Acidizing flowback optimization for tight sandstone gas reservoirs

•Velocity sensitivity experiments are performed in this paper.•The relationship between choke size and wellhead pressure is derived.•An optimized method of acid flowback is established.

The physical properties of Sichuan tight sandstone formations include low porosity and low permeability. Fortunately, micro-fractures are well developed in this area, and the development of a reservoir is thus possible. Acidification can repair reservoir damage and improve single-well production; however, gas well production can change after acidizing: some wells improve, while others decline. After many studies, the flowback system after acidification has been shown to play an important role in determining the acidizing effect. Therefore, optimizing the flowback system after acidification can significantly influence the results of acidizing. A series of velocity sensitivity experiments have been performed, and their results show that the velocity sensitivity is high. Based on fluid mechanics principles, an optimization model of the acid flowback is constructed using experimental results; as a result, the relationship between the pressure drop in the wellhead and the choke size can be calculated, and a reasonable choke during the process of acid flowback can be determined using the methods described in this paper. The results are of great significance in optimizing the flowback system after acidification and also in enhancing the gas production of single wells.