基于PIV/PTV的平板裂缝支撑剂输送试验研究

Experimental Study of Proppant Transport in Flat Fracture Based on PIV/PTV

为了解水力压裂过程中水力裂缝内支撑剂的铺置规律,基于平板裂缝开展了支撑剂输送试验,分析了泵注排量、压裂液黏度、注入位置、支撑剂类型对支撑剂铺置过程的影响;运用PIV/PTV技术,测试了压裂液-支撑剂两相运动速度,从颗粒运动角度分析了不同因素对最终砂堤形态的影响。试验发现:平板单缝内支撑剂铺置存在“裂缝前端先堆积至平衡高度,再稳定向后端铺置”和“砂堤整体纵向增长,稳定向后端铺置”2种典型模式,2种模式可以在泵注的不同阶段出现并转换;砂堤不同位置形态主控因素存在差异,注入位置与排量主要控制前缘形态,黏度与排量主要控制中部形态,黏度主要控制后缘形态;在裂缝远端,支撑剂沉降存在“回流式”和“直接式”2种模式,前者受涡流控制,后者则仅依靠重力沉降;现场施工时可考虑“定向射孔+大排量中高黏70/140目石英砂(主体支撑剂)+40/70目陶粒架桥+大排量中高黏70/140目石英砂长距离输送+排量尾追40/70目陶粒”,兼顾缝长方向远距离铺置和近井地带裂缝与井筒的高连通性。平板裂缝内支撑剂运移与铺置规律试验结果可以为页岩储层压裂主裂缝内支撑剂高效铺置及储层改造工艺参数优化提供参考。

In order to study the placement behaviors of proppants in fractures during hydraulic fracturing,proppant transport tests were carried out based on flat fractures,and the influence of pump injection displacement,fracturing fluid viscosity,injection position,and proppant type on the placement process of proppants was studied.By using particle image velocimetry(PIV)/particle track velocimetry(PTV)technology,a two-phase flow velocity test of fracturing fluid-proppant was carried out,and the influence of different factors on final sand embankment shape was analyzed from the perspective of particle motion.The test results showed that:①there were two typical modes of proppant placement in single flat fracture.The first one was that the front end of the fracture accumulated to the equilibrium height first,and the push-type back end was placed,while the second indicated the mode of overall longitudinal growth of sand embankments.The two modes could appear and transform at different stages of pumping.②There were different controlling factors in the shape of sand embankments at different positions.The injection position and displacement primarily controlled the leading edge shape;the viscosity and displacement mainly controlled the middle shape,and the viscosity mainly controlled the trailing edge shape.③At the distal end of the fracture,there were two modes of proppant settlement,namely backflow type and direct type.The former was controlled by eddy current,while the latter only depended on gravity settlement.④Directional perforation+70/140-mesh quartz sand with large displacement and medium-high viscosity(main proppant)+40/70-mesh ceramsite bridging+long-distance transportation of 70/140-mesh quartz sand with large displacement and medium-high viscosity+40/70-mesh ceramsite of displacement tail chasing could be considered in field construction,which took into account the long-distance placement in direction of fracture length and the high connectivity between fractures and wellbores in the near-wellbore area.It was concluded that the experimental study on the transport and placement of proppants in the flat fracture can provide a reference for the efficient placement of proppants in the main fracture of shale reservoir fracturing and the optimization of reservoir stimulation process parameters.