Distribution, Depositional Environments and Organic Matter Enrichment of Marine Shale in China

Abstract

Marine organic-rich shale is the main target for shale gas exploration in China and commercial production has been achieved in South China. It is of great significance for shale gas exploration to investigate the distribution, analyze their depositional environments and understand the enrichment mechanics of organic matter of the marine shale in China. Marine deposition in China predominantly distributes in the three cratonic areas, i. e. Yangtze, the North China and Tarim cratons. The strata correlation between those in three cratons shows that the marine organic-rich shale mainly occurs in the Yangtze and Tarim areas, but does not in the North China area. In the Yangtze area, the Lower Cambrian and Upper Ordovician to Lower Silurian are main horizons of marine organic-rich shale. The Lower Cambrian organic-rich shale mainly distributes in northern Shichuan Province (Qiongzhuoshi Fm.), Guizhou Province and western Hunan Province (Niutitang Fm.), western Hubei Province (Shuijingtuo Fm.), western Zhejiang Province and southern Anhui Province (Hetang Fm.), southern and northern Jiangshu Province (Mufushan Fm). The Upper Ordovician to Lower Silurian distributes in the Middle-Upper Yangtze area (Wufeng Fm. (O3w) and Longmaxi Fm. (S1l)), and the Lower Yangtze area (Wufeng Fm. (O3w) and Gaojiabian Fm. (S1g)). In the Tarim area, the Lower Cambrian and Lower Ordovician are main strata of marine organic-rich shale. The Lower Cambrian and Lower Ordovician organic-rich shale mainly distributes in Manjiaer depression (Xidashan Fm (ϵ1x), Heituwa Fm. (O1h)) and northern Tarim (Yuertushi Fm. (ϵ1y), Shaergan Fm. (O1s)). These organic-rich shale deposited in different environments, including deep shelf, deep shelf with hydrothermal activity, shallow shelf and restricted shelf bay. The depositional environments for most of the Lower Cambrian are characterized by deep shelf with hydrothermal activity in the northern Tarim and the southeastern Yangtze, and for the Lower Ordovician and the Lower Silurian by the restricted shelf bays in both Yangtze and Tarim. There are different enrichments of TOC in the shale depositing in the different environments. There is the highest TOC in the shale depositing in the deep shelf with hydrothermal activity, reaching 5–15%, and then in that in the restricted shelf bays, reaching 4–5%. The TOC in the shale of the normal deep and shallow shelf is usually 2–5% and <0.5–2.5%, respectively.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015