石油与天然气地质 ›› 2025, Vol. 46 ›› Issue (5): 1554-1581.doi: 10.11743/ogg20250511

• 油气地质 • 上一篇    

鄂尔多斯盆地三叠系延长组长8-长9油层组泥页岩储层孔隙和微裂缝发育特征与页岩油勘探前景

张佳琦1,2(), 赵靖舟1,3(), 曹磊1,3, 叶卿元2   

  1. 1.西安石油大学 地球科学与工程学院，陕西 西安 710065
    2.长庆油田 页岩油开发分公司，陕西 西安 710018
    3.陕西省油气成藏地质学重点实验室，陕西 西安 710065
  • 收稿日期:2025-06-30 修回日期:2025-09-17 出版日期:2025-10-30 发布日期:2025-10-29
  • 通讯作者: 赵靖舟 E-mail:1061862954@qq.com;jzzhao@xsyu.edu.cn
  • 第一作者简介:张佳琦（2000—），女，硕士、助理工程师，非常规油气地质。E-mail：1061862954@qq.com。
  • 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);陕西省教育厅自然科学专项科研计划项目(22JK0505)

Pore and microfracture characteristics and shale oil exploration prospects of shale reservoirs in the 8th to 9th oil groups of the Triassic Yanchang Formation， Ordos Basin

Jiaqi ZHANG1,2(), Jingzhou ZHAO1,3(), lei CAO1,3, Qingyuan YE2   

  1. 1.School of Earth Sciences and Engineering，Xi’an Shiyou University，Xi’an，Shaanxi 710065，China
    2.Shale Oil Development Branch，Changqing Oilfield Company，PetroChina，Xi’an，Shaanxi 710018，China
    3.Shaanxi Key Laboratory of Petroleum Accumulation Geology，Xi’an，Shaanxi 710065，China
  • Received:2025-06-30 Revised:2025-09-17 Online:2025-10-30 Published:2025-10-29
  • Contact: Jingzhou ZHAO E-mail:1061862954@qq.com;jzzhao@xsyu.edu.cn

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摘要：

鄂尔多斯盆地三叠系延长组长8-长9油层组泥页岩矿物组成与孔隙、微裂缝发育特征及其对页岩油富集和可动性的影响尚不十分清楚。通过X射线衍射、场发射扫描电镜、CO2吸附、低温氮气吸附、高压压汞和地化实验分析测试资料，对长8-长9油层组页岩储层特征及其控油性进行了综合研究。研究结果表明：①研究区长8-长9油层组页岩具有长英质黏土页岩、黏土质长英页岩和黏土-长英混合页岩3种岩相。长8油层组主要为长英质黏土页岩和黏土质长英页岩岩相，长9油层组3种岩相均比较发育。②根据孔、缝发育情况、可压裂性和可动油富集程度综合评价，黏土质长英页岩岩相最优，黏土质-长英质混合页岩岩相次之，长英质黏土页岩岩相较差。③储层发育有机质孔、晶间孔、粒间孔、溶蚀孔和微裂缝。长8-长9油层组泥页岩总有机碳含量（TOC）与微孔和介孔孔体积具有明显正相关关系，但其有机质孔发育程度不及长7油层组页岩。微裂缝比较发育，主要为生烃增压产生的异常高压层理缝，其次为压溶层理缝及有机质收缩缝。④影响研究区孔隙和微裂缝发育的关键因素为高TOC、高有机质成熟度和高脆性矿物含量。高TOC和高有机质成熟度有利于有机质孔的发育和生烃成因异常高压缝的形成；碳酸盐胶结作用抑制孔隙发育并充填裂缝；高黏土矿物含量有利于微孔发育，但对介孔和宏孔发育具有不利影响。⑤可动油富集的主控因素包括TOC（< 4%）、有机质成熟度［镜质体反射率（Ro） > 1.2%］、脆性矿物含量（> 60%）和裂缝发育程度（裂缝线密度 > 1.6 × 104条/m）。⑥研究区页岩油甜点评价标准为Ⅰ类甜点油饱和度指数（OSI） > 100 mg/g，页岩油可动性最佳，集中分布在富县、甘泉及志丹东部地区，这些地区是研究区最有利的页岩油富集区，具有较好的勘探前景；Ⅱ类甜点OSI = 70 ~ 100 mg/g，页岩油具有可动性；Ⅲ类甜点OSI < 70 mg/g，页岩油动用难度较大，该类页岩油在研究区占主导地位。

