Secondary Stabilization: An Explanation for Gas-Liquid Co-Production After a Rapid Production Decrease in Low Permeability Gas Wells

Numerous field practices suggest that, low permeability gas wells can always once again achieve a stable gas-liquid co-production after a rapid decrease of gas production, and effectively deliver the liquid at the gas rate far below the critical rate determined by liquid loading models. However, scarce research has been done on this production phenomenon. The purpose of this paper is to improve the understanding of this gas-liquid co-production phenomenon and point out the triggering conditions and stability mechanism of this stable production state which breaks through the classic liquid loading criteria. A transient multiphase flow simulator is used to establish synthetic cases, and repeatedly execute the unabridged dynamic process of liquid loading under different production conditions, which is difficult to perform in actual production. Then, the characteristics of stable production and liquid loading in low-permeability gas wells are explored. Based on the concept of nodal analysis, a new approach is proposed to evaluate the production status and predict the liquid loading of low permeability gas wells. And subsequently, the phenomenon of secondary stabilization is defined to explain the production state at lower gas flowrates. The transient simulation results show that, at the onset of liquid loading in low permeability gas wells, gas flowrates are well below the predicted values of conventional liquid loading criteria, which are consistent with field observations. The newly presented approach that defines the onset of liquid loading in terms of the tangency of IPR and TPR instead of the minimum pressure point of the TPR curve matches the simulation results quite well. This reveals that the stable productions of low permeability gas wells are not only dependent on wellbore flow features, but also largely related to the reservoir properties whose influences are not obvious and easily ignored in conventional gas wells. The most significant new finding is that in a specific range of LGRs which are often encountered in actual production, low-permeability gas wells can achieve stable production once again at lower gas flowrates, after undergoing the first liquid loading. The concept of secondary stabilization is introduced to explain this phenomenon, which defines as the situation where IPR and TPR intersect again at the latter half of the dual-stepped TPR curve. To a considerable extent, this concept can explain the abnormal stable productions that seriously deviate from liquid loading point. The current work realizes the production status analysis of low-permeability gas well which is more matched with field observation, and provides a theoretical basis for abnormal stable production of low-permeability gas well. Thus it could help field engineers to better master the production status of low-permeability gas well, so as to avoid unnecessary intervention or implement appropriate measures.