稠油储层核磁共振孔隙度校正方法

受原油粘度的影响,利用核磁共振（NMR）测井获取的稠油储层的测井NMR孔隙度远低于地层的真实孔隙度,给稠油储层评价和NMR测井技术的应用带来极大挑战.为提高稠油储层孔隙度计算精度,必须对测井NMR孔隙度进行稠油校正.本研究选取我国南海东部盆地某油田韩江组10块代表性岩心样品,分别开展了原始状态、饱含稠油、残余油和饱含水状态的NMR实验.研究了孔隙含油相对体积对岩心NMR孔隙度的影响,并建立了基于地层深测向电阻率分类的岩心NMR孔隙度校正模型.将基于实验结果建立的岩心NMR孔隙度校正模型推广到实际地层,对目标区域A14井稠油储层实测测井NMR孔隙度进行处理的结果表明：本文提出的方法能够有效地校正孔隙含稠油对实测测井NMR孔隙度的影响,得到地层的真实孔隙度;校正前、后的稠油储层测井NMR孔隙度与常规气驱法测量的岩心孔隙度之间的相对误差由11.19%降低到4.84%.     

渤海J油田储层核磁共振测井孔隙度影响因素分析及校正

渤海J油田沙河街组储层核磁共振（NMR）测井孔隙度和岩心NMR孔隙度均低于岩心氦孔隙度，这种现象影响了NMR测井的应用效果．通过开展岩心NMR实验，对该研究区仪器采集参数、井眼环境以及储层流体性质等因素进行分析，发现造成储层NMR测井孔隙度偏低的主要原因是高矿化度泥浆滤液侵入．基于饱和不同矿化度盐水对T₂谱的影响规律，确定了需要对T₂谱进行形态校正的矿化度下限值，并建立了对应不同矿化度的T₂谱形态校正模型及NMR孔隙度校正方法．应用结果表明，校正后的NMR测井孔隙度与岩心氦孔隙度的平均相对误差从13.56%下降至2.81%，有效提高了NMR测井孔隙度的精度．     

岩心核磁共振实验对低孔低渗碳酸盐岩储层的适应性研究

低孔低渗碳酸盐岩储层矿物成分复杂、岩石骨架参数难以确定、储集空间类型多样、孔隙结构及孔渗关系复杂、常规测井曲线响应特征不明显，使其测井评价极其困难．本文利用核磁共振测井定量评价低孔低渗碳酸盐岩储层岩心的孔隙结构、计算储层参数．利用T₂谱分布曲线分析孔隙结构、计算T₂截止值；在此基础上计算岩心总孔隙度、有效孔隙度、束缚水孔隙度、渗透率等储层参数，并与常规岩心实验结果进行对比分析；最后，总结出核磁共振测井在低孔低渗储层中的应用优势与局限，为核磁共振测井评价模型的建立提供基础数据．     

基于二维核磁共振弛豫谱的雷四段孔隙度计算方法

基于常规测井资料的体积模型和一维核磁共振（NMR）测井资料的固定截止值法，可以计算地层孔隙度，但是扩径段孔隙度计算结果偏大.本文通过川西海相雷四段岩心样品NMR实验和实测二维NMR测井资料，开展扩径段的T₂、T₁孔隙度计算方法研究.首先总结不同孔径流体在T₂谱和T₁谱上的响应特征，分析钻井液流体峰截止值的分布范围和影响因素，建立钻井液流体弛豫时间截止值的计算模型；然后根据未扩径段和扩径段的粘土束缚水弛豫时间截止值确定原则，确立变粘土束缚水弛豫时间截止值的有效孔隙度计算方法.多口井的应用效果表明，基于T₁谱的孔隙度计算结果精度更高、定量分析误差小，能有效解决扩径段孔隙度计算结果偏大的问题，满足储层评价的要求.     

核磁共振测井受激回波校正方法研究

核磁共振测井中,受激回波导致CPMG序列中前2个回波与期望值存在较大差异,严重影响仪器信噪比和储层评价效果. 为进一步改善核磁共振测井仪性能,通过探究受激回波产生机理,揭示其对CPMG回波串作用规律,提出了受激回波的校正方法. 同时针对仪器负载不同,相同发射功率产生射频场强度各异的特性,建立受激回波校正系数与射频场强的数学关系,在不同应用环境中实现对CPMG测量结果的校正. 实验表明,在信噪比较低的应用环境中,采用传统的舍去前2个回波的方法误差达24.58%,而该文设计的校正算法误差仅为4.9%.     

