PDF(6735 KB)
Sedimentary environment and organic matter enrichment mechanism of the Lower Cambrian Yuertusi Formation in Tahe area, Tarim Basin
ZHANG Wenwen, XU Qinqi, SHANG Kai, ZHANG Nan, LIAO Qifeng, LIN Jingwen, LI Shuai
Marine Origin Petroleum Geology ›› 2025, Vol. 30 ›› Issue (1) : 17-29.
PDF(6735 KB)
PDF(6735 KB)
Sedimentary environment and organic matter enrichment mechanism of the Lower Cambrian Yuertusi Formation in Tahe area, Tarim Basin
The Lower Cambrian Yuertusi Formation is an important source rock layer in Tarim Basin. The research on the organic matter enrichment mechanism could provide valuable guidance for the exploration of ultra-deep marine oil and gas reserves. Based on data of mineral petrology, inorganic geochemistry, and elemental analysis of Well A, combined with data of Well LT1 cited from reference, this study explores the sedimentary paleoenvironment of the Yuertusi Formation source rock in Tarim Basin and its control on organic matter enrichment, with integrated element geochemical indicators such as paleoproductivity, redox conditions and others. The results show that: (1) Yuertusi Formation in the Tahe area has high organic matter content, and the organic matter quality of the lower section, with an average TOC of 6%, is superior to the upper section. (2) Paleoproductivity level (P/Ti, Babio), water retention degree (Mo/TOC, Co·Mn), terrigenous detrital input (Ti/Al) and anoxia degree (Ni/Co, U/Th, V/Sc) show a gradual decreasing trend from early to late period of Yuertusi Formation. (3) Closely corresponded with variations in the sedimentary paleoenvironment induced by sea level fluctuations, the organic matter enrichment in the Yuertusi Formation is jointly influenced by preservation conditions, weak hydrothermal activity, and upwelling currents. In the early stage of Yuertusi, under a sea level of relatively low, a medium-high water retention developed, and the weak hydrothermal activity made the bottom seawater being in an anoxic state, and the long-term anoxic and sulfidation environment was conducive to the preservation of organic matter, thus the lower section of Yuertusi Formation with high TOC formed. In the late stage of Yuertusi, the sea level experienced fluctuating rise and gradual decline, the water retention degree reduced under the high sea level, and when the sea level decreased significantly, the environment gradually changed from anoxic to oxygen-poor, which may lead to the oxidation and decomposition of some organic matter, thus the upper section with low TOC formed.
geochemical characteristics / paleoenvironment / organic matter enrichment / Yuertusi Formation / Cambrian / Tahe area / Tarim Basin
| [1] |
杨海军, 陈永权, 田军, 等. 塔里木盆地轮探1井超深层油气勘探重大发现与意义[J]. 中国石油勘探, 2020, 25(2): 62-72.
