--> Abstract: Comparison of Generated, Charged and Present Reservoir Gases in Ordos Upper Paleozoic Coal-Generated Gas Field: Revelation of Formation Processes, by Ping'an Peng, Yanhua Shuai, Se Gong, and Yanrong Zou; #90039 (2005)

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Comparison of Generated, Charged and Present Reservoir Gases in Ordos Upper Paleozoic Coal-Generated Gas Field: Revelation of Formation Processes

Ping'an Peng, Yanhua Shuai, Se Gong, and Yanrong Zou
SKLOG, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China

The study of gas formation processes is difficult simply because of the simple compositions and carbon isotope ratios of gases. The present paper, a formation process of Ordos Upper Paleozoic gas field is investigated by comparison of generated, charged and present reservoir gas. The compositions and carbon isotope ratios of gas generated were obtained by means of kinetic modeling of gas generation from source rock coal measure. The compositions and isotope ratios of gas in inclusion represent those filled to the reservoir. The massive data of gas compositions and carbon isotope ratios in present reservoir are readily available in the literatures. The comparison between generated gas and inclusion gas gains insights into the primary migration process while the comparison between inclusion gas and reservoir gas gives the clues for second alteration of gases. The results show that primary migration did not affect the carbon isotope ratio of methane and ethane but did change the composition of gas significantly. The generated gas was much wetter than it was in inclusion. Regarding to the second alteration of the gas field, Ordos Basin was uplifted after 100ma; and many geologists thought that the second alteration would significantly change the gas compositions and carbon isotope ratios in reservoir. However, the gases in inclusion and in reservoir are similar either in compositions or carbon isotope ratios, which imply that the second alteration did not take effect. This is consistent with the low porosity and permeability of reservoir of this large gas field. When gas charged into the reservoir it is difficult to release afterwards.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005