Microfacies and Depositional Environment of the Lower Qamchuqa Formation in Bai-Hassan Oilfield / Northern Iraq

Abstract

The Lower Qamchuqa (Shu'aiba) Formation with Aptian age is a shallow-marine carbonate that observed for the first time at the outcrop section in northern Iraq in Qamchuqa Gorge. For the present study, data of coring and cutting samples, thin section, and gamma ray log for the studied formation from the well BH-96 in Bai-Hassan Oilfield were used to determine the microfacies and sedimentary environment of the formation. The thickness of studied section was 49m from the upper part of the formation. The lithology of the studied section composed of shaly limestone with a 2m thick shale bed in the upper part of the studied section followed by successions of limestone and dolomitic limestone of thicknesses 19m and 11m respectively at the middle and lower part of the studied section. Three microfacies and six sub-microfacies types were identified in the formation which are the lime mudstone microfacies (subdivided to non-fossiliferous mudstone and fossiliferous mudstone sub-microfacies), the lime wackestone microfacies (subdivided to benthic foraminiferal wackestone, orbitolina wackestone, bioclasts wackestone sub-microfacies and pelloidal wackestone sub-microfacies), and the lime packstone microfacies. The identified microfacies were compared to the standard microfacies zones and appeared to be representing open marine and restricted platform environments.