基于氮气吸附-核磁共振-氩离子抛光场发射扫描电镜研究川西须五段泥质岩储层孔隙结构

摘要

微观孔隙作为泥质岩的有效储集空间,其孔隙结构参数是作为气藏评价及资源量估算的重要依据.本文应用氮气吸附法(NAM)、核磁共振法(NMR)、氩离子抛光及场发射扫描电镜(AIP-FESEM)研究川西须五段泥质岩微观孔隙特征,结果表明:①氩离子抛光及场发射扫描电镜在表征微观孔隙形态与类别时有一定优势,但定量表征孔隙参数时,受图像二值化阈值的影响,表征结果偏差较大,可结合氮气吸附法来定量表征其孔径大小;②核磁共振受岩石骨架影响小,能够更精细反映岩石的物性条件,可定量计算孔隙度与可动流体饱和度,但对样品的孔隙形态反映较差;③综合上述三种方法,在须五段泥质岩中可识别出一定量的纳米级中、大孔,孔径大多介于几十纳米到几百纳米之间,孔隙连通性差,孔隙度主要介于2.3%~7.4%之间,孔隙类型以粒间孔、晶间孔最发育,有机孔隙、微裂缝次之,粒内孔隙最不发育.总体而言,融合了三种技术方法能更精确、更全面地反映泥质岩孔隙结构特征,能得到更完善的储层孔隙结构参数,在定量表征泥质岩孔隙结构中具有广泛的应用前景.%Micropore is the effective reservoir for argillaceous rocks, and its structure parameter is the important parameter for the evaluation of gas reservoir and the estimation of the amount of resources.The Nitrogen Adsorption Method (NAM), Nuclear Magnetic Resonance (NMR), and Argon Ionization-Field Emission Scanning Electron Microscopy (AIP-FESEM) were used to analyze micropore characteristics of argillaceous rocks in the 5th Member of Xujiahe Formation of Western Sichuan.The results show that: (1) AIP-FESEM has unparalleled advantages in characterizing the morphology and classification of microscopic pores.However, when it was used to quantify the pore parameter, the deviation of results is large, due to the threshold of image binarization.Therefore, it should be combined with the nitrogen adsorption method to quantify its pore size (in Fig.4).(2) As NMR is less affected by the rock skeleton, it can reflect physical properties of the rock more finely.However, the pore shape is poorly reflected by this technique (in Fig.3).(3) Based on the three methods, a certain amount of nanometer scale pore can be identified in the 5th Member of Xujiahe Formation.The pores are mostly several tens of nanometers to several hundred nanometers which have poor porosity of 2.3%-7.4% (in Table 1).The intergranular pores and intercrystalline pores of argillaceous rocks are the most developed, organic pores and micro-cracks aresecodary, and the granule pores least developed.In general, the combination of three techniques can reflect the structural characteristics of argillaceous rocks more accurately and comprehensively, and obtain more perfect pore structure parameters, which has wide application prospects in the quantitative characterization of pore structure of argillaceous rocks.