The Hydrocarbon Inclusions and Significance of Hydrocarbon Accumulation in Ordovician Reservoirs in Eastern Tazhong Area,Tarim Basin

A stage(the Stage-Ⅲ) of hydrocarbon inclusion with strong brown-red fluorescence is discovered in the Ordovician carbonate reservoir in eastern Tazhong area,which is different from the other parts of Tazhong area.There are three stages of hydrocarbon inclusions which contributed to the hydrocarbon accumulation in this area.Based on the composition characteristics,phase diagrams,temperature and pressure of them,it is proved that the Stage-Ⅱ inclusion was formed in late Hercynian movement and the oil originated from the Middle-Upper Ordovician was preserved;the Stage-Ⅳ inclusion formed in late Himalayan movement and the large-scale condensate oil-gas charging decomposing from the Cambrian crude allows the Ordovician oil in Tazhong area to be of mixed feature of Middle-Upper Ordovician and Cambrian oils.This stage condensate charging is the reason for prevalent existence of 25-lower hopane series in oil reservoirs in Tazhong area as the great contributor;and the Stage-Ⅲ formed in Yanshan-early Himalayan movement and high-maturity oil from the Cambrian only accumulated in the Middle-Lower Ordovician and Cambrian reservoirs in eastern Tazhong area,which explains the normal oil reservoir can be found in the eastern Tazhong,while condensate reservoirs have been mainly found in the other areas of Tazhong.