LONG-TERM BEHAVIOR OF CO2-RICH FLUID IN THE LITTLE GRAND WASH FAULT, UTAH, USA
The petrographic features of the Mancos shale in the hanging wall of the fault have been studied and compared with the unaltered Mancos shale that not influenced by the CO2-rich fluid. A small-scale travertine at the junction of the main fault and a small relay fault was discovered was deposited by the CO2-rich fluid that penetrating the deformed Mancos shales. The stable isotope coupled with petrographic methods were used to distinguish the depositional/early diagenetic carbonates and the CO2-rich fluid derived carbonates. The result shows the CO2-rich fluid could precipitate up to 24% of calcite against the whole rock (%weight) at the damaged zone of the Mancos shale that 15m away from the Little Grand Wash fault, while the Mancos further than 17m from the main fault contains no CO2-rich fluid induced precipitation. The water/rock interaction model has been established to quantitatively illustrate reaction pathways under different water-rock contact schemes. The final conclusion for the natural analogue is, the CO2-rich fluid can only penetrate and interact with the deformed shales that associated with fault. No evidence show the intact Mancos has been affected by the CO2-rich fluid. The result has implications for the future siting for the potential geological storage sites, especially for the assessment of integrity of the fault-associated seals.