Study on Formation Mechanism of Abrasive Water jet Rock Breaking and Perforation

Abrasive water jet (AWJ) perforation is an effective mean of stimulation in oil and gas wells. However, the mechanism of perforation formation and its parameter regulation are still problems. This paper designed and carried out experiments on the variation of hole shape under AWJ perforation. By analyzing the variation in perforation shape with jet time, the rock breaking damage caused by AWJ and the flow characteristics in the perforation were quantitatively characterized. The results show that the process of perforation formation is the coupling result of three kinds of physical effects, that is, the inflow increases the hole depth by vertically impacting the hole tip; The backflow increases the hole diameter by diving the hole wall; The fluid mechanical energy dissipates along the path, which makes the perforation evolution slow down in the late perforation period. Because the rock breaking ability of inflow is stronger than that of backflow, the ratio of hole depth and hole diameter of AWJ perforation increases with the increase of jet time. With jet time 5~300 s, the ratio of hole depth to hole diameter increased from 7 to 28. The rock breaking ability of the backflow decreases from the tip to the orifice. The action time of the backflow on the hole wall increases from the tip to the orifice. Under the dual influence of rock breaking ability and rock breaking time, the hole develops from cone to spindle and the degree of spindle increases. With the increase of jet time and hole depth, the fluid mechanical energy loss was intensified. The change rate of hole depth decreased to 11.3% and the change rate of hole diameter decreased to 4.3%. The evolution of the AWJ perforation became slow. The research results are expected to provide a theoretical basis for high efficiency perforation and controlled perforation shape.