The Upper Ordovician-Lower Silurian Longmaxi Shale in the Upper Yangtze block represents one of the most important shale gas plays in China. The shale composition,porosity,organic thermal maturity,and methane sorption were investigated at the Qilongcun section in the Dingshan area,southeastern Sichuan Basin. The results show that the Upper Ordovician-Lower Silurian Longmaxi Shale contains:(1) sapropelic I organic matter;(2) a 40-m thick bedded sequence where total organic carbon(TOC) content is > 2%;(3) a 30-m thick layer at the base of the Longmaxi Shale with a brittle mineral content higher than 50%; and(4) a mean methane adsorption capacity of 1.80 cm^3/g(7 MPa pressure). A positive correlation between TOC and sorbed gas indicates that organic matter content exerts an important control on methane storage capacity. Based on the analysis of the shale reservoir characteristics,the lower member of the Longmaxi Shale can thus be considered a favorable stratum for shale gas exploration and exploitation. It has similar reservoir characteristics with the Longmaxi Shale in the Jiaoshiba area tested with a high-yield industrial gas flow. However,based on tectonic analysis,differences in the level of industrial gas flow between the low-yield study area and the high-yield Jiaoshiba area may result from different tectonic preservation conditions. Evidence from these studies indicates the shale gas potential of the Longmaxi Shale is constrained by the reservoir and preservation conditions.
四川盆地西部的上三叠统须家河组作为反演前陆盆地构造演化的物质基础,因缺少精确的同位素地层年龄阻碍了对盆山演化的进一步理解.作者在四川盆地西部须家河组中发现了一套火山（碎屑）岩夹层,通过LA -IC P-M SU -Pb同位素定量分析,获得1 件凝灰岩样品中岩浆锆石的结晶年龄,其加权平均值为（214. 7 ± 1. 6） M a,属于晚三叠世诺利期.该年龄结果对四川盆地西部须家河组岩石地层单元的划分与对比可提供重要参考,同时为进一步约束龙门山隆升与川西前陆盆地的演化、古特提斯洋关闭等重大事件时限提供了新证据.基于四川盆地及周缘的区域火山活动对比结果,表明诺利期中期（210-222 Ma B. P .） 是中国西部地区一次强烈的区域火山喷发阶段,其范围从羌塘地体延伸到东E 仑地体,所对应的构造事件并非传统的印支运动作用.
The Upper Ordovician–Lower Silurian mudstones(including the Wufeng, Guanyinqiao and Longmaxi Formations) in the Sichuan Basin are some of the most important shale gas plays in China. In order to enhance our understanding of the process of formation of organic carbon up to 10%, optical, microscopy and geochemical methods have been used to investigate the petrographic and geochemical characteristics of the formation. Firstly, three mudstone lithofacies were identified based on a wide variety of mudstone laminations. These are:(a) indistinctly laminated mudstone;(b) parallellaminated mudstone; and(c) nonparallel-laminated mudstone. Then, combining with the evidence from depocenter migration, Th/U ratios and total organic carbon, the abundant organo-minerallic fabrics suggest that organic carbon was preferentially deposited and preserved in anoxic, low energy and stagnant water conditions during deposition of the Wufeng and Longmaxi Formations. On the contrary, the Guanyinqiao Formation with poor organic carbon was deposited in oxic and high-energy water conditions.
Lei YangBo RanYu-Yue HanShu-Gen LiuYue-Hao YeChristopher XiaoWei SunDi YangGuo-Dong XiaShi-Yu Wang
