Fractal evaluation method for comprehensive sweet spot interval of Yingxiongling shale oil reservoir in horizontal fracturing wells, Qaidam Basin

doi:10.3969/j.issn.1672-7703.2025.02.012

Abstract

Abstract: The evaluation of comprehensive sweet spots of shale oil reservoir involves both geological and engineering factors. A conventional logging curve based fractal characteristic method has been proposed to evaluate comprehensive sweet spot interval of shale oil reservoir in horizontal fracturing wells. Taking Chaiping 2 and Chaiping 4 horizontal fracturing wells in sweet spot zone of Yingxiongling shale oil reservoir in Qinghai Oilfield as case studies, fractal characteristic parameters are extracted from conventional well logging data. By integrating post-fracturing production profile monitoring data, and applying gray relation analysis method, parameters such as weighted multifractal spectrum width (Δα') and weighted fractal dimension (D') are introduced to establish a production capacity evaluation standard based on fractal characterization. The results show that the weighted fractal evaluation index for Class Ⅰ comprehensive sweet spot is 0.75<Δα'≤1, 0<D'≤0.25, that for Class Ⅱ comprehensive sweet spot is 0.35<Δα'≤0.75, 0.25<D'≤0.8, and that for Class Ⅲ comprehensive sweet spot is 0<Δα'≤0.35, 0.8<D'≤1. After validated by Well Chaiping 14-2, it is indicated that an overall accuracy reaches up 72.7%, which is significantly higher than 30.1% by conventional method. This integrated fractal evaluation approach provides technical support for precise identification and high-efficiency development of comprehensive sweet spot intervals of shale oil reservoirs.

Key words: Logging curve, multifractal spectrum, fractal dimension, gray relation analysis, shale oil

CLC Number:

P631

Li Juhua, Lian Cuihao, Lei Zhengdong, Lin Hai, Liu Shiduo, Wan Youyu, Lei Fengyu. Fractal evaluation method for comprehensive sweet spot interval of Yingxiongling shale oil reservoir in horizontal fracturing wells, Qaidam Basin[J]. China Petroleum Exploration, 2025, 30(2): 159-168.

