Erosive wear characteristic of rock impacted by abrasive gas jet

Assisted drilling with non-liquid technologies,such as supercritical CO2 jet,are more and more important in natural gas exploration,especially in coal-bed methane exploration. As a kind of non-liquid technologies,abrasive gas jet is widely used to drill metal and glass. It is also powerful enough to break coal and rock,which is the primary pre-condition of its usage in coal-bed methane exploration. To understand the rock erosion wear mechanism of abrasive gas jet is critical important to apply the technology preferably and widely. However,the existing erosion mechanism mostly neglects the effect of rebound abrasive. To this end,the experiments of limestone erosion by the abrasive gas jet under different kinds of abrasives and different stand-off distances were carried out. The experiment results show that the erosion pit has an approximate inverted cone-shape. The bottom of erosion pit is of hemispherical. There is an annular platform above the hemispherical bottom,which connects the bottom and side of erosion pit. The primary reason that induces the peculiar shape of erosion pit is the specific flow field of abrasive gas jet. There is an annular region be-tween the axis and boundary of the abrasive gas jet,and there is no abrasive in the annular region. The abrasive around the axis induces the formation of hemispherical bottom. After rebounding,the abrasive around axis moves to the annular region. The rebound abrasive with high velocity enlarges both the diameters of hemispherical bottom and erosion pit and induces the formation of annular platform. The failure characteristics of different areas of the erosion pit were ana-lyzed by Scanning Electron Microscopy (SEM). It can be concluded that the failure models of different spots are dif-ferent. The failure is caused by the impact stress wave of the incident abrasive at the base of the hemispherical bottom. Plastic deformation is the primary failure model induced by the rebound abrasive at the side of hemispherical bottom. The plastic deformation induced by incident abrasive and fatigue failure induced by rebound abrasive are the primary failure model at the annular platform. Fatigue failure induced by rebound abrasive is the primary model failure at the side of erosion pit. The rock failure reason of abrasive with different hardness is the same,but the rock damaged by hard abrasive has rougher surface and higher rock breakage efficiency.