Seismic Expression of Karst-Related Features and 3D Seismic Evidence of the Effects of Carbonate Karst Collapse and Fault System on Hydrocarbon Migration Path in Merjan-West Kifl Oil Fields, Center of Iraq

A seismic study of 2D/3D data Volume of Merjan-West Kifl oil fields, in central Iraq, was conducted to delineate karst features and fault systems in the area and their role in hydrocarbon migration. 3D Seismic data depict karst features and faults that act as a pathway to migrate hydrocarbons from Late Jurassic source rocks (Sargelue and Sulaiy formations) to the Early Cretaceous reservoir rocks (Hartha, Sadi, Nahr Umr, and Zubair formations) in the area. Most of the Cretaceous carbonate formations, such as Yamama, Shuaiba, and Mishrif in the area, have undergone chemical erosion after deposition and diagenesis, generating karst features. Their surfaces appear as irregular depressions at erosion or collapse of deeper karst hole locations. The seismic reflection image below the karst feature is poor because they have significantly slower velocities than the surrounding sediments. Consequently, high contrast in acoustic impedance occurs, and the seismic reflection signature is distinctive as a Gull-winged depression in cross-section. This was permitted to delineate and map the karst in the area. The size of these karsts is usually a few meters to a few hundred. Delineation of the karst features was attempted utilizing seismic attributes mapping using a variance cube. Seismic attributes were applied to confirm the physical properties and behavior of karsts. They were illustrated with low frequency and high reflection magnitude.