Abstract: The change of oil saturation in the reservoir will affect the interaction between CO₂ and reservoir fluid. In order to study the effect of water saturation on the oil recovery of glutenite tight reservoir by CO₂ huff-n-puff, tests were conducted on the dissolution, expansion and huff-n-puff of CO₂ in oil and water at different water saturation based on the reservoir conditions of Mahu glutenite tight reservoirs, Xinjiang. The results show that as the water saturation was increased, the solubility of CO₂ in oil and water was decreased from 6.08 mol/L to 2.01 mol/L, the expanding volume was decreased from the highest 1.53 times to 1.09 times, the effect of CO₂ interaction with crude oil gradually weakened, and the maximum cumulative recovery percent was 20.21%; the development effect of CO₂ huff-n-puff was better when the water saturation was less than 45.0%; when the water saturation was lower than 50.3%, asphaltene deposition was dominant, with decrease in reservoir permeability; when the water saturation was higher than 50.3%, mineral dissolution was dominant, with increase in reservoir permeability. The study results play a guiding role in the efficient development of tight oil reservoirs.

Key words: glutenite tight reservoir, solubility, expansion, CO₂ huff-n-puff, permeability