Study on Formation Mechanism of Abrasive Water jet Rock Breaking and Perforation
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摘要: 磨料水射流射孔是一种有效的油气井射孔增产手段,然而,孔道形成机制及其参数调控规律仍是亟待解决的问题之一。本文设计并开展了磨料水射流射孔孔道变化规律实验,结果表明,孔道形成过程是三种物理作用耦合的结果,即入流垂直冲蚀孔尖岩石加深孔道;返流以小角度冲蚀孔壁岩石达到扩径作用;沿程流体机械能耗散使得射孔后期孔道演化变缓。由于入流破岩能力远强于返流破岩能力,磨料水射流射孔孔道的孔深和孔径的比值随喷射时间的增加而增大,喷射5~300 s,孔深与孔径的比值由7增长到28。返流的破岩能力由孔尖到孔口递减,返流对孔壁岩石的累积作用时间由孔尖到孔口递增,二者的共同影响使孔道由圆锥状向纺锤状演化。随着喷射时间增加,孔深增加,沿程流体机械能耗散加剧,孔深变化率降低至11.3%、孔径变化率降低至4.3%,孔形演化变缓。研究结果有望为磨料水射流高效射孔和孔道形状控制提供理论基础。
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关键词:
Abstract: 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.-
Key words:
- Abrasive water jet /
- Rock breaking /
- Perforation /
- Fluid-structure interaction /
- Experiment research
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