References

[1] 赵文智，胡素云，侯连华，等．中国陆相页岩油类型、资源潜力及与致密油的边界[J]．石油勘探与开发，2020,47(1):1-10．
Zh a o Wenzhi, Hu Suyun, Hou Lianhua, et al. Types and resource potential of continental shale oil in China and its boundary with tight oil[J]. Petroleum Exploration and Development, 2020,47(1):1-10．
[2] 金之钧，朱如凯，梁新平，等．当前陆相页岩油勘探开发值得关注的几个问题[J]．石油勘探与开发，2021,48(6):1276-1287．
Jin Zhijun，Zhu Rukai, Liang Xinping, et al．Several issues worthy of attention in current lacustrine shale oil exploration and development[J]．Petroleum Exploration and Development，2021,48(6):1276-1287.
[3] 王建，郭秋麟，赵晨蕾，等. 中国主要盆地页岩油气资源潜力及发展前景[J]. 石油学报，2023,44(12):2033-2044.
Wang Jian, Guo Qiulin, Zhao Chenlei, et al. Potential sand prospects of shale oil gas resources in major basins of China[J]. Acta Petrolei Sinica，2023,44(12):2033-2044.
[4] 韩成，陈旋，陈杰，等．三塘湖盆地芦草沟组页岩油测井评价技术进展[J]．新疆石油地质，2020,41(6):740-747．
Han Cheng, Chen Xuan, Chen Jie, et al. Progress of well logging evaluation techniques for shale oil of Lucaogou Formation in Santanghu Basin[J]. Xinjiang Petroleum Geology,2020,41(6):740-747.
[5] 匡立春，侯连华，杨智，等．陆相页岩油储层评价关键参数及方法[J].石油学报，2021,42(1):1-14．
Kuang Lichun, Hou Lianhua, Yang Zhi, et al． Key parameters and methods of lacustrine shale oil reservoir characterization[J]. Acta Petrolei Sinica，2021,42(1):1-14．
[6] 李国欣，刘国强，侯雨庭，等．陆相页岩油有利岩相优选与压裂参数优化方法[J]．石油学报，2021,42(11):1405-1416．
Li Guoxin, Liu Guoqiang, Hou Yuting, et al. Optimization method of favorable lithofacies and fracturing parameter for continental shale oil[J]. Acta Petrolei Sinica, 2021,42(11):1405-1416.
[7] Lai Jin, Su Yang, Xiao Lu, et al. Application of geophysical well logs in solving geologic issues: past, present and future prospect[J]．Geoscience Frontiers, 2024,15(3):1-34.
[8] 刘国强．非常规油气勘探测井评价技术的挑战与对策[J]．石油勘探与开发，2021,48(5):891-902．
Liu Guoqiang. Challenges and countermeasures of log evaluation in unconventional petroleum exploration[J]. Petroleum Exploration and Development，2021,48(5):891-902．
[9] 夏宏泉, 赖俊, 李高仁, 等. 基于测井资料的页岩油储层甜点预测[J].西南石油大学学报( 自然科学版)，2021,43(4):199-207.
Xia Hongquan, Lai Jun, Li Gaoren, et al. Prediction of shale oil reservoir sweet spots based on logging data[J]. Journal of Southwest Petroleum University (Science & Technology Edition), 2021,43(4):199-207.
[10] 石玉江，蔡文渊，刘国强，等. 页岩油储层孔隙流体的全直径岩心二维核磁共振图谱特征及评价方法[J]. 中国石油勘探，2023,28(3):132-144.
Shi Yujiang, Cai Wenyuan, Liu Guoqiang, et al. Fulldiameter core 2D NMR logging characteristics and evaluation methods of pore fluid in shale oil reservoirs[J]. China Petroleum Exploration, 2023,28(3):132-144.
[11] 张驰，关平，张济华，等. 分形理论表征非常规油气储层孔隙结构特征研究进展[J]. 北京大学学报( 自然科学版)，2023,59(5):897-908.
Zhang Chi, Guan Ping, Zhang Jihua, et al. A review of the progress on fractal theory to characterize the pore structure of unconventional oil and gas reservoirs[J]. Acta Scientiarum Naturalium Universitatis Pekinensis, 2023,59(5):897-908.
[12] Mishra D K, Samad S K, Varma A K, et al. Pore geometrical complexity and fractal facets of Permian shales and coals from Auranga Basin, Jharkhand, India[J]. Journal of Natural Gas Science and Engineering, 2018,52(4):25-43.
[13] 张琴，梁峰，梁萍萍，等. 页岩分形特征及主控因素研究：以威远页岩气田龙马溪组页岩为例[J]. 中国矿业大学学报，2020,49(1):110-122.
Zhang Qin, Liang Feng, Liang Pingping, et al. Study on fractal characteristics and controlling factors of shale: a case of Longmaxi shale in weiyuan shale gas field[J]. Journal of China University of Mining & Technology, 2020,49(1):110-122.
[14] 李菊花，郑斌．微观孔隙分形表征新方法及其在页岩储层中的应用[J].天然气工业，2015,35(5):52-59.
Li Juhua, Zheng Bin. A new method for fractal characterization of microscopic pores and its application in shale reservoirs[J]. Natural Gas Industry, 2015，35(5): 52-59.
[15] 尹娜，薛莲花，姜呈馥，等. 富有机质页岩生烃阶段孔隙演化及分形特征[J]. 天然气地球科学，2018,29(12):1817-1828.
