中扬子鄂西地区牛蹄塘组页岩储层特征及含气性研究

Shale Gas Reservoir and Gas-Bearing Properties of Middle Yangtze Niutitang Formation in Western Hubei

下寒武统牛蹄塘组为鄂西地区重要的页岩气勘探目的层之一,针对牛蹄塘组页岩储层及含气性特征研究薄弱的现状,利用钻井及地层剖面资料,对研究区岩石地层及沉积相、页岩埋深及厚度、地球化学特征、储层物性及含气性特征进行综合分析。研究表明:鄂西地区牛蹄塘组依据岩性特征可以分为2段;研究区主要发育浅水及深水陆棚相,以深水陆棚相分布面积最广,兴山县-宜昌市发育3个水下隆起;页岩厚度中心主要分布在来凤县-恩施市及神农架2个地区,厚度可达200.0 m以上;牛蹄塘组由下至上TOC逐渐降低,高值区主要分布在咸丰-鹤峰一带,总体上TOC以大于2.00%的高及特高级别为主,R o为2.0%~3.5%,以高成熟为主;矿物组分以黏土矿物及石英为主,黏土矿物由下至上逐渐增多;牛蹄塘组主要为低孔特低渗储层类型;牛蹄塘组由下至上呈现含气量先急剧变大再缓慢降低的趋势,含气量峰值位于牛蹄塘组一段下部,含气性较好的地区位于黄陵背斜东南翼。综合研究认为,鄂西地区牛蹄塘组勘探有利区主要位于深水陆棚相内的宽缓背斜翼部、且远离区域断裂带的地区。研究结果可为鄂西地区牛蹄塘组页岩气勘探井位部署提供参考依据。

The Lower Cambrian Niutitang Formation is one of the major shale gas exploration fields in western Hubei.In order to further understanding the shale gas reservoir and gas-bearing properties of the Niutitang Formation,drilling and stratigraphic profile data were used to comprehensively analyze the rock formation,sedimentary facies,shale burial depth,shale thickness,geochemical properties,reservoir physical and gas-bearing properties.Research indicates that the Niutitang Formation in western Hubei can be divided into two members a ccording to the lithofacies.Shallow-water and deep-water shelf facies are dominant in this area with the wider distribution of deep-water shelf facies.There are three underwater uplifts in Xingshan County-Yichang City.Laifeng County-Enshi City and Shennongjia shows the maximum shale thickness of more than 200.0 m.The TOC of Niutitang Formation gradually decreases from bottom to top.The Xianfeng-Hefeng area shows a high regional TOC distribution and the corresponding TOC is dominated by high and extra-high levels of greater than 2.00%.The R o is about 2.0%~3.5%in high maturity stage.The mineral components are dominated by clay minerals and quartz,and the clay mineral content gradually increases from bottom to top.The Niutitang Formation is considered as a low-porosity and ultra-low permeability reservoir.The gas content of Niutitang Formation increases rapidly and then gradually decreases.The lower part of the Niutitang Formation shows a maximum gas content in the longitudinal direction and the relatively high gas content laterally distributes in the southeast flank of the Huangling anticline.Comprehensive analysis suggests that the favorable exploration zones are locates in the wide and gentle anticline wings within the deep-water shelf facies and far away from the regional fault zone.This research could provide certain reference for the shale gas exploration well deployment in the Niutitang Formation of Western Hubei.