Mud diapirs and folds in the South Caspian Basin: Geometry and syn-sedimentary evolution of structures with petroleum interest

Abstract

The South Caspian Sea is floored by a presumable oceanic crust and it was generated during the Arabia-Eurasia collision in Mesozoic times. Plate convergence has triggered deformation and subsidence forming a hydrocarbon-rich province with active oil and gas production. From the Late Miocene to Present, the western margin of the basin has been strongly controlled by uplift and deformation of the Caucasus Mountains, which has promoted flexure of the crust, fast subsidence and an enormous rate of sedimentation towards the Kura deltaic system. Depocenters in the basin reach up to 20 km depth, which represents one of the major sedimentary accumulations in the World. The Productive Series (PS; Late Miocene-Late Pliocene, 5.9 to ~3.4-3.1 Ma) were deposited as a 6 km-thick marineto- deltaic sequence, overlaid by the here referred as the Post- Productive Series sequence (Post-PS; Late Pliocene to Present, <3.4-3.1). Mud accumulations are widespread in the South Caspian Basin (SCB) shaping innumerable shale diapirs and mud volcanoes. Diapir geometry depicts welldelineated bodies usually connected with depleted feeder channels. The regional source rock for mud structures is the Maykop Formation (Late Eocene to Early Miocene, ~36-16.5 Ma). This shale-rich unit is also the major source rock for hydrocarbons in the area. Hydrocarbons are majorly stored in the PS reservoirs and are trapped by a Late Pliocene regional unconformity that represents a stratigraphic seal in the top of the PS (~3.4-3.1 Ma). This thesis has studied the Kirgan-Araz Deniz anticline (abbreviated as KAD) within the Kurdashi structure, which involves the folded PS and the Post-PS packages. Our work is based on the interpretation of over 700 km2 of seismic data from a post-stack 3D seismic dataset migrated in depth, which has been correlated with drill and logging information from the Araz Deniz IX exploration well. This valuable information has been provided by REPSOL. The fold is a NW-SE anticline located in the western margin of the SCB, in offshore Azerbaijan, to the South of the Kura River mouth. Our research is focused on the reconstruction of the threedimensional geometry of the structure, and the shape of the overpressured-mud bodies that pierce the anticline. Deformation and sedimentation rates are also estimated to reconstruct the accurate growth history of this anticline.