Abstract: Natural gas accumulation is a process of dynamic balance between gas accumulation and gas fugitive emission, in which the inflow and preservation of gas are the key factors for gas reservoir.The preservation of gas-bearing basin primarily depends on its cap rock, late tectonic movement, forming time of gas reservoir, gas supply area and intensity. Normally, a largegas field has its hydrocarbon-generating intensity of over 20x10⁸ m³/km². The study shows that from the whole to the local, usingmultiple methods and parameters for systematic analysis is a foundation of proper hold and understanding of petroleum prospectsin an area. This paper stresses the effect of pressure seal on gas accumulation and preservation. The pressure system can be asan important index for discrimination of whether a gas-bearing basin possesses sealing and preservation conditions on the whole ornot.

Key words: gas-bearing basin, natural gas reservoir, gas inflow, preservation, cap rock, breakthrough pressure, pressure system