Fluid inclusions as constraints in a three-dimensional hydro-thermo-mechanical model of the Paris basin, France
Résumé
Fluid inclusion homogenization temperatures and three-dimensional hydro-thermo-mechanical modelling were combined to constrain fluid flow, solute and heat transport in the Paris basin, France, focusing on the two main petroleum reservoirs i.e. the Dogger and the Triassic (Keuper) formations. The average homogenization temperatures of two-phase aqueous inclusions in different samples range from 66 degrees C to 88 degrees C in the Dogger calcite cement, from 106 degrees C to 118 degrees C in the Keuper dolomite cement and from 89 degrees C to 126 degrees C in the Keuper quartz and K-feldspar cements. The maximum homogenization temperatures for inclusions in the Keuper quartz and K-feldspar cements were 17-47 degrees C higher than present-day temperatures in the boreholes at similar depths. Processes that might explain higher temperatures in the past were examined through numerical simulations and sensitivity tests. A warmer climate in the Late Cretaceous-Early Tertiary resulted in a temperature rise of only 8 degrees C. Late Cretaceous chalk had a thermal blanketing effect that resulted in simulated temperatures as high as 15-20 degrees C above the present day ones. An additional 300 m deposition and subsequent erosion of chalk, not taken into account so far, has to be considered to simulate the high palaeo-temperatures recorded by fluid inclusions in both reservoirs. In view of the simulated thermal history of the basin, in the Keuper, an age of about 85 Ma is consistent with quartz/K-feldspar temperatures and an age of about 65 Ma is in agreement with the precipitation temperature of the dolomite cement. Our models suggest an age of about 50 Ma for the Dogger calcite cementation.