A new look at the components of the petroleum system of the South Caspian Basin

Detailed knowledge of the petroleum systems of mature petroleum provinces is often lacking. This has often resulted from the early discovery of most of these provincesʹ reserves. The South Caspian basin represents one such province. The “modern” era of petroleum exploration in the South Caspian began more than 100 years ago. Even with this long history several aspects of the petroleum system have remained largely speculation. Among the key questions are:• s the primary hydrocarbon source for the region? and when has hydrocarbon generation taken place? ploration be extended beyond known stratigraphic and areal limits? integrated geologic and geochemical studies have attempted to answer these and other questions for the petroleum system of the South Caspian basin. These studies attempted to overcome prior problems associated with limited sample availability, severity of surface weathering, data quality and completeness. This study confirmed the Maykop Suite as the primary oil source, but restricted its stratigraphic distribution. Organic carbon content within the Maykop ranged upward to 14.28 wt.%, with hydrocarbon generation potentials (S2) approaching 75 mg HC/g rock. Source rock deposition was cyclic and included both oil- and gas-prone episodes. Geochemically, the regionʹs oils are highly variable as a result of their complex and variable migration and alteration histories rather than their derivation from multiple source rock units. The oils display similar molecular and isotopic compositions to the extracted Maykop samples confirming their genetic relationship. The range in carbon isotope values reflects secular changes within the Maykop Suite source. Unlike some earlier studies, this study showed that all of the oils were generated within the conventional “oil-window” (Ro≈0.9–1.0%). This places the source system at depths in excess of 5 km and emphasizes the role that vertical migration played in the development of the basinʹs hydrocarbon accumulations. There is evidence that migration was episodic, possibly related to punctuated generation or the opening of conduits through the activity of mud diapirs. Model results also suggest that the rapid Plio–Pleistocene subsidence and sedimentation were the primary controls on hydrocarbon generation. and other geochemical investigations confirm the potential for the extension of the known petroleum system beyond its current stratigraphic and areal limits.