为改善支撑剂在裂缝中的铺置形态和提高压裂增产效果,采用实验模拟方法,应用可视化裂缝平板装置开展压裂液携砂实验,结合支撑剂颗粒的微观运动轨迹和砂堤的宏观形状,描述缝内砂堤的形成过程,分析黏性和非黏性压裂液携砂方式的区别,研究射孔孔眼间干扰、压裂液排量、压裂液黏度和施工砂比对缝内砂堤形态的影响规律。结果表明:支撑剂在裂缝中的运移是流化和沉积共同作用的结果,以流化拖拽和输送为主;黏性压裂液中流化层和砂堤之间可形成不流动的液体薄层,对颗粒具有托举作用,减小流体和颗粒间的摩擦和碰撞;砂堤的形成过程共经历砂堤形成、生长、平衡状态和活塞状推进4个阶段,在射孔孔眼干扰和液体冲蚀的共同影响下,形成的砂堤形态可由堆积角、平衡高度和前进角表征,裂缝内存在近井筒和缝高方向的无砂区;砂堤的平衡高度主要取决于支撑剂颗粒的运动速度,与施工排量和压裂液黏度成反比,与砂比成正比。该研究可为压裂施工参数优化提供参考。
In order to improve the proppant displacement in the fracture and enhance the fracturing stimulation effect, the experiment on proppant carrying capacity of fracturing fluid was conducted with experimental simulation method and visual-panel fracture device, the formation of in-fracture sand bank was characterized in combination with the microscopic movement trajectory of the proppant particles and the macroscopic shape of sand bank, the difference in sand carrying modes was analyzed between of viscous and non-viscous fracturing fluids, and the effects on the displacement pattern of sand dike was studies in terms of fracture inter-perforation disturbance, fracturing fluid displacement, fracturing fluid viscosity and construction sand ratio. The results indicated that the proppant in fractures migrated under the joint action of fluidization and sedimentation, mainly dragged and transported under the action of fluidization; an immobile thin layer of fluid was formed between the fluidized layer and sand bank in viscous fracturing fluid to support the particles, reducing the friction and collision between the fluid and the particles; the formation of the sand bank includes four stages, that is, sand bank formation, development, balancing and piston-like forwarding, the formed sand bank could be characterized by accumulating angle, balancing height and advancing angle under the joint effect of perforation disturbance and fluid erosion, and there were no sand zones in the fractures near the wellbore and in the direction of fracture height; the balancing height of the sand bank mainly depended on the movement speed of proppant particles, inversely proportional to the construction displacement and the fracturing fluid viscosity and directly proportional to the sand ratio. This study provides a reference for the optimization of fracturing operation parameters.
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