Coupled Evaluation of DFN Models and Well Hydraulics for Improved Estimation of Hydraulic Fracture Apertures

To characterise the fracture network geometry of a fluid reservoir, fundamental parameters are used in a DFN simulation algorithm. However, evaluating the hydrodynamic behaviour of such rock bodies also requires apertures of individual fractures. Aperture is usually not treated as an independent variable; rather, it is derived from length. A common approach is a linear relationship, a = A*L, where A is the aperture coefficient. The fracture’s free volume varies with the aperture coefficient, which influences the modelled fractured porosity and permeability. Since post-tectonic fluid-rock interactions can considerably alter the original apertures, the relationship between fracture length and aperture may vary across a reservoir, complicating hydrodynamic modelling. Therefore, from a hydrodynamic perspective, the hydraulic aperture should be used instead of the physical aperture. In this paper, transmissivity data and DFN models are analysed simultaneously to estimate reliable aperture coefficients. The method is demonstrated using the fractured Mórágy Granite body in SW Hungary. In the context of the radioactive waste depository project, numerous wells penetrated the fractured granite. Transmissivity data and DFN models from 238 intervals are used to calibrate aperture coefficient values. The associated porosity data are employed to construct a porosity log for each well, and analyse poro-perm diagrams.