2020 年1 月，位于塔北隆起轮南低凸起的轮探1 井在8200m 之下的下寒武统白云岩中获得轻质原油， 塔里木古老克拉通超深层油气勘探获得重大突破。通过对轮探1 井发现情况描述与超深层寒武系盐下油藏发现历程分 析，旨在为其他类似地区新区、新层系、新类型的勘探提供借鉴与参考。轮探1 井钻揭寒武系玉尔吐斯组一套优质烃 源岩，以及阿瓦塔格组蒸发膏岩/ 沙依里克组—吾松格尔组白云岩储层与玉尔吐斯组泥岩/ 震旦系奇格布拉克组白 云岩风化壳储层两套储盖组合。轮探1 井产层为吾松格尔组，为正常温压系统的挥发性油藏；震旦系奇格布拉克组风 化壳获得微量天然气。塔里木盆地台盆区勘探经历了从碎屑岩到碳酸盐岩、从碳酸盐岩到盐下白云岩的两次战略转移; 轮探1 井是第二次战略转移的重要标志，具有里程碑意义。轮探1 井成藏有利条件在于具有继承性稳定古隆起与优质 的生储盖组合；通过类比，分析了塔里木盆地寒武系盐下白云岩勘探前景，指出塔中—古城、塔北南斜坡、麦盖提斜 坡北—柯坪等有利区为下步勘探重点区带。
In January 2020, light crude oil was obtained from Lower Cambrian dolomite with burial depth deeper than 8200 m in Well Luntan-1, which is located in the Lunnan low bulge in the Tabei uplift. The result indicated a major breakthrough in ultradeep oil and gas exploration in the old craton of Tarim. This paper describes the process of discovering Well Luntan-1 and analyzes the discovery history of the ultra-deep Cambrian subsalt oil reservoirs, with the intention of providing reference for the exploration of new zones, new strata and new types in other similar areas. According to drilling results from Well Luntan-1, a set of high-quality source rocks is developed in the Cambrian Yuertusi Formation, and there are 2 sets of reservoir-cap assemblage. One is evaporite gypsum cap rocks in the Awatage Formation and dolomite reservoir in the Shayilike – Wusonggeer Formations. The other is mudstone cap rocks in the Yuertusi Formation and dolomite weathering crust reservoir in the Sinian Qigebulake Formation. The production layer in Well Luntan-1 is the Wusonggeer Formation, which is a volatile-oil reservoir with normal temperature and pressure gradients. In addition, trace natural gas was obtained from the weathering crust of the Sinian Qigebulake Formation. Exploration of the platform-basin transitional area in the Tarim Basin has experienced 2 strategic shifts: from clastic rocks to carbonate rocks, and from carbonate rocks to pre-salt dolomite. Well Luntan-1 is an important symbol of the second strategic shift, which is of milestone significance. The favorable accumulation conditions of Well Luntan-1 are the successive development of stable paleo- uplift and the high-quality source-reservoir-cap assemblages. Through analogy, this paper analyzes the exploration prospects for the Cambrian pre-salt dolomite in the Tarim Basin, and points out that favorable areas, such as the Tazhong-Gucheng area, the south slope of the Tabei area, and the northern Maigaiti slope-Keping area, are the key areas for the next steps in exploration.
|
| [2] |
乔博, 高志前, 樊太亮, 等. 塔里木盆地寒武系台缘结构特征及其演化[J]. 断块油气田, 2014, 21(1): 7-11.
|
| [3] |
吕海涛, 耿锋, 尚凯. 塔里木盆地寒武系盐下领域勘探关键问题与攻关方向[J]. 石油与天然气地质, 2022, 43(5): 1049-1058.
|
| [4] |
杨赟昊, 高志前, 樊太亮, 等. 下寒武统黑色岩系沉积环境与控烃差异: 以塔里木盆地西北缘和东北缘为例[J]. 断块油气田, 2022, 29(1): 47-52.
|
| [5] |
朱传玲, 闫华, 云露, 等. 塔里木盆地沙雅隆起星火1井寒武系烃源岩特征[J]. 石油实验地质, 2014, 36(5): 626-632.
|
| [6] |
陈新军, 蔡希源, 高志前, 等. 寒武、奥陶纪海平面变化与烃源岩发育关系: 以塔里木盆地为例[J]. 天然气工业, 2005, 25(10): 18-20, I0020.
|
| [7] |
金值民, 谭秀成, 唐浩, 等. 浅水超覆沉积富有机质细粒沉积物沉积环境与岩石学特征: 以塔里木盆地西北部寒武系玉尔吐斯组为例[J]. 石油勘探与开发, 2020, 47(3): 476-489.
