Clay Minerals and Organic Matter from Deeply Buried Ordovician-Silurian Shale in Western Iraq: Implications for Maturity and Hydrocarbon Generation

Abstract

The present work is conducted on the Paleozoic (Ordovician) Khabour and the (Silurian) Akkas shales in the Akkas-1 well of western Iraq. The study is aiming to determine the implications of clay mineral transformation, organic mineral distribution and maturity of hydrocarbon generation, using X-ray diffraction (XRD), scanning electron microscopy (SEM) in addition to organic matter concentrations. 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, high content of organic matter is recorded in addition to abundant vitrinite and low content of grainy organic matter (Tasmanites) and pyrite. Illite and kaolinite are commonly found in addition to chlorite and illite-smectite clay minerals. Conversion of smectite to mixed-layer illite-smectite (I-S) and an increase in vitrinite reflectance are commonly observed below 2500 m depth in the studied formations, which 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.

Paleoenvironmental Conditions of the Harur Formation (Early Carboniferous), Northern Iraq: Insights from Mineralogy and Elemental Geochemistry

“…Furthermore, kaolinite is an excellent predictor of a humid climate, whereas smectite and smectite mixed layers are byproducts of a warm, moist climate [35]. Chlorite, on the other hand, does not typically survive in cool, moist environments, its presence in sediments as a detrital clay is a good indicator of cool/dry climates [37,38]. All of the data presented above is consistent with the Devonian-early Carboniferous paleoclimate of the broad shelf depositional basin, including the Harur Formation in Iraq, which was located between tropical and subtropical southern hemispheres [14].…”

Paleoenvironmental conditions during deposition of Kolosh and Gercus formations in northern Iraq as deduced from clay mineral distributions

“…Highly sensitive changes in clay mineral structures due to changes in temperature and pH in their surroundings make them useful indicators for changes in paleoenvironmental conditions [1]. Generally, clay minerals are the products of sedimentation and diagenesis under certain circumstances related to provenance, climate, and water conditions; therefore, they have important implications for interpreting the paleoenvironmental and paleoclimatic history [2][3][4][5]. In the Cenozoic sedimentary successions from northern Iraq, clay minerals of Paleocene to Eocene rocks (Figure 1) representing the Kolosh and Gercus formations were subjected to a detailed mineralogical study.…”