基于C#的二维核磁共振测井观测模式设计软件的开发

二维核磁共振测井观测模式是以获取特定地层信息为目标的数据采集方式，它直接决定着核磁共振谱仪对不同类型储层的适应性以及获取原始数据的可信度．本文从观测模式的组成元素以及工作机理出发，采用C#语言开发了一套具有可视化功能的二维核磁共振测井观测模式设计软件．该软件支持二维核磁共振测井以及核磁共振岩心分析仪的观测模式设计，同时提供了三种采集参数编辑方式、观测模式优化机制以及图形化显示等功能，实现了观测模式的灵活调整，解决了当前主流二维核磁共振测井观测模式中存在的采集参数固定、不宜灵活调整从而导致所采集的原始数据信噪比低下、储层中流体弛豫特性加载不完全等问题．此外，软件还提供了观测模式的采集参数信息以及采集时序信息的输出功能等．     

一种基于组分补偿的二维核磁共振测井数据高精度处理方法

二维核磁共振技术能够对储层中各类含氢流体进行无损、快速、定量的测量和表征，但受限于采集方式和参数，核磁共振设备在对页岩油等致密储层中的有机质、沥青等超快弛豫组分进行检测时，经常出现由于信号采集不完整所导致的二维谱中流体组分缺失或不准的问题.本文提出了基于超快弛豫组分补偿技术的T₂-T₁二维谱高精度反演方法，该方法将一维核磁共振前端信号补偿技术进行推广，通过在二维核磁数据反演前对回波数据进行组分补偿，能够有效解决二维核磁共振测井前端信号漏失的问题.实验及测井数据的应用表明，该方法在页岩油等富含快弛豫组分信号的储层中，可以得到更加精准和完整的储层信息.     

三维感应成像测井仪设计与实现*

砂泥岩薄互层电阻率准确测量是提高泥质砂岩储层计算的一项重要工作。为了解决薄互层电阻率准确测量问题,该文提出一种三维感应成像测井仪的设计与实现方法。首先,基于感应电磁测量方法,设计由1个三轴发射器、4个单轴接收阵列和3个三轴的接收阵列组成的三维探测器。在此基础上,通过三维线圈系参数与结构创新设计、多频循环发射、高精度多道同步采集、高性能发射接收一体化集成等技术实现,在每一个深度点可获取78个电导率测量值。最后,利用数据校正与处理技术来消除各种环境影响,经过理论模型和实际资料的处理结果均证实,该仪器处理得到5条不同径向探测深度的水平电阻率与垂向电阻率、地层倾角等曲线,实现了对薄互层电阻率的准确测量。     

Improved Halbach sensor for NMR scanning of drill cores

A lightweight Halbach magnet system for use in nuclear magnetic resonance (NMR) studies on drill cores was designed and built. It features an improved homogeneous magnetic field with a strength of 0.22 T and a maximum accessible sensitive volume. Additionally, it is furnished with a sliding table for automatic scans of cylindrical samples. This device is optimized for nondestructive online measurements of porosity and pore size distributions of water-saturated full cylindrical and split semicylindrical drill cores of different diameters. The porosity of core plugs with diameters from 20 to 80 mm can be measured routinely using exchangeable radiofrequency coils. Advanced NMR techniques that provide 2D T(1)-T(2) correlations with an average measurement time of 30 min and permeability estimates can be performed with a special insert suitable for small core plugs with diameter and length of 20 mm.     

油井样品NMR T2谱的影响因素及T2截止值的确定方法

T₂ 谱是核磁共振（NMR）测、录井技术应用与解释、评价的基础. 岩样T₂ 谱受仪器测量参数、样品性质（岩性、颗粒大小、样品粒度、样品干湿状态、孔隙流体含量及性质、磁化率、润湿性）及地层水矿化度等因素的影响. T₂ 截止值是T₂ 谱中最重要的参数之一,选取的科学性与准确性直接影响到核磁共振测量结果. 通过文献查询,对T2 谱的影响因素及T₂ 截止值的确定方法进行了分析.     

