Gas accumulation rules and exploration prospects of volcanic rocks of deep formations in Songliao basin, northeast China

摘要

Deep formations of Songliao basin are defined as between basement and second member of Quantou formation in lower Cretaceous, including later Jurassic Huoshiling formation, early Cretaceous Shahezi formation, Yincheng formation, Denglouku formation and 1-2 members of Quantou formation. Songliao basin was made up of groups separated fault depressions in Shahezi age of early Cretaceous. The volcanic rocks in Yincheng and Huoshiling formations are the major reservoirs for deep gas. By the means of systematically analyzing the form conditions, accumulation patterns and exploration prospects of the deep gas, it is suggested that the deep volcanic gas pools are characterized by the short distant migration for gas, locating around main trough and along the fault. The existence of deep volcanic gas pools are controlled by source rocks. High quality volcanic reservoir takes controls of the extent of the gas pools. The locations and high production of volcanic gas pools are controlled by faults. Generally, the source rocks, reservoirs and faults all make the contribution to the formation of volcanic gas pools. From the point of view of the forming conditions of deep volcanic gas pools, it is suggested that the beneficial tectonic zone with both development of the source rock and the volcanic reservoir are the favorable exploration zone. For exploration prospects, the most practical fault depressions are Xujiaweizi, Changlin and Yingtai, the replacing ones are Gudian, Shuangliao, Wangfu, Shuangcheng and Dehui fault depressions, while the prepared ones are Daan, Renminzhen, Lishu, Yushudong, Yushu, Yingshan, Gulong and Lindian fault depressions and so on. For deep gas exploration, the volcanic rock is the major exploration object, the minor one is the glutenite. The mainly exploration layer system is Yingcheng formation. The replaced layer systems are Huoshiling formation, Shahezi formation and Denglouku formation.