Abstract: A lot of researches were conducted so as to systematically evaluate the geological conditions for shale gas accumulation in the lower Cambrian Qiongzhusi Formation, Yunnan province, including field surveys on 18 geological sections, TOC and Ro measurements on 110 shale samples, mineral composition measurement on 22 shale samples with X-ray diffraction technique, porosity and permeability analysis on 9 shale samples with mercury intrusion porosimetry (MIP) and nitrogen adsorption techniques, and shale pore type analysis with SEM. The results show that the Qiongzhusi outcrop is located in the northeastern, eastern and northwestern parts of Yunnan, and is deeply buried in the western and southern parts due to tectonic movements. The Qiongzhusi Formation was deposited under a broad epicontinental sea environment, where the widespread continental shelf environment was beneficial for the enrichment of organic matters. The organic-rich shale is characterized by large thickness (generally>30 m), high organic matter abundance (average TOC>2%), high thermal evolution of organic matters (mainly Type Ⅰ and Ⅱ₁ ), high content of brittle minerals (averagely>70%), well-developed pores with good connectivity, and the maximum adsorbed gas of 3.755 cm³/g on average. Compared to the shale in the Sichuan Basin and North America, the Qiongzhusi Formation in Yunnan holds good shale gas accumulation conditions and can be considered as the target for shale gas exploration.

Key words: shale gas, accumulation conditions, Qiongzhusi Formation, Yunnan, organic-rich shale