Characterization and Modelization of the Geometrical and Flow Properties of Fractured Carbonates: Application to Amellago Outcrop Data
I. Malinouskaya¹, P. M. Adler¹, J.-F.Thovert², and V. Mourzenko²
¹UPMC Sisyphe, Paris, France
²Institut PPRIME, Futuroscope, France
Fractures influence the hydraulic and transport properties of the natural geological formations. The purpose of the present work is to predict the properties of the fractured carbonates, in particular, the percolation status and permeability.
These properties can be obtained either using theoretical predictions for some standard cases or applying direct numerical simulations. Both approaches are based on statistical geometrical characteristics of the fracture networks. In the first case, existing models are directly applied. In the second case, the hydraulic properties are obtained by solving the governing flow equations which are written on the local scale and applied to the fracture network represented in an explicit way. Since a real fully described 3D sample cannot be provided, reconstructed ones are obtained based on the statistical geometrical characteristics of the real networks. Therefore, these characteristics are essential for the prediction of the hydraulic properties whatever the method.
The statistical geometrical characteristics are not always available in explicit form. In order to determine them, some measurements of the field data are required. There are several stereological methods which can be used to determine the required parameters from the available field measurements [1, 2, 5, 6].
We study data collected from several windows in the Amellago outcrop. These data include field measurements of the fracture orientations and trace maps drawn from photographs, represented by coordinates of trace end points. Field measurements on an horizontal pavement are also provided. They consist in a list of trace lengths, of the corresponding azimuths and of the nature of the trace terminations (inside or outside of the observation domain).
The hydraulic properties are obtained as follows. The observations from several windows in the Amellago outcrop and the corresponding trace maps are studied. The treatement and subsequent analysis of the available field data allow to determine or calibrate the model parameters. Then, the permeability tensor is derived using existing theoretical models for generic cases. These estimations are easy in terms of computations, but they do not include any specific features and therefore they can only provide a priori and possibly rough approximations. Finally, full numerical simulations are performed.
The methods which are applied to obtain the geometrical characteristics of the fracture networks using the available field observations are presented. The model parameters are determined and used for the theoretical predictions and for the direct numerical simulations.
The influence of the various parameters on the network properties can be examined by modifying values of the model parameters (2) or of the measured quantities in (1). This can provide indications about the sensibility of the predictions on the field data, about which ones should be determined with special care and which ones could be estimated in a more approximate way, and possibly guidelines for data acquisition.
AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012