AUTHOR=Zhang Lin , Liu Dan , Gao Yongjin , Zhang Min 

TITLE=Geochemical Characteristics of Gas and Flowback Water in Lake Facies Shale: A Case Study From the Junggar Basin, China

JOURNAL=Frontiers in Earth Science

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.635893

DOI=10.3389/feart.2021.635893

ISSN=2296-6463

ABSTRACT=<p>The chemical and isotopic compositions of the natural gas and the co-produced flowback water from the XJC 1 well in Junggar Basin, China, were analyzed to determine the origin of gases in the Permian Lucaogou Formation (P<sub>2</sub>l) and the Triassic Karamay Formation (T<sub>2</sub>k) in the Bogda Mountain periphery area of the Southern Junggar Basin. The value of carbon isotope composition of the P<sub>2</sub>l lacustrine shale gas in the Junggar Basin was between the shale gas in Chang 7 Formation of Triassic (T<sub>1</sub>y<sub>7</sub>) in the Ordos Basin and that in the Xu 5 Formation of Triassic (T<sub>3</sub>x<sub>5</sub>) in the Sichuan Basin. The difference in gas carbon isotope is primarily because the parent materials were different. A comparison between compositions in the flowback water reveals that the P<sub>2</sub>l water is of NaHCO<sub>3</sub> type while the T<sub>2</sub>k water is of NaCl type, and the salinity of the latter is higher than the former, indicating a connection between P<sub>2</sub>l source rock and the T<sub>2</sub>k reservoir. In combination with the structural setting in the study area, the gas filling mode was proposed as follows: the gas generated from the lacustrine source rocks of the Permian Lucaogou Formation is stored in nearby lithological reservoirs from the Permian. Petroleum was also transported along the faults to the shallow layer of the Karamay Formation over long distances before it entered the Triassic reservoir.</p>