The lower limit of reservoir physical properties for hydrocarbon accumulation determines whether hydrocarbons can charge the reservoir and provides an important basis for the evaluation of reservoir oil-bearing effectiveness in actual production. Data such as drilling, core, mercury injection, inclusion, and oil testing were used to the glutenite reservoir in the first member of the Badaowan Formation (J₁b₁) in the western slope of the Mahu Sag, Junggar Basin. The results show that using the mercury injection parameter method, the porosity lower limit of the current effective reservoir in the first member of the Badaowan Formation in the study area is determined to be 9.6%, and the permeability lower limit is 0.382×10^-3 μm². There are two stages of oil inclusions, and the homogenization temperature distribution of hydrocarbon inclusions shows bimodal two-stage characteristics. The first member of the Badaowan Formation has experienced two stages of hydrocarbon accumulation processes: early charging in the early Yanshan period and late adjustment in the late Himalayan period. The middle diagenesis stage A in the study area is divided into three sub-stages: A₁, A₂, and A₃. It is determined that the influencing factors of reservoir porosity at a certain depth in the three segments of middle diagenesis stage A₁, A₂, and A₃ are sorting coefficient and median grain size. A comprehensive influence factor of porosity F is established by using the PCA algorithm, and a porosity restoration chart is established. It is determined that the porosity lower limit during the hydrocarbon charging period of the Badaowan Formation in the Maxi Slope is 21%, and the porosity lower limit during the reservoir adjustment period is 15.2%. The conclusion holds that the glutenite reservoir in the first member of the Badaowan Formation in the study area mainly entered the middle diagenesis stage A₂ and A₃ during the reservoir accumulation, adjustment, and charging period, with low porosity and densified reservoir. The study area has experienced a “first densification, then accumulation” diagenetic-hydrocarbon accumulation evolution process, thus forming the current low oil saturation reservoir. The research results have important scientific significance for the hydrocarbon accumulation mechanism of low saturation reservoirs, and provide a geological basis for the large-scale exploration and development of low saturation reservoirs in the first member of the Badaowan Formation in the Mahu Sag.