Formation and distribution of volcanic CO2 gas pools in Songliao basin

The unique tectonic setting and rift evolution of Songliao basin resulted in the formation and enrichment of volcanic CO2 gas pools. Mesozoic-Cenozoic volcano-magmatic activities developed in Songliao rift basin, with characteristics of multi-phase eruption, wide distribution and good reservoir condition. Volcanic activities were generally central vent eruption, mainly developing medium-basic and acidic volcanic assemblages, rhyolite, tuff and other rock types, two types of explosive facie and effusive facie. Mesozoic volcanic rocks are widely distributed in the basin, including Upper Jurassic Huoshiling Formation, Lower Cretaceous Yingcheng Formation constituting favorable reservoir of deep level of the basin, while Cenozoic volcanic rocks more exposed outside the basin and less drilled in the basin. Highly-enriched CO2 in the basin is of mantle-derived inorganic origin caused by mantle-derived magma degassing during Qingshankou and Cenozoic volcanic activity period. The formation of volcanic CO2gas pools are mainly controlled by the background of deep structure, deep-large faults and Mesozoic-Cenozoic volcanic rocks. Discovered volcanic CO2 gas pools are mostly distributed in volcanic rocks of Yingcheng Formation in ancient central uplift and its adjacent faulted depression, characterized with point-belt distribution and local enrichment. Based on the controlling factor analysis, five CO 2 accumulation plays were predicted. Key words Volcanic rock reservoir; CO2gas pool; Origin; Distribution; Songliao basin.