Application of new techniques in real time estimation of volume fractions of two-phase flow systems in the oil industry is still being developed. Volume fractions in gas-liquid and liquid-liquid real time systems are estimated based on principles of acoustic chemometrics. The feasibility of applying acoustic chemometrics for on-line monitoring of volume fractions of trace concentrations of liquid-liquid mixtures has been investigated.

Acoustic chemometrics is a relatively new technique for on-line process monitoring based on characterization of system vibrations generated by industrial processes. Gas-liquid and liquid-liquid mixtures were pumped through a rig. In order to generate acoustic signal, two orifice plates were mounted (horizontal and vertical pipeline). The acoustic sensors were mounted on these plates since earlier feasibility study demonstrated this position as optimum. The spectra from the acoustic sensor were transformed from time domain to frequency domain by Fast Fourier Transform (FFT) together with other signal processing techniques prior to multivariate calibration. Subsequent applications of Partial Least Squares regression PLS-R were used to calibrate a multivariate prediction model for online monitoring of volume fractions in the pipeline.

In both gas-liquid and liquid-liquid two phase systems, concentrations from 0-–100% levels were investigated. The pressure drop in the system was approximately 1.5bar and was kept constant throughout the process. The temperature in the rig was also maintained at a constant value throughout the experimental process. One model each based on test set validation was developed for both the gas-liquid and liquid-liquid systems. These models were then used to estimate on-line volume fractions in both systems. The average Root Mean Square Error of Prediction (RMSEP) for both the gas-liquid and liquid-liquid systems did not exceed ±5 and 8% respectively. The correlation between the predicted and measured in both systems was approximately 0.98.

The results from applying acoustic chemometric techniques in estimating on-line volume fractions of gas-liquid and liquid-liquid systems were promising but more experimental work is needed to explore the effect of all relevant process conditions/variations in such systems.