Factors And Patterns Of Gas Accumulation In Volcanic Rocks Of Yingcheng Formation In The East Of Changling Fault Depression,Songliao Basin

The study area is in the east of Changling Depression in the Songliao basin,and volcanic gas reservoir is the important gas reservoir type in this area,through the research of factors and rule of volcanic gas reservoir's forming,it is important to the favorable area optimization.Based on the drilling core,SEM,porosity-permeability test and the analysis of plane porosity of 21 well drillings,this paper studies the types and characteristics volcanic reservoir carefully,it also forecasts the spatial distribution characteristics of favorable reservoir;by the statistics of mudstone thickness in Denglouku Formation of single well and forming a plan of the statistics,this paper analyses the plane distributive characteristics of cap rock;through the analysis of the relationship between source rock's thickness,distribution and the production rate,this paper also studies the relationship between source rock,migration and production rate.Based on the study above,this paper dissect the typical gas reservoirs,explores the main controlling factor of gas reservoir,and prefers favorable targets initially.The results show that the study area mainly developed four types of volcanic rock reservoirs: porous rhyolite,rhyolitic tuff lava,blocky rhyolite reservoirs and basalt reservoirs.The porous rhyolite reservoir is mainly with primary porosity and micro fractures,belonging to higher-highest porosity and low-higher permeability reservoir.The rhyolite tuff lava reservoir mainly developed devitrified pore and structural fractures,belonging to medium porosity and very low permeability reservoir.The blocky rhyolite reservoir mainly developed fractures,belonging to very low porosity and very low permeability reservoir.Because the degree of crystallization of basalt is better than rhyolitic volcanic rock,the devitrified pore in the matrix is poor developed.But the majority of primary porosity and micro fractures in the basalt of the study area are packed,so Reservoir development is the worst.Building on the good understanding of reservoir's development mechanism,and according to the controlling factors above,this paper makes the classification and evaluation of volcanic reservoirs.By the relationship between source rocks,gas reservoirs,cap rocks,migration conditions,traps and production rate of gas wells,this paper considers that volcanic rock reservoirs of I-II types and structural trap are the two key factors of the volcanic gas reservoirs in the study area.the study area develops three types of gas reservoirs: porous rhyolite reservoir,rhyolite tuff lava reservoir and rhyolite reservoir.The porous rhyolite reservoir is characterized by superposition of commercial gas reservoirs vertically and horizontally,forming large reservoir with high production rate.The rhyolite tuff lava reservoir is blocky gas reservoir with moderate gas production and small area of gas reservoir.The rhyolite reservoir is also blocky gas reservoir and has poor reservoir quality,and rhyolite reservoir is conditioned by the less even distribution of reservoir condition and the limitation of cap rock's scale,so it restricts the forming of gas reservoir on a large scale,and can only reach commercial production after fracturing.