Effect of tight sandstone gas reservoir wettability on liquid traps damage

In tight sandstone reservoirs, the liquid traps may be readily damaged by invasion of external work fluid. The wettabiity of rock surface has a significant impact on the damage degree to liquid traps. The fluorocarbon surfactant Zonyl8740 was used to treat the cores, reduce the surface energy of the cores and obtain cores with different wetting degree. Through experiment on core displacement and capillary spontaneous imbibition, the irreducible water saturation and spontaneous imbibition oil/water dynamic of gas wet cores and liquid wet cores were studied respectively. The core flow test with initial water saturation was built, and the damage degrees to liquid trap were compared, before and after gas-wet reversing agent was added to the drilling fluid. Experiments show that inversion of liquid wetting on tight sandstone surface to preferential gas wetting can significantly weaken the spontaneous imbibition effective of capillary, and reduce the spontaneous imbibition amount and the final retained saturation. Gas wet reverse agent can effectively reduce the damage to liquid traps by drilling fluid and has a guiding significance to preventing damage to liquid traps in tight sandstone reservoirs.