脉冲加砂压裂支撑剂铺置状态的CFD模拟

CFD Simulation of Proppant Placement for Impulse Sand Fracturing

脉冲加砂压裂过程中,支撑剂的有效铺置是形成高速油气渗流通道及获得高裂缝导流能力的基础条件。针对物理模拟实验受装置承压能力、泵注排量和材料成本限制等缺点,应用CFD(计算流体力学)方法模拟计算了携砂液与中顶液交替注入时的流动状态,分析了不同黏度比、注入速度及脉冲间隔时间对支撑剂铺置状态的影响。研究结果表明,增大携砂液与中顶液黏度比,通道率与支撑剂有效铺置距离减小,支撑剂簇团分散效果变差,现场施工时黏度比不宜超过5;注入速度增大,支撑剂有效铺置距离和通道率增大,但支撑剂分散性变差,综合考虑通道率和砂团分散效果,折算现场合理施工排量为3.2~4.3m3/min;过短或过长的脉冲间隔时间均不利于有效渗流通道的形成,脉冲间隔时间为整个脉冲周期的0.5~0.6倍时效果较好。

In the process of impulse sand fracturing,effective placement of proppant was the basic condition for generating high-speed seepage channels and obtaining high conductivity of fractures.In view of the limitation of system pressure,pumping injection rate and material cost for physical simulation facility,CFD(Computational Fluid Dynamics)method was applied to simulate the flow state of proppant-laden fluid and interval fluid by injecting alternately,the influence of different viscosity ratios,injection rate and impulse interval time on placement of proppant was analyzed.The simulation results indicate that the increase of viscosity ratio would reduce the channel rate and the effective placement distance of proppant,and the dispersion effect of proppant cluster would be poor.The viscosity ratio should not exceed 5in the process of impulse fracturing.With the increase of injection rate,the effective placement distance of proppant and channel rate tend to increase,but its dispersion is reduced.By integrally taking the channel rate and dispersion effect of sand into consideration,the optimal operation pumping rate is 3.2~4.3m3/min.Neither too long nor too short impulse interval time is not favorable for generating effective seepage channels,when the impulse interval timeis 0.5~0.6 times as long as the impulse period,the result is better.