鄂西咸丰地区上奥陶统五峰组-下志留统龙马溪组页岩非均质性特征

Anisotropic Features of Shale in Wufeng Formation-Longmaxi Formation in Xianfeng Area,Western Hubei

页岩非均质性特征对页岩气的聚集、保存以及后期生产压裂等均有重大影响,因此在研究咸地2井五峰组-龙马溪组页岩非均质性特征基础上,分析探讨其对本区页岩气富集的影响。以咸地2井层序识别为基础,从宏观和微观两个方面阐述了本区页岩非均质性的特征。宏观非均质性特征为:砂质条带发育情况和黄铁矿发育情况具有一定的负相关性;页理发育多少与黄铁矿发育含量之间大致呈正相关性、与砂质条带发育情况基本呈现负相关性。砂质条带代表的陆源供给增大、水动力环境增强的沉积环境,不利于黄铁矿以及页理的发育。微观非均质性特征为:TOC含量自下而上为先增加后急剧减少到平稳减少,然后逐渐略微增大;五峰组-龙马溪组脆性矿物海侵体系域较高位体系域发育,石英含量海侵体系域较高位体系域发育,五峰组脆性矿物(石英+长石+碳酸盐+黄铁矿)自下而上含量增大,龙马溪组脆性矿物从下往上总体呈减小趋势,但在龙马溪组中部呈现两个阶段的脆性矿物含量变大过程。石英含量与TOC之间有较好的正相关关系,而与黏土含量的相关性不明显,这种相关性由五峰组-龙马溪组环境所控制。

Anisotropic features of shale have major impact on shale gas accumulation, preservation, later stage production and fracturing. Thus on the basis of study on anisotropic features of shale in the well XD2 Wufeng Formation-Longmaxi Formation, analyzed and discussed the features impact on shale gas enrichment in the area. Based on well XD2 sequence identification, has expounded shale anisotropic features in the area from macroscopic and microscopic two aspects. The macroscopic features have: the development of sandy banding and pyrite has certain negative correlativity;between foliation development and pyrite content present positive correlativity more or less, while with sandy banding development basically negative correlativity;sandy banding represented terrigenous supply increasing, and hydrodynamic enhancing environment is disadvantage to pyrite and foliation development. The microscopic features have: from bottom to top, TOC content increasing first, then dramatically decreasing to gently decreasing, and then gradually increasing slightly;the development of brittle minerals in the two formations is higher in transgressive systems tract than in highstand systems tract, and quartz content is higher in transgressive systems tract than in highstand systems tract;in Wufeng Formation, brittle minerals (quartz, feldspar, carbonate and pyrite) content is increasing from bottom to top, in Longmaxi Formation is decreasing from bottom to top as a whole, but presents brittle mineral contents increasing process in two stages. Between quartz content and TOC has better positive correlativity, while with clay content is insignificant, such correlativity is controlled by sedimentary environment of the two formations.