倾斜气井积液临界气相流速预测新模型

井筒积液是气井生产过程中常见的现象，特别对于页岩气、致密气等低渗透性气井，积液产生一定的背压会使得气井产量进一步降低，严重情况下会导致气井停产。准确预测气井积液临界气相流速可以指导生产者及时采取积液防治措施。斜井中液膜在重力作用下不均匀分布，使得其内部的积液研究较为复杂。通过对比已有的实验和理论研究，分析认为液膜的反向流动是积液的主要原因，并且起始于井筒横截面底部最厚处的液膜；通过分析斜井井筒中液膜速度分布规律，确定以液膜与井壁剪切应力为0作为积液判定条件。基于环雾流型并考虑斜井井筒中液膜周向不均匀分布、气芯液滴夹带的影响，建立适用于不同管径、不同液相流量的全倾角气井积液预测新模型。利用井斜角为0°~88°的实验数据、直井和斜井的现场生产数据对新模型及已有的6种积液预测模型进行分析验证的结果显示，基于零液壁剪切应力的新模型相比于其他模型更能准确地预测全倾角气井积液临界气相流速。

A new prediction model of the critical gas velocity for liquid loading in deviated gas wells

Wellbore liquid loading is a common phenomenon during the production of gas wells, especially for low-permeability gas wells such as tight gas or shale gas wells. Back pressure caused by the liquid loading will further lower the yield of gas wells, which may even halt the production of gas wells under severe situation. Accurate prediction of the critical gas velocity for liquid loading in gas wells can guide producers to timely take prevention measures against liquid loading. Due to the uneven distribution of liquid film in deviated gas wells under the gravity, the study of liquid loading tends to be complex. Through the comparison of existing experiments and theoretical studies, it is considered that the reverse flow of liquid film is the primary cause of liquid loading, which starts from the thickest film at the bottom of the cross section of wellbore. By analyzing the profile of liquid film velocity in the wellbore of deviated wells, zero liquid-wall shear stress is determined as the criterion for the onset of liquid loading. Based on annular-mist regime and considering the impacts of uneven circumferential distribution of liquid film in the wellbore and droplet entrainment in gas core, a new annular-mist flow model for predicting the liquid loading in vertical and deviated gas wells was established, which is applicable in the case of different tubing diameters and different liquid flow rates. The new model and six existing critical-gas-velocity prediction models were analyzed and verified against the experimental data of inclination angle ranging from 0° to 88° and the field production data of vertical and deviated gas wells. Compared with other models, the new model based on zero liquid-wall shear stress can predict the critical gas velocity of liquid loading in vertical and deviated gas wells more accurately.