Serhat Tonkul completed his PhD in Environmental Science and Engineering at the İzmir Institute of Technology, where his research focused on geothermal systems, CO₂-fluid-rock interactions, critical raw materials, and numerical modelling of geothermal reservoirs. During his doctoral studies, he contributed to the EU Horizon projects REFLECT and CRM-geothermal and worked as a visiting researcher at the Delft University of Technology (TU Delft) in the Netherlands.
Serhat investigated how geothermal fluids interact with reservoir rocks, and how these interactions influence resource sustainability. His work combined field investigations, laboratory analyses, geochemical modelling, and numerical reservoir simulations to better understand the coupled thermal, hydraulic, and geochemical processes operating in high-enthalpy geothermal systems. His work on the characterization of Sb scaling and fluids in saline geothermal power plants of the Germencik Region, Turkey and on the effect of degassing on scaling in the hypersaline system of Tuzla geothermal field, Turkey, have been published already.
Figure 1: During fieldwork in the Tuzla region, Serhat and other CRM-geothermal researchers investigate analogue rocks from geothermal reservoir formations.
Serhat expanded this work towards reservoir-scale numerical modelling. Using advanced thermal-hydraulic and reactive transport simulations, he evaluated the long-term impacts of fluid reinjection and fluid-CO₂ co-injection on reservoir pressure evolution, heat recovery, and geothermal sustainability. His results demonstrate how fluid-rock-CO₂ interactions influence subsurface flow redistribution and reservoir performance over different timescales. For example, Figure 2 shows his results on the expansion of the CO₂ concentration in the geothermal brine during extended injection times. The study is published: Tonkul, S., Erol, S., Baba, A., & Regenspurg, S. (2026). Fluid–CO₂ injection in a hypersaline volcanic systems: a reactive transport and experimental evaluation with application to the Tuzla Geothermal Field, Türkiye. Geothermal Energy, 14(1), 2.
Figure 2: Temporal evolution of CO₂ mole fraction (XCO₂) in the Tuzla geothermal reservoir during 30 years of fluid-CO₂ co-injection, shown at selected time steps. “INJ” marks the injection well, while wells with “PROD” are productions wells.
To support his numerical studies, Serhat conducted a series of CO₂-fluid rock dissolution/precipitation reactions (see Figure 3). He used reservoir rock samples in a batch setup under pressure of up to 4.4 MPa and at temperatures of up to 200 °C. The reservoir fluid coming from Tuzla geothermal field was enriched with CO₂. He observed that CO₂. injection led to the dissolution of feldspar, but also the precipitation of secondary minerals. Both processes would affect the permeability of the reservoir and, consequently, the sustainability of heat and mineral extraction.
Serhat’s full thesis is available here.
