川东北上二叠统吴家坪组一段火山碎屑岩储层发育类型及天然气成藏模式

Development types and natural gas accumulation patterns of volcaniclastic reservoirs in the first member of Upper Permian Wujiaping Formation in northeastern Sichuan Basin

  • 摘要: 四川盆地及其周缘天然气资源丰富,火成岩/火山碎屑岩非常规油气藏展现出巨大勘探潜力,受峨眉山地裂运动影响,川东北吴家坪组一段(吴一段)沉积期发育一套火山碎屑岩,但其天然气储层类型和成藏模式尚不明确。以LY1井和YB701井为主,结合多口探井测井、岩心描述、地化数据、储层资料等,明确了川东北吴一段火山碎屑岩天然气储层发育类型和成藏模式。研究结果表明:①不同区域吴一段垂向岩性组合差异大、非均质性强,整体以生屑灰岩与火山碎屑岩互层特征。②吴一段发育“自生自储”型和“近源储集”型两类勘探领域。“自生自储”型储层具有高TOC含量、高含气、高孔隙的特征;“近源储集”型储层具有低TOC含量、低含气、高孔隙的特征。③两类储层发育空间展布受控于距火山喷发机构的距离和沉积环境的影响,储层储集空间均以黏土矿物收缩孔、溶蚀孔、微裂缝为主,有机孔欠发育;孔隙结构主要以介孔为主,微孔次之,保存条件优越。④吴一段发育两类天然气成藏模式,在储层空间展布和供烃方式上存在差异,普光地区整体呈“三明治”结构,多源供烃特征;元坝地区整体呈“两层楼”结构,单源供烃特征。研究成果对吴一段火山碎屑岩天然气勘探评价具有指导借鉴意义。

     

    Abstract: The Sichuan Basin and its periphery are rich in natural gas resources, and unconventional oil and gas reservoirs in igneous/volcaniclastic rocks show great exploration potential. Influenced by the Emei Taphrogenesis, a set of volcaniclastic rocks developed during the deposition of the first member of the Wujiaping Formation (Wu1 member) in the northeastern Sichuan Basin. However, the reservoir types and natural gas accumulation patterns of these volcaniclastic rocks remain unclear. Focusing on well LY1 and well YB701, combined with logging data from multiple exploration wells, core descriptions, geochemical data, and reservoir information, this study clarified the development types and accumulation patterns of natural gas reservoirs in volcaniclastic rocks of the Wu1 member in the northeastern Sichuan Basin. The results showed that: ① The vertical lithological assemblages in the Wu1 member varied greatly across different regions, exhibiting strong heterogeneity, and were generally characterized by interbeds of bioclastic limestone and volcaniclastic rocks. ② The Wu1 member developed two exploration types of reservoirs: "self-generating and self-storing" type and "near-source" type. The "self-generating and self-storing" reservoir type was characterized by high total organic carbon (TOC), high gas content, and high porosity, whereas the "near-source reservoir" type was characterized by low TOC, low gas content, and high porosity. ③ The spatial distribution of the two reservoir types was controlled by the distance from volcanic vents and depositional environment. The reservoir storage space was dominated by clay mineral shrinkage pores, dissolution pores, and microfractures, while organic pores were underdeveloped. The pore structure was dominated by mesopores, followed by micropores, and the preservation conditions were excellent. ④ Two types of natural gas accumulation patterns were developed in the Wu1 member, and there were differences between the two patterns in terms of reservoir spatial distribution and hydrocarbon supply. The Puguang area was characterized by a "sandwich" structure with multiple sources of hydrocarbon supply, whereas the Yuanba area was characterized by a "two-story" structure with a single source of hydrocarbon supply. This study provides guidance and reference significance for the exploration and evaluation of natural gas from volcaniclastic rocks in the Wu1 member.

     

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