| Abstract |
A laboratory experimental simulation and geochemical modelling study of the re-injection of caustic-dosed brine into diorite have been performed. The experimental simulation (at 150oC) used a one-pass, continuous-flow, fluid-rock interaction apparatus. The experimental fluid was caustic-dosed re-injection brine and the rock material was crushed, sieved and cleaned diorite. At 150oC, the behaviour of SiO2, Ca and Al were indicative of precipitation of a Ca-aluminosilicate mineral, likely a zeolite or clay. SEM-EDS examination of the run products showed dissolution of the primary minerals. Precipitated phases were a Ca-aluminosilicate, conjectured to be a zeolite but could also be a Ca-rich clay mineral, and calcite. Eight geochemical software models were performed simulating interaction between re-injection brine and bypass fluid both with and without caustic dosing. Fluid-rock interaction with the various fluid compositions results in increases in rock mass due to precipitation of secondary phases including quartz, K-feldspar, muscovite, zeolite, clay and calcite. In three of the models, where amorphous silica was assumed to be the stable polymorph, mineral precipitation ceased at high water/rock ratio. The experimental results provide information on fluid/rock interactions during the initial stages of re-injection while the modelling provides information on the longer term effects of these interactions. In the case of three of the geochemical models, it is possible that fracture permeability will remain open and caustic dosing may be at least partially effective. |