Geochemical Accumulation Analysis Of The Ordovician In The Haupha Area Of ??the Northern Tarim Basin

In recent years,with the further research and increasing exploration degree of the Halahatang depression in Tabei uplift,since the Repu block at the south slope of the depression is on the advantage pathway of oil and gas,it's confirmed that the Ordovician carbonate reservoir has enormous resource potential.However,there still exist many problems such as unclear source of oil and gas.the complex accumulation period and accumulation model,and undefined enrichment regulation of oil and gas.Based on the method of whole-hydrocarbon geochemistry of the Ordovician carbonate reservoir,combined with the burial history of source rock,evolution characteristics of structure and reservoir,the paper carried out the comprehensive judgment about the source of oil and gas,determined the migration and accumulation of the reservoir forming periods,summarizes the reservoir forming mechanism,optimized the main controlling factors of the reservoir,and established the typical hydrocarbon accumulation mode.The crude oil from the Ordovician carbonate reservoir in the study area has the characteristics of low density,rich alkanes and lean arene.The C7 compounds shows the dominant of the n-heptane,so the crude oil comes from the type I kerogen.And the Mango palaeogeothermal confirmes that the maturity of crude oil is comparatively high.At the same time,the similar fingerprint feature of the middle molecule hydrocarbon indicates that the oil and gas in the area has a unified source.The hydrocarbon biomarker generally shows the characteristics of high level of the long chain Tricyclic terpane and Ts/Tm value.The existence of a critical mass of the isoprenoid compounds shows the strong reducing environment.Above all,the main oil sources of the Ordovician carbonate reservoir is from the Cambrian hydrocarbon source rocks.The major component of the natural gas at Repu block is methane.And the dry coefficient of gas is between 0.7 to 0.85,the natural gas belongs to the reservoir associated gas.During the later period,the gas migrated from south to north alters the early reservoir in Repu area,so the Ordovician traps are usually the type of reservoir with gas cap based,also,with a few gas-washing condensate reservoir.Meanwhile,oil and gas migration has two-way charging mechanism of vertical and horizontal orientation.There are three periods of the hydrocarbon accumulation in study area.During the middle-late caledonian period,the source rock in Manjiaer depression at the southern part of the Halahatang depression and from the deep strata in study area reached the oil window,and entered into the stage of massive oil generation.The oil migrate to Ordovician reservoir and Ordovician reservoir formed.In late hercynian period,it is the adjustment period of oil.During the himalayan period,the Cambrian condensate gas migrated upward along the fracture,the gas-washing transformation occurred the overlying reservoirs,and it formed the reservoir with gas cap and gas-washing condensate reservoir.The factors,such as thermal evolution of the hydrocarbon source rock,multiphase tectonic fracture activity,secondary gas-cut transformation and the distribution of the pores,holes and crack in reservoir,play a vital role in the hydrocarbon accumulation of the ordovician carbonate reservoir.