In order to evaluate the growth of fractures for cuttings re-injection, a solid transport model is included in a solidfluid coupled hydraulic fracturing simulator. The fracture geometry is a critical factor affecting the safety of the re-injection operation, and solid particle flow in the fractures is known to have a dominant effect on the fracture propagation. To improve the accuracy of the simulation, the finite element method (FEM) is introduced for modeling the particle motion in the fracture fluid. In the model, opening of the fracture, interaction between multiple particles, and change in viscosity by the solid concentration are taken into account. Numerical examples shown here reveal that the fracture geometry is highly dependent on the concentration of the solid due to the change of gravity and slurry viscosity. The injected solid concentration is one of the few controllable parameters, thus the results suggest the feasibility of geometry control.
Hydraulic fracturing technique is widely used in the petroleum industry for stimulating wells. Another application of the technology is drill cuttings reinjection, in which huge fractures are created in formations around wellbores to contain the slurrified solid waste produced by the drillings .
The major concern of cuttings re-injection is a breakthrough of fracture into adjacent formations and surfaces. If a fracture propagates into usable aquifers, petroleum reservoirs, or the surface or seabed, it can cause the grave environmental pollution and operational risk. Although this operation requires careful design of the fracture growth, there are few controllable factors, and those that are controllable are also restricted by operation margins. A numerical study using a solid transport model in the fracture shows that the solid concentration of the injected cuttings slurry influences the fracture growth significantly through the leak-off character of the formation .
The authors have developed another numerical simulator of hydraulic fracturing, in which the true three-dimensional geometry and interaction of multiple fractures are considered . The solid transport model is added to the fully coupled model of fluid flow in the fracture and opening of the fracture in an elastic medium. For the cuttings slurry problem, we need an accurate solution for the case of a high concentration of solid particles.
In this paper, we demonstrate a solid transport model that considers the effect of the fracture wall and in the interaction of multiple particles. Furthermore, some numerical results for different concentrations of injected solids are shown to exhibit the effect of this parameter on the final geometry of the fracture. The slurry viscosity and vertical pressure gradient can be manipulated by varying the solid concentration in the slurry, so the fracture growth is controllable by this parameter.
A fully coupled model of a hydraulic fracturing simulator is developed for the design of well stimulation in complicated stress state and well and fracture geometries . The coupled solution of the fluid pressure and fracture opening is computed using the displacement discontinuity (DD) methodfor solid, and the finite element method (FEM) for Newtonian or non-Newtonian fluid.