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1 Chevron Energy Technology Company, 1500 Louisiana Street, Houston, Texas 77002; BarryKatz{at}Chevron.com
2 Chevron International Exploration and Production Company, 1500 Louisiana Street, Houston, Texas 77002
Barry Jay Katz received his B.S. degree in geology from Brooklyn College and his Ph.D. in marine geology and geophysics from the University of Miami. He has held various technical and supervisory positions in Texaco's, ChevronTexaco's, and Chevron's technology organizations since joining Texaco in 1979. Barry is currently a Chevron Fellow and team leader for hydrocarbon charge in Chevron's Energy Technology Company.
Vaughn Robison received his Ph.D. in geology from the University of Oklahoma. After beginning his career conducting geochemical research as part of Texaco's Technology organization, he has been part of exploration teams working west Africa and the Gulf of Mexico. He is currently an area manager for the Global Exploration New Ventures Team in Chevron's International Exploration and Production Company.
As exploration migrates into deeper water, crude-oil quality becomes increasingly important. Variations in oil quality, which are reflected in such properties as API gravity, viscosity, sulfur content, and acid number impact both value and producibility. In fact, issues of oil quality in deep water may, in some cases, be more critical than issues of hydrocarbon volume. Problems associated with deep water are commonly thought to be amplified largely as a result of the expansion of the biodegradation window. The expanded window is a result of lower temperatures at the mud line. A review of data from the Gulf of Mexico and the Gulf of Guinea reveals that other factors may have a greater influence on oil quality. For example, in the Gulf of Mexico, strong evidence exists that the nature of the source rock is a major factor in establishing sulfur content and API gravity. Oils derived from an Upper Jurassic Oxfordian calcareous source rock generate oils with higher sulfur contents than those derived from Cretaceous argillaceous source rocks. In the Gulf of Guinea, although many of the newly discovered pools are shallowly buried and evidence for biodegradation exists, crude-oil quality is mitigated by multiple charging events. In both regions, evidence also exists for phase segregation, which introduces light oils and condensates into the shallow part of the sedimentary sequence. Both phase segregation and multiple charging events appear to be largely a result of an individual trap's structural evolution. The available data, therefore, suggest that some of the risks associated with oil quality may be reduced through a more detailed assessment of a prospect's filling history and structural evolution and an understanding of the nature of the source facies. However, there clearly are such situations as offshore Brazil, where the risks associated with oil quality appear more difficult to mitigate.
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  B. J. Katz, J. J. Meneses-Rocha, and U. Hernandez-Romano A review and technical summary of the AAPG/Associacion Mexicana de Geologos Petroleros Hedberg Research Conference on heavy oil: Origin, prediction, and production in deep waters AAPG Bulletin, October 1, 2007; 91(10): 1437 - 1447. [Abstract] [Full Text] [PDF]
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