超临界二氧化碳射流中的颗粒跟随及影响因素

Particle following motion in supercritical carbon dioxide jet and its influence factors

超临界二氧化碳射流具有破岩速度高、门限压力低等优势,加入磨料颗粒形成超临界二氧化碳磨料射流,将取得更高的冲蚀切割效率。为研究超临界二氧化碳磨料射流可行性,采用数值模拟方法,对比分析了单个颗粒在超临界二氧化碳等流体射流中的运动特征,揭示了流体温度、磨料粒径对颗粒跟随运动的影响规律。结果表明,与相同条件下在水与压裂液射流中相比,磨料颗粒在超临界二氧化碳射流中运动规律相似,但初始滑脱速度较大、跟随能力较弱,获得的喷射速度与撞击靶件壁面速度较高,表明超临界二氧化碳具有良好的颗粒携带能力;流体温度升高、磨料粒径增大均会使颗粒滑脱速度增大、削弱跟随运动效率,但同时也降低了喷嘴外流场中颗粒所受运动阻力,显著提高了喷射速度与撞击壁面速度。由此可知,对于石英、陶粒等常用磨料材质,在常规储层温度(60~140℃)与粒径范围(20~70目)内,超临界二氧化碳磨料射流可有效形成并进行高效冲蚀切割作业。

Supercritical carbon dioxide （SC-CO2） jet has such advantages as high rock-breaking velocity and low threshold pressure. The addition of abrasive particles will lead to SC-CO2 abrasive jet with high erosion and cutting efficiency. To study the feasibility of SC-CO2 abrasive jet, numerical simulation methods were used to analyze the single-particle motion characteristics in different fluid jets such as SC-CO2 jet and reveal the influence laws of fluid temperature and abrasive size on particle following motion. Results indicate that compared with the water and fracturing fluid jet under equal conditions, abrasive particles have similar motion laws in the SC CO2 jet, characterized by large initial slipping velocity and weak following capacity. However, high jet velocity and large targevwall impinging velocity are obtained, proving that the SC-CO2 has favorable particle carrying capacity. The increase of fluid temperature and abrasive size will not only improve the particle slipping velocity and weaken the particle following motion efficiency, but also reduce the particle motion resistance in the nozzle external flow field and significantly raise the jet velocity and target-wall impinging velocity. As a consequence, in the ranges of conventional reservoir temperature （60-140 ℃ ） and particle diameter （20-70 mesh） for quartz, ceramsite and common abrasive materials, SC-CO2 abrasive jet is expected to be formed for highly efficient erosion and cutting operations.