低场核磁共振技术在煤炭岩相孔隙结构中的应用

摘要

用自旋-自旋弛豫(T2)反演谱研究了哈萨克斯坦(Kazakhstan,KZ)、新疆伊吾县(Yiwu county,YW)、新疆白石湖(Baishi lake,BS)及新疆东坝区(Dongba district,DB)烟煤在饱水前后与饱锰后的岩相结构差异以及孔隙中流体的分布状况.结果表明,各煤样在饱水前,其质子弛豫信号均以束缚水为主,而饱水后,均出现自由水弛豫信号,且后三个煤样的束缚水信号强度明显增强;哈国煤样的自由流体饱和度最大,束缚流体饱和度最小,意味着其含油饱和度最大,是后三个煤样的4?6倍;哈国煤样的孔隙度相对最大,而伊吾县煤样相对最小;经过饱水处理,四个煤样的微孔数量均有所减少,而后三个煤样的小孔数量显著增加;哈国煤样的渗透率高达22.87%,为后三个煤样的3?20倍.这显然与其孔隙度和孔径差异相关,也是不同地域成煤地质环境差异和发育程度不同的反映.%Background: Low-field nuclear magnetic resonance technology, with the advantages of a rapid detection process and no damage to sample, has been widely used in the field of oil exploration, food preservation, building materials. Purpose: The aim of this work is to study the pore structure of the coal samples in different areas and the saturation of the fluid in the pores, which reflects the difference in the lithofacies structure and the distribution of the fluid in the pores. Methods: The porosity, permeability, and fluid saturation of the coal samples before and after saturation of water and manganese were measured by low-field nuclear magnetic resonance. Results and Conclusion:Results show that before saturation the proton relaxation signal of coal samples is dominated by irreducible water, and after saturation the signal of free water in all coal samples appear, and the signal of irreducible water of the coal samples in Yiwu county, Baishi lake and Dongha district are stronger than that before saturation. The saturation of free fluid of samples in Kazakhstan is the highest and that of irreducible water is the lowest. The oil saturation of samples in Kazakhstan is the highest, which is 4?6 times of that in Yiwu county, Baishi lake and Dongba district; the porosity of Kazakhstan coal sample is relatively large and the porosity of Yiwu county is relatively small; after saturation the number of micropores in coal samples of Kazakhstan, Yiwu county, Dongba district and Baishi lake are reduced, and the number of small holes in Yiwu county, Dongba district and Baishi lake coal samples is much higher than that before saturation; the penetration rate of Kazakhstan coal samples is 3?20 times of that of domestic coal samples, which is related to the difference in porosity and pore size of each sample, and is also a reflection of the geological environment and the degree of development.