改进的孔隙模型评价流体性质与裂缝孔隙度

随着勘探开发的不断深入,渤海油田面临越来越多的疑难储层,这类储层流体性质识别与裂缝孔隙度评价成为测井评价的难点。本文依据Biot理论,描述了存在裂隙条件下的含裂隙Biot理论,形成改进的孔隙介质模型。根据该模型利用阵列声波测井数据进行反演得到裂缝孔隙度,同时通过流体置换,得到不同流体对应的岩石体积模量,对其进行交会判别流体性质,实现了阵列声波测井裂缝孔隙度定量评价与流体性质识别综合应用。利用该模型对渤海油田十几口井进行计算,结果表明该方法对于常规砂泥岩和复杂岩性储层均能取得较好效果,本文提出的储层流体性质识别与裂缝孔隙度评价方法,有助于扩展阵列声声波测井的应用范围。     

Spatially resolved measurement of rock core porosity

Density weighted, centric scan, Conical SPRITE MRI techniques are applied in the current work for local porosity measurements in fluid saturated porous media. The methodology is tested on a series of sandstone core samples. These samples vary in both porosity and degree of local heterogeneity due to bedding plane structure. The MRI porosity measurement is in good agreement with traditional gravimetric measurements of porosity. Spatially resolved porosity measurements reveal significant porosity variation in some samples. This novel MRI technique should have applications to the characterization of local porosity in a wide variety of porous media.     

随钻中子地层孔隙度测量装置设计

传统碾米机靠操作员视觉感官来判断碾米性能,不能实现碾米机的智能自检,其识别精准度差。针对传统碾米机识别精度和智能化程度低等问题,设计了光电监测碾米机性能的在线监测系统,提出了以一种低廉价格芯片STC89C52为微处理器,以硅光电池作为光电传感器对物料品质进行信号采集。工作过程中能周期性计算碾米机碾米性能,根据其效率为碾米机的转速、碾白间隙、进出口流量等提供调整策略。经试验分析,该系统识别准确率可达99.5%以上,同时也为粮食品质检测的数字化、智能化提供了一种新方法。     

陆相储层岩石核磁共振物理特征的实验研究

以中国大量存在的陆相沉积岩为对象,系统研究了岩石核磁共振特征与岩石物理性质的关系,详细阐述了将核磁共振测量参数正确地转化为石油工业可直接应用的油层物理参数的方法,对比阐明了核磁共振测量结果与常规岩心分析的异同.针对我国陆相沉积岩核磁共振的特有性质,与国外的一些研究结果进行了对比. 本文研究结果对在中国开展核磁共振石油工业应用具有重要意义.     

Influential Factors of Internal Magnetic Field Gradient in Reservoir Rock and Its Effects on NMR Response

Nuclear magnetic resonance (NMR) plays a significant role in porous media analysis and petroleum exploration, but its response is significantly influenced by the internal magnetic field gradient in fluid saturated porous medium, which obviously limits the accuracy of rock core analysis and logging interpretation. The influential factors of the internal magnetic field gradient in formation and its influences on NMR response are studied in this paper, based on NMR mechanism through one- and two-dimensional core NMR experiments. The results indicate that the internal magnetic field gradient is positively correlated with the static magnetic field strength and the magnetic susceptibility difference between pore fluid and solid grains, while it presents negative correlation with pore radius. The internal magnetic field gradient produces an additional diffusion relaxation in hydrogen relaxation system and accelerates the attenuation of magnetization vector. As a result, T₂ spectrum shifts to the left and NMR porosity and diffusion coefficient of the fluid could be inaccurate. This research sets a foundation for the NMR porosity correction and fluid distribution on T₂-G maps based on the internal magnetic field gradient correction.     

Effects and Corrections for Mobile NMR Measurement

Nuclear magnetic resonance (NMR) under motion has drawn significant attention in recent years. Motion of the NMR probe has serious effects on NMR measurement. For example, NMR logging normally runs at downhole condition with tool motion at a speed of 30 ft/min. We propose here methods for motion corrections of NMR data based on the quantitative analysis of motion effects on polarization and echo acquisition. We also produced a multi-functional NMR scanning system to verify the theoretical analysis. Presented experiments demonstrate that the theoretical and experimental results match very well.     

