三向应力下砾岩的动力学特性及能耗分析

Investigation on dynamic mechanical behaviors and energy consumption of conglomerate under three-dimensional static stress

塔里木油田库车山前巨厚砾石层钻井井底岩石处于冲击与地应力的复杂载荷状态,是制约该区块钻井效率的主要难题,探明三向应力条件下砾岩的动载力学特性与能耗规律是砾石层破岩提速的关键。通过真三轴霍普金森压杆试验分析中等应变率下砾岩的动载强度与变形特征,研究动载应变率对砾岩力学特性及能耗规律的影响。结果表明:冲击载荷下砾岩抵抗变形的能力随应变率的提高显著增强,试样的破坏时间缩短,应力增长速率提高,强度和破坏应变增加。构建三向应力下岩石的动载损伤本构模型和能耗模型,得到中等应变率下岩石的动载强度、破坏时间和能耗特征与加载应变率呈幂函数关系,该模型计算结果与砾岩的试验测试结果吻合度较高,表明所建立的模型可准确描述砾岩的动载破坏过程,从而为深部砾石层钻井破岩过程研究提供参考。

When drilling through a thick conglomerate formation,the bottom hole rock under a huge gravel layer is in a load state with complex impact forces and in-situ stresses,which is the main problem restricting the drilling efficiency in the front region of Kuqa Mountain in Tarim Oilfield.It is therefore of great importance to investigate the dynamic mechanical properties and energy consumption of conglomerate rocks under coupled three-dimensional static stresses and uniaxial impact load.In this study,the dynamic strength and deformation characteristics of conglomerate rocks under a medium strain rate were studied using a true triaxial split Hopkinson pressure bar(3D SHPB)testing set-up,and the influence mechanisms of the loading strain rate on the mechanical properties and energy consumption of conglomerate were analyzed.The experimental results show that the deformation resistance of conglomerate rocks under an impact load increases significantly with the rising of its strain rate,and the failure time of the rock specimen decreases.Meanwhile the stress growth rate increases,and the dynamic strength and the failure strain increase.A dynamic damage constitutive model and an energy consumption model of the conglomerate rock subjected to coupled three-dimensional static stress and impact load were established.The data show that the dynamic strength,failure time and energy consumption characteristics of the rock under a medium strain rate are in a power-law relationship with the loading strain rate,and the results of the established models are in accordance with the experimental data of the conglomerate rock,indicating that the theoretical models can accurately describe the failure process of the conglomerate rock under three-dimensional static stress and uniaxial impact load.The research results can provide reference for the study of rock breaking process during drilling in deep gravel formations.