Estimation of volume fractions and flow regime identification in multiphase flow based on gamma measurements and multivariate calibration

Abstract

Gamma measurements combined with multivariate calibration were applied to estimate volume fractions and identify flow regimes in multiphase flow. Multiphase flow experiments were carried out with formation water, crude oil and gas from different North Sea gas fields in an industrial scale multiphase flow test facility in Porsgrunn, Norway. The experiments were carried out with a temperature of 80∘C and 100 bar pressure which is comparable to field conditions. Different multiphase flow regimes (stratified-wavy, slug, dispersed and annular) and different volume fractions of oil, water and gas were investigated. A traversable dual energy gamma densitometer instrument consisting of a 30 mCi Ba133 source and a CnZnTd detector with a sampling frequency of 7 Hz was used.111 partial least square prediction models were calibrated based on single-phase experimental data. These models were used to predict all the volume fractions and also to identify the different flow regimes involved. The results from the flow regime identification were promising but the first results for the predictions of volume fractions were not acceptable. Principal component analysis was then applied to the calibration data and some of the calibration and test data in combination. The results from the PCA showed that there were differences between the calibration and test data.An average linear scaling technique was developed to improve the models volume fraction prediction performance. This technique was developed from half of the three-phase data sets and tested on the other half. The root mean square error of prediction (RMSEP) for the test data for gas, oil and water was 37.4%, 39.2% and 6.3% respectively before this technique was applied and 6.5%, 8.9% and 4.4% respectively after this technique was applied. Average linear scaling also improved the flow regime identification plots. Average scaling was then applied to predict the volume fractions and to identify the flow regimes of both the Gas/Oil and Gas/Water two-phase data sets. The RMSEP for gas, oil and water for Gas/Oil test data was 4.8%, 6.0% and 6.8% respectively. In the case of Gas/Water, the RMSEP for gas, oil and water were 6.2%, 9.2% and 5.8% respectively. Likewise their respective flow regimes were also easier to identify after this technique was applied.