Role of Silicate and Aluminate Ions in the Reaction of Sodium Hydroxide With Reservoir Minerals

Abstract

Summary A chemical model is presented for extrapolating laboratory data on mineral/alkali reactions to reservoir time scales. Minerals in sandstone and ions in caustic solution that control sodium hydroxide consumption during alkaline flooding were identified. This work may help operators predict when significant dissolution of the formation will occur and where precipitates will deposit. The dissolution of eight silicate minerals in caustic solution at 24 and 70°C [75 and 158°F] was determined. The minerals studied were quartz, two feldspars (microcline and albite), two micas (muscovite and biotite), and three clays (kaolinite, montmorillonite, and chlorite). The concentrations of sodium, silicate, aluminate, and hydroxide were measured periodically during bottle tests. Balanced chemical reactions are written for quartz, kaolinite, and phillipsite, and the corresponding equilibrium quotients are defined. A kinetic model is presented that includes rate constants, solid/liquid ratios, and equilibrium quotients to account for the effect of solution composition. The model was tested for kaolinite. The equilibrium quotient for kaolinite was found to be three times higher at 70°C [158°F] than at 24°C [75°F]. Dissolution-rate data were fitted successfully with the kinetic model. The reaction of Kern River reservoir sand with sodium hydroxide was studied to test the model. Consumption of sodium hydroxide occurred as predicted. However, caustic consumption was delayed in a slim tube packed with 99% quartz and 1% kaolinite, probably because of reduced nucleation of new minerals.