同心双管分注CO_2井筒流动模型及影响因素

A wellbore flow model of CO_2 separate injection with concentric dual tubes and its affecting factors

针对CO2笼统注入过程中效率低、效果差等问题,提出了同心双管分注CO2技术。根据热量传递原理和流体流动理论,建立了考虑CO2相态变化的同心双管井筒流动与传热的数学模型,利用该模型研究了CO2沿内外管环空和内油管的温度和压力分布规律,分析了井口注入量、注入温度、注入压力、内外管组合、注入层间距对CO2在内外管环空和内油管中的流动压力和温度的影响。结果表明,在内外管井口注入参数相同的条件下,外管直径越大,内外管环空温度越高;当外油管直径不变时,内油管直径减小,内外管环空压力增加,内油管直径大小对内外管环空温度影响小;当内外管直径一定时,井口注入量、注入温度、注入层间距对内外管环空和内油管的温度、压力分布影响较大,而井口注入压力影响幅度较小。

In view of issues of the low efficiency and poor effect in the process of commingled CO2 injection,a CO2 separate injection with concentric dual tubes was proposed.On the basis of the heat transfer principle and fluid flow theory,a mathematical model considering CO2 phase change as flowing along the wellbore of concentric dual tubes and heat transfer was established,with which temperature and pressure distributions of CO2 along the annulus between inner and outer tubes and in the inner tubing string were calculated.Moreover,effects brought about by various factors,such as injection rate,injection temperature,injection pressure,assemblage of inner and outer tubes,interval of injection layers etc.,on the pressure and temperature of CO2 flowing both in the annulus between inner and outer tubes and in the inner tubing string were investigated as well.The results indicate that on condition that wellhead injection parameters of inner and outer tubes are the same,the bigger the diameter of the outer tube,the higher the temperature of the annulus between inner and outer tubes.If the diameter of the outer tube keeps constant,the pressure of the annulus will increase with decreasing the diameter of the inner tube that has a small influence on the temperature of the annulus.When inner and outer tubes have definite diameters,the wellhead injection rate,injection temperature and intervals of injection layers may all have significant effects on temperature and pressure distributions of the annulus and the inner tube,while the wellhead injection pressure affects them a little.