关键词: 同心双管, 分层, 注CO_{2 ,} 井筒流动, 压力分布, 温度分布

Abstract:

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.

Key words: concentric dual tube, separate layer, carbon dioxide injection, wellbore flow, pressure distribution, temperature distribution