Fault Pattern and Structure Configuration of Apsheron Sill, South Caspian Basin, New Insight from High Quality OBN Seismic

Abstract

Abstract As one of the major oil-producing belts in the South Caspian basin, the Apsheron Sill holds tens of structure-related reservoirs which are closely originated with the tectonic evolution and performed complex fault patterns. Previous study paid high attention to the east Azerbaijan area with reporting lots of case study, however, the west Cheleken peninsula is still in high ambiguity. To enhance understanding of the east Apsheron ridge, an integrated study is conducted mainly based on new acquired 3D OBN seismic in Cheleken concession. The AI-based technology is adopted to illustrate the complex fault system for the first time with using huge database of similar structure cases. Seismic geometrical attributes and RGB fusion method are used to demonstrate the fault assemblage. Analogue study was also carried out between the Cheleken faults and physical stimulation, aiming to better understand the geometrical and kinetic feature. Furthermore, the structure reconstruction technique is used to capture the strati-structure evolution. According to this study, two typical fault patterns are identified, positive flower structure cut in the middle-deep red series, and negative flower structure bearing in Apsheron-middle red bed series. The flower structure sometimes shows the schematic of complex palm-tree. These two sets of structure patterns represents the trans-pression in early-middle Pliocene and trans-extension in the late Pliocene-Pleistocene. Some detached faults cut from Apsheron stratigraphic interval and terminated at CH1 shale which related to the later regional extension and strain releasing. In Cheleken concession, two fault belts are identified, Zhdanov in the north and Lam in the south. Some transform faults occurs between these two belts to accommodate the lateral strata shearing or rotation. In the map view, fault assemblage performs feature of en-echelon and horsetail spray, which represents the dextral strike-slip of Apsheron Sill. Typically, the Lam and Zhdanov reservoirs are fault-derived structure with continuous growth from middle Pliocene to late Pleistocene. Occurrence of mud volcano in the concession indicates the faults are still active. For the first time, this study gives systematic illustration on the fault pattern and structure configuration of the east Apsheron Sill in terms of good image OBN seismic. The enhancement in structure feature could facilitate the current producing and help de-risk drilling hazards. Furthermore, it would also provide new insight for adjacent reservoirs from the aspect of regional tectonic understanding and structure configuration.