云南省下寒武统筇竹寺组页岩气地质成藏条件探讨

Geological conditions for shale gas accumulation in lower Cambrian Qiongzhusi Formation,Yunnan

为系统评价云南省下寒武统筇竹寺组页岩气地质成藏条件,详细踏勘了18条地质剖面,测定了110个页岩样品的有机碳含量及镜质组反射率,利用X射线衍射技术测定了22个页岩样品的矿物成分,利用压汞、氮气吸附技术分析了9个页岩样品的孔渗特征,利用扫描电镜分析了页岩的孔隙类型。结果表明:筇竹寺组地表出露点位于滇东北、滇东及滇西北,西部和南部地区由于构造作用埋深大;筇竹寺组沉积期为大面积的陆表海环境,广泛发育的陆棚环境利于有机质富集,富有机质页岩具有"四高一厚一富"的特征,优质页岩厚度大(普遍大于30m),有机质丰度高(TOC平均大于2%),有机质类型主要为Ⅰ、Ⅱ1型,有机质热演化程度高,脆性矿物含量高(平均含量大于70%),孔隙发育,连通性好,最大吸附气量平均为3.755cm^3/g。与四川盆地及北美页岩相比,云南省筇竹寺组具有良好的页岩气成藏条件,可将筇竹寺组作为页岩气勘探目的层。

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 R~ 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 envirorunent, where the widespread continental shelf environment was beneficial for the enrichment of organic matters. The organic-rich shale is characterized by large thickness （generally 〉30m）, 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.