A Downhole Fluorimeter for Measuring Flow Processes in Geothermal and EGS Wellbores

Abstract

The conventional approach to measuring flow downhole in geothermal or EGS wellbores is through the use of a mechanical spinner tool, which makes use of a rotating paddle suspended and lowered (or raised) through the wellbore on a cable. But, such tools are notorious for failing-especially at high flow rates and at high temperatures. Likewise, non-uniform wellbore diameters greatly complicate spinner-tool data interpretation. An alternative approach to measuring flow rates in a geothermal or EGS wellbore is described. Making use of conventional tracer dilution methods, the tool is designed to work under both laminar and turbulent flow regimes. Volumetric flow rate measurement will allow the tool to accurately measure flow even through washout regions where borehole diameter varies. The tool is designed to be deployed on a single-conductor wireline and will be heat shielded. An optical fiber bundle will serve both to deliver the tool’s excitation light signal and to return the emission signal from the fluorescent dye that will be introduced from a pump attached to the end of the tool. Temperature and pressure measurements will also be made using Resistance Temperature Detectors (RTD) and pressure transducers.