Objective Combining with the development process requirements of "multi-scale and high-density" for tight gas reservoirs, and based on the design idea of "medium and low molecular weight + enhanced chain rigidity + supramolecular aggregation + salt resistant monomer" and the method of controllable free radical polymerization is adopted to introduce the rigid skeleton functional monomer of hydrophobic chain lacking electricity and the strong polar sulfonic acid salt resistant functional monomer into the molecular chain, and the integrated variable viscosity and anti-salt drag reducing agent is developed in combination with the composite suspension technology.

Methods The comprehensive properties of the integrated variable viscosity and anti-salt drag reducing agent were studied by experimental methods. The solubility, viscosity increasing and sand carrying properties, salt and temperature resistance and resistance reducing properties of drag reducing agents were investigated.

Results The resistance reduction rate of integrated variable viscosity with a dosage of 0.03 wt% and anti-salt drag reducing agent in clean water could reach 81%. In brine with salinity over 20 000 mg/L, the viscosity retention rate was 91%, and the resistance reduction rate remained above 75%. The viscosity of the system could be adjusted in real time from 3.4 mPa·s to 60 mPa·s by adjusting the amount of resistance drag reducing agent. Compared with the same type of conventional emulsion type drag reducer, the static sand suspension ability was greatly improved, and it could meet the construction requirements of reservoirs above 150 ℃. Using the integrated variable viscosity slick water system combined with multi-scale high-density fracture fracturing technology to implement 7 wells in the tight gas field in western Sichuan, the construction success rate was 100%, the average resistance reduction rate of single well was 81%, the sand adding intensity was 3.86 t/m, which was 7.7 times of the conventional integrated slick water in the early stage, and the effect of field application is remarkable.

Conclusions The excellent performance of the integrated variable viscosity and anti-salt drag reducing agent could meet the comprehensive requirements of the field construction, and the field application proves that it has a good application prospect.