Analysis of organic inclusions using fluorescence microscopy and micro-FT. IR techniques

Abstract

Organic inclusions from the Shahejie Formation of the Eogene period in the Bohai Gulf Basin, eastern China, were examined using micro-FT. IR and fluorescence microscopy in addition to the measurement of their homogenization temperatures (T h). Two populations of organic inclusions were recognized, the primary and the secondary organic inclusions. The primary organic inclusions contain organic materials with relatively long alkyl chains ( the carbon atom number is 15 to 17), whereas the secondary organic inclusions contain a certain amount of H2S besides organic materials which have relatively short alkyl chains with the carbon atom number of 5 to 6. The Th values of the primary organic inclusions are within the range of 87–91°C, lower than those of the secondary organic inclusions (T h = 98–105°C ), suggesting that the primary organic inclusions experienced a lower degree of thermal evolution than the secondary inclusions. This inference is consistent with the fluorescence spectroscopic characteristics and parameters (T max Q values) of the organic inclusions. Data from the organic inclusions together with the petroleum geology setting revealed that the primary inclusions resulted from the migration of hydrocarbons generated within the strata they are hosted, whereas the secondary organic inclusions were trapped in the process of secondary hydrocarbons expelled out of the source rocks to the locations where they were accumulated. The thermal properties of the organic inclusions are consistent with the maturation of the oil generated from the Shahejie Formation. The abundance of the organic inclusions and their characteristics indicate that the member Es3 of the Shahejie Formation is highly potential for oil accumulation. The results could provide essential clues to petroleum exploration in the Bohai Gulf Basin.