以塔里木盆地西北部阿克苏—柯坪—乌什地区寒武系玉尔吐斯组露头剖面为例,通过对露头剖面的宏、微观研究,对富有机质细粒沉积岩形成环境进行分析。研究发现：①玉尔吐斯组下部为富有机质细粒沉积岩或与硅质岩的薄韵律互层,向上变为陆源碎屑混积的颗粒滩和逆粒序的碳酸盐岩;②与暗色泥页岩韵律互层的薄层灰岩具逆粒序;③薄层状硅质岩具交代残余颗粒结构、叠层状构造和孔洞胶结组构;④混积颗粒滩变浅序列顶部具铁质结壳层,其下见溶沟、溶缝及囊状溶洞、近地表喀斯特（塑形）角砾以及岩溶系统内的角砾、陆源碎屑充填物等,这些均为暴露岩溶标志;⑤露头和地震剖面上,不整合面或暴露面之上的富有机质细粒沉积岩具典型的超覆特征。综合分析认为,寒武系玉尔吐斯组富有机质细粒沉积物形成于缺氧—次氧化的受限海湾澙湖环境,其形成可能受高的古生产力、氧交换不畅共同控制,进而建立了其浅水超覆沉积模式。结果将有助于丰富完善富有机质细粒沉积岩沉积学理论。图12参60
|
| [8] |
张春宇, 管树巍, 吴林, 等. 塔西北地区早寒武世玉尔吐斯组热液作用及沉积模式[J]. 地学前缘, 2019, 26(1): 202-211.
埃迪卡拉纪寒武纪之交全球沉积了一套黑色泥页岩和硅质岩组合，塔里木盆地早寒武世玉尔吐斯组即包含这样一套组合，并被认为是塔里木古生界主力烃源岩之一，然而目前对这套岩石组合的成因及沉积过程的研究还相对薄弱。在野外研究的基础上，将玉尔吐斯组分为5段，分为两个海进海退旋回，认为其总体沉积于缓坡背景之上。对第一段硅质岩进行主量元素及稀土元素分析，结果显示其含有较低的Al/(Al+Fe+Mn)和较高的Fe/Ti值(均值分别为0.29和108.24)。在AlFeMn和Fe/TiAl(Al+Fe+Mn)图解上，多数样品落入热液作用范围，表明硅质岩主要受热液作用控制。硅质岩REE配分模式显示其不具有Eu的正异常和LREE富集的特征，这显示了海水对热液的稀释作用。靠近热液盆内口的库勒和什艾日克剖面发育较厚的硅质岩和一系列滑移变形构造。早寒武世时期，南天山洋已经打开，硅质热液广泛发育于整个塔北的深水和浅水区，这些迹象表明该区早寒武世仍然有很强的伸展构造活动。
Black shale and chert suites were deposited during the Edicarian-Cambrian transition all around the world. The Early Cambrian Yurtus Formation in the Tarim Basin contains this rock suites and was considered to be one of the major Paleozoic source rocks in Tarim. However, the origin and depositional process of the rock suites are poorly understood. In this contribution, our field study shows that the Yurtus Formation can be divided into five stages and comprises two transgression-regression cycles. The cherts of stage 1 are characterized by low Al/(Al+Fe+Mn) (average 0.29) and high Fe/Ti (average 108.24) ratios. In AlFeMn and Fe/TiAl/(Al+Fe+Mn) diagrams, most of the samples show strong hydrothermal influence. Lacking pronounced positive Eu anomaly (average 0.84) and no LREE enrichment in the cherts REE pattern suggests seawater involvement to the sediment. Kule and Shiairike profiles near the hydrothermal vent are characterized by thicker chert and related deformation. In the Early Cambrian, the South Tianshan Ocean evolved into a mature ocean with silica-rich hydrothermal fluid spreading widely in the shallow and deep environment across northern Tarim Basin, reflecting strong extensional tectonic activities in this area.<br>
|
| [9] |
马庆佑, 曹自成, 蒋华山, 等. 塔河—顺北地区走滑断裂带的通源性及其与油气富集的关系[J]. 海相油气地质, 2020, 25(4): 327-334.
|
| [10] |
邱华标, 印婷, 曹自成, 等. 塔里木盆地塔中北坡走滑断裂特征与奥陶系油气勘探[J]. 海相油气地质, 2017, 22(4): 44-52.
|
| [11] |
朱光有, 胡剑风, 陈永权, 等. 塔里木盆地轮探1井下寒武统玉尔吐斯组烃源岩地球化学特征与形成环境[J]. 地质学报, 2022, 96(6): 2116-2130.
