TDLAS-based distributed monitoring method for multi-component gas leakage in crude oil storage tanks

This work presents a multi-point distributed monitoring system based on tunable diode laser absorption spectroscopy for measuring methane, propane, and butane concentrations resulting from crude oil leakage, along with auxiliary oxygen detection for explosion risk assessment. A multi-strategy retrieval scheme is employed: wavelength modulation spectroscopy for oxygen, direct absorption spectroscopy for methane, and a combined harmonic-direct absorption algorithm with partial least squares regression for overlapping propane and butane spectra. A hierarchical optical fiber architecture distributes laser sources to multiple sensing units. Experimental detection limits reached 17 ppm (methane), 0.66% (oxygen), 84 ppm (propane), and 219 ppm (butane). A signal correction method based on intensity normalization enabled model transfer across sensing units. Field tests confirmed strong consistency, with intraclass correlation coefficients across all channels exceeding 0.84 at steady state. This study provides a reliable and scalable solution for leakage monitoring in large-scale storage tanks.