摘要
深部岩体原位应力赋存状态一直是“黑箱”问题,基于岩心的应力测试技术已成为有效的解决手段之一。在深部原位应力环境钻进过程中时常出现岩心饼化现象,为了探索其在砂岩中的形成机制,利用PFC2D研究了不同原位应力条件下钻进过程中的裂纹分布和能量演化,获得了易发生岩心饼化的特定原位应力条件。应用自主开发的测试系统验证了实验室环境内岩心饼化所需的应力条件,并分析了岩心破裂特征、断面形貌与原位应力之间的关系。结果表明,原位应力越高,在钻进过程中岩石产生的拉裂纹越多,尤其是在孔壁和岩心根部,而岩心处裂纹从外表面向内部发展。更高的原位应力水平同样会导致更强的能量转换,进而引发岩石破裂。岩心饼化的形成需满足特定的应力条件。当径向应力(σ_(r))为最大主应力且保持45 MPa恒定、轴向应力(σa)为25 MPa或30 MPa时,岩心根部均会发生饼化现象。随着σ_(r)和σa之间差值或钻进深度的增加,岩心厚度减小,导致断面更光滑、分形维数更小,从而使岩心饼化现象更加显著。该研究可为科学阐明深部原位应力条件下岩心饼化的形成机制提供必要的技术和数据支持。
Core discing often occurs during drilling under deep in-situ stress environment.To determine its formation mechanism in sandstone under deep in-situ stress environment,PFC2D was used to study the crack distribution and energy evolution during drilling under different in-situ stress,and specific in-situ stress conditions prone to core discing were obtained.An independently developed testing system was utilized to verify the stress conditions required for core discing in laboratory settings,and to analyze the relationship between the failure and fracture surface morphology characteristics of the core and in-situ stress.The results show that the higher the in-situ stress,the more tensile cracks will be generated in the rock during drilling,especially at the hole wall and the root of the core.The cracks in the core develop from the outside surface inward.Higher in-situ stress levels also result in greater energy transformation,leading to fracture of the rock.The formation of core discing requires specific stress conditions.Core discing occurs at the root of the core when the radial stress(σ_(r))is the maximum principal stress at a constant value of 45 MPa and the axial stress(σa)is either 25 MPa or 30 MPa.When the difference betweenσ_(r)andσa increases or the drilling depth increases,the disc thickness decreases,resulting in smoother fracture surfaces and smaller fractal dimensions and thus more pronounced core discing.This study can provide technical and data support for scientifically elucidating the formation mechanism of core discing under deep in-situ stress conditions.
作者
李飞
高明忠
叶思琪
谢晶
邓虎超
杨本高
刘军军
杨尊东
唐瑞烽
LI Fei;GAO Ming-zhong;YE Si-qi;XIE Jing;DENG Hu-chao;YANG Ben-gao;LIU Jun-jun;YANG Zun-dong;TANG Rui-feng(State Key Laboratory of Intelligent Construction and Healthy Operation and Maintenance of Deep Underground Engineering,College of Water Resource and Hydropower,Sichuan University,Chengdu 610065,China;Guangdong Provincial Key Laboratory of Deep Earth Sciences and Geothermal Energy Exploitation and Utilization,Institute of Deep Earth Sciences and Green Energy,College of Civil and Transportation Engineering,College of Civil and Transportation Engineering,Shenzhen University,Shenzhen 518060,China;Power China Chengdu Engineering Corporation Limited,Chengdu 611130,China)
基金
Project(2023NSFSC0004)supported by Sichuan Science and Technology Program,China
Projects(52225403,51827901)supported by the National Natural Science Foundation of China
Project(2021-CMCU-KFZD001)supported by the Open Fund of State Key Laboratory of Coal Mining and Clean Utilization,China。
关键词
深部岩体
原位应力
饼化形成机制
裂纹分布
能量演化
宏观破裂特征
断面形貌
deep rock mass
in-situ stress
discing formation mechanism
crack distribution
energy evolution
macroscopic failure characteristics
fracture surface morphology