|
| [12] |
肖斌, 郭东旭, 冯明飞, 等. 渝东北五峰组—龙马溪组黑色页岩有机质富集主控因素[J]. 断块油气田, 2024, 31(1): 18-25, 49.
|
| [13] |
|
| [14] |
付小东, 陈娅娜, 罗冰, 等. 四川盆地北部中二叠统茅口组孤峰段优质烃源岩特征及其油气地质意义[J]. 地质学报, 2021, 95(6): 1903-1920.
|
| [15] |
|
| [16] |
肖斌, 刘树根, 冉波, 等. 基于元素Mn、Co、Cd、Mo的海相沉积岩有机质富集因素判别指标在四川盆地北缘的应用[J]. 地质论评, 2019, 65(6): 1316-1330.
|
| [17] |
|
| [18] |
|
| [19] |
|
| [20] |
何龙, 王云鹏, 陈多福, 等. 重庆南川地区五峰组—龙马溪组黑色页岩沉积环境与有机质富集关系[J]. 天然气地球科学, 2019, 30(2): 203-218.
利用有机碳、硫以及主量元素和微量元素等地球化学方法，分析了重庆东南部南川县三泉剖面的上奥陶统五峰组黑色页岩、观音桥段泥灰岩、下志留统龙马溪组黑色页岩的沉积环境与有机质的富集关系。结果表明，五峰组中上段和龙马溪组下段为有机质富集层段,Ba、P显示晚奥陶世—早志留世四川盆地内具有较高的生产力水平；V/Cr、Ni/Co和S/C等指示五峰组沉积时为缺氧还原条件,冰期观音桥段为富氧—贫氧环境，龙马溪组为厌氧硫化环境；Mo/TOC表明五峰组页岩受局限盆地控制，观音桥段和龙马溪组为中等—弱滞留环境；Ce异常揭示了冰期前后古海平面的变化对海底氧化还原条件造成的影响；TOC与Ba、Ti/Al的弱相关性表明初级生产力水平与陆源碎屑对五峰组—龙马溪组黑色页岩有机质的富集影响较小；而与V/Cr、Ni/Co的正相关性则表明缺氧还原的沉积环境是影响五峰组—龙马溪组黑色页岩有机质富集的主要因素。
The enrichment of organic matter in black shale is a controversial issue among the researchers and critical problem in the exploration of shale gas.In order to discuss the relationship between sedimentary environment and organic matter accumulation in black shale of Wufeng Formation,Longmaxi Formation and limestone of Guanyinqiao Bed,multiple geochemical method,such as organic carbon,sulfur contents,major and trace elements,are tested from the Sanquan section in the southeast of Chongqing.Research results show that the organic carbon is enriched in the middle to upper part of Wufeng Formation and the bottom of Longmaxi Formation.Ba and P contents exhibit a high primary productivity during Late Ordovician-Early Silurian in Sichuan Basin.Redox proxies(V/Cr,Ni/Co and S/C) indicate that Wufeng Formation deposited in an anoxic environment and Longmaxi Formation deposited in euxinic condition,but Guanyinqiao Bed was predominated by oxic-dysoxic environment during the glaciation.Mo/TOC shows a strong restricted water mass controlled the accumulation of Wufeng Formation and a moderate-weak restriction of Longmaxi Formation and Guanyinqiao Bed,respectively.Ce anomaly reveals that the fluctuation of sealevel affected the redox condition of bottom water.The poor relation between TOC and Ba,Ti/Al suggests primary productivity and terrigenous clastics are not the major factors controlling the enrichment of organic matter,but an anoxic environment is the predominant condition causing the accumulation and preservation of organic matter suggested by a positive relation among TOC and V/Cr,Ni/Co.
|
| [21] |
|
| [22] |
|
| [23] |
|
| [24] |
孙候雪, 郝芳, 王奇, 等. 早寒武世玉尔吐斯组烃源岩沉积环境与有机质富集机制[J]. 高校地质学报, 2024, 30(5): 622-633.
|
/
| 〈 |
|
〉 |
