Characteristics of natural fractures and its influence on shale oil enrichment and preservation in Member 2 of Funing Formation in Gaoyou sag, Subei Basin

doi:10.13745/j.esf.sf.2024.6.17

Abstract

Abstract:

Significant breakthrough has been made in shale oil exploration in Member 2 of the Funing Formation in Gaoyou sag, Subei Basin, a key area for increasing petroleum reserve and production. The advancement of shale oil exploration in the study area, however, is hindered by a lack of understanding of the complex fracture system and its impact on shale oil enrichment and preservation. In this contribution, we systematically analyze the characteristics of nature fractures using core logging, thin section, scanning electron microscopy, and Maps and Qemscan methods; the impact of fracture types on shale oil enrichment and preservation are further revealed through organogeochemical analysis of frozen cores, combined with well production data. Structural fractures such as layer-perpendicular and layer-controlled fractures are widely developed in shales of Mmember 2 of the Funing Formation, as well as nonstructural fractures such as bedding fractures and compression fractures. The development of layer-perpendicular fractures is controlled by lithology and structural location, while layer-controlled fractures mainly develop in brittle layers such as dolomite bands, sand/dolomite mixed bands, and bedding calcite veins. The bedding fractures are mainly caused by abnormal high pressure and are concentrated in the middle and lower parts of the study area. The bedding factures and the layer-controlled fractures and caves are conducive to shale oil enrichment, as they are not only favorable storage spaces but also efficient flow channels. Layer-perpendicular fractures show higher effectiveness of shale oil (S₁) enrichment compared to shale matrix; however, they can also be efficient oil seepage channels due to vertical and horizontal connectivity. This causes unfavorable preservation condition at the sweet spot “lower Ⅴ” in subsegment Ⅴ, but has less impact on subsegment Ⅳ. In general, the smaller the planar distance from the fault and the larger the fault scale is, the more developed and unfavorable the structural fractures are for shale oil preservation.

Key words: natural fractures, shale oil, enrichment and preservation, Member 2 of Funing Formation, Gaoyou sag, Subei Basin

CLC Number:

SUN Yaxiong, LIANG Bing, QIU Xuming, DUAN Hongliang, FU Qian, ZHOU Jinfeng, LIU Shili, QIU Yongfeng, HU Huiting, GONG Lei. Characteristics of natural fractures and its influence on shale oil enrichment and preservation in Member 2 of Funing Formation in Gaoyou sag, Subei Basin[J]. Earth Science Frontiers, 2024, 31(5): 61-74.

Figures/Tables 13

Fig.1 Distribution of shale thickness, TOC content and Ro value in Member 2 of Funing Formation in Gaoyou sag

Fig.2 Comprehensive stratigraphic colunm diagram of the study area

Fig.3 Image logging interpretation of fracture density in three wells

Fig.4 Characteristics of structural fractures in core specimens

Fig.5 Characteristics of nonstructural fractures in core specimens

Fig.6 Characteristics of microfractures

Fig.7 Main controlling factors for the development of bedding fractures

Fig.8 Characteristic parameters for structural fractures

Fig.9 Share of oil production by each fracturing section of well HY3HF

Fig.10 Bedding-parallel fibrous calcite veins and their microstructures

Fig.11 Dolomite bands and their microstructures

Fig.12 Relationship between natural fractures and shale oil enrichment and preservation

Fig.13 Development of structural fractures and key differences between sweet spots

