Modeling fully transient two-phase flow in the near-wellbore region during liquid loading in gas wells

In oil and gas field operations, the dynamic interactions between reservoir and wellbore cannot be ignored, especially during transient flow in the near-wellbore region. A particular instance of transient flow in the near-wellbore region is the intermittent response of a reservoir that is typical of liquid loading in gas wells. Despite the high level of attention that the industry has devoted to the alleviation of liquid loading, the fundamental understanding of the associated phenomena is still surprisingly weak. This applies not only to the flows in the wells, but also to the ways in which these flows interact with those in the reservoir. This paper presents the results of a numerical modeling effort using bespoke code written at Texas A and M University, to identify the pressure profile in the near-wellbore region during fully transient flow conditions for a synthetic, low permeability gas reservoir. The results show a “U-shaped” pressure profile along the reservoir radius in the near-wellbore region. The existence of such pressure profile might explain the re-injection of the heavier liquid phase into the reservoir during liquid unloading in gas wells. A comparison of the results with those obtained using a commercial reservoir simulator show the limitations of the latter, which is unable to mimic re-injection of the liquid into the near-wellbore region