水锤激励下压裂管柱振动响应特性研究（英文）

启停泵工况下,由于边界条件突变,压裂管柱内初始流动平衡体系被打破,产生水锤现象,从而造成管内液体流动参数随时间突变。水锤现象将引起管柱的剧烈振动,严重时甚至会造成管柱破裂与失效。为定量分析启停泵工况下压裂管柱的水锤效应及振动响应,建立了压裂液-管柱的流固耦合四方程模型,采用特征线法和空间插值法分析了井口及不同井深处管柱内的流速、动压力、轴向振动速度以及轴向附加应力的变化规律。研究结果表明:启泵过程中,由于压裂泵组排液流量具有一定周期性,会引起压裂管内液体流动压力变化,从而产生管柱附加应力,可能引发管柱振动;压裂液的压力波动值及管柱轴向振动速度随着井深的增加而减小。停泵阶段,受管内液体压力积聚影响,井口附近产生水锤压力波,并向井下传播,此时井口压力变化值最大,井底最小。此外,受管内压力变化影响,压裂管柱产生附加轴向拉力,且井口处最大、井底处最小。相较启泵工况,停泵工况更容易对管柱产生破坏。

Vibration response of fracturing tubing induced by water hammer

During pump-starting and pump-stopping process, the initial equilibrium system in the fracturing tubing is broken because of the sudden change of boundary conditions, resulting in water hammer, which then results in the sudden change of fluid flow parameters. Water hammer causes severe vibration, which may damage the tubing or cause sealing failure of premium connections. To quantitatively analyze the water hammer effect and vibration characteristic in pump-starting and pump-stopping process, characterized lines method and spatial interpolation method were adopted to analyze the velocities and dynamic pressures of fracturing fluid, as well as the axial velocities and additional stresses of tubing at wellhead and different depths. It shows that in pump-starting process, because the flow rate of fracturing pump group is periodic, the fluid flow pressure in the fracturing tubing will change, resulting in additional stress of tubing, which may cause the vibration of tubing. The fluctuations of dynamic pressure and the axial velocities of tubing decrease with increased depth. In pump-stopping process, influenced by the accumulation of liquid pressure in the tubing, pressure wave is generated near the wellhead and propagates downhole. The change of pressure at wellhead is the largest and the smallest at the bottom. In addition, affected by the change of pressure in the tubing, additional axial tension produced by the fracturing tubing is also the largest at the wellhead and the smallest at the bottom. Compared with the pump-starting process, the pump-stopping process is easier to damage the tubing.