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6079114 
Journal Article 
Generation and Migration of Petroleum 
Selley, RC; Sonnenberg, SA; Selley, RC; Sonnenberg, SA 
2015 
Academic Press 
Boston 
Elements of Petroleum Geology (Third Edition) 
191-253 
WOS:000409115300006 
Any theory of petroleum generation must explain the following geologic observations: most accumulations of hydrocarbons occur in sedimentary basins; in many cases hydrocarbon accumulations are completely encased by impermeable sedimentary rocks; and commercial accumulations in the basement are always in lateral continuity with sedimentary rocks. Thus, the majority of commercial quantities of petroleum are formed by thermal maturation of organic matter. The major groups of chemicals that occur in organic matter in plants and animals are proteins, carbohydrates, lipids, and lignins. These chemicals constitute the organic matter, which is transformed into kerogen with burial diagenesis. The amount of organic matter buried in sediments is related to the ratio of organic productivity and destruction. The preservation of organic matter in seas and oceans is favored by anoxic bottom conditions and rapid sedimentation rates. Four major settings for anoxic environments favorable for the preservation of organic matter in sediments are: stratified lakes, barred basins, continental shelves with upwelling, and ocean basin anoxic events. The organic productivity and preservation in continental environments occurs mainly in swamps. Formation of kerogen occurs in the shallow subsurface at near normal temperatures and pressures. It involves biogenic decay of organic matter. Methane, carbon dioxide, and water are given off by the organic matter, leaving a complex hydrocarbon termed kerogen. This major phase in the evolution of organic matter in response to burial is called diagenesis. Three types of kerogen are identifiable: type I (algal), type II (liptinitic), and type III (humic). Type I tends to generate oil; type II generates oil and gas; and type III generates gas. This stage is followed by the catagenesis stage, which occurs in the deeper subsurface as burial continues and pressures increase. Petroleum is released from kerogen during catagenesis. Oil generation occurs between 60°C and 120°C, and gas generation between 120°C and 225°C. An empirical relationship between oil occurrence and clay dehydration suggests that flushing of water from compacting clays plays an important role in primary migration. The third stage verging on metamorphism is called metagenesis and is a stage where generally only methane is expelled. Petroleum migration involves primary and secondary migration. Primary migration is the emigration of hydrocarbons from the source rock (shales) into permeable carrier beds (sandstones and limestones). Secondary migration refers to subsequent movement of oil and gas within permeable carrier beds and reservoirs. Primary migration theories are debated but include: expulsion as protopetroleum; expulsion as petroleum in solution; expulsion as globules of oil in water; and expulsion as a continuous phase. 
Clay dehydration; Diagenesis, catagenesis, metagenesis; Expulsion of oil; Kerogen; Maturity of source rocks; Organic matter; Organic productivity; Proteins, carbohydrates, lipids, and lignins 
Sonnenberg, Stephen A.