Shale Oil Mobility Evaluation and Multi-Scale Characterization of Oil Occurrence Space of Liushagang Formation in Weixinan Sag, Beibuwan Basin
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摘要: 为了明确北部湾盆地涠西南凹陷流沙港组页岩油赋存空间及可动性特征，采用岩石薄片鉴定、荧光观测、扫描电镜、氮气吸附、高压压汞、数字岩心分析、核磁共振、多温阶热解等实验技术，对涠西南凹陷流沙港组不同类型页岩油的储层孔隙结构、页岩油赋存空间及可动性特征进行定性分析和定量表征.结果表明：（1）基质型页岩油储层主要发育纳米级的有机孔、黄铁矿晶间孔、黏土矿物粒间孔、以及层理缝、有机质粒缘收缩缝；基质型页岩油主要赋存在孔喉半径小于10 nm的储集空间内.纹层型页岩除了发育纳米‒微米级的有机孔、晶间孔及微裂缝外，还发育粒间孔、粒内孔等；纹层型页岩油主要赋存在孔喉半径为10~50 nm之间的储集空间内.夹层型页岩主要发育纳米‒微米级的晶间孔、粒间孔、粒内孔及溶蚀孔等；夹层型页岩油主要赋存在孔喉半径介于100~1 000 nm的储集空间内.（2）不同类型页岩油可动性差异明显，其中夹层型页岩油可动性最好，最大可动油含量为22.78~42.63 mg/g，平均32.71 mg/g，可动油比例高达80%以上；纹层型页岩油可动性次之，最大可动油含量为1.78~16.35 mg/g，平均10.88 mg/g，可动油比例在60%左右；基质型页岩油可动油含量和可动油比例最小.（3）有机质丰度与成熟度、储层物性及矿物组成等共同控制了页岩油的可动性；当Ro为1.0%左右，TOC介于1.5%~4%之间，页岩储层可动油最为富集；另外，储层孔喉半径越大、物性越好、脆性矿物含量越高、黏土矿物含量越低，页岩油可动性越好.基于上述研究成果，夹层型页岩具有较大的赋存空间及较好的可动性，是涠西南凹陷页岩油勘探的首选类型，并推动海上页岩油钻探获得重大突破.Abstract: In order to clarify the occurrence space and mobility characteristics of shale oil in the Liushagang Formation of the Weixinan Sag in Beibuwan Basin, comprehensive experimental techniques such as thin section identification, fluorescence observation, scanning electron microscopy, nitrogen adsorption, high-pressure mercury injection, digital core analysis, nuclear magnetic resonance, and multi-temperature pyrolysis were utilized to qualitatively and quantitatively investigate the pore structure, occurrence space, and mobility characteristics of different types of shale oil reservoirs in the Liushagang Formation of the Weixinan Sag. Results show that: (1) matrix-type shales mainly contain nanoscale pores in organic matter, intergranular pores in pyrite, interparticle pores in clay minerals, fractures at bedding interface, as well as shrinkage fractures on the edge of organic matter particles. Oil in the matrix-type shales mainly stores in pores with pore throat radius less than 10 nm. In addition to organic pores, intergranular pores and microfractures, there are intergranular and intragranular pores developed in laminated shale oil reservoirs. Oil in the laminated shales mainly stores in pore spaces with pore throat radius between 10 nm and 50 nm. The "sandwiched" shales mainly contain intergranular pores, intergranular pores, intraparticle pores, and dissolution-related pores at the nanometer to micrometer scale. Oil in the "sandwiched" shales mainly exists in pore spaces with pore throat radius ranging from 100 to 1 000 nm. (2) There are significant differences in the oil mobility of different types of shales. Among them, the "sandwiched" shales have the best mobility. The maximum movable oil content of the "sandwiched" shales is between 22.78 and 42.63 mg/g (averaging 32.71 mg/g), and the movable oil proportion is higher than 80%. The second is the laminated shales, with the maximum movable oil content of 1.78-16.35 mg/g (averaging 10.88 mg/g), and the movable oil proportion of about 60%. The matrix-type shales have the lowest movable oil content and movable oil proportion. (3) The abundance and thermal maturity of organic matter, reservoir pore space, and mineral composition control the shale oil mobility; When the thermal maturity (Ro) is around 1.0% and TOC content is between 1.5% and 4%, shale reservoirs are mostly enriched in movable oil. In addition, the larger the pore throat radius, the better the physical properties, the higher content of brittle minerals, the lower content of clay minerals, the better shale oil movability. Based on the above results, the "sandwiched" shales have the largest storage space and the best mobility, and are the preferred target for shale oil exploration in the Weixinan Sag. These are the basis for the significant breakthroughs in offshore shale oil drilling.
