Preliminary kinetic study on rock-fluid interaction of the enhanced geothermal systems in Cooper Basin, South Australia

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 granites from Haberno 3 well (Cooper Basin, South Australia). Samples of drill cutting from a borehole 5 km deep were reacted with pure water in autoclaves (no mixing) at 120ºC, 140ºC, 160ºC, 170ºC, 200ºC, and 220ºC for 56 days. Drill cuttings were also used for rock-water interaction experiments in a titanium flow through geothermal cell at 250ºC at saturated vapor pressure (35 bar). Fluid and rock samples were analyzed prior to and after circulating the water through the crushed sample of the rock (diameter: 100-200um) for 1, 3, 5, 10, 17 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 (SiO2) concentration. Experimental results showed that the silica concentration is 320ppm after 28 days interaction in the flow-through cell, which is quite low, compared to the literature. However, this deviation may be due to the increasing of other dissolved species which reduce 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.