The Sedimentary–Migration–Igneous Hypothesis of Oil Formation

Abstract

Physical–chemical simulation of the conditions of hydrocarbon formation at the Erema–Chona oil accumulation (Lena–Tunguska petroleum province) revealed that methane and organic matter accumulates at the basin bottom at the stage of sedimentogenesis (T = 35°C, P = 0.1 MPa). At the stage of diagenesis (T = 60°C, P = 5–10 MPa) (60–100 m depth), during the formation of oil-source rocks, films and drops of oil appear and pentane C5H12 forms. At the stage of catagenesis, at 250 m depth, hexene C6H14 forms; at 2000 m, heptene C7H16; at 3100 m, octane C8H12; and at 3800 m (T = 90°C, P = 110 MPa), nonane C9H20. In the period of apocatagenesis and metamorphism at 13–15 km depth (T = 105°C, P = 450 MPa), dodecane C10H22 forms, whereas at T = 200°C undecane C11Н24 appears. With temperature and pressure increased up to 250°C and 490 MPa, respectively, at about 15 km depth, a large group of hydrocarbons forms: liquid ones include the range from dodecane C12H26 to pentadecane C15H32, while solid ones range from hexadecane C16H34 to octadecane C18H38. Finally, when the pressure reaches 850 MPa, at 25 km depth, isoprenoids ranging from nonadecane C19H40 to tetracosane C24H50 appear, as well as other hydrocarbons. Proceeding from the modeling results, it is obvious that hydrocarbon formation at depths down to 25 km cannot be explained solely by any hypothesis of organic or inorganic oil generation. A new sedimentary–migration–igneous hypothesis of oil formation is proposed. Its basic idea is that methane from the bottom of water basins and organic matter act as sources of hydrocarbons down to 3800–4000 m depth, replaced by deep mantle methane at 13–15 and 25 km depth.