缩扩管内携砂压裂液的压力损失实验与数值模拟

The coupling between the turbulent flow formed by sand-carrying fracturing fluid and particle swarm dynamics is the source of pressure loss in contraction-expansion pipe. By building experiment system, this paper studies the pressure loss of the sand-carrying guar gum fracturing fluid in the contraction-expansion pipe, and the findings are shown as follows:the resistance-reducing ratio of contraction-expansion pipe presents an exponential decrease with the increase of flow rate and variable diameter ratio, while increases linearly with the increase of proppant mass concentration (sand ratio). Through fitting, an equation is obtained to calculate the resistance-reducing ratio of the sand-carrying guar gum fracturing fluid in the contraction-expansion pipe. Considering the dynamic coupling among turbulent flow, particle swarm collisions and accumulation of non-Newtonian fluids, a numerical analysis model and corresponding calculation method are established for solid-liquid two-phase coupling of sand-carrying fracturing fluid in the contraction-expansion pipe. The errors of numerical simulation results and the experimental pressure loss are not more than 10%, thus verifying the accuracy of the above numerical model and calculation method. The numerical simulation studies indicate that fluid velocity is larger than particle velocity on the contraction-expansion pipe end face, where the particle collision rate and stagnation rate are relatively high. There is a large vortex region on the contraction pipe end face, and the vortex flow rate increases with the increasing of proppant mass concentration. When the proppant mass concentration is increased from 0 (no particles)to 700 kg/m³ (sand ratio of 56%), the pressure loss of the contraction-expansion pipe is increased by 15%, which is basically consistent with the result obtained by experiment (16%). The increment in pressure loss of the sudden contraction pipe and the sudden expansion pipe is 22% and 12%, respectively.