On Thermobaric Conditions of Occurrence and Origin of Oil in the Deepwater Part of the Gulf of Mexico

The article makes an attempt to provide a genetic assessment of the deep-sea oil deposits discovered in the Gulf of Mexico based on the analysis of thermobaric conditions of oil occurrence and isotope-geochemical properties. This task is solved by means of scientific-theoretical generalization and analysis of the results of studies of the Gulf of Mexico basin carried out in recent years. It has been established that deepwater (sea depths greater than 1000 m) hydrocarbon (HC) systems have features that are not typical for hydrocarbon systems of onshore and the adjacent shallow-water shelf zone. In particular, deepwater parts have lower temperature gradients and increased formation pressures, which contribute to the preservation of liquid hydrocarbons at greater depths than previously assumed. According to the carbon isotope composition, oils of the Gulf of Mexico are of biogenic origin. The performed comparative analysis of thermobaric conditions of the deepwater parts of the South Caspian Basin (SCB) and the Gulf of Mexico showed their similar nature. However, unlike the Gulf of Mexico, low temperature gradients and increased formation pressures in the deepwater part of the CSB are associated with high sedimentation rates and a large thickness of the sedimentary complex. This, together with the predominantly gas prone organic matter of the source rocks, contributed to more intense gas formation processes in the lower parts of the sedimentary section of the SCB, which is manifested by the widespread development of mud volcanism. It is concluded that in the deepwater part of the SCB, unlike in the Gulf of Mexico, the discovery of oil deposits is unlikely.