Abstract
For successful geothermal reservoir exploration, accurate temperature estimation is essential. Since reservoir temperature estimation frequently involves high uncertainties when using conventional solute geothermometers, a new statistical approach is proposed. The focus of this study is on the development of a new multicomponent geothermometer tool which requires a significantly reduced data set compared to existing approaches. The method is validated against reservoir temperature measurements in the Krafla and the Reykjanes geothermal systems. A site-specific basaltic mineral set was selected as the basis to compute the equilibrium temperatures. These high-enthalpy geothermal reservoirs are located in the neo-volcanic zone of Iceland where the fluid temperatures are known to reach up to 350 °C at a depth of 2000 m. During ascent, the fluid composition is prone to changes as well as possible phase segregation due to depressurization and boiling. Therefore, to reduce the uncertainty of temperature estimations, reservoir temperature conditions are numerically reconstructed with sensitivity analyses considering pH, aluminium concentration, and steam loss. The evaluation of the geochemical data and the sensitivity analyses were calculated via a numerical in-house tool called MulT_predict. In all cases, the temperature estimations match with the in situ temperatures measured at Krafla and Reykjanes. The development of this method tends to be a promising and precise tool for reservoir temperature estimation. The developed methodology is a fast and easy-to-handle exploration tool that can be applied to standard geochemical data without the need for a sophisticated gas analysis yet obtaining very accurate results.
Highlights
A reliable temperature estimation for a targeted geothermal reservoir, which lays the foundation for the prediction of producible energy, is essential for a successful exploration campaign
The original data of Krafla and Reykjanes (Appendices 1, 3) are corrected for Conclusion and outlook This application of multicomponent geothermometry is a promising tool for reservoir temperature estimations
This specific approach comprises a devised basalt-specific mineral set and a subsequent sensitivity analysis based on a standard chemical analysis of the fluid composition without the need for a sophisticated gas analysis
Summary
A reliable temperature estimation for a targeted geothermal reservoir, which lays the foundation for the prediction of producible energy, is essential for a successful exploration campaign. Secondary processes may change the fluid composition and the equilibrium while migrating to the earth surface These variations can result in large uncertainties for the reservoir temperature determination using solute geothermometers (Nitschke et al 2018). Corrections were established to overcome interferences from secondary processes such as dilution, boiling, and mixing of fluids affecting the temperature estimation (Cooper et al 2013; Peiffer et al 2014; Spycher et al 2014). These methods need an additional gas analysis for precise temperature estimations. Nitschke et al (2017) introduced a method to reconstruct in situ conditions of the reservoir temperature by varying sensitive parameters, especially pH and aluminium concentration as well as steam loss, to further reduce the uncertainty of equilibrium temperatures
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