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Document Title: 
MPFM 1900VI® 
Functional Description 
 
Roxar Project Title: 
 
Customer Purchase Title: 
 
Roxar Project No: 
 
Customer Purchase No.: 
 
 
 
Customer Doc. No.: 
 
 
E 2006.08.30 Updated Uncertainty Specifications JS JC FEB 
D 2006.03.31 Minor Layout Changes ØS GAS GAS 
C 2005.06.30 Revised according to Product Upgrades GAS/CDS JES MB 
B 2005.01.03 TCE Implementation SH JC GS 
A 2005.01.03 New Revision System SH JC JC 
Revision Issue date Reason for issue Author Checked Approved 
Roxar Document No.: 
000354 
 
Revision: 
E 
Total no. of pages: 
 33 
 
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Functional Description 
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Table of Contents 
TABLE OF CONTENTS..................................................................................................................2 
1. INTRODUCTION.................................................................................................................3 
2. ABBREVIATIONS...............................................................................................................3 
3. FUNCTIONAL OVERVIEW ...................................................................................................4 
3.1 BLOCK DIAGRAM OF MAIN COMPONENTS ............................................................................4 
3.2 OVERVIEW OF MAIN SYSTEM COMPONENTS AND THEIR FUNCTION .................................5 
3.3 CAPACITIVE SENSOR .............................................................................................................7 
3.4 INDUCTIVE SENSOR ...................................................................................................................9 
3.5 GAMMA DENSITOMETER.....................................................................................................11 
3.6 VENTURI ...............................................................................................................................12 
3.7 PRESSURE AND TEMPERATURE TRANSMITTERS ...............................................................13 
3.8 METER CONFIGURATION .....................................................................................................14 
4. PRINCIPLE OF OPERATION ......................................................................................15 
4.1 FRACTION MEASUREMENT...................................................................................................16 
4.2 VELOCITY MEASUREMENT ...................................................................................................19 
4.3 SIGNAL ANALYSIS................................................................................................................23 
4.4 OIL CONTINUOUS AND WATER CONTINUOUS FLOW.........................................................25 
5. OPERATING RANGE AND ACCURACY ..................................................................26 
5.1 RECOMMENDED INSTALLATION METHOD...........................................................................26 
5.2 OPERATING RANGE ..............................................................................................................28 
5.3 MEASUREMENT UNCERTAINTY ............................................................................................30 
5.4 EFFECTS FROM CHANGES IN FLUID PROPERTIES..............................................................32 
6. EFFECT OF SAND, SCALE, WAX AND EROSION .............................................33 
6.1 DEPOSITION OF WAX ..........................................................................................................33 
6.2 PRESENCE OF SOLIDS/SAND ..............................................................................................33 
6.3 SCALE ...................................................................................................................................33 
6.4 EROSION...............................................................................................................................33 
 
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Functional Description 
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1. INTRODUCTION 
The functional description of the Roxar MPFM 1900VI®, including the description of its 
principle of operation, is kept to a level that will help the reader understand how the meter 
works, without going too far into details. Basically, the MPFM 1900VI® consists of six 
building blocks of which many should be familiar to an instrumentation operator. These 
include temperature and pressure transmitters, a differential pressure transmitter and a 
gamma densitometer. Other building blocks are perhaps not as familiar, like the in-line 
capacitance and inductive sensors. 
 
This document provides an overview of the mentioned modules and how they interact 
making it easier to understand the behavior of the meter and probably prevent the feeling of 
working with a “Black Box”. 
2. ABBREVIATIONS 
 
MPFM MULTIPHASE FLOW METER 
GVF Gas Volume Fraction 
WC Water Cut 
GOR Gas-Oil-Ratio 
WLR Water in Liquid Ratio 
WTr Transition point oil/water continuous liquid phase 
PC Personal Computer 
PVT Pressure Volume Temperature 
MMI Man Machine Interface 
 
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3. FUNCTIONAL OVERVIEW 
Figure 1 below is a schematic overview of the meter’s different modules. Although 
general, it provides an insight to the meter’s components and an alternative Flow 
Computer (FC) setup (FC installed in safe area). 
3.1 Block diagram of main components 
 
 
Figure 1 Schematic overview of the MPFM 1900VI. The coloring of the sketch reflects 
the different modules. Table 1 below applies the same color coding when describing 
these modules 
Venturi 
 Inductive 
 Sensor 
 Cap. 
 
Sensor 
 
 Differential 
 Pressure 
 Transmitter 
 
 
 Pressure 
 Transmitter 
 
 
 Field - 
 Electronics (Ex 
i) 
 
 Integrated 
 flow temp. 
 
