Abstract:

Volcanic edifices of the Yingcheng Formation and the Huoshiling Formation in the Songliao basin are classified into 3 types. They are pyroclastic, composite and lava volcanic edifices. According to chemical composition of rocks,each type is subdivided into acid subtype or intermediate-basic subtype. Most of volcanic edifices of the Yingcheng Formation are acid subtype. The percentage of acid lava volcanic edifice is 33% in northern basin and 38% in southern basin. The proportion of intermediate-basic volcanic edifices in northern basin is more than that in southern basin.The volcanic gas pool of Songliao basin isstructural-lithological type. The depth of gas-water interface changes greatly. Internal characteristics of gas pools are controlled by volcanic edifices type.The shape of gas layer within acid pyroclastic volcanic edifice is sill or tabular, and the thickness changes little. The shape of gas layer within acid composite and lava volcanic edifice is mound or sill, and the thickness changes little. The shape of gas layer within intermediate-basic lava volcanic edifice is mound or wedge, and the thickness changes rapidly. The volcanic gas pool forming in Songliao basin is controlled by effective source rocks, faults of communicating source rocks, porosity and permeability. The industrial gas pool of Songliao basin is accumulated in acid lava volcanic edifices, which contributes 50% in northern basin and 38% in southern basin. The efficiency of gas pool formation of intermediatebasic volcanic edifices in northern basin ishigher than that in southern basin. The acid composite edifices have the maximum productivity of single well. The productivity of acid volcanic edifices is higher than intermediate-basic. The volcanic exploration direction should be focused on the targets with effective source rocks and faults of communicating source rocks. Firstly, aim at the acid volcanic edifice. Secondly, find the intermediate-basic volcanic edifice.

Key words: Songliao basin, volcanic edifices types, characteristics of gas pool, exploration direction, volcanic rocks