Experimental and Modelling Investigation of Flow Models for Low-Temperature Geothermal Wells

Abstract Geothermal energy extraction involves complex multiphase flow within downhole tubulars. Efficient fluid flow management is pivotal for maximizing energy recovery and ensuring safe operations in geothermal energy systems. Particularly, accurate characterization of multiphase flow, comprising water, steam, and gaseous components, is critical for optimizing geothermal power generation. However, measurement uncertainty and maintenance challenges impede the precise monitoring of flow rates and composition in harsh geothermal environments. This study addresses the imperative need for improved flow modeling in geothermal wells by evaluating various modeling techniques. The primary goal is to analyze the models capable of estimating flow rates and water/steam ratios using an experimental pressure and temperature dataset. Such models offer a cost-effective and accurate alternative to conventional flow meters, particularly for multiphase flows. The proposed study evaluates empirical correlations and mechanistic models, particularly for water-steam flow in the low to moderate temperature range. A 50.8 mm-ID, 7.6 m-tall vertical flow loop was operated at 25, 60, and 80 °C with liquid superficial velocities (vsl) from 0.006 to 0.30 m s⁻¹ and gas superficial velocities (vsg) from 0.6 to 9.1 m s⁻¹, yielding 214 steady slug-flow tests. Differential-pressure transducers, thermocouples, and high-speed video provided liquid-holdup and pressure-gradient data with quantified uncertainties and also documented the prevailing flow regime. Model predictions obtained from representative mechanistic frameworks (MODEL 1, MODEL 2 Unified 2015) were compared with the experimental results. The analysis identifies the property adjustments and holdup closures required for each model to reproduce the observed pressure and holdup trends under moderate-temperature water–air conditions, thereby demonstrating how calibrated multiphase models can replace intrusive flow-metering techniques in geothermal wells and informing future extensions to higher-temperature and flashing regimes. By advancing flow characterization capabilities, this research contributes to the broader objective of transitioning toward a renewable energy landscape.