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Key words:
- shale oil /
- occurrence space /
- mobility /
- movable oil content /
- Weixinan Sag /
- Beibuwan Basin /
- petroleum geology
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图 2 北部湾盆地涠西南凹陷及周缘构造区划简图
Fig. 2. Sketch map showing structure units in Weixinan Sag and its margin, Beibuwan Basin
图 4 北部湾盆地涠西南凹陷不同类型页岩油特征
Fig. 4. Types and characteristics of shale oil in Weixinan Sag, Beibuwan Basin
图 5 涠西南凹陷不同类型页岩油储层铸体薄片与扫描电镜特征图
a. WY-1井，基质型，2 959 m流二段下层序油页岩，单偏光；b. WY-5井，基质型，2 520 m流二段下层序油页岩，扫描电镜，×20 000；c. WY-1井，基质型，2 959 m流二段下层序油页岩扫描电镜，×8 000；d. WY-5井，纹层型，2 546 m流二段下层序油页岩，单偏光；e. WY-5井，纹层型，2 546 m流二段下层序油页岩扫描电镜，×10 000；f. WY-5井，纹层型，2 553 m流二段下层序油页岩扫描电镜，×30 000；g. WY-1井，纹层型，3 053 m流二段下层序粉砂岩，单偏光；h. WY-1井，纹层型，3 053 m流二段下层序粉砂岩扫描电镜，×200；i. WY-6井，纹层型，2 923 m流二段下层序粉砂岩扫描电镜，×1 000；j. WY-1井，夹层型，3 060.2 m流三段上层序泥岩，单偏光；k. WY-1井，夹层型，3 060.2 m流三段上层序泥岩扫描电镜，×5 000；l. WY-1井，夹层型，3 060.2 m流三段上层序泥岩扫描电镜，×6 000；m. WY-1井，夹层型，3 059.8 m流三段上层序细砂岩，单偏光；n. WY-7井，夹层型，2 541 m流三段上层序细砂岩扫描电镜，×1 400；o. WY-7井，夹层型，2 441.2 m流三段上层序细砂岩扫描电镜，×2 800
Fig. 5. Thin section and SEM images of different kinds of shales in Weixinan Sag
图 6 涠西南凹陷不同类型页岩油三维聚焦离子束扫描电镜成像图及孔隙网络模型
a. WZ12-2-A10S1井，基质型，3 158.6 m流二段下层序油页岩三维聚焦离子束扫描；b. WZ12-2-A10S1井，基质型，3 158.6 m流二段下层序油页岩孔隙三维模型；c. WZ12-2-A10S1井，基质型，3 158.6 m流二段下层序油页岩孔隙网络模型；d. WY-1井，纹层型，3 021 m流二段下层序油页岩三维聚焦离子束扫描；e. WY-1井，纹层型，3 021 m流二段下层序油页岩孔隙三维模型；f. WY-1井，纹层型，3 021 m流二段下层序油页岩孔隙网络模型；g. WY-1井，夹层型，3 026.98 m流三段上层序粉砂岩三维聚焦离子束扫描；h. WY-1井，夹层型，3 026.98 m流三段上层序粉砂岩孔隙三维模型；i. WY-1井，夹层型，3 026.98 m流三段上层序粉砂岩孔隙网络模型
Fig. 6. 3D FIB-SEM images and pore network models of different kinds of shales in Weixinan Sag
图 7 涠西南凹陷不同类型页岩油激光共聚焦照片
a. WZ12-2-A10S1，3 164.46 m，基质型单偏光照片；b. WZ12-2-A10S1井，3 164.46 m，基质型激光共聚焦照片；c. WY-1井，3 010.2 m，纹层型单偏光照片；d. WY-1井，3 010.2 m，夹层型激光共聚焦照片；e. WY-1井，3 026.6 m，夹层型单偏光照片；f. WY-1井，3 026.6 m，夹层型单偏光照片
