中国海相超深层油气地质条件、成藏演化及有利勘探方向

通过对中国海相超深层油气区域构造背景、石油地质条件分析及典型地区(古)油气藏解剖,研究海相超深层油气成藏演化过程及富集主控因素。中国海相超深层油气主要分布在四川、塔里木和鄂尔多斯3大克拉通盆地,界定其埋藏深度大于6000 m,赋存层系为前寒武系及下古生界为主的古老海相层系。中国海相超深层烃源岩发育受全球超大陆聚、散旋回为背景的克拉通裂陷及克拉通坳陷控制,在四川盆地发育层系最多、塔里木盆地其次、鄂尔多斯盆发育规模有待进一步证实;储集层以碳酸盐岩为主,储集性能受早期高能滩体、后期叠加溶蚀及断裂作用共同控制;区域盖层包括膏盐岩、泥页岩与致密碳酸盐岩3大类。中国海相超深层普遍经历了两期油藏、古油藏裂解成气(或部分裂解)、裂解气(或高过成熟油气)晚期定型等演化阶段,油气富集受静态和动态地质要素耦合控制,主力生烃中心、高能相带叠加岩溶规模储集层、巨厚膏盐岩或泥页岩盖层、稳定保持圈闭条件是超深层油气富集关键因素。海相超深层具有克拉通内裂陷周缘、克拉通内坳陷周缘和克拉通边缘3个有利勘探方向。

Geological conditions,reservoir evolution and favorable exploration directions of marine ultra-deep oil and gas in China

By analyzing the structural background,petroleum geological conditions,and typical regional(paleo)oil and gas reservoirs in marine ultra-deep oil and gas regions in China,this paper reveals the evolution process of marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation.The marine ultra-deep oil and gas resources in China at burial depth of greater than 6000 m are mainly distributed in the Precambrian and Lower Paleozoic ancient marine strata in the Sichuan,Tarim and Ordos cratonic basins.The global breakup-convergence cycles of the supercontinent control the evolution of intracratonic rifts,cratonic marginal rifts,and intracratonic depressions.The Sichuan Basin is dominant in source rocks,followed by the Tarim Basin.The early high-energy sedimentary environment and the later dissolution and faulting control the development of high-quality carbonate reservoirs.The regional caprocks are dominated by gypsum salt rocks,shale,and tight carbonate rock.The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming,thermal(complete or partial)cracking of oil in paleo-reservoir into gas,and late accumulation of kerogen-cracked gas(high-over mature oil and gas).The oil and gas accumulation is controlled by static and dynamic geological elements jointly.Major hydrocarbon-generation center,high quality and large-scale reservoir resulted from karstification of high energy facies belt,thick gypsum rock or shale caprock,and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas.Based on petroleum geological conditions,factors affecting hydrocarbon accumulation and evolution,and the latest exploration knowledge,we propose three favorable exploration directions,i.e.the areas around intracratonic rift and intracratonic depression,and craton margin.