Sedimentology and Petroleum Potential of Chia Gara Formation (Late Jurassic – Early Cretaceous) in Three Different Tectonic Zones in Northern Iraq and Kurdistan Region

The sedimentology and petroleum potential of Chia Gara Formation (Late Jurassic – Early Cretaceous; Tithonian – Berriasian) in Northern Iraq are studied. The formation is exposed in the High Folded and Imbricated Zones of Iraq. Two outcrops and one well located in three different tectonic zones were chosen for current study. The selected sections are Banik (Duhok Governorate), Barsarin, (Erbil Governorate), and Aj-12 well (Salahaddin Governorate). The Chia Gara Formation is lithologically composed of black shale, thin bedded brown argillaceous limestone, thin to medium yellowish limestone, and marly limestone in uppermost part. The petrographic investigation of limestone beds along with microfacies analysis of limestones were based on 97 thin sections. Petrographic study shows that the matrix is mainly composed of micrite, various diagenetic processes had influenced limestones of the Chia Gara Formation, such as neomorphism, dissolution, calcification, cementation, compaction and fracturing. The rocks of Chia Gara Formation display high porosity that included fracture, vuggy and moldic types. However, porosity was later destroyed by digenetic processes. Consequently, the permeability is considered to be low. Source rock potential of Chia Gara Formation was also studied. The average values for TOC% of the formation were 1.70, 3.40 and 0.89 for Barsarin, Banik and Aj-12 sections, showing Good, Very Good, and Fair organic carbon respectively. The Pyrolysis, executed for studied samples, revealed that kerogen in Banik section and Aj-12 well belong to Types II and III kerogen, whereas Barsarin section obtained Types III and IV kerogen. Pyrolysis Parameters and diagrams suggested mature stage in Banik and Barsarin sections, and immature (or late immature) stage in well Aj-12. The plot of TOC% versus S1+S2 parameter indicated poor to excellent type of source rock in the studied formation. Vitrinite Reflectance (R%) and (TAI) indicated Oil Window and Early Gas Window in Barsarin, Oil Window in Banik, and Early Oil Window in well Aj-12.