水平井段超临界CO_2携岩数值模拟

Numerical simulation of cuttings transport capability of supercritical carbon dioxide in horizontal wells

超临界CO2是一种极具潜力的钻完井介质,研究其携岩机制是超临界CO2钻井技术的重要发展方向。以实测数据设置环空入口岩屑粒径分布,考虑流场中CO2密度和黏度与温度、压力条件的耦合关系及钻杆转动的影响,对温度、压力、排量、转速、岩屑直径、岩屑体积分数及偏心度对携岩效率的影响进行数值模拟分析。结果表明:岩屑床中小颗粒的体积分数下降,大颗粒体积分数的增幅随直径增大而减小;CO2携岩能力随温度的降低和压力的升高而增强,影响规律与室内试验结果相符;增大排量、降低机械钻速可提高CO2携岩效率,而钻杆转速对携岩效率影响甚微;偏心度为0.8时携岩最为困难;水平井钻进时应添加增黏剂以改善CO2携岩效果。

Supercritical CO2 can be one of the most promising drilling and completion fluids,so it is of fundamental and practical importance to investigate its cuttings carrying mechanism. Numerical simulation was conducted to investigate the effects of various factors onCO2s cuttings carrying capability,including temperature,pressure,rotation speed and cuttingssize and production rate,in which the cuttings size distribution at the annulus entrance was set based on the measurement data in the experiments. In addition,the influence of coupled relationship between the density and viscosity of CO2 as a function of temperature and pressure and the rotation of drill pipe was considered in the numerical simulation. The results show that the cuttings carrying capability of CO2 can be improved by reducing temperature or increasing pressure,and the simulation results are consistent with that of the experiments. It is also found that the rotation speed of drill pipe has little influence on the cutting carrying capability,and the minimum of cuttings carrying capability appeared when the annulus eccentricity equals 0. 8. The cuttings carrying capability can also be improved by increasing the displacement capacity or reducing the penetration rate,while viscofier can be added to improve the cuttings carrying capability of CO2 in horizontal well drilling.