Effect of Cationic Polyacrylamide on Gas–Water Seepage in Quartz Sands before and after Methane Hydrate Formation

Excessive water production impacted marine natural gas hydrate production. Cationic polyacrylamide (CPAM), one kind of chemical reagent, was used for the first time to selectively reduce water production while having less impact on gas production. After quartz sands with an absolute permeability of 100–1000 mD were treated with CPAM, the water phase permeability was reduced to 1/15, while the gas phase permeability almost had no change. Furthermore, CPAM was effective in controlling water flow in quartz sands with an absolute permeability range of 100–1000 mD. The water phase permeability initially decreased and then stabilized as the concentration of CPAM increased from 500 to 20,000 ppm. Additionally, the formation of methane hydrate in pretreated quartz sands with CPAM led to a greater reduction in quartz sands’ permeability than the sum of the respective reduction for CPAM treatment and methane hydrate formation. In addition, compared to quartz sands treated only with CPAM, the dissociation of 5% methane hydrate significantly increased the permeability of CPAM-treated quartz sands, but the permeability was smaller than that before CPAM treatment.