中国古老海相碳酸盐岩油气成藏组合的评价方法及其应用

中国古老海相碳酸盐岩油气成藏地质条件复杂,在其有利区带的评价优选过程中,目前尚存在只重视勘探目标（圈闭或储集体）,而忽视其他成藏要素（如烃源岩）的问题,导致一些勘探实践的失败。为此,在系统梳理塔里木、四川等盆地深层海相碳酸盐岩油气成藏地质条件的基础上,提出将成藏组合作为中国古老海相碳酸盐岩油气勘探中的重要评价单元,重点开展烃源条件、储集条件及源-储配置关系研究的观点。根据源-储配置关系,将古老海相碳酸盐岩成藏组合分为同构造期成藏组合及跨构造期成藏组合两大类型;储集体类型是海相碳酸盐岩成藏组合评价中最为重要的评价参数,也是进一步划分成藏组合类型的重要依据。对于以地层-岩性圈闭为主体的碳酸盐岩油气成藏组合,建议采用“储层层位+储集体类型”对其命名,实用性更强。最后,以鄂尔多斯盆地奥陶系为实例,阐述了古老海相碳酸盐岩油气成藏组合的特征,并指出该区奥陶系马家沟组可分为4个成藏组合,其中马五₅-马五₁₀亚段的成藏组合条件最为优越,天然气勘探潜力大,是值得加强勘探的重点目标。

Assessing ancient marine carbonate plays in China

Geologic conditions of ancient marine carbonate plays in China are very complex. During play fairway mapping, it is common to focus only on the recognition of exploration targets (traps or reservoirs), but to neglect other elements (such as source rocks) concerning hydrocarbon reservoiring, leading to the failure of exploration in some areas. To solve these problems, the geologic conditions of the deep marine carbonate plays in petroliferous basins including Tarim and Sichuan were systematically analyzed for establishing a solid basis of study. By taking a play as an important assessment unit of the ancient marine carbonate reservoirs in China, we performed research on source rock conditions, reservoir conditions, and source rock & reservoir rock combination. The ancient marine carbonate plays are divided into two groups, namely syntectonic cycle plays and conjunct tectonic cycle plays according to the source reservoir rock combinations. A reservoir type is both an important parameter for the evaluation of marine carbonate plays and a major basis for the subdivision of plays. As to the carbonate plays dominated by stratigraphic lithologic traps, it is proposed to name them as "a reservoir horizon plus reservoir type". Finally, the features of carbonate plays were discussed by taking the Ordovician reservoirs in the Ordos Basin as an example. Four plays can be recognized in the Ordovician Majiagou Fm in this basin. Among these plays, the M₅⁵ (the fifth interval of the 5^th member of Majiagou Fm) M₅¹⁰ (the tenth interval of the 5 ^th member of Majiagou Fm) play is the most favorable one in terms of geologic conditions, thus it is a major exploration target in the future.