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Characterisation of the mean and time dependent properties of inclined oil-in- water pipe flows using dual-sensor probes G. Lucas and Xin Zhao University of Huddersfield, UK

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In the oil industry, horizontal and inclined oil-in-water flows are frequently encountered. Dual-sensor conductance probes and arrays of probes are presented for measuring the time averaged and the time dependent local properties of such flows including the oil droplet axial velocity and the local oil volume fraction. The experimental results from the dual sensor arrays have been used for comparison with, and validation of, numerical models of inclined oil-in-water flow. The probe arrays enable time dependent intermittent structures, such as Kelvin-Helholtz waves, to be observed.

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Video1. Qw =3.5m 3 /h ;Qo= 1.0m 3 /h; incline angle = 30°(from the vertical) Click here to view the animation

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Dual-sensor probe design and mathematical model Local oil volume fraction from N bubbles Local oil velocity from N bubbles

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To obtain accurate estimates of the oil velocity and the oil volume fraction it is necessary to sample a minimum number N of bubbles. In the present study, for ‘Time averaged’ data, this was achieved using a ‘Time Window’ or ‘Sampling Interval of 60 seconds’ For ‘Time Dependent’ data a ‘Sampling Interval’ of 0.05 seconds was used

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Time averaged local oil volume fraction and velocity distributions obtained in inclined oil-in water flow in an 80mm diameter pipe 80mm inclined oil-water test loop 80mm internal diameter, 2.5m long test section. A traverse mechanism was used to move an individual dual-sensor probe to each of 61 spatial locations in the flow cross section. A 60 second sampling interval was used to obtain time averaged local oil volume and local oil velocity measurements.

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The local volume fraction and the local axial velocity profile distribution of 30 degree inclined pipe (80mm,Qw=3.5m 3 /h,Qoil=1.0m 3 /h) Measuring time averaged values of the local oil volume fraction and the local axial oil velocity using a traverse mechanism

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Locations of the four dual-sensor probes in the 80mm diameter pipe To measure the time dependent flow properties at different locations on a diameter of an 80mm pipe an array of four dual-sensor probes is used. The local oil volume fraction and the local oil velocity is measured at each probe averaged over a ‘sampling interval’ or ‘time window’ of 0.05 seconds.

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Volume fraction data from the dual-sensor array can be plotted using a grid where y represents probe position in pipe and t represents time (in time steps T of 0.05 seconds). 16 time steps are displayed in each frame. By introducing the mean axial oil velocity u o in the cross section, the time axis can be converted to a distance d where d=16× u o ×T. In the following slide, u o =0.4m/s and so the axial pipe length shown is 320mm.

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Volume fraction and after interpolated volume fraction Black-white pixel volume fraction and the interpolated data (inclination angle =30 degrees )

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In inclined oil water flows there is a large velocity gradient, with the oil droplets travelling much faster at the upper side of the inclined pipe than at the lower side. By introducing the mean axial oil velocity u o,p measured at the position of the p th probe the pixel length l p can be adjusted to represent the distance travelled by the oil droplets in the sampling interval T (where T=0.05 seconds) as follows: l p =T u o,p This method of data representation can help to reveal time dependent flow properties such as the ‘breaking’ of Kelvin-Helmholtz wave structures in the flow.

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Successive frames of local oil volume fraction data separated by 0.05s. Pixel length is dependent upon local axial oil velocity at the given probe.

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An array of 11 dual-sensor probes was used to investigate the mean and time dependent properties of inclined oil-in-water flows in a 150mm diameter 15m long flow loop at Schlumberger Cambridge Research Array of 11 dual-sensor probesArray mounted in 150mm diameter flow loop

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Local oil volume fraction versus time Each row represents data taken at a given probe location Each column represents a time interval of 0.05 seconds

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Local oil volume fraction vs time (sampling interval =0.05s) (Qw=16.4m3/hr; Qo = 6 m3/hr; inclination angle = 45°) Click here to view the animation

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Local oil volume fraction and local oil axial velocity vs time (sampling interval =0.05s) (Qw=16.4m3/hr; Qo = 6 m3/hr; inclination angle = 45°) Click here to view the animation

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Interpolated local oil volume fraction and local axial oil velocity vs time (sampling interval = 0.05s) (Qw=16.4m3/hr; Qo = 6 m3/hr; inclination angle = 45°) Click here to view the animation

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Mean oil volume fraction versus probe position (Qw=16.4, Qo=6, theta=45 degrees) Upper side of inclined pipe Lower side of inclined pipe

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Mean oil axial velocity versus probe position (Qw=16.4, Qo=6, theta=45 degrees) Upper side of inclined pipe Lower side of inclined pipe

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Characterisation of time dependent flows by investigating standard deviation of flow phenomena over different time windows

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Standard deviation of oil volume fraction fluctuations versus k for top 8 probes (Qw=16.4, Qo=6, theta=45 degrees) ‘Time window’ 0.05 seconds ‘Time window’ 0.8 seconds ‘Time window’ 25.6 seconds

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Standard deviation of oil axial velocity fluctuations versus k for top 8 probes (Qw=16.4, Qo=6, theta=45 degrees) ‘Time window’ 0.05 seconds ‘Time window’ 0.8 seconds ‘Time window’ 25.6 seconds

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Nottingham model of inclined oil-water flow (Qw=16.4m3/hr; Qo = 6 m3/hr; inclination angle = 45°) Click here to view the animation

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Local oil volume fraction and oil axial velocity vs time from Nottingham model using a sampling interval of 0.05s (Qw=16.4m3/hr; Qo = 6 m3/hr; inclination angle = 45°) Data taken from numerical model at a distance of 0.9L from inlet where L is the modelled pipe length - and at positions corresponding to the 11 probes used in the equivalent experiment at the same flow conditions. Click here to view the animation

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Mean oil volume fraction versus probe position (Qw=16.4, Qo=6, inclination=45 degrees) Comparison of experimental data with results from Nottingham model

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Standard deviation of oil volume fraction fluctuations versus k from Nottingham model (at positions corresponding to top 8 probes used in experiments) Qw=16.4, Qo=6, inclination=45 degrees ‘Time window’ 0.05 seconds ‘Time window’ 0.8 seconds ‘Time window’ 25.6 seconds

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ITS Z8000 ERT system (ITS) EIT system experiments

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An ITS Z8000 dual-plane ERT system was used to measure the Kelvin-Helmholtz (K-H) wave speed in vertical and inclined oil-in-water flows in a pipe of diameter 80mm. The K-H wave speed was obtained by cross correlating conductance data obtained from the two planes at 450 frames per second per plane. For each inclination angle,10 different flow conditions were investigated for which the homogeneous velocity was in the range 0.11m/s to 0.49 m/s and the mean oil volume fraction was in the range 0.04 to 0.26.

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K-H wave speed versus homogeneous velocity in an 80mm diameter pipe Initial results suggest that the K-H wave speed may provide a method for measuring the homogeneous velocity (mixture superficial velocity) in inclined oil-water flows.

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