地层超临界CO2侵入时井筒流动与传热研究

Wellbore Flow and Heat Transfer During Formation Supercritical CO_2 Invasion

随着油气勘探开发不断深入,越来越多的CO_2或者高含CO_2气田被开采,考虑到CO_2物性对压力温度非常敏感,若忽略相态转变和传热影响造成井筒压力误差较大,易造成井涌、井喷等严重钻井事故,针对CO_2的物理性质并考虑其在井筒内相态变化,将井筒传热、压力与CO_2物性参数耦合迭代计算,建立了超临界CO_2侵入时井筒流动与传热的数学模型,计算结果表明:CO_2流体在环空上升过程中由超临界或者液态转化为气态,相态转变点上部为气液两相流下部为井筒拟单相流;SC-CO_2侵入对环空温度和压力均有影响,侵入速度越大,井底温度越高,但是对环空出口温度影响较小;井底压力随侵入量的增大先急剧减小后缓慢增大;随着井口回压增大,井底压力增大,但影响程度逐渐减小.

With the development of oil and gas reservoirs exploration, an increasing number of carbon dioxide （CO2） gas reservoirs, especially those containing high content of CO2 are developed in the world. Considering the pressure and temperature sensitivity of CO2, there is a big error if the phase transition and heat transfer are neglected in the drilling process, and the kick or blowout is easy to occur. Considering the physical properties of CO2 and its phase transition in wellbore, a mathematical model for wellbore flow and heat transfer during formation supercritical CO2 （SC-CO2） invasion was established. Heat transfer and pressure was coupling calculated along with CO2 physical properties parameters in the paper. The results indicate that CO2 transforms from supercritical or liquid to gas state during its rising in the annulus, and the flow above the phase transition point is two-phase flow and the pressure gradient is small in the annulus, while the flow below the phase transition point is single-phase flow and the pressure gradient is large in the annulus. The distributions of pressure and temperature are both influenced by SC-CO2 invasion, the bottom-hole temperature increases with the increase of SC-C02 influx rate, but the annular wellhead temperature is little impacted by SC-CO2 invasion; the bottom-hole pressure first decreases rapidly, and then increases as SC-CO2 influx rate increases. The backpressure greatly af- fects the bottom-hole pressure, but the amplitude of affecting diminishes as the backpressure increases.