石油与天然气地质 ›› 2025, Vol. 46 ›› Issue (5): 1410-1429.doi: 10.11743/ogg20250503

• 油气地质 • 上一篇    

鄂尔多斯盆地陕北地区延长组长8与长9油层组烃源岩分布与地球化学特征及页岩油资源潜力评价

曹磊1,2(), 闫新智3, 李辉4, 吴伟涛1,2, 白玉彬1,2, 赵子龙1,2   

  1. 1.西安石油大学 地球科学与工程学院，陕西 西安 710065
    2.陕西省油气成藏地质学重点实验室，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.中国石油与天然气有限公司 长庆油田分公司 勘探事业部，陕西 西安 710018
  • 收稿日期:2025-07-31 修回日期:2025-09-04 出版日期:2025-10-30 发布日期:2025-10-29
  • 第一作者简介:曹磊（1992—），男，博士、副教授、硕士研究生导师，油气地球化学与油气成藏地质学。E-mail：leicao@xsyu.edu.cn。
  • 基金项目:
    国家自然科学基金青年基金项目(42202185);中国博士后科学基金项目(2022MD713801);陕西省教育厅科技计划项目(22JK0505)

Geochemical characteristics， distribution， and shale oil resource potential of source rocks in the 8th and 9th oil groups of the Yanchang Formation， northern Shaanxi， Ordos Basin

Lei CAO1,2(), Xinzhi YAN3, Hui LI4, Weitao WU1,2, Yubin BAI1,2, Zilong ZHAO1,2   

  1. 1.School of Earth Sciences and Engineering，Xi’an Shiyou University，Xi’an，Shaanxi 710065，China
    2.Shaanxi Key Laboratory of Petroleum Accumulation Geology，Xi’an，Shaanxi 710065，China
    3.Exploration Department of Yanchang Oilfield Co. ，Ltd. ，Yan’an，Shaanxi 716000，China
    4.Petroleum Exploration Division，Changqing Oilfield Company，PetroChina，Xi’an，Shaanxi 710018，China
  • Received:2025-07-31 Revised:2025-09-04 Online:2025-10-30 Published:2025-10-29

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摘要：

基于岩心观察、地球化学、测井、录井、原油物性和试油资料，研究了鄂尔多斯盆地陕北地区延长组（长）8和长9油层组烃源岩地球化学特征、烃源岩分布特征及研究区延长组下组合致密油成藏规律，计算了页岩油资源量。研究结果表明：①鄂尔多斯盆地陕北地区长8和长9油层组粉砂质泥岩、泥岩和页岩总有机碳含量（TOC）主要在1.0% ~ 16.0%，平均值为4.8%，有机质丰度为好-很好烃源岩；干酪根类型指数（TI）在47 ~ 92，平均值为70，δ13C干酪根介于-29.8‰ ~ -25.9‰，平均值为-27.8‰，有机质类型主要为Ⅱ1型；最高热解峰温（Tmax）介于444 ~ 470 ℃，平均值为456 ℃，镜质体反射率（Ro）在0.72% ~ 1.56%，平均值为1.16%，有机质主要处于成熟-高熟阶段。②研究区长8和长9油层组各油层亚组均发育TOC大于1.0%且Ro大于0.70%的有效烃源岩，长9油层组李家畔页岩烃源岩最好，其次为长82油层亚组、长81油层亚组和长9油层组烃源岩。长9油层组李家畔页岩从定边—甘泉有逐渐变厚趋势，厚度4.0 ~ 17.0 m，平均厚度7.5 m，沉积中心主要在甘泉和安塞南部，厚度大于10.0 m的区域面积约为3 574 km2，甘泉地区最厚超过35.0 m。长8油层组烃源岩在志丹、甘泉和富县一带规模分布，长81油层亚组单层最大连续厚度超过10.0 m，长82油层亚组单层最大连续厚度超过30.0 m。③研究区延长组下组合烃源岩发育张家滩页岩（A）型、“张家滩页岩+李家畔页岩”（B）型、“张家滩页岩+长82油层亚组底部烃源岩+李家畔页岩”（C）型和“张家滩页岩+长8油层组中部烃源岩+李家畔页岩”（D）型4种垂向组合分布类型。烃源岩既是生油岩也是封盖层，B，C和D型长8油层组致密油藏油源和封盖条件相对较好，试油出油率较高。④根据烃源岩含油饱和度指数（OSI）、游离烃含量（S1）、氯仿沥青“A”含量、饱和烃含量和芳烃含量参数结合大庆古龙页岩油及国外页岩油勘探开发经验，以有效烃源岩OSI大于100 mg/g，介于70 ~ 100 mg/g和小于70 mg/g为标准划分出易动用（Ⅰ类）、潜在可动用（Ⅱ类）和难动用（Ⅲ类）3类页岩油资源。粉砂质泥岩既具有生烃能力，储集空间又优于泥岩和页岩，是最好的Ⅰ类页岩油岩性。计算得出研究区Ⅰ类页岩油资源量为3.8 × 108 t，Ⅱ类页岩油资源量为7.5 × 108 t，Ⅲ类页岩油资源量为29.5 × 108 t。

