Characteristics of Nano-pores of Clay Minerals in Tight Reservoirs and Their Effects on Reservoir Properties: A Case Study of Yanchang-6 Oil Formation in Ordos Basin

WANG He1,2, SHI Yongmin1,2,†, ZHANG Zhiqiang1,2, SUN Tong1,2, SHI Shiyuan1,2, GUAN Ping1,2, XU Dawei3

1. School of Earth and Space Sciences, Peking University, Beijing 100871; 2. Institute of Oil and Gas, Peking University, Beijing 100871; 3. School of Petroleum Engineering, University of Science and Technology of Missouri, Rolla MO 65401; † Corresponding author, E-mail: sym@pku.edu.cn

Abstract In view of the lack of quantitative characterization of intercrystalline pores of clay minerals in tight sandstone reservoirs, the development characteristics of clay minerals and intercrystalline pore in Yanchang-6 oil formation in Ordos Basin were studied based on scanning electron microscope image and energy spectrum analysis. The intercrystalline pore parameters were quantified, and the intercrystalline pores of different types of clay minerals were characterized qualitatively and quantitatively. On this basis, the contribution of different types of clay minerals to reservoir porosity was calculated according to the mineral content, and the mechanism of its influence on the physical properties of tight reservoirs was explored. The results showed that there were significant differences in the development characteristics of different clay minerals and the characteristics of intercrystalline pores. The size trend of pore throat and facial rate of clay minerals was illite/smectite formation > chlorite > illite. Clay mineral development characteristics and pore structure were the main influencing factors of reservoir physical properties and residual oil distribution. Key words tight sandstone reservoir; clay minerals; intercrystalline pore; quantitative characterization; reservoir property; Ordos Basin; Yangchang Formation