Clay minerals and organic matter from deeply buried Ordovician-Silurian shale in western Iraq: implications for maturity and hydrocarbon generation
The present work is conducted on the Paleozoic (Ordovician) Khabour and the (Silurian) Akkas shales in the Akkas-1 well of western Iraq aiming to determine the implications of clay mineral transformation and organic mineral distribution and maturity for hydrocarbon generation using X-ray diffraction (XRD), scanning electron microscopy (SEM) in addition to organic matter concentrates. In the shale of the Khabour Formation, amorphous organic matter is common and includes various Tasmanite-type organic matter, vitrinite, inertinite and bituminite. The main clay minerals observed include; illite, chlorite, kaolinite, in addition to mixed-layer illite-smectite and rare smectite. In Silurian shale, a lot of organic matter is recorded in addition to abundant vitrinite, some grainy organic matter (Tasmanites) and pyrite with common illite, kaolinite in addition to chlorite and illite-smectite clay minerals. Conversion of smectite to mixed-layer illite-smectite (I-S) and increase in vitrinite reflectance are commonly observed below 2500 m depth in the studied formations and this coincides with oil and gas generation. These results could be used as an indication of higher maturity and hydrocarbon generation in the deeply buried shale of the Khabour and Akkas formations in western Iraq.