关键词: 成藏特点, 勘探领域, 中国海相盆地, 超深层, 碳酸盐岩, 成藏特点, 勘探领域, 中国海相盆地, 超深层, 碳酸盐岩

Abstract: Searching for oil and gas in ultra-deep carbonate sequences in marine basins is becoming one of the major trends of future petroleum exploration in China. In recent years, major oil and gas discoveries have been made in the exploration of deep and ultra-deep sequences in petroliferous basins such as Tarim, Sichuan and Erdos. Based on analysis of the basic characteristics of the typical ultra-deep carbonate reservoirs in Tahe oilfield and the deep northern slope in Tazhong of Tarim Basin and Yuanba gas field of Sichuan Basin, it is concluded that hydrocarbon accumulation in ultra-deep marine carbonate is mainly controlled by 4 basic factors: (1) High quality source rocks. In low geothermal settings, source rocks of various biological combinations and lithologic types generated abundant hydrocarbons via multiple mechanisms such as kerogen, ancient oil reservoirs and dispersed dissoluble organic matter; (2) High quality reservoirs. The development and distribution of high quality reservoirs are jointly controlled by structure, sequence, lighology, fluid and their timing, among which faulting, dolomitization and thermal fluid activity are especially crucial to the formation of high quality ultra-deep reservoirs; (3) Multiple sealing mechanisms. Regional caprock, local caprock and direct caprock of various lithologies provide favorable conditions for the sealing and preservation of hydrocarbons; (4) Favorable hydrocarbon migration pathways. Effective combinations of unconformities, faults and carrier beds with various types of traps on paleo-highs and paleo-slopes determine the pattern and efficiency of hydrocarbon migration and accumulation. Ultra-deep marine carbonates in China have huge oil and gas resource potential, predominantly gas potential. In Tarim Basin, the exploration domains of the ultra-deep carbonates mainly distribute in the Cambrian and Ordovician in the pitching ends, slope zones and sags outside the structural highs of large uplifts; in Sichuan Basin, they mainly occur in the lower marine sequence assemblage outside central Sichuan and in the upper marine sequence assemblages in foreland areas of western and northeastern Sichuan; in Erdos Basin, they mainly include the Ordovician of Tianhuan syncline and thrust front.

Key words: carbonate rock, hydroc arbon accumulation characteristics, exploration domain, China marine basin, ultra-deep sequence, China marine basin, ultra-deep sequence, carbonate rock, hydroc arbon accumulation characteristics, exploration domain