--> The Origin of Supergiant Hydrocarbon Accumulations (Isotope Geochemical and Geodynamic Aspects) Title

Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins

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The Origin of Supergiant Hydrocarbon Accumulations (Isotope Geochemical and Geodynamic Aspects) Title

Abstract

Half a century ago, the largest petroleum geologist of the USA Hollis Hedberg at the end of his great review of the geological aspect of the origin of petroleum has formulated the main conclusion — a variety of petroleum genesis connected, associated with different processes of their formation from different kinds of organic matter, accumulated and transformed into different geological environments, in different thermodynamic conditions, with different mechanisms of petroleum migration. In fact, H. Hedberg suggested the idea of some kind of petroleum polygenesis. The main task of further research on this problem, he stated that way: “The need is to arrive at general principles which singly or in combination may have been the major contributors to the genesis of the great bulk of the world's petroleum.” (Hedberg, 1964, p. 1798). For the last years, a great deal of information was accumulated on the environments of origin, not only oil but also gas and condensate in their deposits and fields. In the last decade non-traditional fields and unconventional resources began to exploit more and more extensive. Tight gas and oil, shale gas and oil, water-dissolved gas had its own specific of the genesis and the formation of their accumulations. Particular importance should be paid to heavy oil and gas hydrates, the main accumulations of which are found in the near-surface interval of the sedimentary section and were formed in the absence of covers and structural traps. Their huge resources spread very unevenly and show superimposition of the processes of oil-gas accumulation with respect to rock sections of oil-gas regions in general. Mud volcanoes demonstrate their role in large-scale discharges of hydrocarbon fluids in the formation of gas condensate and oil-gas fields. Energetic of the invasion of these fluids is shown for abnormally high reservoir pressure in the active geodynamic regions from the deepest to the subsurface horizons of the sedimentary section. Discharges of hydrocarbon fluids may participate in the enrichment of organic matter and bituminous components of sedimentary complexes from the stage of sedimentation. At catagenesis stages their flows can participate in the formation of shale oil and gas, equally with other varieties of traditional and non-traditional fields. The explanation of the genesis of the great bulk of the hydrocarbon resources of traditional and non-conventional types now requires participation of deep hydrocarbon fluids, the genesis of which may be connected with both juvenile and recycle sources of carbon and hydrogen (Carbon in Earth, 2013). H. Hedberg in one of his articles put forward the idea of the relation of the genesis of petroleum with the recycling of organic matter in subduction zones in the form of witty illustration — figure. This idea was further supported and developed of a number of researchers. However, the traditional interpretation of the isotopic composition of helium as a criterion of deep mantle processes did not contribute to the use of this method of research in petroleum geology. We have made multiregional generalization of the published data on isotopic composition of helium in the gas composition of oil-gas fields. The results of an alternative interpretation of these data were presented at a number of international conferences (Valyaev, Dremin 2013, 2015a, 2015b. 2016). They coordinate with the recycling of crustal material in the processes of generation of deep hydrocarbon fluids. The results of the interpretation of isotope-helium and carbon-helium data made it possible to distinguish two types of oil and gas regions with moderate (less than 0.1 Ra) and high (0.1-6.5 Ra) values of the isotope-helium ratios (3He/4He). These types correlate with two types of hydrocarbon branch of degassing of the Earth and differences in geodynamic conditions of recycling processing of crustal material. Counter convective recycling determines the scales and polygenesis of the processes of oil and gas generation and oil and gas accumulation, including the processes of formation of super giant hydrocarbon accumulations and resources. Conclusions 1. A variety of oils processes and environments of the formation of their deposits even to a greater extent manifested in the formation of complex oil and gas accumulations of traditional and non-traditional types. In recent studies, the idea of some kind of polygenesis of petroleum put forward by H. Hedberg is developed in a number of concepts mixed and hybrid formation of oil-gas fields, as well as in concepts of polygenesis (A. Dmitrievsky and others). 2. The problem of the “genesis of the great bulk of the world's petroleum” formulated by H. Hedberg now refers to the resources of traditional and non-traditional oil-gas fields in general. Its solution will obviously require the use of the processes of convectional recycling and mantle-crust interaction in the formation of these fields and resources.