井筒环雾流传热模型及其在深水气井水合物生成风险分析中的应用

Heat transfer model for annular-mist flow and its application in hydrate formation risk analysis during deepwater gas well testing

该文采用Hewitt流型判别法,表明深水含水气井测试时井筒内多为环雾流,考虑了气核与液膜间速度及热力学性质差异,建立了环雾流传热模型,与南海某深水气井实测数据对比,模型预测误差在5%以内。计算表明,忽略含水影响的气体单相模型在含水量大于0.1%时,泥线以上井筒压力和温度预测误差均超过10%,应用该研究建立的环雾流模型则可以得到更准确的结果。含水会使泥线以上一定范围内井段井筒温度显著降低,压力损失增大。产气量较低时,含水量对水合物生成风险基本无影响;产气量较高时,含水量会使得水合物生成区域下界下移,水合物生成区域增大,并使过冷度增大,更容易诱导水合物生成,水合物生成风险增大,需要增加水合物抑制剂用量,并加深注入位置。产水会使无水合物生成所对应的临界产气量增大,需要调整水合物抑制剂用量和注入位置。

Annular-mist flow in the tubing during deepwater water-content gas-well testing is confirmed with Hewitt＇s flow pattern prediction method. Considering the difference of velocity and thermodynamic properties between gas core and liquid film, an annular-mist heat transfer model is established in order to predict the wellbore temperature distribution. The model is verified with deepwater gas well testing data from South China Sea. The prediction error of the proposed model is less than 5%. The water content has a significant influence on wellbore pressure and temperature distribution, which can not be ignored. The wellbore pressure and temperature above mud line become lower when water is produced. The influence of water content on hydrate formation region is negligible while gas production is low. But when the gas production is high, the hydrate formation region and the subcooling become larger, making hydrates easier to form. To ensure the testing operation, the required amount of hydrate inhibitor must be increased and the injection point should be lowered. The critical gas production with no hydrates form in the wellbore increases when water is produced. Thus the amount of hydrate inhibitor used and the injection point should be adjusted accordingly.