直井段超临界二氧化碳携岩数值模拟分析

Numerical simulation of cutting-carrying efficiency of supercritical carbon dioxide in vertical well

二氧化碳携岩问题是超临界二氧化碳钻井技术应用于油气藏钻探开发的基础问题。依据井下工况,考虑岩屑粒径分布规律的影响及二氧化碳密度和黏度等物性参数与流场温压条件的耦合关系,数值模拟分析了粒径分布变化规律及各工况参数对携岩效率的影响规律。结果发现:粒径分布变化规律不与颗粒直径呈正相关,证实了选用欧拉模型以考虑颗粒间干扰来模拟携岩问题的合理性;温压条件影响粒径分布变化规律,携岩返速对粒径分布规律影响甚微。携岩效率随压力升高、温度降低而提高,规律与室内实验结果相符。提高排量、降低机速有利于改善携岩效果,实测临界携岩返速高于依据最小动能原理的计算值。随偏心度增大,携岩效率先降低后提高,临界偏心度为0.8。所得结论为发展实际技术提供支撑。

Cutting-carrying mechanism of CO2 is basic for rational hydralics design,which helps to achieve safe and efficient use of drilling with supercritical carbon dioxide.In this view,change law of partical size distribution and influences of drilling parameters on cutting-carrying efficiency is simulated and analyzed,with consideration of the influences of physical parameters change of CO2.Results show that there is no positive correlation between change law of partical size distribution and partical diameter for the existence of mutual interference,which demonstrates Oulerian method used to analyze cutting-carrying mechanism feasible.Pressure and temperature influences the change law of partical size distribution,and the cutting-carrying efficiency increases as the increase of pressure and the decrease of temperature,which agrees with experimental results.Larger displacement and lower ROP helps to improve cutting-carrying efficiency,and actual critical displacement is larger than theoretical value calculated with Ahemd method.The cuttingcarrying efficiency decreases as eccentricity increases and then increases as the eccentricity is beyond 0.8.Outcomes offers important basis for the improvement of practical skills.