Numerical Analysis of Particulate Flow Applied to Fluid Loss Control in Fractured Channels

Abstract

The aim of this work is to numerically investigate the particulate flow applied to filling fractures in wellbores during the drilling operation. In order to do so, the drill hole is considered in the vertical position and the fracture is defined transversal to the borehole. The wellbore is assumed to be impermeable throughout its entire length, except for the fluid inlet, outlet and the fracture point. The fracture is impermeable so that the fluid loss occurs only at its end. The analysis procedure is divided into two parts: the first one regards to the fluid loss due to the presence of a fracture in a channel (which is treated as a single-phase flow). This is a necessary step to correctly determine the boundary condition at the end of fracture by associating the amount of fluid to be lost according to a specific pressure. In the second part, the fracture filling process with the fluid-solid flow is accomplished as some of the particles carried along the channel flow take the fluid path being eventually lost through the fracture. The fracture filling process is finished when the fluid loss reduction achieves a steady plateau, despite the complete fracture obturation provided by the particles deposition. The particulate flow is numerically modeled via an Eulerian-Lagrangian approach. The Dense Discrete Phase Model (DDPM) deals with the phase coupling; the particle collisions (which happen mainly inside the fracture) are modeled through the Discrete Element Method (DEM). Results are shown in terms of both the historic of the fluid loss and the channel inlet pressure. The influence of geometric (fracture length), particle injection (diameter, concentration and density) and flow parameters (Reynolds number and fluid dynamic viscosity) over the length, height and position of the particle bed formed along the fracture as well the filling time is investigated. A better understanding of the fracture filling process is provided since all sensitivity parameters can alter not only the geometric characteristics of the bed and the steady state fluid loss, but also the time required to finish the process. The Reynolds number increases with the particles bed initial position and due to the higher flow velocity the bed length is increased as well. However, the bed height is reduced and the time required to partially obturate the fracture is raised. For safety issues in the operation during the filling process the increase of Re has shown a smaller pressure buildup in the system. To improve the fluid loss reduction at the end of the filling process, a decrease of Re and an increase of fluid viscosity is required. Such reduction is more dramatic when the diameter and the density of the particles are decreased.