Stochastic 1-D reactive transport simulations to assess silica and carbonate phases during the CO 2 reinjection process in metasediments

Abstract

One proposed method to mitigate carbon emission is to mineralize the CO 2 in deep geothermal reservoirs while mixing the coproduced CO 2 with the effluent fluid for reinjection. The injection fluid temperature fluctuates due to the mixing process between CO 2 -charged water and the effluent fluid, and compressor interruptions change the thermodynamic conditions that influence the fluidrock interaction in the reservoir. Mineral dissolution or precipitations are associated with changes in permeability and porosity that affect the flow and, eventually, the lifespan of the reservoir. A combined stochastic-reactive transport simulation approach is useful for inspection purposes. Moreover, the stochastic algorithm validates the deterministic reactive transport simulation and demonstrates the time evolution of a chemically reacting system in the reservoir. This study examines a range of injection temperatures between 80 degrees C and 120 degrees C to evaluate silica and calcite precipitation along a flow path. One-dimensional (1-D) reactive transport and compartmentbased stochastic reaction-diffusion-advection Gillespie algorithms are carried out. The 1-D model represents a reservoir feed zone of around 2300 m. Two common metasediment rock types are evaluated for inspection. The first one is the muscovite schist, which has approximately 60% quartz, and the second is the quartz schist, consisting of roughly 90% quartz. The stochastic method can be applied more effectively if the chemical system is completely defined with proper reaction rates as a function of temperature. The mixing ratio of the coproduced CO 2 over the effluent fluid is around 0.0028. Simulation results show that CO 2 is partially sequestrated as calcite within the first 10 m of the entrance to the reservoir and plugs the pores completely in the muscovite schist scenario. Chalcedony and alpha-cristobalite precipitate as secondary minerals evenly along the flow path. CO 2 injection into a quartz schist layer is more appropriate for geochemical interactions below 120 degrees C.