Zoe K. Shipton1, James P. Evans1, Peter T. Kolesar1
(1) Utah State University, Logan, UT
ABSTRACT: Analysis of CO2-charged Fluid Migration along Faults in Naturally Occuring Gas Systems
The Little Grand and Salt Wash faults (south-eastern Utah) allow us to examine clay-rich fault zones. The in situ properties and structure of these fault rocks are important in predicting sealing capability and fault integrity in hydrocarbon reservoirs. Due to the poor preservation of faults in these rocks, there is little detailed field data to make predictions regarding the behavior of these faults. The Little Grand and Salt Wash normal faults are therefore ideal for testing long-term three-dimensional hydrologic behavior of clay-richfaults at the oil-field scale. The faults cut Jurassic to Cretaceous sandstones, shales, and siltstones producing clay-rich gouge that should be a barrier to flow. However, numerous veins, tufa deposits, and CO2 charged springs are associated with the faults indicating that the seal has failed numerous times in their history. Well data show that the faults cut the Paradox Formation at depth, consistent with our geochemical and isotopic data showing that the veins and present day fluids are/were sourced from Paleozoic marine rocks. Thus the CO2 charged waters are migrating 2-3 km vertically upward. Variations in water chemistries suggest that the faults compartmentalize the current hydrologic system, or capture waters that have evolved to different chemistries in the regional hydrologic system. We also suggest that the faults are a seal to lateral migration of gas. Our results show how the composition of the fault evolved, how fault rock properties vary as a function of structural and stratigraphic position, and constrain models of fault transmissibility and seal behavior.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado