温差效应下页岩力学劣化特征及损伤演化机制

Mechanical Deterioration Characteristics and Damage Evolution Mechanism of Shale Under Thermal Gradient Effects

摘要

页岩气开发面临储层改造难度大、渗透率低等挑战，液氮压裂作为无水化储层改造技术可规避传统水力压裂的水敏损害和环境污染问题，但其热冲击效应对页岩力学劣化的影响机制尚不明晰。为研究液氮冻结作用下深层页岩气储层的力学强度变化规律和裂缝形态特征，通过单轴压缩实验与模拟测试了页岩温度、液氮循环次数及层理倾角下页岩的力学强度与破坏模式，分析了液氮冻结前后微观结构变化。结果表明，页岩劣化损伤特征受冷却时间、温差效应度及循环次数控制，表现为微裂纹扩展、裂纹网络复杂化及力学强度下降。高温差可以增强液氮对岩石力学强度的劣化作用。循环次数增加进一步加剧岩石基质损伤和强度弱化，但效应逐步减弱并趋于稳定。不同层理倾角显著影响页岩破坏模式，倾角60^◦时抗压强度最低，而倾角90^◦时表现出更高的力学强度。页岩非均质较强的情况，液氮作用能有效形成复杂缝网，降低力学强度。研究建立的“温度-循环-结构”协同损伤模型，为深层页岩储层液氮压裂的时间调控、循环参数优化、层理方位及非均质性效果提供了关键理论支撑。

Abstract

Shale gas development is faced with challenges such as difficulties in reservoir stimulation and low permeability. Liquid nitrogen fracturing, as a waterless reservoir stimulation technology, can circumvent the water sensitivity damage and environmental pollution issues associated with traditional hydraulic fracturing. However, the mechanism by which its thermal shock effect influences the mechanical degradation of shale remains unclear. To investigate the mechanical strength variation and fracture morphology characteristics of deep shale gas reservoirs under liquid nitrogen freezing, uniaxial compression experiments were conducted to measure the mechanical strength of shale at different temperatures and liquid nitrogen cycling times. The failure modes of shale at various temperatures were compared, and microstructural changes before and after liquid nitrogen freezing were analyzed. The results show that the deterioration and damage characteristics of shale are governed by cooling time, preheating temperature, and thermal gradient effects, manifested as microcrack propagation, increased fracture network complexity, and reduced mechanical strength. A higher thermal gradient enhances the deterioration effect of liquid nitrogen on the mechanical strength of the rock. Increased cycling times further exacerbate matrix damage and strength weakening, although the effect diminishes and stabilizes over time. The failure mode of shale is significantly influenced by bedding angles, with a minimum compressive strength observed at 60 ◦, and a 90 ◦ bedding angle exhibits higher mechanical strength. In the case of strong non-homogeneity of shale, liquid nitrogen can effectively form a complex network of seams and reduce the mechanical strength. The synergistic damage model of “temperature-circulation-structure” established in this study provides a key theoretical support for the time regulation, optimization of circulation parameters, orientation of layers and non-homogeneous effect of liquid nitrogen fracturing in deep shale reservoirs.

关键词

液氮压裂 / 深层页岩 / 温差效应 / 力学强度 / 损伤演化

Key words

liquid nitrogen fracturing / deep shale / temperature effect / mechanical strength / damage evolution

参考文献

[1] 郭旭升， 赵永强， 申宝剑， 等. 中国南方海相页岩气勘探理论：回顾与展望[J]. 地质学报， 2022， 96（1）： 172-182. doi： 10.3969/j.issn.0001-5717.2022.01.014

[2] GUO Xusheng, ZHAO Yongqiang, SHEN Baojian, et al. Marine shale gas exploration theory in southern China: Review and prospects[J]. Acta Geologica Sinica, 2022, 96(1): 172-182. doi: 10.3969/j.issn.0001-5717.2022.01.014

[3] 沈骋， 郭兴午， 陈马林， 等. 深层页岩气水平井储层压裂改造技术[J]. 天然气工业， 2019， 39（10）： 68-75. doi： 10.3787/j.issn.1000-0976.2019.10.008

[4] SHEN Cheng, GUO Xingwu, CHEN Malin, et al. Horizontal well fracturing stimulation technology for deep shale gas reservoirs[J]. Natural Gas Industry, 2019, 39(10): 68-75. doi: 10.3787/j.issn.1000-0976.2019.10.008

[5] 张金发， 管英柱， 陈菊， 等. 页岩气压裂技术进展及发展建议[J]. 能源与环保， 2021， 43（10）： 102-109. doi： 10.19389/j.cnki.1003-0506.2021.10.019

[6] ZHANG Jinfa, GUAN Yingzhu, CHEN Ju, et al. Progress and development suggestion of shale gas fracturing technology[J]. China Energy and Environmental Protection, 2021, 43(10): 102-109. doi: 10.19389/j.cnki.1003-0506.2021.10.019

[7] 洪宇， 闫建平， 郭伟， 等. 川南深层页岩气储层岩石力学参数及各向异性特征[J]. 天然气勘探与开发， 2025， 48（1）： 30-39. doi： 10.12055/gaskk.issn.1673-3177.2025.01.004

[8] HONG Yu, YAN Jianping, GUO Wei, et al. Mechanical parameters and anisotropy of deep shale-gas reservoir rocks, southern Sichuan Basin[J]. Natural Gas Exploration and Development, 2025, 48(1): 30-39. doi: 10.12055/gaskk.issn.1673-3177.2025.01.004

[9] 刘惠民， 王敏生， 李中超， 等. 中国页岩油勘探开发面临的挑战与高效运营机制研究[J]. 石油钻探技术， 2024， 52（3）： 1-10. doi： 10.11911/syztjs.2024052

[10] LIU Huimin, WANG Minsheng, LI Zhongchao, et al. Challenges and efficient operation mechanism of shale oil exploration and development in China[J]. Petroleum Drilling Techniques, 2024, 52(3): 1-10. doi: 10.11911/syztjs.2024052

[11] SHAO Zuliang, TANG Xuhai, WANG Xiaoguang . The influence of liquid nitrogen cooling on fracture toughness of granite rocks at elevated temperatures: An experimental study[J]. Engineering Fracture Mechanics, 2021, 246: 107628. doi: 10.1016/j.engfracmech.2021.107628

[12] ELWEGAA K, EMADI H. Improving oil recovery from shale oil reservoirs using cyclic cold nitrogen injection: An experimental study[J]. Fuel, 2019, 254: 115716. doi: 10.1016/j.fuel.2019.115716

[13] 崔壮， 侯冰. 深层页岩巴西劈裂破坏力学行为数值模拟研究[J]. 石油钻探技术， 2024， 52（2）： 218-228. doi： 10.11911/syztjs.2024032

[14] CUI Zhuang, HOU Bing. A numerical simulation for damage mechanical behavior of Brazilian splitting test of deep shales[J]. Petroleum Drilling Techniques, 2024, 52(2): 218-228. doi: 10.11911/syztjs.2024032

[15] STAFF J P T. Field applications of cryogenic nitrogen as a hydraulic-fracturing fluid[J]. Journal of Petroleum Technology, 1998, 50(3): 38-39. doi: 10.2118/0398-0038-JPT

[16] CAI Chengzheng, LI Gensheng, HUANG Zhongwei, et al. Rock pore structure damage due to freeze during liquid nitrogen fracturing[J]. Arabian Journal for Science and Engineering, 2014, 39(12): 9249-9257. doi: 10.1007/s13369-014-1472-1

[17] CAI Chengzheng, LI Gensheng, HUANG Zhongwei, et al. Experiment of coal damage due to super-cooling with liquid nitrogen[J]. Journal of Natural Gas Science and Engineering, 2015, 22: 42-48. doi: 10.1016/j.jngse.2014.11.016

