超临界CO2钻井水平井段携岩能力数值模拟

摘要

The density of supercritical carbon dioxide is relatively heavy, close to liquid density; its viscosity is small and close to gas viscosity. In order to research the cutting-carrying ability of supercritical carbon dioxide drilling in horizontal section, a mathematical model was built describing cutting-carrying process in the horizontal eccentric annulus with supercritical carbon dioxide; at the same time, the physical model was built according to the characteristics of horizontal eccentric annulus. The cutting-carrying law in horizontal section at different viscosities and densities of supercritical carbon dioxide was simulated with CFD simulation software. The cutting-carrying ability of supercritical carbon dioxide increases with increasing density and viscosity, but there exists a critical density, when the density of supercritical carbon dioxide is smaller than that, the cutting-carrying ability will decrease apparently, and the smaller the density of supercritical carbon dioxide is, the worse the cutting-carrying ability will be. We can control the back pressure of wellhead to change the density of supercritical carbon dioxide in the wellbore while drilling and to comply with the cutting-carrying request, but the ground pump pressure should be appropriate to avoid higher load.%超临界CO2流体的密度较大,与液体接近;其黏度较低,接近干气体.为了研究水平段钻井过程中超临界CO2的携岩能力;建立了描述超临界CO2流体在水平偏心环空中携带岩屑过程的数学模型,同时根据水平偏心环空的特点建立了物理模型.利用CFD数值模拟软件,对不同黏度、不同密度超临界CO2流体在水平井段的携岩规律进行了模拟.计算结果表明,超临界CO2流体的携岩能力随着其密度和黏度的增加而增强,但超临界CO2水平井段携岩存在一个临界密度,小于这个密度时其携岩能力将明显降低,且密度越小携岩能力越差.超临界CO2钻井过程中,可以通过控制井口回压来达到控制超临界CO2密度的目的,以达到携岩要求,但要注意地面泵压,以免负载过高.图4表1参13