by numerical simulation and field NMR logging data. The research shows that the clustering results based on GMM method have good correlations with the shape and distribution of the T;spectrum, pore structure, and petroleum productivity, providing a new means for quantitative identification of pore structure, reservoir grading, and oil and gas productivity evaluation.

用核磁T2谱数据计算复杂孔隙结构岩石的渗透率

本文提供了一种利用分析核磁T2谱线数据来计算复杂孔隙结构岩石的渗透率的方法。对于多数地层,其渗透率与孔隙结构相关性极好,即孔隙结构对渗透率起主要的作用,本文通过分析核磁共振T2谱线,选取6个特征参数,并用特征参数表征孔隙结构,进一步通过多元线性回归算法,计算出复杂孔隙结构岩石的渗透率。该方法能够较好地计算出复杂孔隙结构岩石的渗透率,并且能够更好地反应孔隙度的变化趋势。相比较于常规岩心分析物性参数多元回归的计算方法来说,本计算方法只需要知道T2谱线的参数值即可进行运算,具备简便性;同时,对于不同地区,在计算时,只需要替换多元线性回归公式中的系数方可运算,通过增加特征参数的选取还可以提高精确度,具备很高的灵活性。对定量计算复杂孔隙结构岩石的渗透率具有重要意义。

基于核磁共振T2图谱测量岩心裂缝孔隙度

核磁共振具有测试时间少,对岩样无损害,无副作用等优点,逐渐在测量储层孔隙结构特征中得到广泛应用。通过核磁共振分析系统AniMR-150,对15个普通岩心以及6个数字岩心进行不同回波间隔的多次测量,可以得到以下结论:普通孔隙型岩心的T_2谱具有一个波峰,分布于T_2截止线的左右,峰值不高,幅度比较小,此波峰代表了岩心的小孔隙特征,说明岩心孔隙度较小,岩心孔隙不发育;具有小孔隙与裂缝的特征的孔缝型岩心T_2谱呈双峰分布,且两峰不连续,右边波峰比前面更大,分布范围较大,左边波峰代表小孔隙,右边代表裂缝。

核磁共振T2谱拐点位置分段的伪毛细管压力曲线计算

为了进一步提高非线性分段幂函数法的计算精度以及将该方法用于单峰T2谱,提出基于核磁共振T2谱拐点位置(非T2谱谷值)分大、中、小孔3段的幂函数法,该方法同时适用于单峰T2谱和双峰T2谱。将计算结果与压汞实验结果对比,新方法拓展了幂函数法的应用范围,提高了计算精度,使得无论是单峰T2谱还是双峰T2谱转换后的伪毛细管压力曲线与实测毛细管压力曲线都能吻合得非常好,为利用核磁共振测井T2谱进行精确的岩石孔隙结构评价奠定了基础。

油包水型原油乳状液核磁共振T2谱特征与形成机理分析

为认识油包水型原油乳状液核磁共振T2谱中各峰的形成机理,采用低场核磁共振CPMG自旋回波法测量了不同含水率的油包水型原油乳状液,分析了油包水型原油乳状液的T2谱特征,探讨了T2谱中各个峰的形成机理,并通过含Mn Cl2·4H2O油包水型原油乳状液的核磁共振实验进行了验证。结果表明:油包水型原油乳状液T2谱中存在三个峰,连续相中的原油发生自由流体弛豫形成T2A峰,被油束缚在分散相水滴表面的水发生表面流体弛豫形成T2B峰,远离液滴表面液滴内部的水发生自由流体弛豫形成T2C峰;含Mn Cl2·4H2O油包水型原油乳状液的T2谱中含有两个峰,未受Mn Cl2·4H2O影响的原油自由弛豫形成T2N峰;Mn Cl2·4H2O使水的自由弛豫和表面弛豫时间缩短,共同形成T2M峰,验证了原油乳状液T2谱中各个峰的弛豫机理分析。这些结果为利用低场核磁共振T2谱深入研究原油乳状液的性质奠定了基础。

An algorithm for multi-exponential inversion of T_2 spectrum in nuclear magnetic resonance

NMR logging can provide the permeability parameter and abundant stratigraphical information such as total porosity,oil,gas and water saturation,oil viscosity,etc. And these physical parameters can be obtained by T2 spectrum inversion. NMR inversion is an important part in logging interpretation. The authors describe a multi-exponential inversion algorithm,solid iteration redress technique( SIRT),and apply the algorithm in real data and compare the results with those based on singular value decomposition( SVD). It shows that SIRT algorithm is easier to be understood and implemented,and the time spent in SIRT is much shorter than that of SVD algorithm. And the non-negative property of T2 spectrum is much easier to be implemented. It can match the results based on SVD very well. SIRT algorithm can be used in T2 spectrum inversion for NMR analysis.

