基于核磁共振实验对页岩孔隙结构及分形特征研究——以荆门地区YT2井五峰组—龙马溪组为例

Research on Pore Structure and Fractal Characteristics of Shale Based on Nuclear Magnetic Resonance Experiments——Taking the Wufeng Formation-Longmaxi Formation of Well YT2 in Jingmen Area as an Example

页岩气是化石能源低碳化革命的重要能源补充。孔隙结构特征是衡量和评价页岩储层的重要指标。以荆门地区五峰组—龙马溪组页岩为例,通过选取荆门地区页岩样品进行有机地球化学、矿物组成等分析的基础上,基于核磁共振(NMR)测试和分形分析,对比了核磁孔隙度与常规水测孔隙度的相关性,研究了页岩全尺寸孔隙结构和分形特征。结果表明:荆门地区研究层位核磁共振孔隙度与常规孔隙度具有较好的相关性。荆门地区YT2井核磁共振孔径主要为2~100nm,孔隙体积主要由中小孔提供。孔径为2~100nm范围内提供的孔隙度从样品YT2-4、YT2-18、YT2-2、YT2-11、YT2-12依次减小。NMR模型分形曲线并非直线,具有明显的转折点,页岩中小孔和大孔微观孔隙结构特征呈现出明显的各向异性分形特征。有机质含量与矿物组成对分形维数有明显的控制作用。应用核磁共振技术可以有效对页岩微观孔隙结构与形态特征进行分析,为页岩储层评价和页岩孔隙非均质性研究表明了新的思路。

Shale gas is an important energy supplement for the low-carbon revolution of fossil energy.Pore structure characteristics are important indicators to measure and evaluate shale reservoirs.In this paper,taking the Wufeng Formation-Longmaxi Formation shale in the Jingmen area as an example,based on the analysis of organic geochemistry and mineral composition of shale samples in the Jingmen area,based on nuclear magnetic resonance(NMR)test and fractal analysis,the nuclear magnetic pores were compared.The correlation between porosity and conventional water-measured porosity was studied,and the full-scale pore structure and fractal characteristics of shale were studied.The results show that the NMR porosity of the research horizon in the Jingmen area has a good correlation with the conventional porosity.The NMR pore size of Well YT2 in the Jingmen area is mainly between 2 and 100 nm,and the pore volume is mainly provided by small and medium pores.The porosity provided by the pore size in the range of 2~100 nm decreases sequentially from samples YT2-4,YT2-18,YT2-2,YT2-11,and YT2-12.The fractal curve of the NMR model is not a straight line but has obvious turning points.The microscopic pore structure characteristics of small pores and macropores in shale show obvious anisotropic fractal characteristics.The organic matter content and mineral composition have obvious control effects on the fractal dimension.The application of nuclear magnetic resonance technology can effectively analyze the microscopic pore structure and morphological characteristics of shale,which provides a new idea for shale reservoir evaluation and shale pore heterogeneity research.