Volcanic rock reservoirs mechanism in North Songliao Basin Xujiaweizi Fault Depression

The Xushen gas field locates in Xujiaweizi Fault Depression of North Songliao Basin.It is so far the greatest volcanic rock gas field in China.The Xushen gas field develops typical Yingcheng Formation volcanic rocks. The Yingcheng Formation volcanic rocks have such characteristic as extensive distribution range,great thickness, and complex lithology.By using methods such as core and scanning electron microscope observation,body of casting slice,analysis and assay,we found the lithology of Yingcheng Formation volcanic rocks consist of not only acidic rhyolite,rhyolite-cementing tuff,but also neutral andesite,andesite-agglomerate and basic basalt.We conducted subtly researchs.The purpose is to see into the cause-mechanism of volcanic rocks reservoirs,and then provide reliable evidences in conducting oil-gas exploration,seeking favorable reservoirs and improving the success rate of prospecting well.Researches have made clearly that acidic rhyolite,rhyolite-cementing tuffs develop generally preferable original pore,but volcanic breccias and volcanic agglomerates commonly develop volcanic primary fracture.These establish foundation for forming superior volcanic reservoirs.Deep fluid activities and selectivity dissolution during diagenesis not only magnify volcanic effective reservoir space,but also improve volcanic reservoir space structure.Diaclases formed by tectonic movement provide main gallery for deep fluid activity and oil-gas migration,and that them magnify effectively volcanic reservoir apace.