[18] 黄中伟， 位江巍， 李根生， 等. 液氮冻结对岩石抗拉及抗压强度影响试验研究[J]. 岩土力学， 2016， 37（3）： 694-700， 834. doi： 10.16285/j.rsm.2016.03.011

[19] HUANG Zhongwei, WEI Jiangwei, LI Gensheng, et al. An experimental study of tensile and compressive strength of rocks under cryogenic nitrogen freezing[J]. Rock and Soil Mechanics, 2016, 37(3): 694-700, 834. doi: 10.16285/j.rsm.2016.03.011

[20] 翟成， 孙勇. 低温循环致裂煤体孔隙结构演化规律试验研究[J]. 煤炭科学技术， 2017， 45（6）： 24-29. doi： 10.13199/j.cnki.cst.2017.06.004

[21] ZHAI Cheng, SUN Yong. Experimental study on evolution of pore structure in coal after cyclic cryogenic fracturing[J]. Coal Science and Technology, 2017, 45(6): 24-29. doi: 10.13199/j.cnki.cst.2017.06.004

[22] QIN Lei, ZHAI Cheng, LIU Shimin, et al. Changes in the petrophysical properties of coal subjected to liquid nitrogen freeze-thaw: A nuclear magnetic resonance investigation[J]. Fuel, 2017, 194: 102-114. doi: 10.1016/j.fuel.2017.01.005

[23] WU Xiaoguang, HUANG Zhongwei, SONG Hengyu, et al. Variations of physical and mechanical properties of heated granite after rapid cooling with liquid nitrogen[J]. Rock Mechanics and Rock Engineering, 2019, 52(7): 2123-2139. doi: 10.1007/s00603-018-1727-3

[24] 王翔， 冯永超. 鄂尔多斯盆地南缘华北探区页岩油储层岩石力学特性实验研究[J]. 非常规油气， 2024， 11（1）： 110-118. doi： 10.19901/j.fcgyq.2024.01.14

[25] WANG Xiang, FENG Yongchao. Experimental study on rock mechanical properties of shale oil reservoir in North China exploration, southern Ordos Basin[J]. Unconventional Oil & Gas, 2024, 11(1): 110-118. doi: 10.19901/j.fcgyq.2024.01.14

[26] WU Xiaoguang, HUANG Zhongwei, ZHANG Shikun, et al. Damage analysis of high-temperature rocks subjected to LN₂ thermal shock[J]. Rock Mechanics and Rock Engineering, 2019, 52(8): 2585-2603. doi: 10.1007/s00603-018-1711-y

[27] 朱万成， 魏晨慧， 田军， 等. 岩石损伤过程中的热-流-力耦合模型及其应用初探[J]. 岩土力学， 2009， 30（12）： 3851-3857. doi： 10.16285/j.rsm.2009.12.017

[28] ZHU Wancheng, WEI Chenhui, TIAN Jun, et al. Coupled thermal-hydraulic-mechanical model during rock damage and its preliminary application[J]. Rock and Soil Mechanics, 2009, 30(12): 3851-3857. doi: 10.16285/j.rsm.2009.12.017

[29] 陈骞， 王志良， 申林方， 等. 基于热力耦合的近场动力学方法高温岩石水力压裂数值模拟[J]. 岩土力学， 2024， 45（8）： 2502-2514. doi： 10.16285/j.rsm.2023.1447

[30] CHEN Qian, WANG Zhiliang, SHEN Linfang, et al. Numerical simulation of high-temperature rock hydraulic fracturing based on coupled thermo-mechanical peridynamics[J]. Rock and Soil Mechanics, 2024, 45(8): 2502-2514. doi: 10.16285/j.rsm.2023.1447

[31] 孙勇， 翟成， 丛钰洲， 等. 温度冲击效应诱导干热岩孔裂隙结构演化及损伤破坏机制[J]. 煤炭学报， 2024， 49（12）： 4855-4872. doi： 10.13225/j.cnki.jccs.2024.0072

[32] SUN Yong, ZHAI Cheng, CONG Yuzhou, et al. Pore fracture structure evolution and damage failure mechanism of hot dry rock induced by temperature impact effect[J]. Journal of China Coal Society, 2024, 49(12): 4855-4872. doi: 10.13225/j.cnki.jccs.2024.0072

[33] GUO Tiankui, DU Zeming . Meso-numerical simulation of rock triaxial compression based on the damage model[J]. IOP Conference Series: Earth and Environmental Science, 2021, 687: 012134.

