中国海相超深层碳酸盐岩油气成藏特点及勘探领域

Hydrocarbon accumulation characteristics and exploration domains of ultra-deep marine carbonates in China

进入中国海相盆地超深层碳酸盐岩地层中寻找油气是中国未来油气勘探的趋势之一。近年来,在塔里木盆地、四川盆地和鄂尔多斯盆地深层、超深层的油气勘探中,相继取得了重要进展。通过对塔里木盆地塔河油田、塔中北坡深层、四川盆地元坝气田等典型超深层碳酸盐岩油气藏基本特征的分析,认为海相超深层油气成藏主要有4个基本控制因素:(1)不同生物组合、岩性的优质烃源岩在低地温背景下,具有干酪根、古油藏、分散可溶有机质等多元生烃机制,提供了丰富烃源;(2)构造、层序、岩相、流体与时间等因素,联合控制了不同类型优质储层的发育与分布,其中断裂活动、白云岩化和热流体活动对超深层优质储层的形成尤为关键;(3)相对稳定构造背景下,不同岩性的区域盖层、局部盖层和直接盖层的多级封盖有利于油气的封盖与保存;(4)不整合面、断裂和输导层与古隆起、古斜坡背景下各类圈闭的有效组合,决定了油气运聚、成藏的方式和效率。中国海相超深层碳酸盐岩资源潜力巨大,资源类型有油有气,以气为主。塔里木盆地超深层碳酸盐岩主要分布于几大隆起高部位之外的倾没端、斜坡区、凹陷区的寒武系—奥陶系中。四川盆地超深层碳酸盐岩主要分布于除川中地区外的海相下组合和川西、川东北前陆区的海相上组合中。鄂尔多斯盆地天环向斜和冲断带前缘的奥陶系是超深层碳酸盐岩现实的勘探领域。

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.