Visualization experiment of multi-stage alternating injection acid fracturing

Permian formation reservoir in the Sichuan Basin has the characteristics of high temperature(153 °C), strong heterogeneity, thin thickness, low porosity and low permeability(0.8 mD). In the early stage, gelling acid fracturing was mainly used to increase gas production, but the effect was not good, and the average daily production of gas wells after fracturing was 20000–30000 m3. The acid fracturing operation of Permian formation reservoir is faced with the problems of fast acid rock reaction speed under high temperature and low conductivity of acid etching fracture under high closing pressure. In view of the above technical problems, we carried out the visual test experiment of alternating injection acid fracturing. The fingering behavior of steering acid, gelling acid, and fracturing fluid is evaluated through experiments, and gelling acid is polymer gels. Through the experiment, it is clear that in order to achieve a good acid fingering phenomenon, the viscosity ratio should be increased to 20:1, the injection displacement is 50–70 ml/min, the controlled injection series are level 4–5, and the proportion of design acid dosage is 0.3. It can be seen from the 3D rock scanning diagram that with the increase of injection stages, the corrosion ability of acid to fractures is significantly enhanced. Multi-stage alternating injection acid fracturing technology has achieved good application effect in Permian formation of Sichuan Basin. The average gas production of the wells is 1.5 times higher than that of the gelling acid fracturing technology.