Abstract: Aiming at the problem of reservoir pollution in the near well zone of tight gas reservoir in Western Sichuan, the characteristics and components of pollutants are analyzed, and the main pollution types in the near well zone of tight sandstone gas reservoir in Western Sichuan are defined. Secondly, a multi-functional composite plugging removal agent was developed, and the evaluation tests of the physical properties, scale dissolution ability, demulsification and viscosity reduction, core displacement and so on of the new agent were carried out. Thirdly, the near well zone pollution model of fractured wells is established, and the deep purification process of "large liquid injection, strong liquid nitrogen displacement and blowout assistance" is put forward. Finally, it is popularized in Luokou Gas Field and Zhongjiang Gas Field. The results show that the efficiency of the new process measures is 90% and the natural gas production is increased by 1 923$\times$10$^4$ m$^3$, which has achieved obvious economic benefits. The conclusions are as follows:(1) the near well zone pollution of tight sandstone gas reservoir in Western Sichuan is the compound damage of liquid locking, foaming agent emulsification, fracturing fluid damage and scaling crystallization; (2) the multi-functional composite plugging remover has many functions, such as dissolving inorganic scale, breaking emulsion and reducing viscosity, and removing water lock. After displacing the polluted core, the permeability can be increased by 1.74$\sim$2.4 times; (3) the deep purification process of "large liquid injection, strong displacement of liquid nitrogen and blowout assistance" can improve the penetration depth of purification agent in tight reservoir and improve the pollutant flowback efficiency. It has popularization value in similar gas reservoirs.

Key words: tight gas, western Sichuan, near well zone, pollution control, large liquid volume, purify, plugging remover