In-Situ Diagnostics of Multi-Thermal Fluid Injection Parameters Using Stray Radiation Suppression and Circular Cell-Enhanced Laser Absorption Spectroscopy.

Multithermal fluid (MTF) component ratios and injection parameters are critical inputs in offshore heavy oil development, such as injection adjustment and monitoring, productivity prediction, and generator combustion process optimization. We implement simultaneous in situ diagnostics of two emblematic injection parameters, the gas-water ratio (GWR) and noncondensable gases proportion (NCGP), in a pilot-scale environment. A system-level integration of a novel laser absorption spectroscopy multigas sensor system based on integrating stray radiation suppression and a circular cell-enhanced strategy is proposed. A structurally optimized extinction thread in front of a photodetector is designed to reduce the absorption signal distortion under the influence of high-temperature radiation. Meanwhile, we break the limitation of the internal dimensions of the injection tube on the long-path absorption of gas molecules and improve the absorbance signal SNR by 3.42-fold. The present work performed experimental tests using diesel as the primary fuel in a laboratory-scale MTF generation system. The results show that the measurement uncertainties for H₂O/CO₂ concentrations are maintained at ±6.34% and ±6.87%, respectively. The proportion of CO₂ in noncondensable gas is comparable to field data, but the GWR of the simulation system at different injection temperatures is much higher than that of the field injection parameters. The measurement system demonstrates remarkable stability and rapid response, marking a significant milestone as the first reported instance of in situ diagnostics of MTF injection parameters conducted in a laboratory bench test.