Rapid assessment of water phase trapping on gas permeability reduction in typical tight gas reservoirs in China

Abstract

Water phase trapping (WPT) is one of the primary formation damage issues which can cause a steep drop in tight gas production. This paper presented a rapid assessment of the damage potential of WPT in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs involving shallow to ultra-deep layers in China. Typical core samples of the three tight gas reservoirs were selected to perform water imbibition and drainage experiments to mimic the WPT occurrence. After that, the damage degree to core gas permeability induced by WPT was evaluated. Results showed that, for a 16-h vertical water imbibition experiment, the core samples of Daniudi gas reservoir experienced the fastest water imbibition process while the core samples of Keshen 9th gas reservoir established the highest water saturation. After water removal, the ranges of damage degree to core gas permeability induced by the incremental water saturation were 36.07%–78.13%, 36.06%–56.21%, and 61.00%–76.30% in Daniudi, Nanpu 5th, and Keshen 9th tight gas reservoirs, respectively. It found that with the increasing formation depth, tight gas reservoirs can suffer greater damage from WPT not only because of the decline in rock permeability but also the salting out of high salinity formation water. In general, it holds that strong water capillary imbibition phenomenon, low water removal capacity, and high gas permeability damage degree are found to be the striking features of WPT potential on these typical tight gas reservoirs in China.