Wax deposition in sub-sea oil producing pipelines is a concern to the oil producing companies. The deposition of wax in pipelines can cause serious economic implications if not monitored and controlled. Several researchers have developed models and investigated the deposition of wax in crude oil pipelines. As of today, there is no off the shelf instrument available for reliable online estimation of the wax deposition thickness in sub-sea pipelines.Acoustic chemometrics was applied to investigate the potential for online estimation of wax deposition thickness in sub-sea pipelines. This feasibility study was carried out as a so called piggy back on experiments performed at Statoil research centre in Porsgrunn, Norway with real crude oil or waxy gas condensate. The first investigations focussed on the repeatability of the acoustic chemometric technique followed by online prediction of the wax deposition thickness in a single-phase oil flow pipeline. A partial least squares regression model was calibrated and validated with a totally independent data set. The calibrated model had a root mean squared error of prediction of 0.28 mm with a final wax deposition thickness of 3.36 mm, a slope of 0.91 and R 2 of 0.83 which were satisfactory results. The effect of varying oil flow rates on the wax deposition thickness was also investigated. The preliminary results showed the need for further investigations based on a robust experimental design and sample Corresponding author: e-mail: maths.halstensen@hit.no, Tel: +47 35575187, Telefax: +47 35575001 3 pre-processing. The general conclusion that can be drawn from this feasibility study was that the potential of adapting the acoustic chemometric technique for online estimation of the wax deposition thickness exist and must be further investigated.
A combination of gamma measurements and multivariate calibration was applied to estimate multiphase flow mixture density and to identify flow regime. The experiments were conducted using recombined hydrocarbon fluids sampled from an onshore receiving terminal including hydrate thermodynamic inhibitors (monoethylene glycol and methanol (MeOH)). These hydrate inhibitors were added to deionised water at 60% concentration by volume. The experiments were conducted at a temperature of 0 C and a 75-bar pressure, comparable with deep water production on the Norwegian continental shelf. Two angles of inclination (1 and 5 ) and two water cuts (15% and 85%) were investigated. A single-energy gamma densitometer was installed on the test facility for measuring the mixture density, whereas the dual-energy gamma densitometer was traversed linearly from the bottom to the top of the pipe for multivariate calibration and prediction. Seventy partial least square prediction models were calibrated based on single-phase experimental data. These models were used in estimating the mixture density and identifying the flow regime in all the experiments. The estimated mixture densities were accurate as compared with those from the single-energy gamma densitometer with the root mean square error of prediction of 13.6 and 9.7 kg/m 3 for 1 angle of inclination and 17 and 26.6 kg/m 3 for 5 pipe inclination. The models were also able to identify the flow regimes investigated for both 1 and 5 angles of inclination.
Gravity separators are widely used for separation of gas/oil/water/sand from both offshore and onshore oil production facilities. Estimation of the gas/liquid and oil/water interface levels in gravity separators have been a concern since these parameters are important for reliable operation. Most of the instruments on the market today do not provide reliable measurements of both gas/liquid and oil/water interface levels. The few instruments that do provide reliable measurements are however based on radioactive principles. Nevertheless these radioactive instruments possess a strong health, safety and environmental risk. An alternative inexpensive, environmentally friendly, accurate and cost effective way for gas/liquid and oil/water interface level estimation based on pressure measurement is presented. The root mean squared error of prediction (RMSEP) for gas/liquid and oil/water interface level estimation from traversing a pressure sensor based on partial least square regression (PLS-R) were 14.5 mm and 17.7 mm respectively. A comparison of results from models based on PLS-R and ordinary least square regression (OLS-R) techniques proved that the RMSEP from the PLS-R technique was better in estimating the oil/water interface level but in the case of gas/liquid interface level estimation the OLS-R technique was slightly better. It was concluded that the PLS-R technique provided a better overall result and is recommended Corresponding author: e-mail: benjamin.k.arvoh@hit.no, Tel: +47 35575134, Telefax: +47 35575001 3 when pressure measurements in combination with multivariate data analysis is applied for gas/liquid and oil/water interface level estimations in gravity separators.
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