The Impact of Different Clay Mineral Types on the Irreducible Water Saturation in Tight Sandstone Reservoirs: A Case Study of the Lower Shihezi Formation in Hangjinqi Area, Ordos Basin

The type and content of clay minerals in tight sandstone reservoirs of the He-1 member in the Jin-30 well area of Hangjinqi in the northern margin of the Ordos Basin have a significant effect on irreducible water saturation. On the basis of core observation, the petrological characteristics, clay mineral types and occurrence forms, pore structure and irreducible water distribution of the target layer by means of X-ray diffraction analysis, high-resolution scanning electron microscopy, casting thin section analysis, one-dimensional nuclear magnetic resonance experiment and high-pressure mercury injection experiment were studied. The results show that: (1) The average content of clay minerals in the reservoir is 18.36%, and the clay minerals mainly include kaolinite, illite, chlorite and illite/smectite mixed layers. (2) There are differences in the types of clay minerals in different lithofacies: the clay minerals in lithic quartz sandstone are mainly feldspar altered kaolinite, and feldspar intragranular dissolution pores, and kaolinite intergranular pores are developed. The lithic sandstone is mainly composed of lithic and matrix altered illite, and the intragranular dissolution pores filled with illite are developed. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202407150157.