Erosion characteristics and failure mechanism of reservoir rocks under the synergistic effect of ultrasonic cavitation and micro-abrasives

Ultrasonic cavitation erosion of reservoir rocks in distilled water with and without SiO2 micro-abrasives (mean diameter 0.5 μm, mass concentration 1–7 wt%) are conducted. The erosion characteristics of eroded rocks are measured and analyzed. Both the area of cavitation damage zones and the surface roughness are increased when rocks are eroded in water-abrasive mixture. Compared with distilled water, the mass loss in 3 wt% water-abrasive mixture has improved by 69.66–104.23% (average 81.41%) for sandstone, 495.05–665.15% (average 557.38%) for shale, and 158.49–211.92% (average 188.16%) for granite during an erosion time of 5 ∼ 60 min. The promoted erosion can be explained by the synergistic effect of cavitation and micro-abrasives. The failure mechanisms are elucidated for different types of rocks. The erosion of reservoir rocks results from the peeling-off of mineral grains and the breakdown of large mineral crystals. Numerous micro-fractures and pores are produced in the surface of the eroded rocks, creating additional permeable channels for fluid flow. The results demonstrate that the presence of micro-abrasives can increase the ultrasonic cavitation erosion of reservoir rocks, indicating that the addition of micro-abrasives is feasible to enhance the performance of ultrasonic treatment for oil wells in petroleum industry.