We numerically study mechanisms and conditions of fracture initiation in granular material induced by non-Newtonian polymer solutions. A coupling approach of computational fluid dynamics and discrete element method is utilized to model the fluid flow in a porous medium. The flow behavior of polymer solutions and drag force acting on particles are calculated based on a power-law model. The adequacy of the numerical model is confirmed by comparing the results with a laboratory experiment. The numerical results are consistent with the experimental data presenting similar tendencies in dimensionless parameters that incorporate fluid flow rate, rheology, peak pressure, and confining stress. Results show that fluid flow rate, rheology, and solid material characteristics strongly influence fracture initiation behavior. Injecting a more viscous guar-based solution results in wider fractures induced by a grain displacement. A less viscous XG-based solution creates more linear fractures dominated by an infiltration. The peak pressure ratio between two fluids is higher in rigid material compared to softer material. Finally, the dimensionless parameters $1/\Pi_1$ and $\tau_2$, which consider fluid and solid material properties accordingly, are good indicators in determining fracture initiation induced by shear-thinning fluids. Our numerical results show that fracture initiation occurs above $1/\Pi_1 = 0.06$ and $\tau_2 = 2\cdot 10^{-7}$.

翻译：我们数值研究了非牛顿聚合物溶液诱导颗粒材料中裂缝起裂的机制与条件。采用计算流体力学与离散元方法的耦合模型模拟多孔介质中的流体流动。基于幂律模型计算聚合物溶液的流动行为及作用于颗粒上的曳力。通过将数值结果与实验室实验对比，验证了模型的有效性。数值结果与实验数据在无量纲参数（包括流体流速、流变特性、峰值压力及围压）的变化趋势上呈现一致性。结果表明：流体流速、流变特性及固体材料特性强烈影响裂缝起裂行为。注入粘度更高的瓜尔胶基溶液时，颗粒位移会诱发更宽的裂缝；而注入粘度较低的黄原胶基溶液则形成以渗透作用为主的线性裂缝。刚性材料中两种流体的峰值压力比高于柔性材料。最后，分别考虑流体与固体材料特性的无量纲参数$1/\Pi_1$及$\tau_2$可作为判定剪切稀化流体诱发裂缝起裂的有效指标。数值结果表明：当$1/\Pi_1 > 0.06$且$\tau_2 > 2\times10^{-7}$时，裂缝起裂发生。