The Morphological Characteristics of Clay Minerals in Tight Sandstone Reservoir by Atomic Force Microscopy

Tight sandstone gas is an important part of unconventional oil and gas resources, and the study of its reservoir mineralogy has always been a hot spot in the field of unconventional oil and gas research. Clay minerals, as one of the main components of tight sandstone reservoirs, are mainly studied by electron microscopy at present, but due to the influence of their surface charge absorption and the secondary modification of conductive film on the sample surface, it is difficult to accurately characterize their surface topography. However, the pore size of the main body of tight sandstone reservoir is 20-500nm, and clay minerals are one of the main minerals for the development of nano-pores. With the deepening of the research on micro-nano pore system of tight sandstone reservoir, the study on nano-morphology characteristics of clay minerals is becoming more and more important for the evaluation of tight sandstone reservoir. Therefore, it is of great significance to study the nanometer/sub-nanometer morphology of clay minerals for reservoir evaluation. In this paper, atomic force microscopy (AFM) was used to observe that the clay minerals of the mixed layer of Yimon developed parallel step stripes in the late diagenesis stage of the tight sandstone of Xujiahe Formation in Western Sichuan, and a large number of nano-pores were formed in the two sides of the steps, which are the main components of inorganic nano-pores. The chlorite is an ideal crystal growth state with flat surfaces and straight edges. The growth layers are regularly stacked without gaps in the longitudinal direction, and the crystals are in a stable state. The illite developed parallel step stripes or corrugated steps, and the crystal form was irregular and in a metastable state. Secondly, the clay minerals in the late diagenetic stage of the Xujiahe Formation in Western Sichuan have similar structural backgrounds and the same diagenetic evolution sequence. However, AFM has observed that different types of clay minerals in the late diagenetic stage of the Xujiahe Formation in Western Sichuan have different crystal morphology and the degree of ladder development of crystal faces, indicating that there is a spatial coupling relationship between the morphology characteristics of clay minerals and diagenesis. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202404040075.