VOLCANIC FACIES OF THE SONGLIAO BASIN: CLASSIFICATION, CHARACTERISTICS AND RESERVOIR SIGNIFICANCE

The reservoir volcanic rocks of the Songliao Basin include upper Jurassic Huoshiling Formation, lower Cretaceous Yingcheng Formation. Based on the cuttings/core sections and outcrop descriptions as well as 2 4 seismic interpretation of the volcanic rocks around and within the Songliao Basin. The authors of the paper classify the reservoir volcanics into five facies and fifteen sub-facies which are described as to their identifying signatures of lithology, texture, structure and relationship between sub-facies and reservoir features. Sub-facies type is a important controlling factor on the porosity and permeability of the reservoir volcanic rocks. The upper effusive facies sub-facies(Ⅲ3)are rich in both primary vesicles and fault cracks being good reservoir rocks. Circular primary cracks are generally well developed in the extrusive pillow lavas resulted from large-scale unconsolidated body within volcanic dome that is one of the best reservoirs. Loose units, covered by hard volcanic layer and preserved owing to rapid cooling of lava, are common in between the effusive facies. They are good reservoirs, too. Porosity and permeability of volcanic rocks can decrease with buried depth if their diagenesis is compaction dominant. Those are the cases of volcanogenitic sedimentary facies and subfacies of base surge deposits. For the rest facies of the volcanic rocks, reservoir features are not influenced by buried depth.