Organic Geochemical Evaluation of Shale Units of Bokh Formation, Ogaden Basin, Ethiopia

Shale sample from Bokh Formation, Ogaden basin, Ethiopia was assessed for their petroleum potential by Rock-Eval pyrolysis. The Total Organic Carbon (TOC) values range from 0.76 to 0.86 wt%. These values exceed the minimum value of 0.5 wt% required for potential petroleum source rocks. The genetic potential (GP) and hydrogen index (HI) values range from 0.09 to 0.5 mg/g and 8 - 32 mgHC/gTOC, respectively. These values are generally lower than the minimal 2 mg/g GP and 200 mgHC/g HI required for a potential source rock. Several plots from the Rock-Eval pyrolysis data classify the samples as type IV kerogen with no potential to generate hydrocarbons. The Tmax and Production Index (PI) values range from 388°C to 453°C and 0.28 to 0.46, respectively. These values indicate that the shales are thermally matured. These results show that the shales from the Bokh Formation in Ogaden basin have no potential to generate hydrocarbons mainly crude oil, but are thermally matured and may generate natural gas.

埃塞俄比亚欧加登次盆Karoo期碎屑岩成藏组合地质特征与勘探潜力

Karoo期碎屑岩成藏组合是欧加登次盆最重要的天然气成藏组合,Bokh组泥质烃源岩与Calub和Adigrat组砂岩构成了成藏组合最基本的源储要素。在系统解剖油气成藏要素的基础上,认为Karoo期碎屑岩成藏组合发育断块、低幅度背斜、岩性尖灭、下切河道和透镜砂体等圈闭类型。区域性古隆起决定了油气富集区的平面展布,圈闭形成时间决定了充注的有效性,要尽量寻找Bokh组烃源岩白垩纪晚期大规模生排气之前就已形成的圈闭。盆地北部Adigrat组以中—粗砂岩为主,Bodle深埋区以细砂岩为主,宏观上Adigrat组下段物性优于上段,下段将主要以构造型圈闭为主,上段可发育岩性体圈闭。由于Calub组上源下储的格局,侧向运移将占主导地位,盆地内古"凹中隆"最为有利,同时斜坡部位的岩性尖灭体也具有较大潜力。Calub古隆起及周边Calub和Adigrat组储层发育条件最好,断裂体系发育,构造曲率变化大,又处于生烃中心围限中,油气成藏配置条件最佳,是最现实的主攻目标区。