Chronology of Leaking Events and Sealing Processes in Fractured Reservoir: A Natural Example in Utah (USA)*

A multidisciplinary work on complex fluids, migrating from deep reservoirs to the surface in faulted zones, has been led in order to investigate and quantify the episodic opening and sealing of faults above a natural hydrocarbon reservoir and an aquifer locally CO2 enriched, in Green River area, Utah. It is well known that fluids flow through faults, but it is also demonstrated that fault zones may act as impermeable barriers. We consider here that active faults can successively open and close paths for fluids. In the studied example, these cycles are recorded close to the surface by observation of the fluid paths and travertine precipitation. Several methods have been used to investigate the correlation between complex fluid sources and migration processes through reservoirs and faults, and finally with surface precipitation. Field and petrographic work reveal the complexity of travertine structures. Two main types of travertine precipitation have been found: 1) travertine built on surface, and 2) cross-cutting veins, each of them characterized by different crystallisation modes and processes. The link with the evolution of flow rates variation through the fault has been investigated.