Silicone Replication Technology Reveals HPWJ Hole Formation Mechanisms

We reconstructed the morphology of holes using silicone replication technology, and inverted the hole parameters to reveal the law of high-pressure water jet (HPWJ) hole formation under multi-field coupling. The results show that under the multi-field coupling effects, the evolution of the hole exhibits stage-wise characteristics; in the rapid expansion phase, the hole extends rapidly and deeply, forming a “wedge” pattern, and in the stabilization adjustment phase, the rate of hole expansion slows down, and the hole morphology shifts towards an “elliptical” or “teardrop-shaped” form. However, an increase in confining pressure inhibits the transformation of the hole morphology, and as a result, the “wedge-shaped” characteristics of the hole become more pronounced. With constant confining pressure, increased jet pressure significantly enhances both hole depth and volumetric average extension rate, exhibiting a positive correlation. Conversely, with constant jet pressure, increased confining pressure significantly decreases both hole depth and volumetric average extension rate, exhibiting a negative correlation. Based on silicone replication technology, we established a mapping relationship between ‘pore morphology-jet flow and environmental parameters’ which can be used to evaluate the pressure relief and permeability enhancement effects in deep low-permeability coal seams. By optimizing jet parameters, we can expand the scope of pressure relief and permeability improvement in coal seams, thereby enhancing gas drainage efficiency.