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滇东北地区勺寨复向斜五峰组−龙马溪组页岩气地质特征及含气性控制因素

Geological characteristics and gas bearing control factors of shale gas in the Wufeng-Longmaxi Formation of the Shaozhai syncline in northeastern Yunnan

  • 摘要: 滇东北地区勺寨向斜五峰组−龙马溪组发育一套富有机质页岩,具有较好的勘探潜力;但关于其地质特征、含气性特征和主控因素尚不明确。通过系统梳理前人资料并结合最新钻井、剖面资料,对勺寨复向斜五峰组−龙马溪组富有机质页岩的岩石学特征、有机质特征、储集空间特征和含气性特征进行了分析,并就含气性控制性因素进行了探讨。结果表明:勺寨向斜五峰组−龙马溪组为浅水陆棚−深水陆棚沉积,富有机质页岩厚度介于35~105 m;五峰组上段和龙马溪组下段富有机质页岩TOC含量高,多在2% 以上,有机质类型好,具有良好的生烃潜力;优质页岩脆性矿物含量较高,具有较好的可压裂性;储层空间类型多,既有有机质孔、晶间孔、粒内孔为主的页岩气储集孔,又有沟通压裂通道、宏观裂缝的矿物碎裂缝和黏土矿物层间缝。研究区页岩含气量差异较大,高桥地区含气量相对较高但CH4无空气基含量较低,而莲峰地区含气量相对较低但CH4无空气基含量高,均在95%以上。研究认为:同一构造位置页岩总含气量受控于TOC含量、孔体积、孔比表面、黏土矿物含量、黄铁矿含量和碳酸盐岩矿物含量,不同构造部位页岩气含量受控于构造控制下的沉积环境及构造保存条件,构造控制下的深水陆棚、远离大断裂和具有褶皱遮挡的宽缓向斜含气性较好,是研究区页岩气富集的有利区带。

     

    Abstract: A set of organic rich shale with good exploration potential is developed in the Wufeng Formation Longmaxi Formation of the Shaozhai Syncline in northeastern Yunnan; However, its geological characteristics, gas bearing characteristics, and main controlling factors are still unclear. By systematically reviewing previous data and combining with the latest drilling and profile data, the petrological characteristics, organic matter characteristics, reservoir space characteristics, and gas bearing characteristics of organic shale rich in the Wufeng-Longmaxi Formation of the Shaozhai Syncline were analyzed, and the controlling factors of gas bearing properties were discussed. The results show that the Wufeng-Longmaxi Formation in the Shaozhai Syncline is a shallow water shelf deep water shelf deposit, with a thickness of organic rich shale ranging from 35 to 105m; The organic rich shale in the upper section of the Wufeng Formation and the lower section of the Longmaxi Formation has a high TOC content, mostly above 2%, with good organic matter types and good hydrocarbon generation potential; High quality shale has a high content of brittle minerals and good fracturing performance. There are multiple types of reservoir spaces, including shale gas storage pores mainly composed of organic matter pores, intergranular pores, and intra particle pores, as well as mineral fractures and interlayer fractures of clay minerals that communicate with fracturing channels and macroscopic fractures. The gas content of shale in the study area varies greatly. The gas content in the Gaoqiao area is relatively high, but the CH4 air free base content is low. The gas content in the Lianfeng area is relatively low, but the CH4 air free base content is high, both of which are above 95%. The study found: the difference in total gas content of shale at the same structural location is controlled by TOC content, pore volume, pore specific surface area, clay mineral content, pyrite content, and carbonate mineral content. The shale gas content at different structural locations is controlled by the sedimentary environment and preservation conditions under structural control. The deep water continental shelf, wide and gentle synclines far from major faults and with fold shielding under structural control have better gas bearing properties, it is a favorable area for shale gas enrichment in the study area.

     

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