石油与天然气地质 ›› 2025, Vol. 46 ›› Issue (5): 1700-1716.doi: 10.11743/ogg20250519

• 方法技术 • 上一篇    下一篇

鄂尔多斯盆地吴起地区三叠系延长组长6 —长9油层组高自然伽马值砂岩特征及成因

刁豪1,2(), 闫新智3, 赵靖舟2,4(), 马荣4,5   

  1. 1.西安石油大学 石油工程学院,陕西 西安 710065
    2.陕西省油气井及储层渗流与岩石力学重点实验室,陕西 西安 710065
    3.延长油田股份有限公司 勘探部,陕西 延安 716000
    4.西安石油大学 地球科学与工程学院,陕西 西安 710065
    5.延长油田股份有限公司 吴起采油厂,陕西 吴起 717699
  • 收稿日期:2025-08-03 修回日期:2025-09-08 出版日期:2025-10-30 发布日期:2025-10-29
  • 通讯作者: 赵靖舟 E-mail:dhgzgy@163.com;jzzhao@xsyu.edu.cn
  • 第一作者简介:刁豪(1994—),男,博士研究生,油气成藏地质学与非常规油气地质。E-mail: dhgzgy@163.com
  • 基金项目:
    国家自然科学基金项目(42202185);中国博士后基金项目(2022MD713801);陕西省教育厅自然科学研究项目(22JK0505)

Characteristics and genesis of high-gamma sandstones in the 6th to 9th oil groups of the Triassic Yanchang Formation, Wuqi area, Ordos Basin

Hao DIAO1,2(), Xinzhi YAN3, Jingzhou ZHAO2,4(), Rong MA4,5   

  1. 1.College of Petroleum Engineering,Xi’an Shiyou University,Xi’an,Shaanxi 710065,China
    2.Shaanxi Key Laboratory of Well Stability and Fluid & Rock Mechanics in Oil and Gas Reservoirs,Xi’an,Shaanxi 710065,China
    3.Exploration Department,Yanchang Oil Field Co. ,Ltd. ,Yan’an,Shaanxi 716000,China
    4.School of Earth Sciences and Engineering,Xi’an Shiyou University,Xi’an,Shaanxi 710065,China
    5.Wuqi Oil Production Plant,Yanchang Oil Field Co. ,Ltd. ,Wuqi,Shaanxi 717699,China
  • Received:2025-08-03 Revised:2025-09-08 Online:2025-10-30 Published:2025-10-29
  • Contact: Jingzhou ZHAO E-mail:dhgzgy@163.com;jzzhao@xsyu.edu.cn

摘要:

鄂尔多斯盆地吴起地区延长组长6—长9油层组存在高自然伽马值(简称高伽马)砂岩,该类砂岩极易在常规测井解释中被识别为粉砂岩甚至泥岩,从而造成有效储集层厚度的误判。为了准确判识岩性,从岩心观察入手,并结合粒度资料对不同岩性进行精细划分,总结了研究区高伽马砂岩测井响应、岩石学、物性及含油性特征,并对其成因开展了分析与探讨。研究结果表明:①高伽马砂岩在常规测井上响应特征显著,表现为高自然伽马值、高声波时差以及自然电位明显负异常;在自然伽马能谱测井上,则显示出高铀(U)、高钍(Th)及低钾(K)含量特征。②高伽马砂岩相较于普通砂岩,通常具有更高的长石、云母及黏土矿物含量。两类砂岩的孔隙度较为接近,但高伽马砂岩渗透率略低于常规砂岩,含油饱和度亦相对较低,且含油性均随铀、钍和钾等放射性元素含量的增加而呈现降低趋势。③火山活动、沉积环境和黏土矿物类型是高伽马砂岩形成的主控因素。火山活动喷发的碎屑物质提供了丰富的放射性物质来源,研究区东北部和西南部在放射性元素的迁移、聚集及保存条件方面存在不同,尤其是铀与钍元素在不同沉积环境下富集程度差异明显;不同黏土矿物对放射性元素的吸附能力存在差异,伊利石与伊/蒙混层矿物具有较强的吸附能力,而高岭石与绿泥石对放射性元素的吸附作用有限。对吴起地区高伽马砂岩岩性及发育特征开展精细研究,不仅对鄂尔多斯盆地油气储量提升与产能建设具有重要实际意义,而且也能够为中国其他盆地同类储层的勘探与开发提供关键地质依据与理论指导。

关键词: 储层特征, 高自然伽马值砂岩, 长6—长9油层组, 延长组, 三叠系, 鄂尔多斯盆地

Abstract:

Sandstones with high natural gamma-ray (GR) values (also referred to as high-gamma sandstones) occur in the 6th to 9th oil groups of the Yanchang Formation (collectively referred to as the Chang 6‒9 oil groups) in the Wuqi area, Ordos Basin. By conventional log interpretations, these sandstones are often mistakenly identified as siltstones or even mudstones, leading to an underestimation of the effective reservoir thickness. In this study, we conduct a fine-scale lithological division by combining core observations with grain size data. Accordingly, the logging responses, petrological characteristics, physical properties, and oil-bearing properties of high-gamma sandstones in the study area are summarized, followed by an analysis and exploration of their origin. The results indicate that the high-gamma sandstones exhibit significant conventional logging responses, including high GR values, elevated sonic interval transit time, and pronounced negative spontaneous potential (SP) anomalies. In the spectral GR logs, these sandstones show the characteristics of high uranium (U) and thorium (Th) concentrations, along with low potassium (K) concentration. Compared to common sandstones, the high-gamma sandstones generally contain higher contents of feldspar, mica, and clay minerals. Despite comparable porosity, the high-gamma sandstones show slightly lower permeability and oil saturation than common sandstones. Furthermore, their oil-bearing properties tend to decrease with an increase in the concentrations of radioactive elements such as U, Th, and K. The primary factors controlling the formation of the high-gamma sandstones include volcanic activity, sedimentary environment, and clay mineral type. The debris produced by volcanic eruptions supplies abundant radioactive materials for the study area. The northeastern and southwestern parts of the study area show differences in the migration, accumulation, and preservation conditions of radioactive elements, especially U and Th, which exhibit distinct degrees of enrichment under different sedimentary environments. Clay minerals exhibit varying adsorption capacities for radioactive elements. Specifically, illite and mixed-layered illite-montmorillonite demonstrate higher adsorption capacities, whereas kaolinite and chlorite exhibit limited adsorption capacities. Fine-scale investigations of the lithological and developmental characteristics of high-gamma sandstones in the Wuqi area hold great practical significance for increasing hydrocarbon reserves and enhancing productivity in the Ordos Basin, while also providing a key geological basis and theoretical guidance for the exploration and exploitation of similar reservoirs in other basins of China.

Key words: reservoir characterization, high-gamma sandstone, Chang 6?9 oil groups, Yanchang Formation, Triassic, Ordos Basin

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