The Stages and Significance of Ordovician Fluid Inclusions in Tazhong No.1 Slope Break

Based on the penetrating relationship between calcite veins and hydrocarbon-bearing healed cracks,the characteristics of hydrocarbon inclusions and the characteristics of associated brine inclusion temperatures,the hydrocarbon inclusions of Ordovician in Tazhong No.1 slope break are classified into four stages. The first stage is the Late Caledonia that forms black hydrocarbon inclusion,in which hydrocarbon is generated in Cambrian and migrated upward along the Ordovician; the second stage is the Late Hercynian that the Ordovician source rocks begin hydrocarbon expulsion and forming light-brown hydrocarbon inclusion; and then because of the volcanic hydrothermalism in Late Permian,the deep and highly matured hydrocarbons charge into the Ordovician reservoir and form extensive hydrocarbon inclusions of the third stage of inclusion,which is the second and significant hydrocarbon accumulation of Ordovician reservoir in this area. The fourth stage is the Himalayan movement that the structural highs TZ26-TZ62 in Tazhong slope break,a great amount of hydrocarbons is charged into it,which is the third hydrocarbon accumulation of it. After that,the existed hydrocarbon accumulations are modified,natural gas is charged into parts of well blocks and areas. It is concluded that the first and second stages are regarded as the footprint of hydrocarbon migration,the third and fourth stages as the history of hydrocarbon accumulation,which can be regarded as the marks for searching for high-yielding oil and gas in Tazhong No.1 slope break.