冰孔孔壁脆性行为下损伤-破裂过程及稳定控制研究

In order to obtain abundant ice core for analysis changes of natural and ecological environment, maintaining the stability of the borehole wall in the ice drilling is an important technical problem and need to be solved urgently. This project focus on the brittle zone of ice borehole wall, based on the continuum damage mechanics, the fracture mechanics and the dynamics of ice sheets and glaciers and physical simulation experiment, investigating the variation of permeability, stress and strain of ice borehole wall during the damage evolution process, reveal the damage evolution characteristics of ice borehole wall. Investigating propagation mechanism of fractures induced by damage of ice or natural fractures, and research on the rule of fracture extension under the effect of structure-stress-seepage three coupled fields. Through the study of density, viscosity, component of drilling mud acting on ice borehole wall, monitored the stability of borehole wall, establish security window of each drilling fluids parameter, and control the stability of borehole wall accurately. The project results can set up theory and method of stability control of ice borehole wall damage-fracture in brittle zone, which provide theoretical support for the security assurance in process of ice drilling.

分析自然与生态环境变迁需要获取大量冰芯，钻取冰芯的过程中，维持冰层钻孔孔壁的稳定是亟待解决的重要技术难题。项目针对冰层钻孔孔壁的脆性区，基于损伤连续力学、断裂力学、冰盖动力学等理论并结合物理模拟实验，重点研究在水力压差及冰川流动耦合作用下，冰层孔壁损伤量、渗透系数、应力和应变等的演化特性，揭示损伤演化规律；研究由损伤产生或存在原生裂缝的情况下，孔壁裂纹在结构-应力-渗流三场耦合作用下的扩展演化特性，揭示孔壁破裂规律；通过研究常用钻井液密度、粘度、组分等因素对孔壁损伤-破裂的影响，获得在孔壁稳定条件下钻井液各项匹配指标随深度变化的安全窗口，精准控制孔壁稳定。项目成果将建立冰层钻进中孔壁脆性区损伤-破裂控制理论与方法，为极地冰孔安全钻进提供相关的理论依据。

极地冰盖及冰下环境记录着地球气候环境变化的信息及气候演变历史，被誉为地球环境数据的“时间容器”。分析自然与生态环境变迁需要获取大量冰芯，钻取冰芯的过程中，维持冰层钻孔孔壁的稳定是亟待解决的重要技术难题。项目针对冰层钻孔孔壁的脆性区，基于损伤连续力学、断裂力学、冰盖动力学等理论并结合物理模拟实验，重点研究在水力压差及冰川流动耦合作用下，分析了冰孔孔壁的应力状态，建立了冰体的损伤流变模型，揭示损伤演化规律，研究了在不同破坏准则及孔壁状态条件下的冰孔孔壁坍塌及起裂机理，研究了由损伤产生或存在原生裂缝的情况下，孔壁裂纹在结构-应力-渗流三场耦合作用下的扩展演化特性，研究了孔壁水压致裂裂缝与天然裂缝的相互作用，揭示了冰孔孔壁的坍塌及起裂机理与裂纹的扩展规律；通过理论和试验研究了常用钻井液密度、粘度、组分等因素对孔壁损伤-破裂的影响，获得在孔壁稳定条件下钻井液各项匹配指标随深度变化的安全窗口，精准控制孔壁稳定。研究结果表明了在通常情况下，常用的冰钻钻井液能够保持孔壁的稳定，而在冰盖流速较大的区域进行冰层钻探时，孔内钻井液安全压力窗口会相应地减小，孔壁不稳定性加剧。对于孔壁存在非完整结构的情况，冰体的断裂韧性、冰体之间的摩擦系数以及非完整结构内部的裂纹状态是决定钻井液安全压力窗口的重要参数。项目成果将建立冰层钻进中孔壁脆性区损伤-破裂控制理论与方法，为极地冰孔安全钻进提供相关的理论依据。