A model of pressure distribution along the wellbore for the low water-producing gas well with multilayer commingled production

Abstract

Wellbore pressure distribution is the basis of formation pressure prediction and productivity evaluation. Two gas–liquid two-phase flow models with assumption of constant mass and variable mass rate within production layer are established to predict the wellbore pressure during multilayer commingled production, respectively. Model validation shows that the calculation errors of the models meet the requirement of engineering precision. Sensitivity analysis shows that the overall sensitivity of thick-layers pure gas wells to model parameters is higher than that of thin-layer low water-producing gas wells. In addition, the pay zone 1 to pay zone n of the n-layer combined gas production well can be equivalent to a thick pay zone. With the production of gas wells, the wellbore pressure decreases and the gas holdup rate decreases, and the calculation error of wo-phase flow model with the constant mass flow rate in the production zone is significant. As a result, the model with variable mass rate should be adopted during this situation. The proposed analytical models for the first time, to the best of the authors’ knowledge, can accurately calculate the pressure distribution of the wellbore for low water-producing gas well, commonly encountered in tight sandstone gas reservoir (e.g., Ordos basin, China).

Keywords:

• Constant mass
• gas–liquid two-phase flow
• low water-producing gas well
• multilayer commingled production
• variable mass
• wellbore pressure distribution