Porosity Evolution and Sequence Stratigraphy of Khasib Formation (Late Turonian-Coniacian) in Selected Oilfields, Central Iraq

The evolution of porosity and sequence stratigraphy study of the Khasib Formation (Late Turonian-Coniacian) in two wells, in central Iraq were conducted. In the first well EB-X, the Khasib Formation sequences are confined to a depth of 2182-2285 m, with a thickness of about 103 meters, and in the second well Hf-Y, the Khasib Formation sequences are confined to a depth of 2941-2860 meters, with a total thickness of 81 meters. The lithology of the formation is predominantly dark chalky limestone rich in planktonic fossils, with a few thin layers of black shale. The formation lithology progressively shifts higher to shaley limestone rich in planktonic fossils and Calcispheres. On the other hand, the depositional environment of the formation was established by diagnosing six mudstone submicrofacies, five wackestone submicrofacies, and a packstone microfacies, which indicate the formation depositional settings in deep marine environments. Furthermore, the formation is split into three zones based on porosity values: A, B, and C, which are characterized by productive reservoir rock, low-yielding reservoir rock, and medium-productive reservoir rock, respectively. The Khasib formation sequences formed during the Late Turonia to Early Coniacian. As a result, the overall sedimentation period reached 3.1 million years, and the stratigraphic sequence is of the third order