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Lower Silurian Shale Gas Potential in Chongqing Southwest China: Geological Settings and Characteristics of Longmaxi Formation

Zhu, Yu; Li, Dahua; Zhou, Zhenguo; Chen, Chaogang; Yu, Heng; Luo, Fang; Cheng, Lijun

In China, Upper Yangzi area, especially Chongqing and its periphery, is one of the most prolific areas that develop shale gas. Several suits of Paleozoic marine shales developed in Yangzi platform. Most part of Chongqing is in the northwest of the platform and well developed Silurian shales. Silurian Formation is a good hydrocarbon source rock deposited in static and anaerobic settings. Lower Silurian Longmaxi Formation has most developed dark shales. Mainly locating in prolific shale gas accumulating zone in the southeast and east of Sichuan Basin, Chongqing is structurally in moderate-gentle slope of southeast structural belt and steep slope of east-northeast belt in Sichuan Basin. Experiencing multi-phases tectonic activities in evolvement, Chongqing is characterized with early subsidence, late uplifting, long subsidence period and short uplifting period. Forming in blocked and semi-blocked stagnant marine basin, Lower Silurian Longmaxi Formation is shallow-deep shelf deposit which controlled by gulf deep shelf deposit system. It's best known for potential shale gas plays regarding the thick organic rich shales with high organic matter content and high maturity. This shale mainly distributes in southeast and northeast of Chongqing with 10-200m of thickness. It successively and stably stretches in striped along north-east. The shales are mainly characterized by high content of brittle mineral compositon and type I-II1 Kerogen. The average TOC in shale is about 1.8-5.4% and average Ro is about 2.1-3.7%. The shales also have storage for both free gas and adsorbed gas. Therefore, Lower Silurian Longmaxi Formation in the area of southeast and northeast of Chongqing, are currently most prospective shale gas targets.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013