The water-blocking effect is a serious problem when developing tight sandstone gas reservoirs, which can cause a sharp reduction in gas production. Wettability alteration of near-wellbore sand rock surface from superhydrophilicity to superhydrophobicity is an effective method to decrease capillary pressure. In this study, a superhydrophobic fluorinated nano-emulsion was synthesized via a soap-free emulsion polymerization process using methacryloxyethyl trimethyl ammonium chloride, trifluoctyl methacrylate, and styrene as monomers. The effect of the fluorinated monomer concentration on wettability alteration was evaluated by measuring the contact angle of the formation water droplet on the modified glass slides using nano-emulsions with different fluorinated monomer concentrations. The results showed that the nano-emulsion had a good dispersibility and homogeneous particle size of around 90 nm, and with the increase in fluorinated monomer concentration, the contact angle increased. The contact angle was the largest when the fluorinated monomer mass rate concentration reached 50%. The adsorption of nanoparticles could alter the rock wettability from a super hydrophilic state (θ = 7°) to a superhydrophobic state (θ = 150°). The spontaneous imbibition experiments showed that the formation water adsorption quality of the core decreased by 49.7% after being modified by the nano-emulsion. The nano-emulsion showed a good superhydrophobicity and had the potential to be used to reduce the water-blocking damage in the tight gas reservoirs.

The Hechuan gas field is one of the tight gas reservoirs with the highest formation water salinity in China. The content of metal ions, such as calcium, magnesium, iron, and barium, is as high as 20 g/L. Severe scales in near-wellbore reservoir blocks the gas and liquid flow paths, affecting the normal production of gas wells. The analysis of scale samples shows that the scale compositions in the Hechuan gas field are complex, which are composed of calcium carbonate, calcium sulfate, barium sulfate, iron salt, silicate, and other inorganic scales. To dissolve these scales, 14 kinds of laboratory self-made chelating acids named AST-01 to AST-14, sequentially, were evaluated by the descaling rate, in which the chelating acid AST-01 was selected with a dissolution rate of 77.7%. Meanwhile, the optimal concentration and reaction time of AST-01 were investigated, and the concentrations of the corrosion inhibitor, the iron ion stabilizer, and surfactants were also optimized. Then, a chelating acid descaling formula was obtained, which was 15~20% of AST-01 chelating acid + 1.5~2.0% of corrosion inhibitor + 2.5% of iron ion stabilizer + 0.3% of drainage aid. A pilot field trial of this descaling formula was applied in a Hechuan X1 well. A remarkable result was obtained in that the shut-in tubing pressure recovery rate was increased by 14 times, the gas production was increased by 10 times, and the gas well resumed to produce continuously again.