南大西洋两岸被动陆缘盆地结构差异与大油气田分布

以板块构造演化为基础，利用地震、地质等资料，再现南大西洋两岸共轭型被动陆缘盆地原型盆地形成演化过程。首次依据盆地结构差异及沉积充填特征，将研究区被动陆缘盆地进一步划分为“三段”“四类”；结合对已发现大油气田的解剖，搞清了每类盆地大油气田成藏规律，并分别建立了其大油气田成藏模式。认为两岸“三段”“四类”盆地都经过了早期陆内裂谷、过渡期陆间裂谷及漂移期被动陆缘三个原型阶段。南段为下伏裂谷层系比较发育的“断陷型”盆地，上覆坳陷沉积厚度较薄，仅作为区域盖层，形成“裂谷层系构造地层型”大油气田。中段为裂谷、坳陷层系都比较发育且过渡阶段有盐的“含盐断坳型”盆地，以过渡期陆间裂谷盐岩充填为特征，其上、下的漂移期海相及裂谷期湖相页岩均可形成有效烃源岩，海相页岩及盐岩分别作为优质盖层，形成了“盐下碳酸盐岩盐上重力流扇体型”大油气田。北段为裂谷层系分布范围小、坳陷沉积范围广且厚度大的“坳陷型”盆地，受 “窄”陆棚、“陡”陆坡控制，坳陷层系重力流扇体自始至终比较发育，源于坳陷层系下部海相页岩中的油气直接充注于本身内部裙边状分布的重力流复合扇体之中，形成“漂移期重力流扇体群型”大油气田。另外，研究区还发育尼日尔、福斯杜亚马逊、佩罗塔斯三个具有独特构造沉积特征的 “三角洲型”被动陆缘盆地，其特殊性体现在三角洲层系由于沉积速率极高，从陆向海形成生长断裂带-泥岩底辟带-逆冲断裂褶皱带-平缓斜坡带四大环状构造带。除了前三角洲层系可以作为有效烃源岩之外，本身也可以形成自生自储自盖型组合，形成独特的“四大环状构造带型”大油气田，即在由陆向海生长断裂带-泥岩底辟带-逆冲断裂褶皱带-平缓斜坡带四大环状构造带上都可以形成大油气田。

Variations in basin architecture and accumulation of giant oil and gas fields along the passive continent margins of the South Atlantic.

In this study, based on plate tectonic evolution and using seismic and geological data, formation and evolution of prototype basins on the conjugated passive continental margins of the South Atlantic were studied, and ancient sedimentary environment and its controls on the forming conditions of large oil and gas fields were compared segment wise according to variations in basin architecture, and finally the passive continental marginal basins were divided into “three segments” and “four types” to reveal the accumulation law of giant oil and gas fields. As our study showed, the “four types” of basins on “three segments” had gone through three prototype stages: early intra continental rifting, intermediate inter continental rifting, and late drifting passive continental margin. In the southern segment, thin sediments in the “rift type” basin that formed in the drifting stage, developed into the large “rift structural stratigraphic” oil and gas fields. In the middle segment, the “salty rift depression type” basins were filled with inter continental rift salt rocks in the intermediate stage; and upper and lower sections are marine and lacustrine sediments from the drifting and rifting stages, respectively, possibly of high quality. Utilizing salt rock and marine shale as caprocks, the giant oil and gas fields of “pre salt carbonate and post salt turbidity sands” were developed. Finally, in the northern segment, thick marine sediments in the drifting stage in the “depression type” basin, affected by “narrow shelves” and “steep slopes” and controlled by the transform fault, developed into the large “deep water turbidity fan group” oil and gas fields on the basin margin. Our study further showed in the Niger high constructive “delta type” basin, unique delta gravity flow sandstone reservoirs have been formed, and giant oil and gas fields are identified in the inner ring rollover anticline delta sandstone, the middle mud diapir and the outer ring thrust crust.