Characteristics of Fluid Inclusions and Pressure Recovery during Hydrocarbon Accumulation Period in Jurassic Sangonghe Formation in Fukang Sag,Junggar Basin
Formation pressure recovery is of great significance for the analysis of hydrocarbon accumulation process. This study restores the pressure of Jurassic Sangonghe Formation during hydrocarbon accumulation period in Fukang Sag with inclusion observation technology,the inclusion salinity homogenization temperature method and PVTx simulation method. The results show that the overpressure of Jurassic begins from 4500 m,and the overpressure amplitude increases with the increase in buried depth,in Fukang Sag. At the same depth,the overpressure of the main reservoir of Sangonghe Formation is obvious. There are two stages of hydrocarbon inclusions captured in the Sangonghe Formation. The fluorescence colors of hydrocarbon inclusions captured in the first stage which occur inside the quartz particles are mainly yellow and yellowish green,and the main temperature range of associated aqueous inclusions is 85-95 ℃,corresponding to the hydrocarbon accumulation in the middle of Early Cretaceous. Since Neogene,the fluorescence color of hydrocarbon inclusions captured in the second stage,which occur along the healing seams that cut through secondary enlargement of quartz or the whole the after the secondary,is mainly bluish white,and the number of the gas-liquid two-phase hydrocarbon inclusions significantly increases. The homogenization temperature of associated aqueous inclusions is 105-115 ℃,corresponding to hydrocarbon accumulation since the Neogene. During hydrocarbon migration and accumulation,overpressure developed in the Sangonghe Formation. The pressure coefficient in the first stage is 1.39-1.44 and that in the second stage is as high as 2.11. The pressure presents the evolution mode of "pressurization-decompression-strong pressurization". Strong overpressure represents strong hydrocarbon transportation and movement force. It is the key factor for hydrocarbon accumulation in Jurassic tight reservoirs.
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