Abstract: The tight sand reservoirs of the east of Sulige Area in Changqing Oilfield is typical of relatively lower porosity and
much lower permeability in gas reservoirs area. Research of lower limit of reservoir set is the base for distinguishing effective
reservoirs from non-effective ones. We have researched the lower limit of reservoir by several methods. The lower limits of
effective porosity and permeability for reservoirs are determined by productivity simulation technique. On the basis of the
research，the controlling factors of effective reservoirs are discussed. Our research indicates that the low limit of porosity and
permeability is 4.0%5.0% and 0.0750.100 mD，respectively. And the lower limit of gas saturation is 45%. The property of
reservoirs in east Sulige Gas Field is mainly controlled by lithology and sedimentary microfacies. The mechanical compaction is
the key factor which caused the porosity decreasing. Quality of sandstone reservoirs is controlled by the efficiency of corrosion
and alteration. Thickness of sandstone has less influence on the reservoir effectiveness.

Key words: Sulige, multilayer gas reservoirs, productivity simulation technique, lower limit of reservoir physical property, controlling factors of lower limit of reservoir