Effect of the drawdown pressure on the relative permeability in tight gas: A theoretical and experimental study

Abstract

The relative permeability in tight gas is important for the gas production industry. It is reported that the drawdown pressure may affect the immobile water saturation and thus significantly influence the gas-water relative permeability. Precisely predicting the behavior of the relative permeability under different drawdown pressures is thus critically important. The goals of this paper include theoretically and experimentally investigating the effect of the drawdown pressure on the relative permeability. A novel predictive model for the gas-water relative permeability based on fractal theory has been derived, and the corresponding gas flooding tests have been conducted. The predictions of the relative permeability by the proposed model have been validated by comparing them with the experiments conducted. Both the theoretical and experimental results show that the driving pressure has a significant effect on the relative permeability. The predicted and experimental results demonstrate that a lower immobile water saturation produces a wider two-phase region, and a higher gas-water relative permeability corresponds to a higher drawdown pressure. The proposed relative permeability is expressed as a function of the drawdown pressure and other structural parameters (i.e., the pore fractal dimension Df and the tortuosity fractal dimension DT). The effects of the structural parameters on the relative permeability are also discussed.