PREDICTIONS OF AVERAGE SILICA PARTICLE SIZE OVER TIME UNDER GEOTHERMAL CONDITIONS

Abstract

When cooled geothermal brine is reinjected, colloidal silica may form, deposit, and eventually block the fluid pathways in the aquifer, reducing injectivity. Models of silica deposition, the formation of colloidal silica, and especially the growth of silica nanoparticles over time, are of value in the prediction of geothermal well lifetime and the effects of brine treatments and workovers. This paper deals with the growth of silica particles in geothermal brines where silica polymerisation is actively occurring.
Based on the chronomal (Nielsen 1964) and the Ostwald ripening models (Lifshitz and Slyozov 1961, Wagner 1961) and the observations reported by Broge and Iler (1971), Alexander and McWhorter (1976), and Tobler et al. (2009), a semi-empirical silica particle growth model is proposed. It is used to predict silica particle growth over time under typical geothermal conditions, and prepares the groundwork for a model of stability (resistance to aggregation) described in another paper at this conference. The model predictions are compared to the field experiments reported by (Tobler and Benning 2013, Mroczek et al. 2017).