Effect of Salinity on Geothermal Well Performance

Abstract Water salinity plays a critical role on geothermal well performance. This study evaluates how increasing brine salinity, from 0-25 wt% NaCl, impacts flow behavior, thermal output, and energy delivery in a single-phase vertical geothermal well. A steady-state well model was constructed in PIPESIM using fixed reservoir conditions to isolate the influence of salinity alone. Reservoir pressure was held at 4000 psi with a temperature of 150 °C, and no artificial lift was applied. For each salinity level, fluid properties were calculated using validated literature correlations. These included density, viscosity, specific heat capacity, thermal conductivity, and enthalpy at both reservoir and surface conditions. The results show that salinity affects multiple thermophysical properties in ways that degrade production performance. As salinity increases, the fluid becomes denser and more viscous, which increases hydrostatic and frictional pressure losses. At the same time, thermal conductivity and specific heat capacity decrease, limiting the fluid's ability to retain heat during transit. These combined effects result in a lower mass flow rate, reduced wellhead temperature, and diminished surface enthalpy. For instance, the well's flow rate dropped by 75% between the 0 and 25 percent salinity cases, and enthalpy declined by 41% at surface conditions. In addition, the wellhead temperature decreased by roughly 30 °C at the highest salinity level due to lower flow velocity and reduced heat capacity. The findings demonstrate that salinity reduces both the quantity and quality of geothermal energy that can be produced. Failing to incorporate salinity into well models can lead to significant overestimation of flowrate and power potential. This paper highlights the importance of using accurate brine property correlations when designing wells, forecasting performance, and sizing surface facilities. It also provides a framework for understanding how salinity-driven thermophysical changes manifest in geothermal well outputs. The methodology and results are broadly applicable to geothermal fields where high-salinity fluids are present, offering insights into optimizing production strategies under such conditions.