Direct Downhole Temperature Measurement and Real Time Pressure-Enthalpy Model Through Photon Counting Fibre Optic Temperature Sensing

摘要

Temperature, pressure and enthalpy data is very important and valuable, both during geothermal drilling and in well operation. We research the possibility of direct downhole measurement of temperature, free calibration, which will result in a real time pressure and enthalpy reporting model. We report on the development of a downhole geothermal brine pressure and enthalpy model, applied to the state-space T-p-X delineations and density (ρ) correlations in flowing gas, liquid and two-phase systems, using the H_2O-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 our fibre optic temperature sensor system for a direct temperature measurement. We are working 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). We aim to extend the range of the system to kilometre length, by increasing the optical power per pulse and reducing the repetition rate of the excitation laser. We will employ superconducting single photon detectors with improved efficiency (5%) housed in a practical, closed-cycle cooling system.