Investigation of Pore Structure of a Argillaceous Rocks Reservoir in the 5th Member of Xujiahe Formation in Western Sichuan, Using NAM, NMR and AIP-FESEM

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.