Abstract: The igneous rocks occur widely in Chagan sag of Y in gen basin. This paper presents the study of the igneous rock lithofacies and seismic recognition marks, the discussion of the relations between igneous rocks and oil-gas reservoirs, pointing out the favorable zones of igneous reservoirs. The igneous lithofacies types include explosive facies, overflow facies, volcanic-neck facies and volcano sedimentary facies, of which overflow facies is the most developed. According to the characteristics of the volcanic types such as high seismic wave velocity, high density, high magnetic susceptibility, high resistivity and high absorbability of seismic wave, the seismic recognition marks of four volcanic lithofacies and four intrusive lithofacies are set up. It is concluded that the deep fault controls both distribution of the igneous rocks and distribution of igneous traps. The favorable zones of igneous reservoir prospecting should be near the faul-developed belts.

Key words: Chagan sag, igneous lithofacies, recognition mark, igneous reservoir