A theoretical model based on DFN models and 2D DEM numerical modelling has been developed for evaluating the rock mass mechanical properties. The description of the methodology is non-site related and can be applied in any site for this type of characterisation. The methodology was developed in the frame of the Site Investigation programmes for a Deep Repository for spent fuel in Sweden, and validated on sets of data coming from the Äspö Hard Rock Laboratory.

Un modèle theorique base sur des modèles probabilistiques de reseaux de fractures et sur un modèle numerique DEM 2D a ete developpe dans le but de determiner les proprietes mecaniques de la masse rocheuse. La methodologie developpee peut être appliquee à tout type de site pour ce genre de caracterisation. Le modèle a ete elabore dans le cadre des programmes de recherche d'un site d'enfouissement des dechets nucleaires en Suède, et valide par une application au laboratoire de recherche souterrain à Äspö.

Ausgehend von DFN-Modellen und 2D DEM numerischen Modellierungen wurde ein theoretisches Modell fuer die Auswertung von mechanischen Eigenschaften von Fels entwickelt. Die Methodikbeschreibung ist nicht standortspecifisch sondern kan ueberall fuer diesen Typ von Standordkarakteriserung angewendet werden. Die Methodik wurde in Schweden im Rahmen der Standortuntersuchungsprogramme fuer die Endlagerung von verbrauchten Brennelementen entwickelt und ist mit Hilfe von Daten des Äspö Hard Rock Laboratory validiert worden

Introduction

The methodology is developed in the frame of SKB's site investigation programmes for a Deep Repository for spent fuel and meant to be used for the rock mass mechanical characterisation of the sites. The model shall describe the initial stresses and the distribution of rock mechanical properties such as deformation and strength properties for the intact rock, for the fractures, for the deformation zones and for the rock mass viewed as a unit consisting of intact rock and fractures. The strategy established for the development of a Rock Mechanics Site Descriptive Model is presented in Andersson et al., 2002.

The basis of the theoretical approach is to determine the mechanical properties of the rock mass, in any potential site. The methodology is based on Discrete Element Method for the modelling of behaviour of rock masses. The rock mass is modelled as a discontinuous geometry in which contacts between blocks are fractures. The input parameters required for the model are the fracture geometry, and the mechanical properties of fractures and intact rock.

Overview of the methodology Definition of the fracture network

A Discrete Fracture Network (DFN) model was chosen to simulate the fracture network, and the FracManÒ software is used for generating fractures in three dimensions within a given rock volume. The definition of input parameters and the theoretical background of DFN models as developed in FracManÒ are presented in Dershowitz et al., 1998.

Considering the large number of fractures that are generated in a DFN volume (from 1000 to more than 15000 for a 30-m cube) it is at the moment technically difficult to do 3D simulations with a realistic network of discrete disc-shaped fractures.

Keywords:
reservoir geomechanics, wellbore integrity, complex reservoir, fluid modeling, Monte Carlo simulation, hydraulic fracturing, Upstream Oil & Gas, Simulation, Reservoir Characterization, equation of state
Subjects:
Wellbore Design, Hydraulic Fracturing, Reservoir Characterization, Fluid Characterization, Unconventional and Complex Reservoirs, Wellbore integrity, Reservoir geomechanics, Fluid modeling, equations of state, Naturally-fractured reservoirs
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2003. The South African Institute of Mining and Metallurgy. Permission to Distribute - International Society for Rock Mechanics.
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