Experimental Study on the Impact of Clay Distribution and Mineralogy on NMR T2 and Internal Gradient: Insights From Well-Controlled Physical Samples

IF 2.1 4区 工程技术 Q3 ENERGY & FUELS
M. Elsayed, A. El-Husseiny, S. R. Hussaini, Hani Al Mukainah, Mohamed Mahmoud
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引用次数: 2

Abstract

Nuclear magnetic resonance (NMR) is a reliable tool for petrophysical evaluation and the characterization of pore structures. Compared to conventional carbonate reservoirs, sandstone reservoirs contain higher amounts of ferromagnetic and paramagnetic ions (such as iron, nickel, or manganese) usually found in microporous clay aggregates. The interpretation of petrophysical data in sandstone formations can be complicated by variations in clay mineralogy and distribution patterns (laminated, structural, and dispersed). Nevertheless, the impact of clay distribution patterns on NMR signals is not well understood. This study aims to investigate the impact of clay mineralogy and distribution patterns on the T2 relaxation times and internal gradient (i.e., inhomogeneity in the magnetic field). Glass beads were mixed with three different clay minerals characterized by no iron content (kaolinite) to higher iron content (illite and nontronite). The bead-clay mixtures were prepared at a fixed clay content but with variable clay distribution patterns to examine the impact of clay distribution alone. NMR T2 measurements at several echo times were performed on the pure glass beads and the mixtures to evaluate how clay mineralogy and distribution patterns affect the T2 and the internal gradient of the host glass beads. At a given clay distribution pattern, a more significant decrease in T2 relaxation times and a larger increase in the internal gradient of glass beads were observed when adding clays with higher iron content. This is explained by the higher surface relaxivity, and magnetic susceptibility caused when introducing clay with higher iron content. Such an impact can complicate the characterization of NMR-derived pore sizes as similar pore size distribution (PSD) can have very different T2 distribution and the logarithmic mean of T2 relaxation time distribution (T2LM) values. Micro-computed tomography (µCT) images were acquired to compute the PSD to compare it with ones obtained from the NMR measurements. The PSD for the three clay minerals showed almost the same distribution using µCT; however, they showed totally different T2 relaxation times distributions. That is due to the significant impact of the internal gradient causing a distortion in the magnetic field. Thus, careful consideration must be taken before converting the NMR data into PSD. The introduction of iron-free kaolinite resulted in a negligible impact on the internal gradient of glass beads regardless of the clay distribution pattern. On the other hand, the addition of dispersed iron-rich clays (illite and nontronite) results in up to two orders of magnitude increase in internal gradients, compared to mixtures with laminated and structural clays (at the same clay mineralogy and content). Moreover, dispersed clay mixtures display larger changes in T2LM and porosity as a function of increasing echo time. The results from this study suggest that changes in T2LM and the logarithmic mean of the effective internal gradient distribution geff,LM, compared to the clean host sand, can provide insight into iron-rich clay distribution. Larger changes in any given clay content and mineralogy would suggest a more dominant dispersed clay distribution while negligible changes would suggest a laminated distribution.
粘土分布和矿物学对核磁共振T2和内部梯度影响的实验研究:来自良好控制的物理样品的见解
核磁共振(NMR)是岩石物性评价和孔隙结构表征的可靠工具。与传统的碳酸盐岩储层相比,砂岩储层含有更多的铁磁性和顺磁性离子(如铁、镍或锰),通常存在于微孔粘土团聚体中。由于粘土矿物学和分布模式(层状、结构和分散)的变化,砂岩地层岩石物理数据的解释可能会变得复杂。然而,粘土分布模式对核磁共振信号的影响还不是很清楚。本研究旨在探讨粘土矿物和分布模式对T2弛豫时间和内部梯度(即磁场中的不均匀性)的影响。将玻璃微珠与三种不同的粘土矿物(高岭石)混合,这些粘土矿物的特征是低铁含量(高岭石)到高铁含量(伊利石和非土)。在粘土含量固定的情况下,采用不同的粘土分布模式制备了颗粒-粘土混合物,以考察单独粘土分布的影响。在几个回波时间对纯玻璃微珠和混合物进行了核磁共振T2测量,以评估粘土矿学和分布模式如何影响T2和主玻璃微珠的内部梯度。在一定的粘土分布模式下,添加铁含量较高的粘土时,玻璃微珠的T2弛豫时间降低更显著,玻璃微珠内部梯度增加更大。这是由于引入含铁量高的粘土会产生较高的表面弛豫率和磁化率。由于相似的孔径分布(PSD)可能具有非常不同的T2分布和T2弛豫时间分布(T2LM)值的对数平均值,因此这种影响会使核磁共振衍生孔径的表征复杂化。获取微计算机断层扫描(µCT)图像来计算PSD,并将其与核磁共振测量结果进行比较。3种粘土矿物的PSD在µCT上的分布基本一致;然而,它们表现出完全不同的T2弛豫时间分布。这是由于内部梯度造成磁场畸变的显著影响。因此,在将NMR数据转换为PSD之前必须仔细考虑。无铁高岭石的引入对玻璃微珠内部梯度的影响可以忽略不计粘土的分布模式。另一方面,与层状粘土和结构粘土混合物(在相同的粘土矿物和含量下)相比,分散的富铁粘土(伊利石和非膨润土)的加入导致内部梯度增加了两个数量级。此外,随着回波时间的增加,分散粘土混合物的T2LM和孔隙度变化更大。本研究结果表明,T2LM的变化和有效内部梯度分布geff的对数平均值,LM与干净的宿主砂相比,可以深入了解富铁粘土的分布。在任何给定的粘土含量和矿物学上较大的变化表明更占优势的分散粘土分布,而微小的变化则表明层状分布。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
CiteScore
5.30
自引率
0.00%
发文量
68
审稿时长
12 months
期刊介绍: Covers the application of a wide range of topics, including reservoir characterization, geology and geophysics, core analysis, well logging, well testing, reservoir management, enhanced oil recovery, fluid mechanics, performance prediction, reservoir simulation, digital energy, uncertainty/risk assessment, information management, resource and reserve evaluation, portfolio/asset management, project valuation, and petroleum economics.
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