Characteristics of Fluid Inclusion and Its Geological Significance for Middle-upper Proterozoic and Lower Palaeozoic Sub-erathem of Jibei Depression

Key words: 
• aqueous inclusions /
• hydrocarbon inclusions /
• Middle-upper Proterozoic suberathem /
• Palaeozoic subeathem /
• Jibei depression

Abstract: There is a set of marine-facies sedimentary series which are mainly composed of carbonate rock for middle-upper Proterozoic and lower Palaeo-zoic sub-erathem of libel depression. The sedimentary formation have many minerals which are formed by crystallization and recrystallization such ascalcite, fluorite, quartz, barite ect. Through making a systematic study to fluid inclusions characteristics in these minerals, there are six types hy-drocarbon inclusions and three kinds aqueous inclusions have been differentiated. These fluid inclusions separately formed by two immiscible fluid oil-gas and oil field water. During the two immiscible fluid migration, oil field water exist within it妙continuou-v phase, and oil-gas妙dispersed phase(drop, bubble). In these fluid inclusions, the vapor volume of vapor-liquid aqueous inclusions are between 1-10%.and it's salinity between I.73-9.86%( NaCI), and average is 4. 72 % ( NaCl), showing that it came from paleo-seawater. The homogenization temperature of the aqueous inclusions is inthe range 47-173 C，and the homogenized phase is liquid phase which represents the lowerest formation temperature for oil-gas migration and re-servior in the depression. The hydrocarbon inclusions are the direct sign of oil-gas primary and secondary migration, in which the vapor volume ofoil-gas hydrocarbon inclusions is in the range 2-10%，and its homogenization temperature is between 41-186℃ with the oil homogenized phaseshowing that oil-gas migration and reservoir was in oil phase. When forming temperature is lower, the homogenization temperature of hydrocarboninclusion is lower than aqueous inclusion. But when the temperature is higher, the homogenization temperature of aqueous inclusion is lower than hy-drocarbon inclusion. According to the strata sequence of middle-upper Proterozoic and lower Palaeozoic sub-erathem in Jibei depression, the mean homogenizationtemperature of fluid inclusion is higher in the top and bottom of strata, and lower in the middle strata. This is because that there are giant thick-bed-ed volcanic rock covering it. The homogenization temperature of the same foramtion are obviously different in the different parts of the depression,but the direction of oil-gas migration show that is from high temperature to low temperature. In addtion, according to the type and quantity of hydrocarbon inclusions in the different layers, we deduce that the main oil-gas reservoir are Tieling formation, Wumishan formation of middle-upper Proterozoic suberathem and Ordovician system.