References 44

[1]	ZHAO W Z, ZHU R K, HU S Y, et al. Accumulation contribution differences between lacustrine organic-rich shales and mudstones and their significance in shale oil evaluation[J]. Petroleum Exploration and Development, 2020, 47(6): 1160-1171.
[2]	金之钧, 王冠平, 刘光祥, 等. 中国陆相页岩油研究进展与关键科学问题[J]. 石油学报, 2021, 42(7): 821-835. DOI
[3]	黎茂稳, 马晓潇, 金之钧, 等. 中国海、陆相页岩层系岩相组合多样性与非常规油气勘探意义[J]. 石油与天然气地质, 2022, 43(1): 1-25.
[4]	金之钧, 张谦, 朱如凯, 等. 中国陆相页岩油分类及其意义[J]. 石油与天然气地质, 2023, 44(4): 801-819.
[5]	庞正炼, 陶士振, 张琴, 等. 鄂尔多斯盆地延长组7段夹层型页岩层系石油富集规律与主控因素[J]. 地学前缘, 2023, 30(4): 152-163. DOI
[6]	孙龙德, 崔宝文, 朱如凯, 等. 古龙页岩油富集因素评价与生产规律研究[J]. 石油勘探与开发, 2023, 50(3): 441-454. DOI
[7]	刘惠民. 济阳坳陷页岩油勘探实践与前景展望[J]. 中国石油勘探, 2022, 27(1): 73-87. DOI
[8]	朱相羽, 段宏亮, 孙雅雄. 苏北盆地高邮凹陷古近系陆相页岩油勘探突破及意义[J]. 石油学报, 2023, 44(8): 1206-1221, 1257. DOI
[9]	宋国奇, 徐兴友, 李政, 等. 济阳坳陷古近系陆相页岩油产量的影响因素[J]. 石油与天然气地质, 2015, 36(3): 463-471.
[10]	李玉丹. 天然裂缝对页岩油产量可能无重大贡献[J]. 石油与天然气地质, 2023, 44(4): 798.
[11]	朱夏, 徐旺. 中国中新生代沉积盆地[M]. 北京: 石油工业出版社, 1990.
[12]	舒良树, 王博, 王良书, 等. 苏北盆地晚白垩世—新近纪原型盆地分析[J]. 高校地质学报, 2005, 11(4): 534-543.
[13]	邱海峻, 许志琴, 乔德武. 苏北盆地构造演化研究进展[J]. 地质通报, 2006, 25(增刊2): 1117-1120.
[14]	李维, 朱筱敏, 段宏亮, 等. 苏北盆地高邮—金湖凹陷古近系阜宁组细粒沉积岩纹层特征与成因[J]. 古地理学报, 2020, 22(3): 469-482.
[15]	李维. 高邮/金湖凹陷阜宁组二段混合沉积环境与储层特征[D]. 北京: 中国石油大学(北京), 2021.
[16]	陈安定. 苏北盆地构造特征及箕状断陷形成机理[J]. 石油与天然气地质, 2010, 31(2): 140-150.
[17]	李鹤永, 田坤, 邱旭明, 等. 油气优势运移通道形成 “三要素” 分析: 以苏北盆地高邮凹陷XJZ油田为例[J]. 石油实验地质, 2016, 38(5): 577-583.
[18]	邱旭明, 钱诗友, 于雯泉, 等. 苏北盆地 “十二五” 油气勘探主要成果、新认识和技术进展[J]. 中国石油勘探, 2016, 21(3): 62-73.
[19]	邱旭明, 陈伟, 李鹤永, 等. 苏北盆地走滑构造与复杂断块油气成藏[J]. 石油实验地质, 2023, 45(3): 393-401.
[20]	朱光, 姜芹芹, 朴学峰, 等. 基底断层在断陷盆地断层系统发育中的作用: 以苏北盆地南部高邮凹陷为例[J]. 地质学报, 2013, 87(4): 441-452.
[21]	马晓鸣. 高邮凹陷构造特征研究[D]. 青岛: 中国石油大学(华东), 2009.
[22]	曾联波, 巩磊, 宿晓岑, 等. 深层-超深层致密储层天然裂缝分布特征及发育规律[J]. 石油与天然气地质, 2024, 45(1): 1-14.
[23]	丁文龙, 许长春, 久凯, 等. 泥页岩裂缝研究进展[J]. 地球科学进展, 2011, 26(2): 135-144.
[24]	DING W L, ZHU D W, CAI J J, et al. Analysis of the developmental characteristics and major regulating factors of fractures in marine-continental transitional shale-gas reservoirs: a case study of the Carboniferous-Permian strata in the southeastern Ordos Basin, central China[J]. Marine and Petroleum Geology, 2013, 45: 121-133.
[25]	刘敬寿, 丁文龙, 肖子亢, 等. 储层裂缝综合表征与预测研究进展[J]. 地球物理学进展, 2019, 34(6): 2283-2300.
[26]	曾联波. 低渗透砂岩储层裂缝的形成与分布[M]. 北京: 科学出版社, 2008.
[27]	ASHLEY GRIFFITH W, PRAKASH V. Integrating field observations and fracture mechanics models to constrain seismic source parameters for ancient earthquakes[J]. Geology, 2015, 43(9): 763-766.