关键词: 可动性, 孔隙, 裂缝, 储层特征, 页岩油, 长8油层组, 长9油层组, 鄂尔多斯盆地

Abstract:

Shales are well-developed in the 8th to 9th oil groups of the Triassic Yanchang Formation （also referred to as the Chang 8‒9 oil groups） in the Ordos Basin. However， their mineral composition and pore and microfracture characteristics， as well as the impacts of these factors on shale oil enrichment and mobility， remain insufficiently understood. In this study， we comprehensively investigate the shale reservoir characteristics and their controlling effects on shale oil in the Chang 8‒9 oil groups using data from a series of analyses and tests， including X-ray diffraction （XRD）， field emission scanning electron microscopy （FE-SEM）， CO₂ adsorption， low-temperature N2 adsorption， high-pressure mercury injection （HPMI）， and geochemical analyses. The results indicate that the shales in the two oil groups exhibit three lithofacies： felsic clayey shales， clayey felsic shales， and clayey-felsic mixed shales. The Chang 8 oil group is dominated by felsic clayey shales and clayey felsic shales， while all the three lithofacies types are relatively well-developed in the Chang 9 oil group. A comprehensive assessment of pore and microfracture characteristics， fracability， and shale oil mobility reveals that clayey felsic shales are the most favorable lithofacies， followed sequentially by clayey-felsic mixed shales and felsic clayey shales. The shale reservoirs in the two oil groups contain organic pores， intercrystalline pores， intergranular pores， dissolution pores， and microfractures. There are distinct positive correlations between total organic carbon （TOC） content and the volumes of micropores and mesopores. Compared to the Chang 7 oil group， organic pores are less developed in the Chang 8‒9 oil groups. Microfractures are well-developed in both oil groups， primarily including bedding-parallel fractures induced by abnormally high-pressure from hydrocarbon generation， followed by pressure dissolution-induced bedding-parallel fractures and shrinkage fractures in organic matter. Key factors contributing to the development of pores and microfractures in the study area include high TOC content， high organic matter maturity， and high brittle mineral content. Specifically， high TOC content and high organic matter maturity promote the development of organic pores and the formation of bedding-parallel fractures induced by abnormally high-pressure from hydrocarbon generation. In contrast， carbonate cementation inhibits pore development and fills fractures with cements. A high clay mineral content favors micropore development but adversely affects mesopore and macropore growth. Primary factors controlling movable oil enrichment include TOC content （< 4%）， organic matter maturity （vitrinite reflectance （Ro） > 1.2%）， brittle mineral content （> 60%）， and fracture density （> 1.6 × 10⁴/m）. As the assessment criteria for shale oil sweet spots in the study area shown， type Ⅰ sweet spots should have oil saturation index （OSI） values of greater than 100 mg/g， possess the highest shale oil mobility and are primarily distributed in the Fuxian， Ganquan， and eastern Zhidan areas. These areas represent the most favorable shale oil enrichment regions， holding promising exploration prospects. In contrast， type Ⅱ sweet spots are characterized by OSI values ranging from 70 mg/g to 100 mg/g， and exhibit a moderate mobility， while type Ⅲ sweet spots， with OSI values below 70 mg/g， show the lowest mobility. The type Ⅲ shale oil predominates across the study area.

Key words: mobility, pore, fracture, reservoir features, shale oil, Chang 8 oil group, Chang 9 oil group, Ordos Basin

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