TO CONSTRUCT A COMPREHENSIVE INTEGRATED MODEL OF THE DOGGER AQUIFER IN THE PARIS BASIN BY CORRELATING DATA FROM OVER 100 WELLS, MOSTLY DRILLED FOR GEOTHERMAL PURPOSES.
The sedimentary beds of the Paris basin host numerous aquifers. Several of these deep aquifers offer good geothermal energy possibilities, but the main interest was concentrated on the Jurassic limestones of the Dogger. This limestone is better known because it was the subject of intensive drilling for petroleum exploration.
The detailed study of the Dogger reservoir in the Paris basin is a multifield research including specific and various topics: geology, sedimentology, geochemistry, hydrodynamic and thermal modelling. The analysis is focussed on the numerous data collected on the 110 deep geothermal wells.
Including all the available geothermal data, the study of the characterization of the Dogger confirms the heterogenous structure (vertical and lateral) of the reservoir. Except for pressure, the fluid state variables are not systematically correlated with depth, as one can expect in a sedimentary basin. Thermal anomalies suggest the perturbation of the geothermal flux by local or regional fluid velocity. In turn, the geometry of the flow path, and the location of the recharge areas are highly dependent on the geochemical constraints.
The origin of fluids is more complex: chemical parameters favour the hypothesis of a common parent for these waters, with various evolutions depending on regional trend and local velocities.
A main result of this multifield research is the importance of the coupled information coming from the individual and analytical techniques. Each result on a given topic must be consistent with the associated phenomena; this is especially true for hydrodynamics associated with both chemical and thermal fields, a calibration condition for the synthetic model. Up to now, some discrepancies remain, new investigations are required to specify the origin of the fluid salinity, the age of water and the flow path perturbations induced by density effects coupled with topography.
THE WORK CONSISTS OF SEDIMENTOLOGICAL, GEOCHEMICAL AND THERMAL ANALYSIS OF DATA FROM THE WELLS, FOLLOWED BY CONSTRUCTION OF A DETAILED REGIONAL MODEL OF THE HYDRODYNAMIC AND THERMODYNAMIC BEHAVIOUR OF THE RESERVOIR BENEATH THE ILE-DE-FRANCE.
SEDIMENTOLOGICAL ANALYSIS WILL PERMIT IDENTIFICATION AND CORRELATION OF INDIVIDUAL LAYERS WITHIN THE OVERALL DOGGER FORMATION, WHILE ANALYSIS OF DIAGENETIC EFFECTS WILL ALLOW MORE PRECISE TARGETTING OF FUTURE WELLS AND FORECASTING OF GEOTHERMAL RESOURCES. GEOCHEMICAL ANALYSES WILL LEAD TO MODELLING OF THE SOURCES AND CIRCULATION PATHS OF FLUID IN THE RESERVOIR AND TO IMPROVED UNDERSTANDING OF THE MANAGEMENT OF THESE FLUIDS, BOTH IN-SITU AND IN THE SURFACE PLANT. THE THERMAL AND HYDRODYNAMIC ANALYSIS WILL CONTRIBUTE TO THE IDENTIFICATION AND PROPERTIES OF THE CONDUCTING LAYERS WITHIN THE RESERVOIR, PERMITTING BETTER SRRESERVOIR MANAGEMENT. OVERALL, THE MODEL WILL CONTRIBUTE TO:
- OPTIMAL DESIGN OF THE SPACING OF PRODUCTION-REINJECTION WELL PAIRS;
- NINIMISING INTERFERENCE BETWEEN ADJACENT SCHEMES;
- OPTIMAL MANAGEMENT OF THE GEOTHERMAL RESOURCE.