Abstract:  Lithofacies model is an important basis for the study of volcanic oil and gas reservoirs and  has important guiding significance for reservoir prediction and oil and gas reservoir evaluation. A major breakthrough has been made in Mesozoic volcanic rocks in Bohai Sea. With the deepening of exploration work, the inapplicability of volcanic facies models in other regions has become prominent in this area. In order to establish the volcanic facies model of Lower Cretaceous Yixian Formation in Bohai Sea, it provides a basis for the exploration and development of volcanic oil and gas in this area. There are abundant outcrop data in western Liaoning. Based on outcrop geological survey, the lithology, lithofacies and reservoir physical properties are comprehensively studied by means of rock and mineral identification, major and trace element analysis, particle size analysis and surface porosity analysis. The results are as follows, there are two kinds of volcanic emplacement environments in the Yixian Formation of western Liaoning Province: onshore and underwater. According to the classification scheme of five facies 15 subfacies 44 microfacies, three facies five subfacies nine microfacies are identified in this study, which are volcanic pyroclastic flow subfacies crater-near crater microfacies, base surge subfacies crater-near crater microfacies, near source microfacies and far source microfacies；Effusive facies subaerial lava flow subfacies simple lava flow microfaciesand composite lava flow microfacies, effusive facies subaqueous lava flow subfacies composite lava flow microfacies and autochthonous debris accumulation microfacies； Extrusive facies lava dome above water subfacies core microfacies. From high to low, the reservoir surface porosity is explosive facies, effusive facies and extrusive facies. The physical properties of the volcanic crater-near-volcanic microfacies of the pyroclastic flow subfaciesare better than those of the volcanic crater-near-volcanic microfacies of the base surgesubfacies, and the total surface porosity is larger. Effusive facies subaqueous lava flow subfacies autochthonous debris accumulation microfacies in nine identified microfacies have the best reservoir. The subfacies aspect ratio of effusive facies and extrusive facies is better than that of small reservoirs.

Key words: volcanic facies, reservoir, surface porosity, Yixian Formation, Lower Cretaceous, western Liaoning