Abstract: The tight sandstone gas reservoirs in Linxing gas field, Ordos Basin, are key targets for onshore gas development. Due to the structural complexity, reservoir physical properties, and complicated gas-water relationship, most gas wells produce water continuously after fracturing, and their water production rates are very different. Understanding the reasons for irreducible water saturation variation after fracturing is of great significance for formulating effective water control and gas recovery measures to increase well productivity. In this study, representative tight sandstone samples from Linxing gas field were tested by using the gas displacement method to clarify how reservoir properties, production pressure difference, and fracturing fluid affect irreducible water saturation. The results show that the difference in the irreducible water saturation between matrix and fractures is 13.32%-18.36% for Type Ⅰ reservoirs, 28.28%-34.19% for Type Ⅱ reservoirs, and 39.10%-48.15% for Type Ⅲ reservoirs. Hydraulic fractures can significantly improve the water flow capacity of reservoirs, and provide additional water flow pathways. The increased production pressure difference, reduced flow pressure loss and weakened hydrophilic degree are the main mechanisms leading to the weakening capacity of the reservoir in irreducible water and water production of gas wells after fracturing. To control water and produce gas efficiently in tight sandstone gas reservoirs with high water cut after fracturing, measures such as controlling fracturing scale, optimizing production systems, and adjusting fracturing additive amount can be implemented, which will help delay the onset of water breakthrough in gas wells and reduce the overall water production.

Key words: Ordos Basin, Linxing gas field, tight sandstone gas reservoir, hydraulic fracturing, irreducible water saturation, movable water