Modelled Fracture Complexity. For the scenario where the target fault mainly consists of a single fracture we closely follow the numerical modelling approach developed previously for the Soultz-sous-Forêts EGS (Xxxxxx et al., 2010): Pressure diffusion is restricted to a single target fault and mechanical processes are simulated with a slider-block approach. All deformations are assumed to be seismic. The numerical model yields the hydraulic pressure diffusion during geothermal operations as well as the induced seismicity (time, location, magnitude, slip area). After calibration (within Task 7.4), the numerical model can be coupled to simulate the thermal performance during production. For the alternative discrete fracture network (DFN) scenario, a sufficiently sized and well- connected fracture network above percolation threshold is required to allow fluid flow on a reservoir scale. A DFN can be a realistic description of fracture parameter (orientation, size, aperture) and fracture network characteristics (fracture set orientation, density, spacing, connectivity) and can be derived by direct observations at outcrops or from geophysical imaging along wellbores. Modelling fluid flow in a DFN may be performed in two ways (x.x. Xxxx, 2013): The first (deterministic) approach is a direct simulation of fluid flow on fractures of a DFN assuming zero matrix permeability. The second (statistical) approach does not directly simulate fluid flow on fractures. Instead, an equivalent permeability grid is used to represent a DFN. This continuum approach requires calculation of equivalent grid-based permeability tensors from a DFN. In order to model fluid flow in the Porthtowan fault zone once data from drilling becomes available, we will use a hybrid approach combining both approaches, where the DFN of the Porthtowan fault zone is superimposed on the background fracture network, represented by a continuum model, of the Carnmenellis granite. Properties of the continuum model are derived from outcrop studies and observations made in the Rosemanowes HDR project, calculation of the 3D permeability tensor, and subsequent upscaling. Figure 3 summarizes the DFN modelling workflow. Figure 3: Overview of the DFN modelling workflow.
