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Sichuan Basin

The Sichuan Basin located in the central Sichuan Provence of China is a prolific natural gas producing basin. The basin is large covering an area of 230,000km2 and having proven natural gas reserves of 3.69 trillion cubic meters. China's basins are grouped into three main types tensional, compressional and transitional. The Sichuan basin and other central Chinese basins are included in the transitional type of basin. These central basins have been affected by Eurasian plates for the the west and The pacific plate from the east. Thus creating a basin that is both compressional and tensional

File:Sichuan Basin general location map
The Sichuan basin is located in central China with the large city of Chengdu located within the province. (Courtesy of Encyclopedia Britannica 2021)


Tectonic History

The Sichuan basin resided on the western portion of the Yangtze platform during the Paleozoic and early Mesozoic. From the Sinian to Middle Triassic time shallow marine carbonate sedimentation occurred. [1]. The evolution of the Sichuan basin has dual compressional and tensional characteristics cause by both trans-Eurasia Tethys tectonism from the west and the circum-Pacific tensional. A series of thrust fault zones along the western side of the Sichuan basin resulted from the northward moving Indian Plate The petroleum geologic characteristics of Sichuan basin, central China (Conference) [2]

Petroleum Geology

Source Rocks

The US Geological survey assessed the source rock for conventional oil and gas fields in the Sichuan basin. Their assesment from the Lower Cambrian Qiongzhusi Formation, the Upper Ordovician and lower Silurian Wufeng and Longmaxi Formations, and the upper Permian Longtan and Dalong Formations showed organic-rich shales to be the source rock for these areas. They further surveyed these areas for potential uconventional production. The US Geological Survey reports that the organi-rich shales for three of the formations (Qiongzhusi, Wufeng, and Longmaxi) were deposited in deep marine depocenters on the continental shelf near the early Paleozoic Gondwana margin. The fourth formation (Longstan) is a coal-bearing marginal marine to deltaic source rock which also consists of a considerable amount of organic-rich deep marine facies containing Type II organic matter. The fifth formation (Dalong) also has source rock of organic-rich marine shale. [3]

The quality of the source rock in Longmaxi Formation is high quality with a TOC (total organic carbon) up to 6.5%. Tests have shown the source rock yielded rich thermognic during its geological evolution and has some silt composed of up to 40% quartz mineral. These factors combine to demonstrate a source rock with rich organic matter, high thermal maturity degree, and good pool. Because of the type of source rock as well as its basin type, seal conditions, and other factors, the Sichuan Basin is similar to the Michigan and San Juan Basins in the USA. [4]

Traps and Seals

Conventional fields of the Sichuan Basin have traps in anticlines and buried hills. Nonassociated gas traps are found in tightly compressed, faulted anticlines often having surface expression. Stratigraphically trapped accumulations are recognized in several fields. In the Lower and Middle Triassic evaporite beds make excellent seals. These evaporite beds are thickest where 2200 to 3000 m of Lower and Middle Triassic strata accumulated. Some remnants of evaporite-bearing strata at various outcrop locations suggest that the evaporite beds are regional seals. The Feixianguan Formation in the Lower Triassic contains red shale and mudstone which makes another seal practically basinwide. Other seals are provided by Cambrian and Silurian shale beds as thick as 500 m. The effectiveness of these shale and evaporite seas are shown in the abundant gas that remains trapped in the basin. [5]

Future Risks and Uncertainties

As with any energy development there are risks to the climate, landscape, and water. The size of the Sichuan Basin shale reserves is one of the largest in the world. Its impact on the environment of the area is an uncertainty. China is a large and growing nation with large and growing demands on its natural resources.  New technology in the energy industry is allowing more of these resources to be developed

References

  1. Charpentier, R.R., Schenk, C.J., Brownfield, M.E., Cook, T.A., Klett, T.R., Pitman, J.K.,  and Pollastro, R.M., 2012, Assessment of undiscovered conventional oil and gas resources of six geologic provinces of China, 2011: U.S. Geological Survey Fact Sheet 2012-3117, 4 p., https://pubs.er.usgs.gov/publication/fs20123117
  2. Sheng, Li De. The petroleum geologic characteristics of Sichuan basin, central China. United States: N. p., 1991. Web.
  3. Potter, C.J., Schenk, C.J., Charpentier, R.R., Gaswirth, S.B., Klett, T.R., Leathers, H.M., Brownfield, M.E., Mercier, T.J., Tennyson, M.E., and Pitman, J.K., 2015, Assessment of Paleozoic shale gas resources in the Sichuan Basin of China, 2015: U.S. Geological Survey Fact Sheet 2015–3053, 4 p.,
  4. Hu, Hai Yan, et al. “Accumulated Conditions of Shale Gas in the Middle-Low Palaeozoic, Yangtze Platform, China.” Advanced Materials Research, vol. 524–527, Trans Tech Publications, Ltd., May 2012, pp. 122–125. Crossref, doi:10.4028/www.scientific.net/amr.524-527.122.

External Links

https://pubs.usgs.gov/of/1994/0426/report.pdf

https://www.osti.gov/biblio/7024946-petroleum-geologic-characteristics-sichuan-basin-central-china

https://pubs.er.usgs.gov/publication/fs20153053

https://www.scientific.net/AMR.524-527.122

  1. Charpentier, R.R., Schenk, C.J., Brownfield, M.E., Cook, T.A., Klett, T.R., Pitman, J.K.,  and Pollastro, R.M., 2012, Assessment of undiscovered conventional oil and gas resources of six geologic provinces of China, 2011: U.S. Geological Survey Fact Sheet 2012-3117, 4 p., https://pubs.er.usgs.gov/publication/fs20123117
  2. Sheng, Li De. The petroleum geologic characteristics of Sichuan basin, central China. United States: N. p., 1991. Web.
  3. Sheng, Li De. The petroleum geologic characteristics of Sichuan basin, central China. United States: N. p., 1991. Web.
  4. Hu, Hai Yan, et al. “Accumulated Conditions of Shale Gas in the Middle-Low Palaeozoic, Yangtze Platform, China.” Advanced Materials Research, vol. 524–527, Trans Tech Publications, Ltd., May 2012, pp. 122–125. Crossref, doi:10.4028/www.scientific.net/amr.524-527.122.
  5. Charpentier, R.R., Schenk, C.J., Brownfield, M.E., Cook, T.A., Klett, T.R., Pitman, J.K.,  and Pollastro, R.M., 2012, Assessment of undiscovered conventional oil and gas resources of six geologic provinces of China, 2011: U.S. Geological Survey Fact Sheet 2012-3117, 4 p., https://pubs.er.usgs.gov/publication/fs20123117