Abstract：The Carboniferous Huanglong formation in east Sichuan basin, which has general thickness 40～60m and maximum thickness less than 100m，is an important gas reservoir in east Sichuan basin. It was formed in limited bay sedimentary environment which mainly uplifted or subsided before and during Mesozoic era and was mainly folded after Mesozoic era. Drilling, logging and theoretical data show that when 4000～5000m deep Huanglong limestone has hydrocarbon accumulation, its acoustic wave velocity decreases by 400～500m/s. The informations of gas reservoir do exist in seismic section and have corresponding intensity. Because of some unfavourable conditions in the area (i.e.complicated seismic and geologic condition, thin reservoir, big depth and so on), only the clear "bell shape"reflection pattern consisting of the "bright spot"reflection from gas reservoir bottom and the reflection from overlying formation is the important indication of gas reservoir in seismic secrion.
