Modeling Mineral Scaling in Matalibong Sector of Tiwi Geothermal Field, Albay, Bicol, Philippines

Mineral scaling constitutes a major problem in geothermal fields. It imposes adverse impacts on the performance of the power plant as mineral precipitates and clogs facilities, affecting steam production. This paper identifies the processes leading to the formation of calcite, pyrite, and anhydrite as mineral scales in Well-1 located at the Matalibong sector, one of the production sectors in Tiwi Geothermal Field, Albay, Philippines, using CHIM-XPT (2016). Reconstruction of reservoir water, cooling, adiabatic boiling, fluid-fluid mixing, and isothermal simulations were performed. In addition to established temperature and pressure, fluid flow rate and wellbore geometry (pipe length and wellbore inner diameter) were considered as factors in mineral scale formation. Results of the geochemical modeling showed that the mineral scaling in Well-1 could be a product of adiabatic boiling and cooling of mixed cold spring water and reconstructed reservoir water. Key findings show that at a constant temperature, a boiling event occurs when pressure is reduced due to a lower fluid flow rate with respect to its depth leading to the formation of minerals, specifically anhydrite. Decreasing fluid flow rate also triggers adiabatic boiling. Kinetics can promote adiabatic boiling where pressure changes due to fluid flow rate conditions leading to the formation of mineral scales. With this better understanding of how calcite, pyrite, and anhydrite were formed in Well-1, adiabatic boiling and, thus, the formation of the mineral scales can be avoided or minimized by proper monitoring and control of the fluid flow rate in the well.