巴西桑托斯盆地卢拉油田成藏特征及对盐下勘探的启迪

巴西桑托斯盆地卢拉油田(原名图皮油田)盐下地层层序、热史、圈闭演化史等分析表明,卢拉油田的烃源岩为中裂谷层序与上裂谷层序的湖相页岩,储层则以坳陷层序的碳酸盐岩为主;圈闭类型为受尼欧克姆—巴雷姆期裂谷作用形成的地垒所控制的岩性—构造复合圈闭,其形成演化经历了早白垩世尼欧克姆—巴雷姆的裂谷早期、裂谷中期、裂谷晚期、早阿普特的坳陷期、晚阿普特的蒸发岩发育期,以及早白垩世阿尔布以来的油藏圈闭充注期等6个演化阶段;其成藏特征表现为盐下深层晚期中等成熟成藏。认为广泛分布的厚层盐岩(约2000m)及其高热导率的功效极大地延缓了盐下烃源岩的热演化程度,扩展了盐下勘探的深度范围;同时,地垒—地层型油气聚集带成为桑托斯盆地乃至整个巴西东部海上盆地盐下勘探的新领域。

Accumulation Feature of Lula Oilfield and Its Exploratory Implication for Pre-salt Reservoirs in Santos Basin, Brazil

Comprehensive analysis ofpre-salt stratigraphic sequence, thermal history and trap evolution of Lula Oilfield （formerly known as Tupi Oilfield） in Santos Basin, Brazil, shows that the source rock of the oilfield is lacustrine shale of middle-upper rift sequence; its reservoir rock is carbonate of sag sequence; and its trap type is a lithologic-structural combination trap controlled by horsts formatting during Neocomian- Barremian rift stage, that trap evolution of Lula Oilfield experienced six stags, i.e. the early rift, middle rift and late rift stages of Neocomian- Barremian, the sag stage of early Aptian, evaporite stage of late Aptian and the pool formation stag from Albian to now, and that its accumulation feature presents subsalt deeper reservoir, lately gathering and medium mature of source rock. It is concluded that the very thick salt layer （-2000m） effect in distribution and high heat conductivity greatly delayed thermal evolution degree of pre-salt source rocks, and expanded the hydrocarbon exploration depth for the pre-salt section. In addition, the oil-gas accumulation zone of horst-stratum becomes a new exploratory frontier for the whole pre-salt sections, not only in Santos, but also throughout the eastern Brazilian offshore basins.