Experimental investigation on the erosion behaviors of frozen-thawed sandstone under abrasive supercritical CO2 jet impingement

Abstract

An abrasive supercritical CO2 jet (ASJ) was used to erode sandstone subjected to freeze-thaw cycles and the erosion performance was investigated through laboratory experiments. The erosion characteristics of frozen-thawed and unfrozen sandstones under ASJ impingement at various jet temperature, jet pressure, and standoff distance were compared. It was found that the jet operating parameters shows very different effects on the two types of sandstones because of the fundamental differences in microstructure and mechanical properties. Frozen-thawed sandstones are more susceptible to erosion by ASJ impact due to the deterioration of rock physical properties under the periodic freeze-thaw cycles. Conical erosion craters are formed in unfrozen sandstones at all tested standoff distances, while at small standoff distances a regular deep hole is generated in the center of frozen-thawed sandstone with large pieces of rock peeled off around the hole due to jet pressurization. For both types of sandstones, the erosion depth decreases with the increase of jet temperature as the particle impact velocity decreases under the reduced drag force, and the decrease of kinetic energy and number of abrasives near the jet periphery at higher jet temperature results in smaller erosion area. There is a positive correlation between the size of erosion crater and the jet pressure, and the growth rate of frozen-thawed sandstone is much higher. SEM inspections reveal that frozen-thawed specimens show messy eroded surfaces with more diversified microstructural features. Sandstones are eroded predominantly by intergranular fracture, but the proportion of transgranular fracture increases with the increase of freeze-thaw cycle number.