David Smeulders

Abstract:

For the extraction of heat from deep geothermal layers, the creation of fracture networks in these layers is needed. Water is injected under high pressure and fracture initiation and growth is induced. For modeling fracture growth, the Extended Finite Element Model (XFEM) has proven to be a powerful numerical tool. For hydraulic fracturing in low permeable rocks the so-called Enhanced Local Pressure (ELP) model was recently introduced. In this approach, the fluid pressure within the fracture is included as an additional degree of freedom with respect to the original XFEM displacement field, which greatly increases the applicability of the model. The fluid pressures in the fracture and the surrounding porous material, however, are still only coupled by means of a simplified, analytical Terzaghi relation.
In order to further improve the model, the interaction of the fracture fluid flow and the deformable porous medium is studied. We developed a coupled model in which the free flow is described by the Stokes equations and the fluid-saturated porous medium by Biot’s equations. We solve the coupled problem using a staggered FEA approach. The numerical model is shown to fully couple the free flow and the fluid flow in the saturated poro-elastic medium, taking into account the slippage effect and surface flow impedance.
We now combine the coupled free flow model and the ELP method to better predict fracture propagation in fluid-saturated poro-elastic materials and corresponding fracture leak-off rates.

Remij, E.W., J.J.C. Remmers, J.M. Huyghe, and D.M.J. Smeulders (2015). The enhanced local pressure model for the accurate analysis of fluid pressure driven fracture in porous materials. Computer Methods in Applied Mechanics and Engineering, 286:293-312