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首页> 外文期刊>Energy & fuels >Insights into Pore Types and Wettability of a Shale Gas Reservoir by Nuclear Magnetic Resonance: Longmaxi Formation, Sichuan Basin, China
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Insights into Pore Types and Wettability of a Shale Gas Reservoir by Nuclear Magnetic Resonance: Longmaxi Formation, Sichuan Basin, China

机译:核磁共振对页岩气储层孔隙类型和润湿性的认识:中国四川盆地龙马溪组

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摘要

Reservoir properties, such as pore types and wettability, are essential for shale gas reservoir evaluation. However, advanced nuclear magnetic resonance (NMR), which has been routinely used in petrophysical characterization of reservoirs, is barely used to estimate these properties in shale gas reservoirs. In this study, several sets of specially designed NMR measurements, together with total organic carbon (TOC), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and contact angle tests, are used to study the pore types and wettability of Longmaxi shale gas reservoir. Results show that the NMR transversal relaxation time (T-2) spectrum can be used to characterize pore types and wettability of gas shale. Three identified T-2 spectral peaks (0.01-0.4 ms, 0.4-15 ms, and 15 ms) separately correspond to organic pores, inorganic pores, and microfractures, which is consistent with the results of FE-SEM. The T-2 spectra in as-received and water/ oil-imbibitionstates qualitatively prove that the microwettabilities of organic pores, inorganic pores, and microfractures are oil wet, water-wet, and mixed-wet, respectively. In addition, a novel wettability index is defined to reflect the microwettability of pores quantitatively. The dominant minerals and TOC jointly affect the pore wettability index; they show good correlations with the wettability index of inorganic and organic pores, whereas there is no obvious correlation with the wettability index of microfracture. In contact angle measurements, water and oil droplets show different behaviors on the surface of shale specimens, which qualitatively indicates that the macrowettability of Longmaxi gas shale is mixed-wet (both water-wet and oil-wet) and more prone to be oil-wet. After analysis of the theory of characterizing macrowettability by NMR, a new NMR-based model is proposed to characterize the macrowettability quantitatively. In summary, this study proposes novel methods and models to characterize the pore types and wettability, expanding the use of NMR in shale gas reservoirs.
机译:页岩气储层评价中必不可少的储层性质,例如孔隙类型和润湿性。但是,先进的核磁共振(NMR)已被常规地用于储层的岩石物理表征,而几乎没有用于估算页岩气储层的这些性质。在这项研究中,使用了几组经过特殊设计的NMR测量,以及总有机碳(TOC),X射线衍射(XRD),场发射扫描电子显微镜(FE-SEM)和接触角测试,龙马溪页岩气储层的孔隙类型和润湿性结果表明,NMR横向弛豫时间(T-2)光谱可用于表征气页岩的孔隙类型和润湿性。三个确定的T-2光谱峰(0.01-0.4 ms,0.4-15 ms和> 15 ms)分别对应于有机孔,无机孔和微裂缝,这与FE-SEM的结果一致。在接收状态和水/油吸收状态下的T-2光谱定性地证明了有机孔,无机孔和微裂缝的微湿性分别为油湿,水湿和混合湿。另外,定义了新的润湿性指数以定量反映孔的微润湿性。主要矿物质和TOC共同影响孔隙润湿性指数。它们与无机和有机孔隙的润湿性指数显示出良好的相关性,而与微裂缝的润湿性指数没有明显的相关性。在接触角测量中,水和油滴在页岩样品表面上表现出不同的行为,定性地表明Longmaxi气页岩的宏观润湿性是混合-润湿的(水-润湿和油-润湿),并且更容易被油-湿。在通过NMR表征宏观润湿性的理论进行分析之后,提出了一种基于NMR的新模型来定量表征宏观润湿性。总而言之,这项研究提出了表征孔隙类型和润湿性的新方法和模型,从而扩大了页岩气藏中NMR的应用范围。

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