Inter-disciplinary characterisation of carbonate reservoirs. ALBION, a multi-scales dynamic analogue
Résumé
Carbonates probably host the most complex aquifers in terms of organisation of porosity networks and flow behaviour. Their heterogeneity originates at different scales and from numerous processes related to geology, hydrodynamics, chemistry and mechanic. These processes occur during a longterm history from just after the deposition of sediments to present day. At small scale, they provide the rock matrix with its petrophysical, mechanic and geophysical properties. At large scale, they can promote the development of karst networks or flow barriers.
The ALBION Project addresses the question of the relationships between the heterogeneity of carbonate reservoirs from pore to field scale and the heterogeneity of groundwater dynamics, which is induced. An interdisciplinary approach has been developed to tackle genetic processes and their impact on medium properties. Switching back and forth between in-situ multi-physics measurements and integrative modelling allow coupling interpretations and strengthening concepts used to populate reservoir models.
This innovative approach has been applied and enhanced on nested field sites in the Fontaine de Vaucluse catchment area (south-eastern France). The LSBB sector includes the so-called underground laboratory, an almost 4 km long tunnel, and three sets of boreholes drilled in the reservoir. It enables the investigation of flow behaviour for different media (matrix, fractures and karst) at various scales, in different well-known geological conditions and from different natural or experimental settings. Through a micro to meso-scale multi-physics characterization of matrix, relationships between geological, petrophysical and geophysical properties have been investigated, and an integrative classification of rock-types has been proposed. In the central sector of the catchment, near Saint-Christold’Albion, the karst network is well developed with several famous caves, as “Le trou souffleur”. In this area, factors controlling the genesis of karst conduits in the unsaturated zone have been investigated and a conceptual model has been proposed. Lastly, at the aquifer scale, integration of results acquired at lower scales added to numerous geological descriptions and analyses give new insights on the role and importance of the driving parameters of the evolution of the carbonate platform.
In next steps, other sites as the Lagnes-Robion quarry or a new tunnel in the LSBB will complete the disposal in this way. Finally, the assessment of porosity, permeability or geophysical properties of different rock-types at various scales will provide the framework to address the issue of upscaling in carbonates. Thanks to these different studies, a workflow of characterization and modelling has been established to investigate dynamic analogues.