高温高压CO_(2)反应流动相变致裂机理

Mechanism of phase change cracking in high temperature and high pressure CO_(2) reaction flow

利用自主研制的气动力脉冲真三轴试验系统,开展了超临界CO_(2)热冲击致裂高强度混凝土块体试验,探究了热源功率、CO_(2)初始压力对热冲击破岩过程及裂隙损伤演化规律的影响,分析讨论了高温高压CO_(2)相变致裂过程及其裂纹扩展演化规律.充分考虑含能材料反应放热、CO_(2)相态变化、传热传质、瞬态非线性流动以及高压气体驱动损伤演化过程,建立了高温高压CO_(2)热冲击破岩的热-流-固-损伤(THMD)多场耦合模型,进一步分析了CO_(2)温度场、压力场以及损伤演化规律,揭示了高温高压CO_(2)反应流动相变致裂机理.研究结果表明:超临界CO_(2)热冲击致裂过程主要包括:高压气体瞬态释放产生应力波诱导型径向裂缝;相变膨胀的高温高压CO_(2)驱动径向优势裂缝扩展,并产生分支裂缝.其中气动力脉冲峰值压力和瞬时加载速率的增加有助于产生更多的径向裂缝,而CO_(2)初始压力和聚能剂含量的提高会使分支裂缝更容易形成.此外所建立模型的模拟结果与试验结果较为一致,表明了CO_(2)初始压力对岩石致裂效果影响有限,而增加热源功率可以有效扩大岩石损伤范围.研究进一步地揭示了高温高压状态的CO_(2)相变流动致裂机理,对该技术应用于硬岩破除和致裂增渗具有指导意义.

To explore influence of heat source power and initial pressure of CO_(2) on the rock breaking process and fracture evolution law,The aerodynamic pulse true triaxial test system was developed to carry out the experiment of high-strength concrete block cracked by supercritical CO_(2) thermally driven shock cracking.According to the result of experiment,the cracking process and propagation evolution law of CO_(2) phase change at high temperature and high pressure were analyzed and discussed.Correspondingly,coupled Thermo-Hydro-Mechanical-Damageable(THMD)model of high-temperature and high-pressure CO_(2) thermally driven shock rock breaking,including the exothermic reaction of energetic materials,phase change of CO_(2),heat and mass transfer,transient nonlinear flow and fracture propagation and damage evolution process driven by high-pressure gas,was established to further analyze the CO_(2) temperature field,pressure field and damage evolution law and reveal the cracking mechanism of high-temperature and high-pressure CO_(2) reaction flow phase change.The process of supercritical CO_(2) thermally driven shock cracking mainly includes:Stress wave induced radial cracks produced by transient release of high pressure gas;The propagation of radially dominant cracks and the generation of branching cracks driven by CO_(2) phase change expansion,which indicates that increasing in peak aerodynamic pulse pressure and instantaneous loading rate contribute to more radial cracks,while increasing in initial CO_(2) pressure and concentration of energy accumulator make branching cracks easier to form.In addition,the simulation results of the established model which are in good agreement with the test results,indicae that the effect of CO_(2) initial pressure on rock cracking is limited,while the damage range of rock can be extended effectively by increasing heat source power.The research further reveals the mechanism of CO_(2) phase change flow cracking under high temperature and high pressure,and has a guiding significance for the application of this technology in hard rock breaking,fracturing and permeability increasing.