Gas Components Variation and Isotopic Fractionation in the Course of Shale Gas Migration and Transportation by Short Distance

Abstract

Shale gas exists short-distance migration and transportation in the same set of shale reservoirs. However, there are few reports on the geochemical evidences of shale gas short-distance migration, especially the variation of gas components and isotopic fractionation. It is of great significance to indicate migration path and reveal accumulation mechanism of shale gas. Take the Wufeng-Longmaxi shale gas in Jiaoshiba, Changning, Weiyuan and Dingshan block an example, this project firstly investigates basic well information in different tectonic positions, and core sampling is carried out in typical wells. Then gas chromatography and isotopic analytical are conducted to obtain shale gas components and isotopes of methane, ethane, propane and hydrogen. Thirdly, compare the six indexes of methane content, dry coefficient and as well as methane, ethane, propane and hydrogen isotopes among the uplift, slope and sag for the same shale gas reservoir, to make clear the existence of short-distance migration under the guidance of isotope fractionation theory. Finally, combine the physical character differences and the distribution of faults and fractures, revealing the migration path by short distance in each shale gas reservoir. The forecast result is that shale gas migrates laterally along stratification, faults and fractures. In the process of short-distance migration, from the sag to the slope until the uplift, methane content and drying coefficient will increase, and the gas isotopes will decrease resulting from the isotopic fractionation. This project will not only theoretically supplement shale gas migration and accumulation mechanism, but also provide guidance for shale gas exploration and sweet spot evaluation in the Sichuan Basin.

AAPG Datapages/Search and Discovery Article #90351 © 2019 AAPG Foundation 2019 Grants-in-Aid Projects