Abstract: Production capacity evaluation is an important step in the early stage of gas reservoir development. Clarifying the impact of reservoir properties, water saturation, and CO₂ content on gas well productivity is of great significance for accurately evaluating the productivity of low-permeability gas reservoirs.Taking the typical ultra-high temperature, high pressure, and low-permeability gas reservoir in Yinggehai Basin as the research object. Based on the gas-water steady seepage experiments, the influence of water saturation and CO₂ content on the gas seepage capacity of different permeability rock cores was clarified. According to the principle of flow velocity approximation, productivity charts that considers multiple factors was established. The results show that: 1) The increase of water saturation can lead to a decrease in gas permeability. When the water saturation less than the bound water saturation (40%), the average productivity loss rate is about 12% for every 10% increase in water saturation. The movable water lead to gas permeability decrease sharply, and the water saturation increases from 40% to 50%, gas productivity loss of about 70%. 2) In ultra-high temperature and high pressure formations, CO₂ components can significantly reduce the gas permeability. When the CO₂ content is 28%, the production capacity loss rate is around 12%. As the CO₂ content increases, its impact on production capacity gradually increases. When the CO₂ content rises to 70%, the production capacity loss rate is around 60%. Multi-factor production evaluation charts that considering the reservoir permeability, water saturation, CO₂ content, and production pressures has been formed. The results of the study may provide significant theories for the development of similar gas reservoirs.

Key words: ultra-high temperature and high pressure, low permeability gas reservoir, water saturation, CO₂ content, production capacity evaluation