--> Abstract: Fluid Properties Indicated by Natural Gas Isotopes in Gulf of Mexico, by Xinyu Xia, Daniel M. Jarvie, and Yongchun Tang; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Fluid Properties Indicated by Natural Gas Isotopes in Gulf of Mexico

Xinyu Xia1; Daniel M. Jarvie2; Yongchun Tang1

(1) PEER Institute, Covina, CA.

(2) Worldwide Geochemistry, LLC, Humble, TX.

Fluid properties in the petroleum reservoirs changes rapidly along both horizontal and depth profile of Gulf of Mexico (GOM)shore; the heterogeneous distributions of associated gas, wax, and asphaltene increase the exploration risks. Detailed understanding of the processes of petroleum generation, migration, and reservoir alteration is necessary to predict the occurrence of these hazardous substances and to lowering the risks of exploration.

Kinetics of oil and gas generation from different source rocks in GOM were investigated by pyrolysis of various organic matters. The samples for primary cracking (oil and gas generation from kerogen) include several types of immature sources rocks from Cretaceous and Jurassic formation of Garden Banks 754 #1 well, and other comparable immature source rocks such as the Monterey Shale. The samples for secondary cracking (gas generation from oil) include several oil samples from Gulf of Mexico. Hydrocarbon potential, including gas/oil ratio, are derived from the kinetic model for the petroleum plays from different source rocks under different thermal history.

For the alteration of petroleum reservoirs, we investigated the natural gas data and fluid properties, and revealed that the extent of biodegradation can be quantitatively expressed by the relation between the carbon isotope composition of methane and ethane. Meanwhile, the relation between the carbon isotope composition of propane and ethane provides quantitative results of oil cracking. These results are further related to the amounts of asphaltene and associated gas in reservoirs.

As a result, we established the calibrated model to predict the fluid properties in offshore Gulf of Mexico based on geochemistry of associate gas. The results were tested in several case studies.