注气法双梯度钻井隔水管环空温度场模拟

针对注气法双梯度钻井工艺特点，根据不同流型结构特点和传热特性，考虑隔水管环空流体与海水、隔水管环空流体与钻杆内流体的传热关系，建立注气法双梯度钻井隔水管环空多相流控制方程，并给出求解方法。模拟计算结果表明：随着水深增加，环空内流体温度降低，深水低温的影响越明显；随着液体流量增加，环空内温度升高，增幅降低。由于不同流型传热规律的差异，气体流量增加仅在部分井段对温度有较大影响，入口温度升高环空内温度会相应升高，保温层对温度分布影响明显，加装保温层会使环空最低温度高10℃以上。在实际钻井过程中为防止水合物的生成和钻井液胶凝，尽可能提高液相流量，同时隔水管加装保温层，地面循环系统加装加热装置提高钻井液温度。

Simulation computation of temperature field in riser annulus for dual-gradient drilling using gas injection

Considering the feature of dual-gradient drilling technology via gas injection, this study establishes multiphase flow controlling equations for riser annulus in dual-gradient drilling and further provides the solution according to the heat transfer fingerprint of different flow patterns and by taking into account the heat transfer relationships of fluids in riser annulus with seawater and fluids in drilling pipes. The results of simulation computation show that with increasing water depth, the temperature in annulus rises and the impact of low temperature in deep water becomes more profound. As the liquid discharge is increased, the temperature rises while its increment declines. Because of the difference in heat transfer among various flow patterns, gas discharge only has a great effect on temperature in certain well intervals, and the temperature in annulus rises as that at the injection rises. The presence of an insulating layer significantly affects the distribution of temperature and increases the minimum temperature in the riser annulus by up to 10℃. For preventing hydrate formation and drilling fluid gelation, it is recommended to increase the liquid charge as much as possible, cover the riser with an insulating layer, and install heating equipment in the circulating system to boost the drilling fluid temperature.