煤层气水平井扇形磨料射流造穴喷嘴结构设计

现有煤层气开发直井采用水力造穴方式不能确定造穴的几何尺寸和形态,采用机械造穴方式刀杆容易变形、易使工具落入井内,水力-机械复合造穴技术操作复杂、成本高。为此,提出煤层气水平井扇形磨料射流喷射造穴的新思路。采用室内试验和数值模拟相结合的方法,优选和优化了扇形喷嘴的几何结构参数,分析了磨料颗粒在流场中的运动轨迹及加速特性,探索了射流参数和磨料参数对颗粒运动速度的影响规律。研究结果表明:椭圆形出口的扇形喷嘴适用于煤层气水平井喷射造穴;扇形磨料射流的颗粒加速区域主要集中在喷嘴收缩段和射流等速核区域内;流体的速度矢量场特征和磨料的运动轨迹特性表明,喷射造穴的主要作用机理是切割煤体的同时冲击破碎煤块;优化布置不同喷射角度的扇形喷嘴组合、提高喷嘴压降及合理控制砂比,可收到“网格式”切割破碎煤岩的效果,从而达到大范围应力释放的目的。所得结论可为煤层气水平井喷射造穴提供理论基础和设计参考。

Structure Design of Abrasive-Flat-Jet Nozzle for Cavity Completion of Horizontal Coalbed Methane Well

The current hydraulic cave-making methods cannot determine the geometric size and shape of the caverns of vertical wells for coal-bed methane development,while the mechanical cavern-making method is prone to cutter bar deformation and tools falling into the well.The hydraulic-mechanical composite cave-making technology is complicated and high-cost.To address the problem,a new idea of creating cavitation by abrasive flat jet in coalbed methane horizontal wells is proposed.Combining indoor experiment and numerical simulation,the geometric structure parameters of the flat jet nozzle are optimized,the trajectory and acceleration of the abrasive particles in the flow field are analyzed,and the influence of jet parameters and abrasive particle parameters on particle motion velocity is explored.The research results show that the flat jet nozzle with an elliptical outlet is suitable for jetting cavitation in horizontal coal-bed methane well.The particle acceleration area of the abrasive flat jet is mainly concentrated in the nozzle contraction section and the jet potential core.The fluid velocity vector field characteristics and abrasive particle movement trajectory characteristics show that the main mechanism of jetting cavitation is impacting and breaking coal while cutting the coal body.Optimizing the arrangement of flat jet nozzles with different jet angles,increasing nozzle pressure drop and reasonable sand ratio can provide“network type”coal cutting to achieve large-scale stress release.