关键词: 地球化学特征, 烃源岩, 致密油, 页岩油, 长8油层组, 长9油层组, 陕北地区, 鄂尔多斯盆地

Abstract:

Using data from core observations， geochemical analysis， logging， crude oil physical properties， and well tests， we investigate the geochemical characteristics and spatial distribution of hydrocarbon source rocks in the 8th and 9th oil groups of the Yanchang Formation （also referred to as the Chang 8 and Chang 9 oil groups， respectively） in northern Shaanxi， Ordos Basin. The implications of tight oil accumulation within the lower hydrocarbon play of the Yanchang Formation in the study area are explored， and shale oil resources in the area are calculated. The results indicate that the silty mudstones， mudstones， and shales of the Chang 8 and Chang 9 oil groups contain total organic carbon （TOC） content ranging from 1.0% to 16.0% （average： 4.8%）， suggesting that they represent source rocks with organic matter abundance of good to excellent level. The kerogen of the source rocks exhibits type index （TI） values ranging from 47 to 92 （average： 70） and δ¹³Ckerogen values from -25.9‰ to -29.8‰ （average： -27.8‰）， indicating a predominance of type Ⅱ₁ kerogen. The source rocks show peak hydrocarbon pyrolysis temperature （Tmax） ranging from 444 ℃ to 470 ℃ （average： 456 ℃） and Ro values from 0.72% to 1.56% （average： 1.16%）， indicating that the organic matter is primarily in the mature to highly mature stage. Effective source rocks with TOC content > 1.0% and Ro values > 0.70% are identified across all oil sub-groups of the Chang 8 and Chang 9 oil groups. Among them， the Lijiapan shale of the Chang 9 oil group represents the most favorable source rocks， followed by shales of the 2nd and 1st oil sub-groups of the Chang 8 oil group （also referred to as the Chang 82 and Chang 81 oil sub-groups， respectively）， as well as the Chang 9 oil group. The Lijiapan shale of the Chang 9 oil group thickens progressively from Dingbian to Ganquan， with thicknesses ranging from 4.0 m to 17.0 m （average： 7.5 m）. Its primary depocenters are located in Ganquan and southern Ansai， where zones with shale thicknesses exceeding 10.0 m cover an area of approximately 3 574 km². In the Ganquan area， the Lijiapan shale of the Chang 9 oil group shows a thickness of up to a maximum of more than 35.0 m. The source rocks of the Chang 8 oil group are extensively developed in the Zhidan， Ganquan， and Fuxian areas， with those of the Chang 81 and Chang 82 oil sub-groups showing maximum single-layer continuous thicknesses exceeding 10.0 m and 30.0 m， respectively. Vertically， four types of source rock assemblages are identified within the lower hydrocarbon play of the Yanchang Formation： the Zhangjiatan shale （type A）， the Zhangjiatan shale + the Lijiapan shale （type B）， the Zhangjiatan shale + source rocks at the base of the Chang 8₂ oil sub-group + the Lijiapan shale （type C）， and the Zhangjiatan shale + source rocks in the middle Chang 8 oil group + the Lijiapan shale （type D）. Since source rocks act as both oil source rocks and cap rocks， the tight oil reservoirs of the Chang 8 oil group with source rock assemblages of types B， C， and D manifest favorable oil sources and strong sealing performance， which contribute to high tested oil production rates. Effective source rocks are further subdivided based on the oil saturation index （OSI） values， free hydrocarbon content （S1）， chloroform bitumen “A” content， saturated hydrocarbon content， and aromatic hydrocarbon content of source rocks， as well as experience in the exploration and exploitation of the Gulong shale oil in the Daqing oilfield and international analogues. Specifically， effective source rocks with OSI values of greater than 100 mg/g， 70 ~ 100 mg/g， and less than 70 mg/g are categorized as resources with readily movable （class Ⅰ）， potentially movable （class Ⅱ）， and hardly movable （class Ⅲ） shale oil， respectively. Silty mudstones are found bearing class Ⅰ shale oil due to their high hydrocarbon generation capacity and better reservoir spaces than mudstones and shales. The classes Ⅰ， Ⅱ， and Ⅲ shale oil resources in the study area are calculated at 0.38 × 109 t， 0.75 × 109 t， and 2.95 × 109 t， respectively.

Key words: geochemical characteristics, source rock, tight oil, shale oil, 8th oil group of the Yanchang Formation （Chang 8 oil group）, Chang 9 oil group, northern Shaanxi, Ordos Basin

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