The Constrain Of Abyssal Crustal And Mantle Structure To Abiogenetic Gas In Songliao Basin

The carbon isotope of nature gas in more than 30 wells around Xujia Weizi area, Songliao Basin, had been fined has abiogenetic characteristics, that is 13C1< 13C2< 13C3< 13C4. Based on study and analysis of 15s near vertical deep reflect seismic profiles and regional tectonics, discussed the constrain of deep crustal and mantle structure to abiogenetic gas in Songliao Basin, and find the special crustal and mantle structures has an important significance to the generation, migration and accumulation of abiogenetic gas. It was find that developed Low velocity-High conductivity layers in upper and bottom of middle crustal, and infer it is mantle fluid which close related to abiogenetic gas by analysis the polyspectrum characteristics of deep reflect seismic. Often find diapir structure developed under fault depressions where abiogenetic gas was find in Songliao Basin, same as Low velocity-High conductivity layers. the interface of supracrustal and midcrustal and setup the subdetachment belt, also widely developed Low velocity-High conductivity layer at the bottom of midcrustal directly observed from deep reflect seismic profiles, inferred as partial melt phase change belt at bottom of midcrustal according seismic reflect characteristics and polyspectrum anomaly characteristics, most of crustal and mantle scale faults converged it and constructed detachment surface at bottom of midcrustal, and the isostatic adjustment of lithosphere controlled by these abyssal faults and delamination, that is very important for generation, evolution and development of Songliao Basin, and the complicated conducting system for migration abiogenetic gas set up same time. Upwelling mantle material from the deep faults distributed around in fault depression and formatted reservoir bed together with weathered basement. Abyssal crustal and mantle reacted each other, also closed related each other, caused intricate constrain to abiogenetic gas and in crustal and mantle scale a generation, migration, accumulation delicate match geological space formatted in Xujia Weizi area, Songliao Basin..