First coupling of Δ47 thermometry and U-Pb dating to constrain the diagenetic evolution and thermal history of sedimentary basins : the case of the Paris basin (France)

Diagenesis is a crucial process in the development or destruction of reservoir properties, especially in carbonate formations. Exploration and modeling concepts require prior detailed reconstruction of diagenetic history and... [ view full abstract ]

Diagenesis is a crucial process in the development or destruction of reservoir properties, especially in carbonate formations. Exploration and modeling concepts require prior detailed reconstruction of diagenetic history and fluids pathways with three key parameters : (1) the temperature at which diagenetic transformations occur, (2) their absolute age and (3) the source of mineralizing fluids (e.g. meteoric, marine, brine...). This study presents the unprecedented coupling of two recently developed geochemical proxies on carbonate minerals (Δ47 thermometry and U/Pb dating) in order to constrain the thermo-chronological evolution and the paragenetic history of a carbonate reservoir.

Here we applied those proxies on a Middle Jurassic carbonate reservoir unit (Paris basin, 1800m depth), that hosts four successive generations of calcite and dolomite cements. We recorded a multi-steps thermal evolution, beginning with deposition under normal sedimentary temperature (marine TΔ47 between 23° and 30°C) and evolving towards oil window burial conditions. Indeed, the four burial cements show distinguishable Δ47 temperatures from 59° to 90°C, ranging in ages from late Cretaceous (121±4My) to Oligocene (35±6My). We have therefore calibrated a paragenetic sequence both in time and temperature, providing a framework of fluid circulation and petrophysical evolution of the studied reservoir formation. Finally, the time-temperature scenario that we deduced from Δ47 and U-Pb analyses agrees with the modeled thermal history available for the Paris basin (backstripping calibrated with vitrinite reflectance data).

We anticipate that this novel thermochronological approach for studying carbonate diagenesis will provide crucial information on the : (1) thermal history and heat flow regime in sedimentary basins, (2) absolute age of oil and water migration in reservoirs, (3) evolution in time of the reservoirs quality.