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Highlights

Measuring two-phase is important for geothermal reservoir management and monitoring wells output.

The two-phase orifice plate is the most simple and low-cost flow meter for geothermal applications.

A new simplified two-phase flow correlation with high accuracy is developed for measuring flow from geothermal wells.

Six existing and new correlations for measuring two-phase flow rate were examined and compared to the field testing.

CFD modelling is used to predict the flow rate of geothermal fluid through the orifice plate.

Abstract

Measurement of the mass flow rate and enthalpy from two-phase geothermal wells is very important for monitoring individual well performance and for optimum reservoir management. Existing techniques are either expensive (separator and tracer dilution), low accuracy (tracer dilution) or require the geothermal well to be taken out of production (calorimeter and lip pressure methods). The two-phase orifice plate is the most widely examined alternative method and has been implemented in several geothermal fields worldwide. In this work, extensive geothermal field testing data is used to evaluate existing correlations using the concentric sharp-edge orifice plate. A new simplified correlation was then developed with high accuracy for the full range of geothermal reservoir enthalpies (600–2800 kJ/kg) and an analytical model was proposed to predict the pressure drop across the two-phase orifice.

Computational fluid dynamics (CFD) simulation using ANSYS Fluent was used to investigate the pressure profiles, velocity and discharge coefficients of two-phase flow of geothermal fluids through the sharp-edge orifice plate. The model results showed good agreement between the CFD simulations, field test data and the newly proposed pressure drop model. CFD modelling also show that using an eccentric orifice plate results in lower pressure drop than the concentric orifice.

Keywords

Mass flow rate

Enthalpy

Two-phase orifice

Geothermal fluids

Computational fluid dynamics

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