The Sequence Stratigraphic Significance of Ordovician to Silurian Shale Gas Prospects in the Sichuan Basin: A Regional to Global Perspective

Gomez, Sheila; Lavender, Andrew M.; Higton, Jamie
Neftex Petroleum Consultants Ltd, Abingdon, United Kingdom.

The overwhelming success of shale gas and oil exploration in the U.S.A. has resulted in increasing global interest in unconventional resources. According to the U.S. Energy Information Administration, China is estimated to have almost 50% greater reserves than the U.S.A., thereby surpassing the potential of any other country. The Sichuan Basin, in southwestern China, contains several Palaeozoic to Mesozoic prospective shale gas horizons in both marine and non-marine settings.

Over the past four years, we have carried out an in-depth study of public domain data from China. This has involved calibration of the regional stratigraphy to our proprietary global sequence stratigraphic model by using the available biostratigraphic data. This study allows an improved insight into the shale gas opportunities in the Sichuan Basin in a global sequence stratigraphic framework. Key targets for shale gas exploration in the Sichuan Basin include the marine, organic-rich black shales of the Late Ordovician Wufeng Formation and the early Silurian Longmaxi Formation.

Using our sequence stratigraphic framework, in conjunction with our proprietary geodynamic model, we can demonstrate that the origin of these organic-rich intervals is primarily driven by global eustatic sea-level change, influenced locally by tectonic events. Potential shale gas sequences in the Sichuan Basin can be compared to examples in the U.S.A., where organic enrichment and fracability are closely tied to lithological and mechanical character, which in turn can be related to trends in relative sea level and their positions within specific sediment systems tracts.

Our results present a coherent picture of the geographic distribution and deposition of organic matter in the Sichuan Basin. In addition, the application of our global sequence stratigraphic model to the Ordovician-Silurian sequences in the Sichuan Basin is analogous to our models for the Devonian sequences in the U.S.A. and may prove to be a template for the prediction of organic enrichment in similar tectonic settings elsewhere in the Palaeozoic.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012