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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS017 Poster presentation 2387
Hydro-geothermal characters of the Moroccan Atlas
Dr. Massimo Verdoya
Dip.Te.Ris. Universit di Genova IASPEI
Yassine Zarhloule, Abdenbi El Mandour, Paolo Chiozzi, Mimoun Boughriba,
Abderrahim Lahrach
The geological setting of northwestern Morocco is characterized to the west by the Maghrebide orogenic
system, of Alpine age and referred as to the Rif domain, and to the east by the intra-continental
Mesozoic-Cenozoic belt of the Middle Atlas. These ranges form the main recharge zones of deep water
reservoirs. In the Middle Atlas there are several hydrogeological basins with minor shallow aquifers in
the Plio-Quaternary terrains. A marly substratum separates the shallow groundwater from the deeper
artesian aquifer, occurring in the high-permeability Liassic carbonatic sequences and extending
throughout the region. The top of the carbonatic aquifer ranges from 200 to 1300 m depth, and water
temperatures as higher as 50 C were recorded to about 500 m depth. Moreover, numerous springs with
temperature larger than 40 C and a flow which may reach 40 l/s occur in this area. Geothermal data so
far achieved, especially from deep exploration oil wells, point to an increase of terrestrial heat-flow
density from the Rif to the Middle Atlas zone, from about 60 to more than 80 mW/m2, respectively.
Possible explanations should be searched in the regional extensional tectonics which has affected this
area in Plio-Quaternary times yielding intensive volcanic activity. The aim of this paper is to contribute
to the hydro-geothermal characterization of northwestern Morocco by presenting results of
measurements of rock thermo-physical properties and analyzing temperature data available from water
wells reaching the Mesozoic terrains. A number of thermal conductivity measurements were carried out
on a set of samples representative of the stratigraphic sequence of the Middle Atlas. The carbonatic
lithotypes forming the deep aquifer show a relatively high thermal conductivity. Values range from 2.0-
3.1 W/(m K) in limestones to 4.6-5.0 W/(m K) in dolomites. Temperature depth profiles from boreholes
characterized by upward flow of hot water fed by the carbonatic formation are available to 350-500 m
depth. Temperature logs were analyzed by matching thermal data with models of vertical temperature
distribution, which incorporate both heat and mass transfer. Thermo-hydraulic parameters were
calculated from the coefficients of the advective models obtained by means of the least-square fitting
method. The inferred temperature gradient above the advectively perturbed carbonatic formation
exceeds 50 mK/m, thus locally boosting the heat-flow density to values larger than 100 mW/m2.
Analytical modeling of heat and water transfer involved in the deep circulation was attempted along
selected hydro-geological cross-sections. Several hypotheses of basal heat-flow density, porosity,
aquifer thickness and water velocity were tested in order to fit the borehole thermal records. The results
show that temperatures of the deep aquifer are compatible with a topographically driven flow in the
carbonatic formations down to 600-1500 m depth, under conditions of enhanced geothermal gradient.
Keywords: advection, deep aquifers