Abstract: Based on reservoir closely related with the different lithology and facies, looking for superior volcanic reservoir focuses on the identification of volcanic rock facies and subfacies. In this paper, on the base of geological data accumulated in the study of volcanic rocks basin, the formation mechanism of pyroclastic lava in Qingshen gasfield of Songliao Basin and its significance for the identification of volcanic rock facies and log facies were discussed. Studies have shown that the pyroclastic lava have generally five genetic types such as the pyroclastic flow, the foam lava flow, the stream broken oneself, the near-surface magma cryptoexplosion, and the remelting type which are unique petrology and log response characteristics. According to the formation mechanism, petrology and FMI characteristics, the above different five genetic types respectively belong to the hot pyroclastic flow subfacies of eruption facies, the erupting-flowing facies between explosive facies and effusive facies, effusive facies, cryptoexplosive breccia subfacies of volcanic vent facies, volcanic neck subfacies of volcanic vent facies or facies around crater. The results of the study contribute to the accurate identification of volcanic rock facies and subfacies, and the effective forecast of the high quality reservoirs.

Key words: Songliao Basin, pyroclastic lava, mechanism, facies, log facies, volcanic reservoir