[28]	OGATA K, STORTI F, BALSAMO F, et al. Sedimentary facies control on mechanical and fracture stratigraphy in turbidites[J]. Geological Society of America Bulletin, 2017, 129(1/2): 76-92.
[29]	丁文龙, 李超, 李春燕, 等. 页岩裂缝发育主控因素及其对含气性的影响[J]. 地学前缘, 2012, 19(2): 212-220.
[30]	ZHAO G, DING W L, SUN Y X, et al. Fracture development characteristics and controlling factors for reservoirs in the Lower Silurian Longmaxi Formation marine shale of the Sangzhi Block, Hunan Province, China[J]. Journal of Petroleum Science and Engineering, 2020, 184: 106470.
[31]	曾联波, 马诗杰, 田鹤, 等. 富有机质页岩天然裂缝研究进展[J]. 地球科学, 2023, 48(7): 2427-2442.
[32]	DOOLIN D M, MAULDON M. Fracture permeability normal to bedding in layered rock masses[J]. International Journal of Rock Mechanics and Mining Sciences, 2001, 38(2): 199-210.
[33]	LAUBACH S E, DIAZ-TUSHMAN K. Laurentian palaeostress trajectories and ephemeral fracture permeability, Cambrian Eriboll Formation sandstones west of the Moine Thrust Zone, NW Scotland[J]. Journal of the Geological Society, 2009, 166(2): 349-362.
[34]	PATHI V S M. Factors affecting the permeability of gas shales[D]. Vancouver: University of British Columbia, 2008.
[35]	BURTON D, WOOD L J. Geologically-based permeability anisotropy estimates for tidally-influenced reservoirs using quantitative shale data[J]. Petroleum Geoscience, 2013, 19(1): 3-20.
[36]	沈云琦, 金之钧, 苏建政, 等. 中国陆相页岩油储层水平渗透率与垂直渗透率特征: 以渤海湾盆地济阳坳陷和江汉盆地潜江凹陷为例[J]. 石油与天然气地质, 2022, 43(2): 378-389.
[37]	CURTIS J B. Fractured shale-gas systems[J]. AAPG Bulletin, 2002, 86 (11): 1921-1938.
[38]	BOWKER K A. Barnett Shale gas production, Fort Worth Basin: issues and discussion[J]. AAPG Bulletin, 2007, 91(4): 523-533.
[39]	王濡岳, 丁文龙, 龚大建, 等. 黔北地区海相页岩气保存条件: 以贵州岑巩区块下寒武统牛蹄塘组为例[J]. 石油与天然气地质, 2016, 37(1): 45-55.
[40]	马永生, 楼章华, 郭彤楼, 等. 中国南方海相地层油气保存条件综合评价技术体系探讨[J]. 地质学报, 2006, 80(3): 406-417.
[41]	田鹤, 曾联波, 徐翔, 等. 四川盆地涪陵地区海相页岩天然裂缝特征及对页岩气的影响[J]. 石油与天然气地质, 2020, 41(3): 474-483.
[42]	ZENG L B, GONG L, GUAN C, et al. Natural fractures and their contribution to tight gas conglomerate reservoirs: a case study in the northwestern Sichuan Basin, China[J]. Journal of Petroleum Science and Engineering, 2022, 210: 110028.
[43]	LEYTHAEUSER D, SCHAEFER R G, YÜKLER A. Diffusion of light hydrocarbons through near-surface rocks[J]. Nature, 1980, 284(5756): 522-525.
[44]	KROOSS B M, LEYTHAEUSER D, SCHAEFER R G. The quantification of diffusive hydrocarbon losses through cap rocks of natural gas reservoirs: a reevaluation: reply (1)[J]. AAPG Bulletin, 1992, 76 (3): 403-406.