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Comparison between Subaerial and Subaqueous Volcanic Rocks and the Reservoir Significance——Taking Yingcheng Formation in Songliao Basin as Example

ZHANG Yan1,2,SHU Ping2,WANG Pu-jun1,ZHENG Chang-qing1,SHAN Xuan-long11.College of Earth Sciences,Jilin University,Changchun130061,China2.Daqing Exploration & Development Institute,Daqing,Heilongjiang163712,China  
The subaerial and subaqueous volcanic rocks have significant differences in lithology,texture and structure,alteration,occurence,contact with underlying strata,pore and fissure development.Subaerial volcanic rocks mainly comprise lavas,clastic lava,pyroclastic rocks and sedimentary pyroclastic rocks.Subaerial lava has rhyolitic structure.Bedding structure and few reverse hummocky structure formed in pyroclastic rocks.The subaerial volcanic rocks underwent weak alteration and unconformity with underling strata.Ancient weathering crusts and continental plant can be found.Main reservoir spaces in subaerial volcanic rocks are primary pore,condensing shrinkage joint,secondary dissolution pore,cleavage fissure in mineral and structural fracture.Subaqueous volcanic rocks mainly comprise glassy lava,crystal-vitric bedded/sedimentary tuff,bentonite/illite/montmorillonite/zeolite.Subaqueous volcanic rocks have pillow or orbicular structure,horizontal bedding,graded bedding,strong alteration.Subaqueous lava appears domed,lenticular shape,tuff appears stratiform shape,bentonite/illite/montmorillonite/zeolite near crater appears loose conglomeration with volcanic bombs.Contact relation of subaqueous volcanic rocks and underlying strata is conformity,disconformity or erosion.Main reservoir spaces of subaqueous volcanic rocks are primary pore,dissolution holes in amygdaloid body,explosive fracture,intergranular pores,erosion pore and fracture in matrix and phenocrysts and structural fracture.Both subaerial and subaqueous volcanic rocks can be found in Yingcheng Formation of Songliao Basin.Typical characteristics of subaerial volcanic rocks include rhyolitic structure,columnar joint,carbonized wood / silicified wood,angular unconformity contact with underlying strata.Typical features of subaqueous volcanic rocks include perlite with glassy structure and pillow structure,lamellar tuff,bentonite.Most of volcanic reservoirs in Yingcheng Formation of Songliao Basin are subaerial volcanic reservoirs.The inner subfacies of extrusive facies of subaqueous volcanic rocks are good reservoirs.
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