Abstract:

With the tight sandstone gas exploration and development, to study the influencing factors of tight sandstone irreducible water saturationbecomesimportant, as it can effectively guide reservoir description, evaluation, and productivity prediction. As an example of the tight sandstone reservoir in Linxing area in Ordos basin, the influencing factors of irreducible water saturation in tight sandstone were analyzed by casting thin section, X-ray diffraction, nuclear magnetic resonance, high pressure mercury injection, gas-water phase permeability, and scanning electron microscope experiments.The results show that the irreducible water saturation of tight sandstone in the study area is 34.77% - 83.78%, withanaverage of 63.86%, and the T_2cutoff is 3.86 - 65.60 ms withan average of 20.96 ms.The irreducible water saturation of tight sandstone is affected by physical properties, wettability, sensitivity, clay mineral type, mass fraction, and particle size in reservoirs. The smaller the tight sandstone size is, the higher the clay minerals content, and the stronger the rock hydrophilicity; The greaterthe specific surface area and water film thickness of the rock, the higher the capillary and membrane irreducible water. Water sensitivity and salt sensitivity are the main factors causing the damage of permeability. Residual intergranular pores, dissolution intergranular pores, dissolution within grains, intercrystalline pores and micro-fractures are developed in the research area. The types and forms of clay minerals filled in the pores are different, resulting in the complex pore structure of tight sandstone, strong micro-heterogeneity, and largeirregular changes in water saturation.

Key words: Ordosbasin, Linxingarea, lightsandstone, irreduciblewater, wettability, sensitivity