Xenon NMR measurements of permeability and tortuosity in reservoir rocks

In this work we present measurements of permeability, effective porosity and tortuosity on a variety of rock samples using NMR/MRI of thermal and laser-polarized gas. Permeability and effective porosity are measured simultaneously using MRI to monitor the inflow of laser-polarized xenon into the rock core. Tortuosity is determined from measurements of the time-dependent diffusion coefficient using thermal xenon in sealed samples. The initial results from a limited number of rocks indicate inverse correlations between tortuosity and both effective porosity and permeability. Further studies to widen the number of types of rocks studied may eventually aid in explaining the poorly understood connection between permeability and tortuosity of rock cores.     

核磁共振测井TDA识别油气的影响因素

TDA（时域分析）方法是核磁共振测井的主要方法之一,在判断储层流体类型、性质和孔隙度计算方面有很大的优势,但在应用中却存在一定的局限性. 针对TDA方法在流体识别中存在的一些问题,通过数值模拟不同条件的地层对其在油气识别中的影响因素及适用性进行分析. 研究结果表明：TDA主要用来识别轻烃,采用D9TW采集模式采集核磁自旋回波串,TDA能识别的轻质油粘度<9 mPa.s;长极化时间不变,短极化时间T_WS提高到2 s,TDA能识别的轻质油粘度<4 mPa.s. 双T_W回波串的差（差值信号,转换为孔隙度单位称为差分孔隙度）与地层孔隙度、含烃饱和度、含氢指数、极化函数等影响因素正相关. 对于低信噪比的核磁数据,综合各影响因素,发现烃的差分孔隙度要>1.5 p.u.,TDA方法才能有效识别油气和计算孔隙度.     

2D NMR技术在石油测井中的应用

近几年,2D NMR技术得到迅速发展,特别是在核磁共振测井领域. 该文将主要介绍2D NMR技术的脉冲序列、弛豫原理以及2D NMR技术在石油测井中应用. 2D NMR技术是在梯度场的作用下,利用一系列回波时间间隔不同的CPMG脉冲进行测量,利用二维的数学反演得到2D NMR. 2D NMR技术可以直接测量自扩散系数、弛豫时间、原油粘度、含油饱和度、可动水饱和度、孔隙度、渗透率等地层流体性质和岩石物性参数. 从2D NMR谱上,可以直观的区分油、气、水,判断储层润湿性,确定内部磁场梯度等. 2D NMR技术为识别流体类型提供了新方法.     

Estimation of Permeability by Integrating Nuclear Magnetic Resonance (NMR) Logs with Mercury Injection Capillary Pressure (MICP) Data in Tight Gas Sands

It has been a great challenge to determine permeability in tight gas sands due to the generally poor correlation between porosity and permeability. The Schlumberger Doll Research (SDR) and Timur–Coates permeability models, which have been derived for use with nuclear magnetic resonance (NMR) data, also lose their roles. In this study, based on the analysis of the mercury injection experiment data for 20 core plugs, which were drilled from tight gas sands in the Xujiahe Formation of central Sichuan basin, Southwest China, two empirical correlations between the pore structure index ( $ \sqrt {{K \mathord{\left/ {\vphantom {K \varphi }} \right. \kern-0em} \varphi }} $ , defined by the square root of the ratio of rock permeability and porosity) and the R ₃₅ (the pore throat radius corresponding to 35.0 % of mercury injection saturation), the pore structure index and the Swanson parameter have been developed. To consecutively estimate permeability in field applications, based on the study of experimental NMR measurements for 36 core samples, two effective statistical models, which can be used to derive the Swanson parameter and R ₃₅ from the NMR T ₂ logarithmic mean value, have been established. These procedures carried out on the experimental data set can be extended to reservoir conditions to estimate consecutive formation permeability along the intervals with which NMR logs were acquired. The processing results of several field examples using the proposed technique show that the classification scale models are effective only in tight gas reservoirs, whereas the SDR and Timur–Coates models are inapplicable. The R ₃₅-based model is of significance in thin sands with high porosity and high permeability, but the predicted permeability curves in tight gas sands are slightly lower. In tight gas and thin sands, the Swanson parameter model is all credible.