| Abstract |
Kinetic studies on the interactions between rock and circulating fluid are essential for determination of the chemical changes and mineral alteration in geothermal systems. Preliminary mineralogical investigation and geothermal experiments have been performed to investigate the dissolution of the granites from Habanero 3 well (Cooper Basin, South Australia). Samples of drill cuttings from a borehole 5 km deep were reacted with pure water in autoclaves (no mixing) at 120oC, 130oC, 140oC, 160oC, 170oC, 180oC, 200oC, 220oC for 28 days. Drill cuttings were used also for rock-water interaction experiments in a titanium flow through geothermal cell at 250oC at vapour pressure (35 bar). Fluid and rock samples were analysed prior to, and after circulating the water through crushed sample of the rock (diameter: 100 – 200ìm) for 1, 3, 7, 14, 21 and 28 days. Water analyses were undertaken using ICP-MS to determine the cation concentrations, silicomolybdate method using HACH spectrophotometer to determine the reactive silica or silicic acid (H4SiO4) concentrations, and ICP-OES to determine the total dissolved silica concentrations. Rock analyses were conducted using scanning electron microscopy (SEM), and x-ray diffraction (XRD). Experimental results showed that the equilibrium silica concentration is 320ppm which is quite low compared to the literature. However, this deviation may be due to the increasing of other dissolved species which reduces the solubility of the silica over time. Another variable investigated was the dissolution rate constant. The dissolution rate constant obtained was lower than the literature since this study was performed in the absence of mixing. Progressing experiments are being undertaken to investigate and correlate to the variation. |