[34] 郤保平， 吴阳春， 赵阳升. 热冲击作用下花岗岩宏观力学参量与热冲击速度相关规律试验研究[J]. 岩石力学与工程学报， 2019， 38（11）： 2194-2207. doi： 10.13722/j.cnki.jrme.2019.0230

[35] XI Baoping, WU Yangchun, ZHAO Yangsheng. Experimental study on the relationship between macroscopic mechanical parameters of granite and thermal shock velocity under thermal shock[J]. Chinese Journal of Rock Mechanics and Engineering, 2019, 38(11): 2194-2207. doi: 10.13722/j.cnki.jrme.2019.0230

[36] ZHU W C, LIU J, SHENG J C, et al. Analysis of coupled gas flow and deformation process with desorption and Klinkenberg effects in coal seams[J]. International Journal of Rock Mechanics and Mining Sciences, 2007, 44(7): 971-980. doi: 10.1016/j.ijrmms.2006.11.008

[37] 郤保平， 吴阳春， 王帅， 等. 青海共和盆地花岗岩高温热损伤力学特性试验研究[J]. 岩石力学与工程学报， 2020， 39（1）： 69-83. doi： 10.13722/j.cnki.jrme.2019.0182

[38] XI Baoping, WU Yangchun, WANG Shuai, et al. Experimental study on mechanical properties of granite taken from Gonghe Basin, Qinghai Province after high temperature thermal damage[J]. Chinese Journal of Rock Mechanics and Engineering, 2020, 39(1): 69-83. doi: 10.13722/j.cnki.jrme.2019.0182

[39] 张向向. 层理页岩水/气压裂破裂机理与损伤演化规律研究[D]. 徐州： 中国矿业大学， 2019.

[40] ZHANG Xiangxiang. Fracturing mechanism and damage evolution of water/gas fracturing in bedding shale[D]. Xuzhou: China University of Mining and Technology, 2019.

[41] 刘若冰， 魏志红， 加奥启， 等. 川东南地区五峰-龙马溪组深层超压富有机质页岩孔隙结构分形特征及其地质意义[J]. 地球科学， 2023， 48（4）： 1496-1516. doi： 10.3799/dqkx.2022.177

[42] LIU Ruobing, WEI Zhihong, JIA Aoqi, et al. Fractal characteristics of pore structure in deep overpressured organic-rich shale in Wufeng-Longmaxi Formation in Southeast Sichuan and its geological significance[J]. Earth Science, 2023, 48(4): 1496-1516. doi: 10.3799/dqkx.2022.177

[43] WU Xiaoguang, HUANG Zhongwei, LI Ran, et al. Investigation on the damage of high-temperature shale subjected to liquid nitrogen cooling[J]. Journal of Natural Gas Science and Engineering, 2018, 57: 284-294. doi: 10.1016/j.jngse.2018.07.005

[44] 胡雄， 邬长武， 杨秀春， 等. 低渗透煤层微观孔隙结构与煤层气解吸规律[J]. 特种油气藏， 2024， 31（2）： 129-135. doi： 10.3969/j.issn.1006-6535.2024.02.015

[45] HU Xiong, WU Changwu, YANG Xiuchun, et al. Microscopic pore structure and coalbed methane desorption law in low-permeability coal seams[J]. Special Oil & Gas Reservoirs, 2024, 31(2): 129-135. doi: 10.3969/j.issn.1006-6535.2024.02.015