The Coupling Mechanism Of Inorganic CO₂ And Petroleum In Southern Songliao Basin

Along with the progress of natural gas exploration,large scale of inorganic carbon dioxide has been found in Changling area.In fact some inorganic gas was captured in several areas such as Wanjinta,Gudian ,Qian an,Honggang and Changde in Songliao Basin.Such facts indicate that mantle-resource gas exists commonly in the basin,Constituent and isotope of natural gas are the important parameters that can be used to distinguish the type of gas origination.According to the analysis of isotope of natural gas in Southern Songliao Basin,we can conclude that most of the inorganic carbon dioxide is inoganic.The distribution of inorganic natural gas has been studied by several scholars at home and abroad.Generally they often pay attention to the machanism and accumulation of natural gas. After integrating the achievement of ancestors ,such as studying on the tectonic characters of deep layer and high abnormal thermal-flow of Songliao Basin,crust-mantle structure in the deep strata and the leading passages of mantle-genetic carbon dioxide reservoir,we mainly studied the coupling mechanism of inorganic carbon dioxide and petroleum in different depth of the layer.Some important conclusions are acquired:1.The crust low-velocity and high-conduction zone in the deep layer of Songliao Basin may be the magma chamber accummulated in the mid or lower crust and produced from the partly melting inside mantle under the interaction of crust and mantle. The low-velocity and high-conductivity zone may also be the melted lava inside crust under the condition of high thermal flow and shortage of water.2.Different kinds of fault controlled the distribution of inorganic carbon dioxide The generation,migration and accumulation of inorganic carbon dioxide are controlled by different kinds of faults in the basin.Ingeneral,large scale fault such as shell fault controlled the supply of gas,and the basic fault in basin controlled the distribution in different layer of inorganic carbon dioxide,and the fault of late periods mantained the redistribution of inorganic carbon dioxide.The activity of fault in Songliao Basin can be classified into 7 periods.and the intense exercise are mainly 3 times,that is earlly Cretaceous,the times of Qingshankou,and the end of Mingshui formation.Fault in earlly cretaceous contronlled the volcanic eruption and to take shape the advantaged reservior,they also controlled the distribution of crater.Multi-activity faults creat lots of crack in the reservior nearby crater.this is very useful to impprove the penetrability of volcanic reservoir.Fault activity at the end of Mingshui formation caused transportation and accumulation of huge inorganic carbon dioxide.the extent of fault controlled the position of inorganic carbon dioxide reservior.3. Controlling machanism of magamtism and volcatismLava in Yingcheng formation have the characteristics of huge thickness,wide range distribution,are the excellent quality reservoir in the basin.Magamtism and volcatism of Mesozoic in the basin are distributed in four formation.that is Huoshiling formation,Shahezi formation,Yingchengzi formation and Qingshankou formation. magamtism and volcatism of Cenozoic which are seldem found,we can found that at the marginal of basin, volcatism such as Wudalianchi and Datun volcanic.During the formation of Yingcheng, magamtism activity are very popular,heat flow piercement overflow along the fault system,and great scale of volcano-magma were formed.and at the same time,huge amount of carbon dioxide were disipated because of no seal formation . During the time of Qingshankou-Cenozoic, magamtism activity were once more developed,most of the heatflow piercement did not pass through the Huoshiling formation and above formation.Out gas migreted along fault and accumulated in the fracture of lava.At that time,overlap such as Denglouku formation were formed,kept the carbon dioxide reservoiring.4.Hydrocarbon in deep layer has the different origination from iorganic carbon dioxide,the two sides have great distinction on accumulation. In the area with good source rocks,lava will be put into hydrocarbon under the communication by faults.Once the trap meet the accumulation conditions of both hydrocarbon and iorganic carbon dioxide,there will form mix reservoir which contain hydrocarbon and inorganic carbon dioxide.in the area with poor source rocks,under the communication of huge fault, iorganic carbondioxide will be acuumulated.5.The controlling factor in Quantou formation are:,sandstones are continuously distributed in the whole basin,reservoirs are compact in the depression area;oil sources are abundant and with overpressure as the major driving force of hydrocarbon expulsion;The coupling mechanism between inorganic carbon dioxide and petroleum in Quantou formation are:first,petroleum are accumulated at Mingshui formation,and inorganic carbon dioxide invaded oil reservior at Neozoic,The destroy effection of original oil reservior are limited,just becaused that the sandstone almost isolated.then the redistribution of petroleum are only inside the sandstone.The effection of inorganic carbon dioxide to petroleum reservoir are obvious. Waters in reservoir showed high outliner abnormol value in the case of carbondioxide influxion which greately changed total minerlitation of reservoir,and the invasion of iorganic carbon dioxide created abundance of dawsonite.This is very infaust factor to the penetrability of reservoir.