Study of heat and mass transfer in a distensive margin
The Ardeche project, in the southeast basin of
France , is part of "Forages scientifiques de l'Ardeche, G.P.F " program whose
objectives are to investigate the evolution of extensive paleomargins.
Evolutions of physical parameters with depth (porosity, thermal conductivity) have been defined using data from boreholes and litterature data.
Numerical models of heat and
mass transfers hava been carried on the following geometries:
At present time, the calculated temperatures fit those reported for BA1 and
MM1. The model shows that the Uzer fault separates two different hydrological
domains: to the east, a purely conductive thermal zone; to the west, an hydrodynamic
zone where fluids circulate through regional faults downward penetrating the
Hettangian layers, the upper and lower Triassic, and the basement. The presence of
cold fluids at 634m depth along MM1 attests to a downward penetration of fluids in the
sedimentary cover. However, the calculated filtration velocities are very low (some
mm/yr.).
The results obtained have been compared to those deduced from organic matter
and fluid inclusion studies. This model
confirms that at maximum burial, a 2000m cover and a basal heat flow of 80 +/- 5 mW/m2
are compatible with the basin history and with the measured paleo-temperature.
Particularly, in the Largentiere area, the modelling reveals fluid exchange patterns
between the sedimentary layers and the basement, which could be invoked as a
mechanism for mineralization.
