Evaluation of silica scaling potential for selected wells within Olkaria Domes geothermal field, Nakuru county, Kenya

Geothermal energy is a reliable low-emission energy source; however, mineral scaling resulting from physicochemical changes during fluid ascent, flashing, and cooling can limit efficient heat utilisation. In Kenya’s Olkaria Domes geothermal field, amorphous silica deposition remains a major operational constraint affecting separated-brine utilisation and reinjection. This study evaluated silica scaling behaviour in four production wells (OW-921, OW-921A, OW-901A, and OW-901B) using field geochemical data integrated with WATCH and PHREEQC geochemical modelling. Reconstructed reservoir fluids remained undersaturated with respect to amorphous silica under reservoir and current separator conditions (190°C), indicating low scaling risk during existing production operations. Predicted silica saturation temperatures (SSTs) varied considerably among wells, ranging from approximately 70°C to 155°C, with values of 155°C (OW-921), 130°C (OW-921A), 100°C (OW-901A), and 70°C (OW-901B), reflecting well-specific fluid chemistry and scaling susceptibility. Mixing simulations using discharge-weighted contributions from OW-921 (3%), OW-921A (45%), OW-901A (18%), and OW-901B (34%) demonstrated that brine blending reduced silica supersaturation tendencies under representative SP921 separator station operating conditions. The combined separated brines remained undersaturated during secondary utilisation down to approximately 87°C under adiabatic boiling and 110°C under conductive cooling conditions. Reheating simulations further indicated minimum reinjection temperatures of approximately 117°C and 120°C for adiabatic and conductive pathways, respectively, to minimise silica scaling risk. Silica speciation modelling showed that CO 2 degassing increased fluid pH and promoted silicic acid dissociation, thereby delaying silica saturation, while kinetic and hydrodynamic factors were identified as additional controls capable of causing deviations from equilibrium predictions. The results indicate that substantial additional heat recovery from separated brine may be feasible through downstream utilisation pathways without interfering with existing primary steam utilisation. The identified operational thresholds should be interpreted as thermodynamic estimates requiring field validation and operational monitoring. The integrated framework developed provides a transferable approach for optimising secondary heat recovery and reinjection strategies in silica-rich geothermal systems.