Pressure gradient prediction of gas-liquid two-phase pipe flow in horizontal gas wells

Abstract

Accurate prediction of pressure gradient in gas wells is the theoretical basis for dynamic analysis, optimization of production and deliquification technologies design. Due to the complicated wellbore trajectories and flow behavior of horizontal gas wells, the accuracy of any existing prediction model of pressure gradient alone is difficult to meet engineering requirement within a wide range of gas-liquid ratio. Hence, a semi-empirical model of liquid holdup in a vertical wellbore is proposed based on three transition points: annular-churn, churn-slug and slug-bubble transition points. Based on the corresponding relationship between liquid holdups in the vertical pipe and the inclined pipe, a prediction method of liquid holdup in the inclined pipe is proposed, and thus a prediction model of pressure gradient in horizontal wells is established. The results show that the most important step in predicting pressure gradient of gas-liquid two-phase flow is the accurate prediction of liquid holdup. The liquid holdup increases first and then decreases with the increase of the inclination angle. Liquid holdup in inclined pipes can be predicted based on the variation of liquid holdup in the vertical pipe with the inclined angle. The relative performance factor (RPF) of the proposed model is the smallest compared with the gas-well logging data of the reference models, indicating the new model can meet the requirements of engineering calculation accuracy. It is concluded that the new model can be applied to the prediction of gas-liquid two-phase pressure gradient in horizontal gas wells with different production ranges, and can provide technical support for field production analysis.