The Silurian Akkas Formation has been reported and described only in the subsurface of western Iraq. The formation is divided into the lower Hoseiba Member, which contains two high‐TOC “hot” shale intervals that together are around 60 m thick, and the overlying Qaim Member that is composed of lower‐TOC “cold” shales. This study investigates the source rock potential of Akkas Formation shales from the Akkas‐1and Akkas‐3 wells in western Iraq and assesses the relationship between their mineral and elemental contents and their redox depositional conditions and thermal maturity. Twenty‐six shale samples from both members of the Akkas Formation from the Akkas‐1and Akkas‐3 wells were analysed. The results showed that the upper, ~20 m thick“hot” shale interval in the lower Hoseiba Member has good source rock characteristics with an average TOC content of 5.5 wt% and a mean Rock‐Eval S₂ of 10 kg/tonne. Taken together, the two “hot” shale intervals and the intervening “cold” shale of the Hoseiba Member are ~125‐150 m thick and have an average TOC of 3.3 wt% and mean S₂ of 6.2 kg/tonne. The samples from the Hoseiba Member contain mixed Type II / III or Type III kerogen with an HI of up to 296 mgS₂/gTOC. Visual organic‐matter analysis showed that the samples contain dark brown, opaque amorphous organic matter with minor amounts of vitrinite‐like and algal (Tasmanites) material. Pyrolysis – gas chromatography undertaken on a single sample indicated a mature (or higher) algal‐dominated Type II kerogen. High spore and acritarch colour index values and weak or absent fluorescence similarly suggest that the lower part of the Akkas Formation is late mature to early post‐mature for oil generation. “Cold” shales from the Qaim Member in the Akkas‐3 well may locally have good source rock potential, while samples from the upper part of the Qaim Member from the Akkas‐1 well have little source rock potential. Varied results from this interval may reflect source rock heterogeneity and limited sample coverage.

中文翻译：

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伊拉克西部志留纪AKKAS组的有机和无机地球化学与矿物学评估

志留纪Akkas地层仅在伊拉克西部地下得到报道和描述。地层被分为下部的Hoseiba构件和下部的Qaim构件，下部的Hoseiba构件包含两个高TOC的“热”页岩层段，总厚度约60 m，上面的Qaim构件由下部的TOC的“冷”页岩组成。这项研究调查了伊拉克西部Akkas-1和Akkas-3井中Akkas组页岩的烃源岩潜力，并评估了其矿物和元素含量与氧化还原沉积条件和热成熟度之间的关系。分析了来自Akkas-1和Akkas-3井的两个Akkas组成员的页岩样品。结果显示，₂公斤10吨/吨。总的来说，细西坝成员的两个“热”页岩层段和中间的“冷”页岩层厚约125-150 m，平均TOC为3.3重量％，平均S ₂为6.2千克/吨。来自Hoseiba成员的样品含有II型/ III型或III型混合型干酪根，HI最高可达296 mgS _2。/ gTOC。可见的有机物分析表明，样品中含有深棕色，不透明的无定形有机物，并含有少量的镜质体和藻类（塔斯曼石）物质。热解–对单个样品进行的气相色谱分析表明，成熟的（或更高）藻类为主的II型干酪根。较高的孢子和顶基颜色指数值以及较弱或缺少荧光的情况类似地表明，Akkas组的下部成熟到晚期，到生成油后很早。来自Akkas-3井Qaim成员的“冷”页岩在本地可能具有良好的烃源岩潜力，而来自Akkas-1井的Qaim成员上部的样品却没有源岩潜力。该间隔的不同结果可能反映了烃源岩的非均质性和有限的样品覆盖率。