湘西北复杂构造区下寒武统页岩含气性及主控因素分析——以慈页1井为例

Gas-bearing property and main controlling factors of Lower Cambrian shale in complex tectonic area of northwestern Hunan province:a case of well Ciye 1

我国南方地区广泛发育厚度大、有机质含量高的下寒武统海相页岩,但影响页岩含气性的主控因素仍不明确。湘西北复杂构造区下寒武统牛蹄塘组页岩沉积厚度大且埋深适中,在优选出的慈利景龙桥向斜内钻探的页岩气参数井——慈页1井,富有机质泥页岩厚度为149 m,对岩心进行取样,并开展了总有机碳含量、镜质体反射率、矿物成分、储集物性等测试分析,揭示了牛蹄塘组页岩总有机碳质量分数平均为4.83%,底部总有机碳质量分数大于3.0%的连续优质页岩厚达37 m,页岩镜质体反射率(R_o)平均为3.28%。采用岩心直接解吸法测得牛蹄塘组页岩总含气质量体积为0.859 m^3/t,天然气成分中甲烷质量分数平均为78.23%。通过分析湘西北慈利地区构造演化特征,并将慈页1井与周边钻遇的下寒武统页岩钻井关键参数进行对比,阐明影响湘西北地区下寒武统页岩含气性的主控因素为构造保存条件和页岩演化程度。南方雪峰山隆起、黄陵背斜和汉南古陆等古隆起周缘基底稳定,构造保存条件较好,页岩成熟度相对较低,是未来复杂构造区页岩气勘探的重点地区。

The lower Cambrian marine shales with large thickness and high organic content are widely developed in southern China,however the main controlling factors affecting shale gas-bearing property are still not clear.The shale of the Lower Cambrian Niutitang Formation in the complex tectonic area of northwestern Hunan province has a large thickness and medium depth,and the shale gas parameter well Ciye 1,which was drilled in the selected Cili Jinglongqiao syncline,has a thick shale thickness of 149 m.The core samples were taken to analyze total organic carbon(TOC)content,vitrinite reflectance,mineral composition and reservoir properties,revealing that the average TOC content of Niutitang Formation is 4.83%,the bottom high quality shale with TOC content more than 3%has a thickness of 37 m,and the average vitrinite reflectance of shale is 3.28%.The total shale gas content of Niutitang Formation measured by core direct desorption method reaches 0.859 m3/t,and the average methane content in natural gas composition is 78.23%.By analyzing the tectonic evolution characteristics of Cili area in northwestern Hunan,and comparing the key parameters of the Lower Cambrian shale in the surrounding drilling wells with well Ciye 1,the main controlling factors affecting the gas-bearing property of the Lower Cambrian shale in northwestern Hunan are tectonic preservation conditions and shale evolution degree.The palaeo uplifts in southern China such as Xuefeng uplift,Huangling anticline and Hannan old land with stable basement,good preservation conditions and low shale maturity,are the key areas for the further shale gas exploration in complex tectonic areas.