The 4th Member of Xujiahe Formation（Xu4 Member）in Guang’an area of central Sichuan has favorable conditions for natural gas accumulation and broad prospects for exploration and development. However，the reservoir exhibits poor physical properties，characterized by high water saturation and challenging reserves production. The gas reservoir is currently in the early stags of exploration and development. Clarifying the lower limit of reservoir physical properties is essential to understanding the sweet spot characteristics and its genesis，as well as comprehensively evaluating gas reservoirs. Therefore，this study utilized experimental analysis and production test data from Xu4 Member reservoir in Guang’an area. Three methods were employed：porosity-permeability statistical analysis，minimum flow pore-throat radius method，and seven submethods of empirical statistical method，porosity-permeability intersection method，water film thickness method，mercury injection parameter method，J function method，production test method，and distribution function curve method were used to ascertain the lower limits of porosities and permeability of the reservoir respectively. In order to avoid the large deviation caused by a single method，the arithmetic mean values of the results obtained by each method were used as the final lower limit values of the physical properties of Xu4 Member sandstone reservoir in Guang’an area. The results indicated that Xu4 Member reservoir in Guang’an area primarily consists of medium-fine-grained feldspathic lithic sandstone，exhibiting a moderate to high level of compositional maturity and a high level of structural maturity as a whole. The average porosity of the reservoir is 5.98%，while the average permeability is 0.86×10^-3 μm sup>2.Overall，this reservoir is a tight reservoir with low porosity and permeability. It has high water saturation，averaging 65.17%，and strong heterogeneity. The lower limits of porosity determined by the seven submethods are 3.2%，6.5%，6.1%，6.5%，8.1%，3.2%，and 9.5%，respectively，and those of permeability are 0.193×10^-3，0.189×10^-3，0.055×10^-3，0.163×10^-3，0.089×10^-3，0.123×10^-3，and 0.211×10^-3 μm²，respectively. By calculating the arithmetic mean value，the final lower limits of porosities and permeability of Xu4 member reservoir in Guang’an area are 6.2% and 0.146×10^-3 μm²，respectively.