Dynamic Variation of Water Saturation and Its Effect on Aqueous Phase Trapping Damage During Tight Sandstone Gas Well Production.

Abstract

Dynamic variation of water saturation near a wellbore may cause serious aqueous phase trapping (APT) damage in gas well production, especially in partly water-saturated tight sandstone gas reservoirs. In this paper, a prognosis model was deduced and used to characterize the dynamic variation of water saturation. In addition, experimental evaluations of APT damage were conducted to reveal the influence of water saturation changes on APT damage. The results showed that the new model used for the prognosis of the water saturation consists of immobile water and a water film and has good reliability. The results obtained from the model and experiments agreed with each other well; the error is very little and only 2.94%. Decrease of drawdown pressure or increase of hydrostatic pressure will result in increasing water saturation, which is positively correlated with APT damage. The chart curve of APT damage degree versus water saturation indicates that the APT damage degree will increases from 23.14 to 68.27 and 91.37% during the middle-later stages of tight sandstone gas well production, respectively. Finally, results of a sensitivity analysis showed that the surface tension and wetting contact angle have a great significant impact on water saturation. The interfacial modifier could effectively enter the reservoir pores in a near-wellbore zone and continuously act on the reduction of surface tension and increase of wetting contact angle, which is very helpful for releasing APT damage.