TIMING OF FLUID CIRCULATION ALONG FAULTS AT RESERVOIR SCALE

Discolored bands of the Colorado Plateau sandstones, in southern Utah, are famous all over the world. This discoloration, localized in the red sandstone around Laramide uplifts and along fractures and faults, reflects fluid-driven alteration and diagenesis. The main problem is to understand the nature of the fluids which provoked this chemical bleaching. Understandings of these diagenetic mechanisms through time is crucial for the determination of the paleo-sequestration, leakage and circulation of CO₂. In order to gain further insight in this bleaching phenomenon, we conducted a study along Moab and Salt Wash Faults, from Moab to the western side of the San Raphael Swell. Four representative outcrops, characterized by Jurassic formations bleaching of different age and lithology, have been selected (Moab roll-over, Courthouse Canyon, Ten Mile Graben and the western part of the Salt Wash fault). We studied bleached fractures located in different lithologies of the Entrada Formation and the Upper Morrison Formation. To understand the flow history and the interaction between the components of the reservoir-seal-fault systems we used petrography, XRD and trace elements.

Moreover, we studied the quaternary CO₂ leakage sites along the Salt Wash Fault, on thermogenic travertine deposits. Precise time interval and duration for a single paleo-leakage event has been calibrated by U/Th dating and a corresponding CO₂ leakage rate could be calculated.

Integration of structural field work with petrography, geochemistry and dating measurement allow to built a story of the CO₂ leakage in this western part of the Colorado Plateau, from Jurassic to present day.