The Differences Study Of Natural Gas Accumulation Of Triassic Jia-lingjiang And Lei-koupo Formation In Sichuan Basin

For studying the differences of natural gas accumulation of Triassic Jia-lingjiang and Lei-koupo formation in Sichuan Basin,and summarizing the regularity of natural gas' accumulation,the author collected a large number of predecessors' information,studying the different tectonic units' basic geological conditions of hydrocarbon accumulation,including hydrocarbon source condition,reservoir condition,sealing system conditions,conditions,trap conditions and preservation conditions;carefully summarized gas accumulation differences between different tectonic units,including gas source diversity,reservoirs' difference,sedimentary difference,the process of hydrocarbon accumulation diversity,finally summarized the regularity of natural gas accumulation of Triassic Jia-lingjiang and Lei-koupo formation in Sichuan Basin.With the carbon isotope and gas component analysis,to think that the gas source of Jia-lingjiang formations' gas reservoir is complex,is given priority to with exogenous,most areas of the basin is Permian coal type gas or the Permian and Silurian oil type gas hybrid,except the middle of Sichuan basin,the lack of early Permian coal type gas.Through the study of sedimentary facies of Jia-lingjiang formation's every sedimentary times in Sichuan basin,to think that in three times during sea advance and retreat,the sedimentary characteristics of Jia-lingjiang formation is salization to localization to salinization of platform.It can be divided into three phase belt in middle and east of Sichuan basin: sea platform,limited sea platform and evaporative platform.It only develops open sea platform semi-limited—limited sea platform phase in south of Sichuan basin.Through the cores' and rock slices' study,to think that Jia-lingjiang formations' reservoir rock is mainly constituted by limestone and dolomite,familiar types of reservoir space consists of intergranular pore and intragranular pore,dissolved pore,hole,structural fractures,etc.Reservoirs' physical property is characterized by low porosity and low permeability.In the east of Sichuan region is given priority to with type reservoir,porosity and permeability strong correlation;?In the middle of Sichuan region,low porosity,porosity and permeability poor correlation;In the south of Sichuan region,reservoir is generally characterized by low porosity and high permeability,good at cracks' development.Through the differences study of natural gas accumulation process of typical structures in the east and middle and south of Sichuan basin,to think that Permian's high—over maturity oil splitting gas go to the upper rocks mainly rely on hydrocarbon source faults(east and south of Sichuan basin)or high pressure broken crack(middle of Sichuan basin),under the sealing gland condition of regional plaster covering strata,it gathered in carbonate reservoir of Jia-lingjiang formation.The type of trap is lithology trap or structure trap or their combination.The gas pools' of Jia-lingjiang formation today experienced ancient oil pool?ancient gas pool?present gas pool.The ancient oil pool's formation and occurrence time have differences in the basin: First,the middle of Sichuan basin produce Permian's and Fei-xianguan formation's ancient oil pools,and the east and south of Sichuan basin produce Jia-lingjiang formation's ancient oil pools.Secondly,The ancient oil pools of middle and south area formed before the Indosinian Movement,but the ancient oil pools of east area formed at early Jurassic when the Indosinian Movement is over.The natural gas accumulation of Jia-lingjiang formation in Sichuan Basin follow these regularitys: “high pressure driving,fluid flow across formation,fault and fracture dredging,plaster covering and decomposition gas accumulation”.Through general geochemical method and strontium,carbon and oxygen stable isotopic characteristics method researching the gas source of Lei-koupo formation in Sichuan basin,to think that the gas source of Lei-koupo formation gas reservoir is mixing source,the gas source of T2l4 weathering crust gas reservoir which on the top of Lei-koupo formation mainly from the upper Triassic mudstone hydrocarbon source rocks and secondary migration channel mainly is weathering crust;the gas source of T2l3 and T2l1 beach facies reservoir gas reservoir is mainly from Permian hydrocarbon source rocks,the migration pathway is connecting hydrocarbon source fault or cracks.Through contrasting typical wells' reservoir characteristics,the reservoir of Lei-koupo formation have two types: The first is beach facies carbonate reservoir which is mainly controlled by the sedimentary facies,the most developed reservoir space types include primary intergranular pore,birds eye pore,biological body cavity pore and intragranular pore,etc.The second is weathering crust karst reservoir which is controlled by the karst system on the top of Lei-koupo formation,reservoir space types is dolomite intercrystal(dissolved)pore and dissolution pore or seam.The trap types of Lei-koupo formation gas reservoir can be divided into two different categories,one of them is mainly controlled by tectonic insider structural trap gas reservoir;another is mainly controlled by the strata(lithology)tectonic-formation gas reservoir.The direct caprock of Lei-koupo formation gas reservoir also can be divided into two categories,one of them is Upper Triassic mudstone cap rock which upon the karst reservoir that on the top of Lei-koupo formation;another is the gypsum rock inside the insider gas reservoir of Lei-koupo formation.The gas reservoirs' type of Lei-koupo formation can be divided into two categories,the one is karst type structure-formation gas reservoir whose gas source is mainly from overlying hydrocarbon source that does not containing the hydrogen sulfide,the second is inside beach facies reservoir gas reservoir of construction whose gas source is mainly from the underlying source rock containing hydrogen sulfide.The natural gas accumulation of Jia-lingjiang formation in Sichuan Basin follow these regularitys: “gas source from upside or downside,upper gas migration through weathering crust,lower gas migration through faults;reservoir is divided into two kinds,upper is weathering crust karst reservoir and internal is beach facies carbonate reservoir;the trap have two types,there are differences between the top and the insider;upper reservoir blocked by mudstone,internal reservoir blocked by gypsum rock,gas reservoir is divided into two types.”.