Acta Petrolei Sinica ›› 2023, Vol. 44 ›› Issue (4): 598-611.DOI: 10.7623/syxb202304003

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Genesis and reservoir significance of patchy dolostone of the Ordovician Yingshan Formation in Tabei area

Kong Yue1,2, Gao Xiaopeng3, Shi Kaibo1,2, Liu Bo1,2, Jiang Weimin1,2, Yu Jinxin1,2, He Qing1,2, Wu Chun1,2   

  1. 1. School of Earth and Space Sciences, Peking University, Beijing 100871, China;
    2. Institute of Oil and Gas, Peking University, Beijing 100871, China;
    3. Sinopec Petroleum Exploration and Production Research Institute, Beijing 100083, China
  • Received:2021-09-09 Revised:2022-09-27 Online:2023-04-25 Published:2023-05-05

塔北地区奥陶系鹰山组斑状白云岩成因及储层意义

孔悦1,2, 高晓鹏3, 石开波1,2, 刘波1,2, 姜伟民1,2, 于进鑫1,2, 何卿1,2, 吴淳1,2   

  1. 1. 北京大学地球与空间科学学院 北京 100871;
    2. 北京大学石油与天然气研究中心 北京 100871;
    3. 中国石油化工股份有限公司石油勘探开发研究院 北京 100083
  • 通讯作者: 高晓鹏,男,1983年5月生,2012年获中国地质大学(北京)博士学位,现为中国石油化工股份有限公司石油勘探开发研究院高级工程师,主要从事沉积储层、石油地质方面的研究。Email:gaoxp.syky@sinopec.com
  • 作者简介:孔悦,女,1996年12月生,2019年获吉林大学资源勘查工程(石油与天然气方向)学士学位,现为北京大学硕士研究生,主要从事碳酸盐岩沉积-成岩作用研究。Email:kongyue1230@pku.edu.cn
  • 基金资助:
    国家自然科学基金企业创新发展联合基金项目(No.U19B6003)和中国石油化工股份有限公司科技部项目(P19022-7)资助。

Abstract: To investigate the genesis mechanism of patchy dolostone developed in the Upper Member of the Ordovician Yingshan Formation in Tabei area and its significance for oil and gas accumulation, the mechanism of selective dolomitization after bioturbation and reservoir characteristics in the Upper Member of Yingshan Formation were systematically explored based on analyzing the geochemical characteristics of cores, rock thin sections, carbon and oxygen isotopes, whole rock, as well as trace and rare earth elements in microzones. The patchy dolostone is composed of dolomitic patches and ash matrix, and the dolomitic patches account for 30% -75%, distributed along the Thalassinoides burrow, mainly composed of powder crystal-fine crystal dolomite. The dolomitic patches have relatively high Fe, Mn and Ni contents, with the δ13C values ranging from -1.48 ‰ to 0.06 ‰ and the δ18O values ranging from -8.64 ‰ to -6.95 ‰; δ13C and δ18O values of the gray matrix range from -1.93 ‰ to -0.61 ‰ and -8.14 ‰ to -7.08 ‰, respectively. The whole-rock rare-earth elements of both dolomitic patches and gray matrix have flat distribution patterns, and the test results of in-situ microzones indicate that the dolomitic patches have positive Eu anomalies. The formation of patchy dolostone in the Upper Member of Yingshan Formation is controlled by bioturbation and microbial activity. Bioturbation can improve the pore structure of burrow and provide a good transport channel for seawater during the same period; organic matter formed by biological activity inside the burrow provides sufficient nutrients for microbial reproduction, and NH3 generated by microbial degradation of organic matter can raise the pH of microenvironment in the burrow. In the oxidation environment, cyanobacteria generate HCO3- and OH- through photosynthesis and carbon dioxide concentration mechanisms; in the reduction environment, both sulfate reduction and anaerobic oxidation of methane consume SO42-, release Mg2+, and produce HCO3-, which raises the alkalinity of dolomitized fluids. Overall, microbial activity leads to an increase in Mg2+ concentration and CO32- activity under the burrow microenvironment, thus facilitating dolomitization. The dolomitic patches are dominate by well-connected dolomite intercrystal pores, which is of important significance for hydrocarbon accumulation.

Key words: Tarim Basin, Yingshan Formation, patchy dolostone, genesis, bioturbation, reservoir significance

摘要: 塔北地区奥陶系鹰山组上段斑状白云岩发育,为探究其成因机理及油气储集意义,基于岩心、岩石薄片和碳氧同位素、全岩及微区微量元素、稀土元素地球化学特征分析,系统讨论了鹰山组上段生物扰动选择性白云石化作用机理及其储层特征。斑状白云岩由白云质斑块和灰质基质构成,白云质斑块占比为30%~75%,沿Thalassinoides潜穴分布,主要由粉晶-细晶白云石组成。白云质斑块具有相对较高的Fe、Mn及Ni元素含量,δ13C值为-1.48 ‰~0.06‰,δ18O值为-8.64 ‰~-6.95 ‰;灰质基质的δ13C值为-1.93 ‰~-0.61 ‰,δ18O值为-8.14 ‰~-7.08 ‰。白云质斑块和灰质基质的全岩稀土元素配分模式均为"平坦型",原位微区测试结果表明白云质斑块具有Eu正异常。鹰山组上段斑状白云岩的形成受生物扰动和微生物活动控制,生物扰动可改善潜穴部分的孔隙结构,为同期海水提供良好的运移通道;潜穴内部生物活动形成的有机质为其繁盛提供了充足的养料,微生物降解有机质生成NH3可提高潜穴微环境的pH值。在氧化环境中,蓝细菌通过光合作用和二氧化碳浓缩机制生成HCO3-和OH-;在还原环境中,硫酸盐还原作用和甲烷厌氧氧化作用消耗SO42-,释放Mg2+,并生成HCO3-,提高白云石化流体的碱度。整体上,微生物活动导致潜穴微环境中的Mg2+浓度和CO32-活性增加,有利于白云石化作用。白云质斑块发育连通性较好的白云石晶间孔,具有重要的储集意义。

关键词: 塔里木盆地, 鹰山组, 斑状白云岩, 成因, 生物扰动, 储层意义

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