Fluid-Rock Interaction Under Conditions Pertinent to HDR/EGS Reservoir

Abstract

A hydrothermal apparatus capable of operating at up to 50 MPa and up to 400C was designed and fabricated to conduct flow-through and batch fluid-rock interactions experiments. Granite samples of varying mineral compositions were sourced from three different locations. H2O and CO2 flow-through fluid-rock interaction experiments were conducted at 20 MPa and 250C and various flow rates. Effluent fluids collected were analysed using ICP-OES whilst the pulverised granite samples were analysed using XRF, XRD,and SEM analysis. The results showed that, generally, H2O-rock interaction experiments dissolved more granite materials compared with CO2. Moreover, the presence of H2O in CO2-rock interaction experiments made the fluid reactive and enhanced dissolution of granite. However, both H2O and CO2 flow-through experiments showed that equilibrium conditions were not reached even after 15 days of exposure. XRD analysis showed that the bulk composition of granite samples did not change for both H2O and CO2-rock flow-through experiments except in CO2 flow-through experiment with very high H2O content. In addittion, SEM analysis of granite samples from CO2-H2O flow-through experiment showed formation of pits and cavities in some of the mineral surfaces which was associated with the dissolution and precipitation of carbonate minerals.