塔里木盆地西北缘克孜勒布拉克南沟早二叠世巴立克立克组生物礁地质特征
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西南石油大学地球科学与技术学院

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国家自然科学基金项目(41702163, 41702122)


Geological characteristics of Early Permian Baliklik Formation reefs at the south Kezilblak Gully in the northwest margin of the Tarim Basin
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School of Earth Science and Technology, Southwest Petroleum University

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    摘要:

    塔西北二叠系巴立克立克组广泛发育具有油气勘探意义的巨厚的台地边缘生物礁,本文对塔西北克孜勒布拉克南沟出露的典型的二叠系巴立克立克组的生物礁进行了详细的宏微观研究。该套生物礁以生屑滩为礁基,礁核下部主要为蓝绿藻建造的各类微生物岩,其结构组分主要为凝块及破碎的微凝块,次为叠层石,此时的水体能量较低;礁核上部局部发育叶状藻礁,并伴生大量的海生底栖动物,此时礁体开始暴露在浪基面之上,大量发育角砾状灰岩,并遭受大气淡水岩溶的改造。除了台缘带外,塔西北柯坪地区同期的局限台地中也发育小规模的、具微生物岩特征的台内礁滩体,说明该时期区域上的环境条件普遍适宜造礁。巴立克立克组的该套礁滩体的形成时间为早二叠世阿瑟尔期晚期-萨克马尔期,这与早二叠世塔里木大火成岩省早期阶段相当,因此推测该套礁滩体的形成和当时的火山活动产生的火山灰导致南天山洋残余海盆的海水“富营养化”有关。藻类的爆发使得巴立克立克组的该套礁滩体的δ13C值较之康克林组的碳酸盐岩呈现显著正偏移。但是,巴立克立克组的礁滩体受胶结作用等建设性成岩作用的改造程度较深,利于“成岩”,不利“成储”,使得区域上巴立克立克组的礁滩体尽管相带较好,但储渗性极差,唯有受构造裂缝改造部分可发育高渗层。因此,可以确定:塔西北早二叠世巴立克立克组的礁滩储层基本不受相控,主要发育裂缝型储层。因此,今后对于塔西北二叠系礁滩油气藏的勘探应重点关注构造裂缝发育段。本次研究对今后塔西北巴立克立克组生物礁优质储层预测提供了科学依据,对于我国乃至世界范围内二叠系微生物岩的研究也有一定助益。

    Abstract:

    At the Permian Baliklik Formation in the northwest margin of the Tarim Basin, there developed massively thick reef limestone that bears oil and gas exploration significance. This paper makes macro and micro examinations of the reefs which cropped out at Kizilbulak Nangou in the northwest margin of the Tarim Basin. This set of reefs had bioclastic shoals as reef bases. The lower zone of the reef core is mainly composed of microbialite of various types formed by Cyanobacteria, with thrombolite and broken-up microclots as its most dominant structural components, followed by stromatolites. At this time, the hydraulic energy is low. In the upper zone of the reef core locally developed phylloid algal reefs, with a large quantity of marine benthic fauna among them. At this time, the reef body began to expose itself above the wave base, with a large number of brecciated limestone developed, and it was subjected to the transformation of atmospheric freshwater karstification. In addition to the platform margin zone, the synchronous restricted platform in the Keping area in the northwest Tarim Basin also developed small-scale intra-platform reef-shoal complexes, with microbial rock characteristics, indicating that the environmental conditions in the region during this period were generally favorable for reef building. The set of reef-shoal complexes in the Baliklik Formation formed in the late Atherian period of the Early Permian to the Sakmarian Age, contemporary with the early stage of large igneous provinces of Early Permian Tarim Basin. Therefore, it is speculated that the forming of this set of reef-shoal complexes was related to the "eutrophication" of the sea water in the residual basin of the South Tianshan Ocean; the “eutrophication” had been caused by the volcanic ash spurted out by volcanic activities at that time. As a result of the outbreak of algae, the δ13C value of the reef-shoal complexes in the Baliklik Formation shows a significant positive shift compared with that of the carbonate rocks in the Kangkelin Formation. However, the reef-shoal complexes of the Baliklik Formation was much transformed by cementation and other constructive types of diagenesis, unfavorable to the forming of reservoirs. In other words, the reef-shoal complexes of the Baliklik Formation in the region, despite their desirable facies belts, possess poor reservoir permeability; high permeability layers only developed where structural fractures occurred. Therefore, it can be theorized that reef-shoal reservoirs of the Early Permian Baliklik Formation in the northwest margin of the Tarim Basin are, generally speaking, not controlled by facies, and that fractured reservoirs were dominant. Thereupon, exploration of Permian reef-shoal oil and gas reservoirs in the northwest margin of the Tarim Basin should focus on the structural fractured members. In brief, this study is an attempt to provide some scientific basis for the prediction of high-quality reservoirs in the Baliklik Formation reefs of the Tarim Basin, and to promote further research into Permian microbial rocks in China and throughout the world.

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  • 收稿日期:2022-12-18
  • 最后修改日期:2023-03-16
  • 录用日期:2023-03-21
  • 在线发布日期: 2024-01-31
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