Real-time, in situ measurement of H₂O generated during in situ combustion tests using 1f-normalized wavelength modulation spectroscopy with second harmonic detection

Abstract

The development and deployment of a real-time, in situ, non-invasive sensor to monitor the concentration of H 2 O during in situ combustion (ISC) experiments with a heavy-crude oil is described. A real-time sensor to monitor the gas-phase products from ISC can support the study of the kinetics of the complex chemical reactive system in ISC. The mole fraction of H 2 O was measured using tunable diode laser (TDL) absorption spectroscopy coupled with 1 f -normalized wavelength modulation spectroscopy (WMS) and 2 f detection. The WMS 2 f / 1 f strategy was used to enhance sensitivity with effective noise rejection, particularly suitable when characterizing the water vapor evolved from oil–water emulsions. H 2 O was measured at 3934.10 c m − 1 from the fundamental band v 3 . That transition was selected using the HITRAN database to increase the line strength and minimize interference from neighbor compounds. Measurements of H 2 O concentration were conducted at ambient temperature and pressure using a reference cell ( H 2 O = 2 % at 98.6 kPa) to validate the sensor architecture under controlled laboratory environments. The TDL sensor was also successfully validated during real ISC experiments involving heavy-crude oil. Validation and combustion experiments showed the potential of the TDL-based sensor for non-invasive, real-time, in situ measurements of gas-phase species in conditions similar to those of laboratory-scale experimental ISC tests.