Yin Na, Xue Lianhua, Jiang Chengfu, et al. Pore evolution and fractal characteristics during the hydrocarbon generation stage of organic-rich shale[J]. Natural Gas Geoscience, 2018,29(12):1817-1828.
[16] Fan C H, Qin Q R, Hu D F, et al. Fractal characteristics of reservoir structural fracture: a case study of Xujiahe Formation in central Yuanba area, Sichuan Basin[J]. Earth Sciences Research Journal, 2018,22(2):113-118.
[17] Bai H Y, Cao Y, Zhang H, et al. Applying data-drivenbased logistic function and prediction area plot to map mineral prospectivity in the Qinling Orogenic Belt, Central China[J]. Minerals, 2022,12(10):1287.
[18] 张焱，周永章，朱继田. 基于主成份的多重分形法在岩性识别中的应用[J]. 中山大学学报( 自然科学版)，2015,54(3):145-150,157.
Zhang Yan, Zhou Yongzhang, Zhu Jitian. Multi-fractal method’s application based on principal component in lithology Recognition[J]. Acta Scientiarum Naturalium Universitatis Sunyatseni, 2015,54(3):145-150,157.
[19] 陈惠，冯春珍，赵建鹏，等. 基于分形与核磁共振测井的储层孔隙结构表征与分类[J]. 测井技术，2021,45(1):50-55.
Chen Hui, Feng Chunzhen, Zhao Jianpeng, et al. Characterization and classification of reservoir pore structure based on fractal and nuclear magnetic resonance logging[J]. Well Logging Technology, 2021,45(1):50-55.
[20] 王敏，胡松，宁从前，等. 基于测井曲线分形维的碳酸盐岩孔隙结构分类方法[J]. 地球物理学进展，2021,36(2):668-674.
Wang Min, Hu Song, Ning Congqian, et al. Classification method of Carbonate pore structure based on fractal dimension of logging curves[J]. Progress in Geophysics, 2021,36(2):668-674.
[21] 丁明才，吴明录，李轩，等. 分形裂缝性页岩气藏多段压裂水平井瞬态压力特征[J]. 计算物理，2019,36(5):559-568.
Ding Mingcai, Wu Minglu, Li Xuan, et al. Transient pressure characteristics of multistage fractured horizontal wells in fractured shale gas reservoirs[J]. Chinese Journal of Computational Physics,2019,36(5):559-568.
[22] 李国欣，朱如凯，张永庶，等. 柴达木盆地英雄岭页岩油地质特征、评价标准及发现意义[J]. 石油勘探与开发，2022,49(1):18-31.
Li Guoxin, Zhu Rukai, Zhang Yongshu, et al. Geological characteristics, evaluation criteria and discovery significance of Paleogene Yingxiongling shale oil in Qaidam Basin, NW China[J]. Petroleum Exploration and Development, 2022,49(1):18-31.
[23] 邢浩婷，匡立春，伍坤宇，等. 柴达木盆地英雄岭页岩岩相特征及有利源储组合[J]. 中国石油勘探，2024,29(2):70-82.
Xing Haoting, Kuang Lichun, Wu Kunyu, et al. Lithofacies characteristics and favorable source rock-reservoir combination of Yingxiongling shale in Qaidam Basin[J]. China Petroleum Exploration, 2024,29(2):70-82.
[24] 崔俊，毛建英，赵为永，等. 柴达木盆地英雄岭页岩纹层结构特征及石油地质意义[J]. 中国石油勘探，2023,28(5):43-53.
Cui Jun, Mao Jianying, Zhao Weiyong, et al. Characteristics of laminated texture and petroleum geological significance of Yingxiongling shale in Qaidam Basin[J]. China Petroleum Exploration, 2023,28(5):43-53.
[25] Wutherich K, Walker K J. Designing completions in horizontal shale gas wells: perforation strategies[C]. Pittsburgh: SPE Americas Unconventional Resources Conference, 2012:155485.

[26] 陈颙，陈凌. 分形几何学（第二版）[M]. 北京：地震出版社，2018.

Chen Yong, Chen Ling. Fractal Geometry（Second Edition） [M].Beijing: Seismological Press, 2018.

[27] 邹长春, 杨欣德, 潘令枝, 等. 一种基于小波变换的测井曲线去噪新方法[J]. 物探与化探,1999, 23(6):462-466.
Zou Changchun, Yang Xinde, Pan Lingzhi, et al. A new method for de-noising logging curves based on Wavelet Transform[J]. Geophysical and Geochemical Exploration, 1999,23(6):462-466.
[28] 胡宗全.R/S 分析在储层垂向非均质性和裂缝评价中的应用[J]. 石油实验地质,2000, 22(4):382-386.
Hu Zongquan. Application of R/S Analysis in evaluation of reservoir vertical heterogeneity and fracture[J]. Experimental Petroleum Geology, 2000,22(4):382-386.
[29] Bi Xueli, Li Juhua, Lian Cuihao. A comprehensive logging evaluation method for identifying high-quality shale gas reservoirs based on multifractal spectra analysis[J]. Scientific Reports, 2024,14:26107.