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Semi-open hydrous pyrolysis experiments on coal-measure source rocks in the Xihu Sag were conducted to investigate the carbon isotope evolution of kerogen, bitumen, generated expelled oil, and gase...

The Lower Yangtze is considered as a potentially productive shale gas area in China, but only limited research has thus far been carried out there. On the basis of a detailed investigation of fourteen outcrops, eight lithofacies in the Hetang Formation (510–541 Ma), the Gaojiabian Formation (430–443.4 Ma), the Gufeng Formation (270–281 Ma) and the Dalong Formation (252–263 Ma) have been identified: silicalite, siliceous non-calcareous mudstone, siliceous shale, carbonaceous shale, calcareous mudstone, silty–shaly interlaminated mudstone, siltstone and limestone. Three types of fossils were also found in the four formations: sponge spicules, radiolarians and graptolites. Moreover, four key outcrops of the fourteen were suitable for more additional detailed analyses and interpretation of their depositional environments and plausible sequence of the stratigraphic system tracts. As a result, the four potential shale gas formations were all divided into third-order sea-level sequences. Every third-order sequence was further divided into four system tracts, corresponding to an early transgressive system tract (ETST), a late transgressive system tract (LTST), an early highstand system tract (EHST) and a late highstand system tract (LHST). On the basis of the interpretation of the lithofacies and depositional environments in the western area of the Lower Yangtze, sediments can be related to hydrothermal and biological processes, terrigenous clastic input and calcium compensation. These processes were interpreted to occur in a sequential order that we divide into three stages. The ETST period was the first stage, in which hydrothermal upwelling from the open ocean produced a siliceous lithological combination. During the second stage corresponding to the LTST + EHST, our results suggest that some biological communities in the stable deep water provided plenty of organic-rich matter. The LHST period was the third stage, in which terrigenous clastic material was deposited close to the land, and some carbonate sediments began appearing near the platform. Copyright © 2014 John Wiley & Sons, Ltd.

The Yuanba Gas Field is the second largest natural gas reservoir in the Sichuan Basin, SW China. The vast majority of natural gas reserve is embedded in the Changhsingian platform marginal reef complexes. Integration of facies analysis, well-seismic calibration, well logs, seismic profiles, and RMS attribute allows reconstruction of the reef complex structure, and five growth cycles of overlapping accretionary reefs are recognized. The carbonate platform margin reef complex comprises reef core, fore reef and back reef facies associations. The retrograding–prograding growth pattern and northwesterly migrating trends of overlapping accretionary reefs were likely controlled by short-term sea-level changes superimposed by local currents prevailing in the eastern Palaeotethyan Ocean. Copyright © 2012 John Wiley & Sons, Ltd.