Simulation Study on Movement of Solidifying LCMs for Controlling Mud Losses into Fracturing Formations

Solidifying lost circulation materials (LCMs) are always used to control severe mud losses into fractured formations, they control mud losses by forming whole plugs near the borehole wall in the fractures. The solidifying LCMs entering the wellbore often inevitably are mixed with formation fluids. The volume distribution of the LCM slurry and the formation fluids changes with time and location, and is closely related to the physical-chemical properties of the formation fluids, the operation parameters and the geometry of the fractures. Using the computational fluid dynamics (CFD) method, the effects of the density and rheology of solidifying LCM slurries on the volume distribution of the LCM slurry and the formation fluids in the fractures and the flow velocity of the fluids were studied. In this study a 3D wellbore-vertical fracture model was used, the pressure differential used in the simulation was 1.9 MPa, the flow rate of the LCM slurry at the entry of the fractures was 2.5 m/s, the two-phase model was a VOF model, and the in-situ fluids in the wellbore and the fractures were a water based drilling fluid. The simulation results showed that the density and the yield point of the LCM slurry have little effect on the movement of the LCM slurry in the wellbore and the fractures, while the consistency index and the flow index significantly affected the residency of the LCM slurry in the fractures; the higher the consistency index and/or flow index, the lower the flow rate of the LCM slurry inside the fractures, and the higher the volume fraction of the LCM slurry inside the fractures. When the flow rate of the LCM slurry is less than the critical flow rate, the fractures will always be filled with the mixture of the LCM slurry and the drilling fluid. Compared with consistency index, flow index plays a more important role in affecting the residency of LCM slurries in formation fractures. LCM slurries of the Newtonian fluids and the shear-thickening fluids more easily form whole plugs in a fracture. This CFD simulation provides a theoretical basis for the optimization of the rheology of solidifying LCM slurries and is beneficial to the success rate at first try of controlling mud losses with the solidifying LCM slurries.