CFD–DEM simulation of mud cake formation in heterogeneous porous medium for lost circulation control

Abstract

The lost circulation is a problem commonly observed in well drilling operations under overbalanced pressure conditions. Among the geological formation characteristics that can intensify the loss of drilling fluid, the presence of highly permeable regions is one of the most critical. In this case, corrective measures are necessary, like the use of lost circulation materials (LCM) to build a mud cake in the porous substrate, sealing the pores, and controlling the lost circulation. This work presents a numerical study to understand the influence of fluid–particle interaction under dynamic filtration on the process of particle packing in porous media, resembling the use of LCMs to grow a mud cake and reduce the fluid invasion. The flow of an incompressible Newtonian fluid in a porous medium modeled in pore scale is considered, being the voids structured as an anisotropic array of staggered solid cylinders. The LCM is considered as solid and discrete spherical particles (dp= 0.75 mm) immersed in a water–glycerin fluid. A Euler–Lagrange approach to model the liquid–solid two-phase flow is employed, with the simulation being resorted via the dense discrete phase model coupled to the discrete element method (DEM). The DEM computes collision and friction forces present in the particle–particle and particle–wall interactions. Variation effects for different values of the Reynolds number in the vertical channel ReCH,i (125, 250, 500) and the lost circulation intensity measured by the initial fluid loss ratio Qloss (5, 10, 20%) are considered. By releasing solid particles, the fluid loss ratio, relative permeability, particle layer dimensions, and also the vertical channel pressure are altered. For an initial fluid loss ratio of 20%, the decay in Qloss after 60 s for ReCH,i values of 125, 250 and 500 is, respectively, 17%, 13% and 12%. The variation of the initial fluid loss ratio Qloss dramatically influences the number of particles that forms the bed. After 60 s, no particle has entered the porous matrix for Qloss = 5%. When Qloss = 10%, the particles build a bed, and for 20%, the plugging of the substrate occurs.