Experimental Study of Fibre Optic Photon Counting Application: Real Time-Free Calibration Distributed Temperature Measurement and Enthalpy Estimation for Geothermal Well

Abstract

Temperature, pressure and enthalpy data is very important and valuable, both during geothermal drilling and in well operation. The study will research the possibility of direct downhole measurement of temperature and free calibration, which will result in a real time pressure and enthalpy reporting model. The research will report on the development of a downhole geothermal brine pressure and enthalpy model, applied to the state-space T-p-X delineations and density (ñ) correlations in flowing gas, liquid and two-phase systems, using the H2O–NaCl geothermal brine thermodynamic formulation. The model was implemented in C programming, running in the NI Lab Windows/CVI user interface. The model is highly dependent on the fibre optic temperature sensor system for a direct temperature measurement. The experiment works to extend the range of an existing calibration-free fibre optic temperature sensing technique based on photon counting measurements by Raman backscatter (previously developed in collaboration with the US National Institute of Standards and Technology). The research aim is to extend the range of the system to a kilometre length, by increasing the optical power per pulse and reducing the repetition rate of the excitation laser. For this experiment, the test will employ superconducting single photon detectors with improved efficiency (5%) housed in a practical, closed-cycle cooling system. The experiment managed to demonstrate the temperature measurement and estimate the enthalpy using 2 meter of fibre under test, which represent 2 meter of depth. Meanwhile, the experiment of 100 meter of fibre under test are still under investigation after successfully measured low temperature.