压裂液悬砂及支撑剂沉降机理实验研究

压裂液的携砂性能优劣直接影响着支撑剂在裂缝中的输送铺置效果及压后裂缝的有效导流能力。研制了“XS-I型”压裂液悬砂及支撑剂沉降物理模拟实验装置；开展了3种陶粒支撑剂（70/140目、40/70目、30/50目）在SRFP-1型压裂液中的悬砂特性研究，分析了支撑剂在携砂液中的沉降量、沉降速率以及二者随沉降时间的变化规律，得出影响压裂液悬砂性能的主控因素。实验研究表明，携砂液中支撑剂沉降分为快速沉降、缓慢沉降、稳定平衡3个阶段。压裂液黏度是影响压裂液悬砂性能的最主要因素，其次是支撑剂粒径、携砂液砂比。低黏度压裂液仅对70/140目支撑剂有一定悬浮能力（支撑剂充分沉降时间10～20 min），对40/70目和30/50目的支撑剂悬浮性能较差（支撑剂充分沉降时间仅为1.0 min～5.5min），整体悬砂能力较差。中黏度压裂液对70/140目支撑剂悬浮效果好（仅有9.9%～11.1%的支撑剂沉降），在小于15%砂比下对40/70目及30/50目支撑剂有较好的悬浮能力（支撑剂充分沉降时间80 min～240 min）。中高黏度压裂液中，大粒径（30/50目）支撑剂在高砂比（25%～30%）条件下加入，也仅有12%～13.1%的支撑剂沉降，悬砂性能优，适宜作为主加砂阶段的携砂液。研究结果丰富了压裂液悬砂能力测试方法及支撑剂优选评价手段，为压裂液、压裂施工参数的优化及支撑剂的优选，提供基础数据依据。 

Experiment Study on the Mechanisms of Sand Suspension and Settling of Proppant in Fracturing Fluids

The sand carrying performance of a fracturing fluid directly affects the transport and placement of proppant in formation fractures and the effective flow conductance of the fractures after fracturing. A model "XS-I" instrument for simulation experiment on sand suspension and proppant settling has been developed to study the suspension of three ceramsite proppants (particle sizes of 70/140 mesh, 40/70 mesh and 30/50 mesh) in a SRFP-1 fracturing fluid. Using XS-I, the amount of settled proppants, settling rate and the changing pattern of the amount and settling rate with time in suspension fluid were studied and the main factor affecting the sand carrying capacity of a fracturing fluid was obtained. Laboratory experimental results show that the settling of proppants in suspension fluid can be divided into three stages:fast settling, slow settling and stabilized equilibrium. The main factor affecting the suspension capacity of a fracturing fluid is the viscosity of the fracturing fluid, with particle sizes and sand/fluid ratio being the minor affecting factors. Fracturing fluids of low viscosity can only suspend the 70/140 mesh proppant (time for the proppant to completely settle is 10-20 min), but the suspension of the 40/70 mesh and 30/50 mesh proppants in low-viscosity fracturing fluids is poor (time for the proppants to completely settle is only 1.0-5.5 min), and generally speaking the low-viscosity fracturing fluids have poor suspension capacity. Fracturing fluids of medium viscosity have good suspension to the 70/140 mesh proppant (only 9.9%-11.1% of the proppant was settling). When sand concentration is less than 15%, fracturing fluids of medium viscosity have good suspension to the 40/70 mesh and 30/50 mesh proppants (time for the proppants to completely settle is 80 min-240 min). Fracturing fluids of high viscosity have good suspension to large particle size proppants (30/50 mesh) with high concentrations (25%-30%); only 12%-13.1% of the proppant settles down. This means that a high-viscosity fracturing fluid can be used as a sand carrying fluid at the major sand mixing stage. The results of this study provide a new evaluation method for testing the sand carrying capacity of a fracturing fluid and for evaluating and optimizing proppants, and can be used in optimizing fracturing job parameters and selecting proppants.