The Role of Fiber Properties s in LCM Design - A Numerical Approach

To combat the problem of lost circulation during drilling, lost circulation materials (LCM) have most commonly been added to the drilling fluid to seal the fractures and recover the rate of penetration (ROP). In recent years, fibers have become an attractive addition to many lost circulation treatments specifically due to their ability to overlap, intertwine and give rise to net-like structures within the fracture, that are able to effectively cause bridge-initiation and seal fractures. However, the behavior of fibers in particle-laden flow display multi-variate complexity due to the effects of multiple mechanisms - both particle and fluid related, that influence the fibers during flow. As a consequence, evaluating fiber LCMs in the lab in a detailed manner can be very cumbersome and tedious. To overcome this limitation, we developed a validated, Computational Fluid Dynamics coupled Discrete Element Method (CFD-DEM) model to simulate the fiber-laden fluid flow process in millimeter-wide fractures. The effect of fiber concentration, fracture roughness, and fiber stiffness on plugging capability is evaluated. It is found that, although fibers are known to create net-like structures that portray better fracture bridging than conventional LCMs, the bridging mechanism is affected by the bending stiffness of the fibers. We propose two new concepts for the bridging mechanisms of fibers and their effects on the plugging time and maximum plugging pressures for the LCM plugs. This study also attempts to better understand the effect of employing mixed blends of soft and stiff fibers on fracture plugging effectiveness by simulating mixed fibers of different soft-stiff compositions.