Fig. 7. Confocal laser scanning images of different kinds of shales in Weixinan Sag
图 8 涠西南凹陷不同类型页岩油储层氮气吸脱附曲线
a.基质型页岩；b.纹层型页岩；c.夹层型页岩
Fig. 8. Nitrogen adsorption-desorption isotherms of different kinds of shales in Weixinan Sag
图 9 涠西南凹陷不同类型页岩油储层氮气吸附法孔径分布曲线
a.基质型页岩；b.纹层型页岩；c.夹层型页岩
Fig. 9. Pore size distribution curves of different kinds of shales using nitrogen adsorption method in Weixinan Sag
图 10 涠西南凹陷不同类型页岩油储层高压压汞法毛管压力曲线
Fig. 10. High-pressure mercury intrusion capillary pressure curves of different kinds of shales in Weixinan Sag
图 11 涠西南凹陷不同类型页岩油储层压汞法孔喉半径分布曲线
Fig. 11. Pore throat distribution curves of different kinds of shales using MICP method in Weixinan Sag
图 12 涠西南凹陷不同类型页岩油储层荧光薄片特征
a. WY-1井，2 971 m，基质型，单偏光，×10；b. WY-1井，2 971 m，基质型，荧光，×10；c. WY-1井，3 016.3 m，纹层型，单偏光，×10；d. WY-1井，3 016.3 m，纹层型，荧光，×10；e. WY-1井，3 060.2 m，夹层型，单偏光，×10；f. WY-1井，3 060.2 m，夹层型，荧光，×10
Fig. 12. Fluorescence microscopy images of different kinds of shales in Weixinan Sag
图 13 涠西南凹陷不同类型页岩饱和油和离心后的T2谱分布图
a. WY-1井2 956 m流二段下层序油页岩，基质型，可动孔隙度为0.86%，可动流体饱和度为23.2%；b. WY-1井3 027.33 m流二段下层序油页岩，纹层型，可动孔隙度为4.86%，可动流体饱和度为54.5%；c. WY-1井3 254 m流三段上层序粉砂岩，夹层型，可动孔隙度为7.13%，可动流体饱和度为57.2%
Fig. 13. NMR T2 spectrum of oil-saturated and centrifugal shales in Weixinan Sag
图 14 涠西南凹陷不同类型页岩可动油含量及可动油比例
a. 现实可动油含量；b. 最大可动油含量；c. 可动油和吸附油比例
Fig. 14. Movable oil content and proportion of different kinds of shales in Weixinan Sag
图 15 不同类型页岩油实测Ro (a)及可动油指数OSI (b)随埋藏深度变化关系
Fig. 15. The relationship between buried depth and vitrinite reflectance (a) and OSI values (a) of different kinds of shales in Weixinan Sag
图 16 涠西南凹陷不同类型页岩油有机质丰度对S1（a）和OSI（b）的影响
Fig. 16. The relationship between TOC content and S1 (a) and OSI (b) of different kinds of shales in Weixinan Sag
图 17 涠西南凹陷不同类型页岩油OSI与典型矿物含量变化关系
Fig. 17. The relationship between OSI and typical minerals content of different kinds of shale oils in Weixinan Sag
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