伊拉克中部白垩系油藏油源及运移特征

针对伊拉克中部Ahdeb油田白垩系油藏油源不清、油藏特征不明问题,以原油地化分析数据、三维地震解释、包裹体地化分析等作为研究对象,对其油源及运移特征进行分析。研究表明Ahdeb油田白垩系油藏烃类流体均形成于还原-强还原、相对闭塞海相有机质沉积,生物标志物特征对比表明,各油藏油源一致。结合伊拉克地区源岩地化特征对比分析,源岩应为上侏罗统Chia Gara组。运移以垂向为主,通道为受基底Najiad断裂控制形成的南西-北东向开启性走滑断裂,主要向断裂终点上白垩统Khasib组发生垂向运移,运移中遇横向发育高孔渗储层发生侧向运移,为次运移方向。Chia Gara源岩自白垩纪晚期开始排烃,整体可划分为2期运移:第一期发生于晚白垩世-新近纪,流体为低熟源岩排出的重质油,此时圈闭未形成,原油进入Khasib层后沿高孔渗地层向盆缘做大规模运移;第二期为新近纪后扎格罗斯造山运动使地层埋深迅速增加,源岩进入高成熟期排出的相对高成熟原油,随圈闭形成而聚集成藏。

Oil sources and migration characteristics of Cretaceous reservoirs in the Central Iraq

Crude oil geochemical data, 3D seismic interpretation, and inclusion analyses were used to examinesource rocks and migration characteristics of the Ahdeb Oil Field in central Iraq.The results indicate that oils in the Cretaceous reservoirs in the Ahdeb Oil Field all originated from reducing and strongly reducing conditions in relatively closed marine deposits. Biomarkers showed that the Cretaceous reservoirs mainly were sourced from the Upper Jurassic Chia Gara Formation. Oil mainly migrated vertically into the Upper Cretaceous Khasib Formation through the SW-NE oriented strike-slip open faults which were controlled by the Najiad fault system. Lateral migration also took place when oils intersected high-porosity and high-permeability reservoirs (Rumaila, Mishrif and Mauddud). The Chia Gara Formation began to expel oil at the end of the Cretaceous. There were two stages of oil migration. The first one took place from the late Cretaceous to Neogene. Traps were not formed yet, and the heavy oils from low maturity source rocks migrated vertically into the Khasib Formation and laterally to the basin fringe along high-porosity and high-permeability formations. The second migration stage was since the Neogene. Due to the Zagros orogeny, source rocks entered the high maturity stage by rapid subsidence, and expelleda mass of high maturity crude oils, which accumulated after trap formation.