The formation of tight gas is controlled by the low porosity and permeability of sandstone reservoirs.It has been recognized that the accumulation of pervasive low abundance tight gas is possible only when the porosity and permeability of reservoir is above a certain limit value.However

there are no widely accepted criteria for defining this limit value.Based on collection of the measured reservoir property of both domestic and international typical tight gas sands

we stu-died the statistical distribution patterns of permeability and porosity of tight reservoirs

and analyzed the causes for reservoir tightening and the characteristics of tight gas accumulation.Data show that over 80% routine permeability data points have a permeability less than 0.1×10

-3

μm

2

.The corrected in-situ permeability is about one order of magnitude lower than the routine permeability.Taking the routine permeability value of 0.1×10

-3

μm

2

as the upper limit of tight gas sands is reasonable and practical.Statistics of tight gas sands over the world shows that tight sandstone reservoirs have diversity of sedimentary environments

large depth span

and long time range in geological age.Tectonic activity

sedimentary environment and diagenesis are the main factors for the formation of tight reservoir

but they play a different role in different basins.The distribution of tight gas sands can be delineated by analyzing source rock

tectonic movements and rese-rvoir tightness.