Reservoir-Seal-Fault Systems Leakage Evolution Though Time and Space

Thanks to the study of natural CO2 reservoirs, tools are developed in order to understand the CO2 storage efficiency and long-term evolution. The Colorado Plateau red sandstones, in southern Utah, are marked by fluid driven mineralization and alteration along joints, fractures and faults. These traces are considered as evidences for paleo and present-day migration pathways of the exotic fluids coming from reservoirs (located at different depths) to the surface across or along the transfer faulted zones. Understanding these mechanisms through time is crucial not only in the determination of the fault activity, for identifying the transient and permanent processes along this fault system, but also in the long-term paleo-sequestration calibration, and finally in the evaluation of hydrocarbon, gas, water and CO2 migration. In order to investigate the nature and the origin of the different leaking fluids or gas, we conducted a study along Moab and Green River Fault systems, from Moab to the western side of the San Raphael Swell, in Utah. A geological fieldwork highlights several former and current transfer and leakage processes, evidenced by (1) chemical bleaching, (2) gypsum, (3) different kinds of oxides, (4) carbonate precipitations, and (5) present day CO2 expulsion located all along the faults traces from Jurassic units to the present-day surface. Due to the different erosion pattern in the area, access to several reservoir and seals was possible for observation and sampling. This first step allowed to characterize the orientation and position of each leaky fluid family, and to analyze the fluids and carbonate precipitation with respect to the structural context. For instance, the strong impact of salt tectonics implies that some of the faults are probably rooted within this decollement, and that a system of small wavelength syncline/anticline is added a significant variability to the drainage pattern of these faults. In order to define the nature and the origin of the fluids responsible for the traces and seepages observed, we used a multi-disciplinary approach using the different following methods coming from: geology, geochemistry, petrography, XRD, trace elements analyses and U/Th datings. Finally, so as to understand the link between flow and tectonic histories of the reservoir-seal-fault systems, we integrate the analytical and the structural data set. This last step allows to propose a precise chronology and history of the fluid leakage in this western part of the Colorado Plateau, from Jurassic to present day. These combined technical methodologies represents a great tool to understand the leaking, and remediation processes, to characterize the variation through time and space of the fault activity and finally to evaluate the lost volume from reservoirs along a major fault system.