粒子射流喷射钻塞流场特性及参数优化

Flow characteristics and parameter optimization for drilling through cement plug using particle waterjet

为有效利用粒子射流能量,实现粒子射流井底全覆盖并避免对套管壁冲蚀,运用计算流体力学欧拉-拉格朗日方法,建立粒子射流喷射钻塞的计算流体力学模型,阐明固液两相粒子射流喷射钻塞的流场特性,优化设计钻塞参数,并进行试验验证。结果表明粒子冲击塞面后开始反弹,速度明显降低,井底最高压力分布在冲击区;随周向喷嘴个数增加水泥塞冲蚀速率先逐渐增加后减小,6个周向喷嘴时冲蚀速率最大;中心喷嘴的加入消除了井底中心处低速区,使中心漩涡也明显减弱;喷嘴倾斜角为5°时,平均冲蚀率最大,对井壁冲击力最小;喷距为3 cm(约5倍喷嘴直径)钻塞效果较好;全尺寸地面试验表明粒子射流可有效覆盖整个井底,实现水泥塞快速钻进。

In order to make full use of the particle waterjet energy,and to achieve a full coverage of the bottom hole with particle jet and avoid the erosion of casing,a computational fluid dynamics(CFD)model for drilling through cement plug using particle waterjet was established based on an Euler-Lagrange method.The flow characteristics of the solid-liquid two phase particle jet were elucidated,and the operation parameters were optimized with the calculation results verified by the laboratory testing.The results demonstrate that the velocity of the rebounding particles is dramatically reduced after impacting the cement surface.The highest pressure is concentrated on the impact zone of the bottom hole.The cement plug erosion rate increases as the circumferential nozzle number is increased up to its critical value of 6,while the erosion rate is reduced as the circumferential nozzle number exceeds its critical value.Owing to the addition of the central nozzle,the low velocity zone in the center of the bottom hole is eliminated,and the central vortex is weakened significantly.When the nozzle inclination angle is 5°,the average erosion rate becomes the highest,while the impact force acted on the well wall can be significantly reduced.The optimal standoff distance is found to be 3 cm(about 5 times of the nozzle diameter).Also,the results of a full scale laboratory test show that the particle waterjet can effectively cover the entire bottom hole and increase the drilling speed through the cement plug greatly.