MRIL_Prime核磁共振测井T2谱反演算法改进及其软件实现

本文提出了基于奇异值分解算法的改进方法,着重对增强解谱稳定性和非负约束条件处理两个方面对算法进行了改进。基于MATLAB平台开发了一套核磁共振测井数据解谱软件,通过多口井的实际应用表明,该软件的解谱结果与DPP软件结果基本一致,证实了其解谱方法的可靠性和稳定性,取得了较好的实际应用效果。

An Experimental Study on the Effect of a Nanofluid on Oil-Water Relative Permeability

The low porosity and low permeability of tight oil reservoirs call for improvements in the current technologies for oil recovery.Traditional chemical solutions with large molecular size cannot effectively flow through the nanopores of the reservoir.In this study,the feasibility of Nanofluids has been investigated using a high pressure high temperature core-holder and nuclear magnetic resonance(NMR).The results of the experiments indicate that the specified Nanofluids can enhance the tight oil recovery significantly.The water and oil relative permeability curve shifts to the high water saturation side after Nanofluid flooding,thereby demonstrating an increase in the water wettability of the core.In the Nanofluid flooding process the oil recovery was enhanced by 15.1%,compared to waterflooding stage.The T2 spectra using the NMR show that after Nanofluid flooding,a 7.18%increment in oil recovery factor was gained in the small pores,a 4.9%increase in the middle pores,and a 0.29%increase in the large pores.These results confirm that the Nanofluids can improve the flow state in micro-sized pores inside the core and increase the ultimate oil recovery factor.

核磁共振技术在致密岩心孔隙量化表征中的应用

为了实现致密岩心的孔隙量化表征,采用核磁共振(nuclear magnetic resonance,NMR)技术,利用T2弛豫时间和孔隙半径(r)的正比关系可测致密岩心的孔隙度、渗透率和孔径分布,利用核磁共振T2截止值可区分孔隙中的自由流体和束缚流体。从核磁共振表征岩心孔隙的原理出发,分析了核磁共振T2谱与岩心孔隙度、渗透率、孔径分布、孔隙内可动流体的关系。根据上述原理,通过实例验证了核磁共振技术在致密岩心孔隙度和渗透率量化表征中的准确性和适用性。实验岩心的T2截止值和孔径分布测试表明:1号岩心T2截止值为21.85 ms,2号岩心的T2截止值为40.11 ms;1号岩心小孔隙分量大,2号岩心孔隙分布较均匀。截止值的计算结果表明地区经验法得出的T2截止值不完全适用于该区域的致密岩心,有必要建立区域性的截止值变化范围图版。

复杂砾岩油水核磁弛豫特性的实验分析

玛湖凹陷砾岩储层岩性、孔隙结构复杂,造成储层流体识别困难.通过区块原油样品获取原油不同温度下的体弛豫特征,并利用两种不同体弛豫特征的模拟油样开展实验;在此基础上,选取了部分砾岩样品通过真空加压饱和水、高速离心和真空饱和模拟油的方法快速建立了饱和水、束缚水和饱和油状态,进行流体及模拟不同油水饱和状态的核磁实验分析.实验结果表明:岩心饱和水核磁T_(2)谱的分布范围主要受表面弛豫影响,受油相体弛豫性质的影响,不同黏度油样饱和水状态的核磁谱均与饱和水核磁谱存在差异,就本次实验的岩心样品,油样越稀,差异越明显;含油核磁谱分布形态受油相体弛豫、表面弛豫、孔隙结构和润湿性的综合影响.结合油样的体弛豫特性,利用多组分高斯拟合对两种油样饱和的砾岩核磁T_(2)谱进行了分析,尝试对油相体弛豫信号进行了定量评价.

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。