Coupled CFD-DEM analysis of parameters on bridging in the fracture during lost circulation
As an important preventive and remedial application of lost circulation, the optimization of lost circulation materials (LCMs) has become a crucial problem. In order to optimize the design of LCMs, the mechanism of bridging was studied. Based on the theory of solid-liquid flow, a coupled Computational Fluid Dynamics (CFD) – Discrete Element Method (DEM) model was introduced to accurately simulate the dynamic bridging process of plugging particles. The criterion of critical bridging concentration was developed to quantitatively evaluate the effects of Young’s modulus, particle density, particle size distribution (PSD), friction coefficient, fracture geometry, lost circulation velocity and fluid yield stress on bridging capacity. The results show that the plugging zone will become more stable with the increase of particle angularity, Young’s modulus, density of LCMs, lost circulation velocity and the decrease of fluid yield stress. The friction failure is easier to occur, because the stability of plugging zone is more sensitive to the friction between particle and fracture surface. The critical bridging concentration is more sensitive to the ratio of inlet size to outlet size (Rio) with a higher ratio of outlet size to particle size (Ro). For a small outlet size (Ro ≤ 2.5), the bridging state can be observed obviously because the large particles are dominant. When the outlet size is larger (Ro > 3), the stable plugging zone is hard to form because the dense state increases the risk of friction failure. The hindering effect of gravity on the trajectory of particles will be more significant when the fracture extension direction is perpendicular to the gravity direction.
Keywords: Lost circulation, Bridging mechanism, Solid-liquid flow, Critical bridging concentration, CFD-DEM,