蓝尼罗河盆地喀土穆凹陷构造演化及烃源岩发育特征

Tectonic evolution and characteristics of source rocks in Khartoum sag,Blue Nile basin

对蓝尼罗河盆地喀土穆凹陷构造演化特征进行了分析,重新厘定了构造演化阶段,并对主力烃源岩发育特征及油气来源进行了深入分析。研究表明:喀土穆凹陷的形成与演化受控于中非剪切带的活动,该凹陷经历了裂陷Ⅰ期、裂陷Ⅱ期及拗陷期等构造演化阶段。早白垩世裂陷Ⅰ期的强裂陷作用是湖相烃源岩发育的主要时期,综合烃源岩地化指标及油-源对比分析认为Abu Jinn组烃源岩为喀土穆凹陷的主力烃源岩。喀土穆凹陷Abu Jinn组烃源岩与穆格莱德盆地Abu Gabra组主力烃源岩沉积环境类似,为弱氧化-弱还原的沉积环境,且水体较淡。不同构造位置处Abu Jinn组烃源岩有机质类型和甾烷分布差别较大。Abu Jinn组烃源岩热演化程度主要受埋藏深度的控制,但火山活动促进了Abu Jinn组烃源岩的热演化,烃源岩成熟度受火成岩影响范围约为火成岩上下200 m范围。

Based on the structural analysis of Khartoum sag in Blue Nile basin, the tectonic evolution stages are re-divided and the characteristics of major source rocks and oil-source correlation are analyzed. The re-sults show that the formation and evolution of Khartoum sag are controlled by tectonic activity of the Cen-tral African shear zone and the sag develops syn-rift I , syn-rift II and post-rift. The strong rift stage is the main formation period of the source rock. By the comprehensive analysis of the geochemical index of source rock and oil-source correlation, Abu Jinn source rock is considered as major source rock in Khartoum sag. The depositional environment of Abu Jinn source rock in Khartoum sag is similar to Abu Gabra source rock in Muglad basin, both are weak-oxidation and weak-reduction depositional environment with fresh water. Organic matter types and sterane distribution are different with structural positions for Abu Jinn source rock. The thermal evolution of Abu Jinn source rock is mainly controlled by burial depth, but the volcano activities promote the thermal evolution. The maturity of source rock is affected by igneous rocks and the influence scope is within 200 m of igneous rocks.