 Gamma 
 detector 
 
 
 
 Flow 
 Computer 
 (MK II) 
 
Safety 
Barriers 
 RS 232 
RS232/485 
Modbus 
Meter Unit Service Console 
 Flow Computer Unit 
4 pair cable 
Fibre optical cable / 
 
Digitized raw data 
3 core cable (10 meters) 
Hazardous Area Safe Area / Field Enclosure
1 
2 
3 
2 2 
3 
1 
4 5 5 
6 
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3.2 Overview of main system components and their function 
Module Description 
 
Parameter of 
Measurement 
Measuremen
t output 
 
 
1 
 
One meter section applying the following measurement 
principles: 
 
 Venturi flow meter with one differential pressure 
transmitter 
 
 
Differential pressure 
 
 
Velocity 
 
 
 
 
2 
 
Another meter section consisting of the following 
measurement devices: 
 
 Capacitance based multiphase composition (fraction) 
sensor 
 Capacitance based cross-correlation velocity meter 
 Conductivity based multiphase composition sensor 
 Conductivity based cross-correlation velocity meter 
 Gamma densitometer 
 
 
 
Capacitance & 
Conductivity for 
fraction 
measurement, 
 
∆ Signal amplitude 
for X-correlation and 
fraction 
measurement(g) 
 
Flow medium 
absorption rate 
 
 
Velocity, fraction 
and density 
measurements 
 
Velocity by X- 
correlation 
 
Density by 
gamma system. 
 
Fractions by 
Cap/ind. system 
 
 
3 
 
Pressure and temperature transmitters 
 
 
Barg & °C 
 
Pressure and 
temperature 
 
 
 
4 
 
Field electronics comprising: 
 
 One “silver box” containing the electronics running the 
capacitive based measuring principle 
 One “Silver box” containing the electronics running the 
inductive measurements 
 The temperature transmitter 
 Termination stripsTime Series of raw 
data 
 
T amb. 
 
 
Digitized 
raw data 
 
5 
 
One Flow Computer consisting of: 
 
 2 RS-232 serial input/output channels using MODBUS 
protocol. RS485/RS422 or TCP/IP Ethernet interface is 
optional 
 Fiber optical receiver card 
 Power supply 24Vdc. 110 – 230Vac is optional 
 Roxar developed Calculating Unit 
 
 
Engineering units 
describing the 
multiphase flow 
 
 
6 
 
Service Console / User Interface: 
 
 MPFM Service Console Software installed on a 
PC/laptop for system configuration, calibration and 
logging 
 A standard laptop or PC running on windows (XP or 
Win 2000) is adequate 
 
 
Man Machine 
Interface (MMI) 
Table 1 MPFM 1900VI® module description. The different measurement principles are 
being thoroughly described in section 4.0. 
 
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What becomes evident when studying Figure 1 and Table 1 is that module 1 through 3 
comprises of the applied measurement instruments. Module 4 through 6 conditions the 
signals received (from module 1 to 3) and provides the user with engineering outputs. 
Typically outputs are pressure, temperature, mass- and volumetric flow rates, gas void 
fraction, and water cut at the measurement point (actual conditions). Flow rates can 
also be accumulated over time and reported as total volume or total mass. 
 
Mass and volumetric flow rates can also be reported at other pressure and 
temperature conditions, such as separator or standard conditions. The conversion of 
measured mass and volumetric flow rates to other conditions are carried out by using 
a PVT package or by using a built-in simple user configurable PVT equation. In 
addition, the Roxar PVTX package may be supplied. 
 
The meter is configured to apply either the velocity measurements from the x-
correlation meter, from the Venturi meter or from a combination of these two. The 
meter has built in logic in order to select the best velocity measurement with respect to 
a series of given criteria. 
 
The meter has two serial communication links. One dedicated serial link to the 
configuration and monitoring PC (Service Console PC), and one serial link to the 
operator’s production monitoring and control system. 
 
A detailed description of each principle is appropriate prior to a further description on 
how the meter applies the different measurement principles to achieve the final output. 
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3.3 Capacitive sensor 
The purpose of the capacitance sensor in the MPFM 1900VI is to measure the fraction of oil, 
water and gas flowing through the meter. Two well known electrical facets form the 
foundation of the measurement. 
 
Capacitance is a measure of the amount of electric charge stored for a given 
electric potential. The capacitance is usually defined as the total electric charge 
placed on the object divided by the potential of the object: 
 
 
 
 where 
C is the capacitance in farads 
Q is the charge in coulombs 
V is the potential in volts 
 
A capacitor is formed from any two conductors insulated from one another. The 
formula defining capacitance above is valid for a capacitor with conductors 
having equal but opposite charge Q, and the voltage V is the potential 
difference between the two conductors. 
 
Permittivity is the ability of a material to store electric energy by separating 
opposite polarity charges in space. Permittivity is also called the dielectric 
constant. 
 
Functioning as a capacitor, the MPFM 1900VI measures the permittivity of the oil/gas/water 
mixture. The permittivity is different for each of the three components in an oil/gas/water 
mixture, and the permittivity of the mixture is therefore a measure of the fractions of the 
different components. Figure 2 below details the capacitance measurement principle. 
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Water fraction
Capacitance
Gas fraction
Mixture
oil/water/gasC
 
Figure 2 Capacitance measurement principle 
 
The function is achieved by locating electrodes on each side of the spool. The electrodes are 
isolated from the metal in the spool using a polymer plastic material (PEEK) specially suited 
for operation in tough environments. By placing an electrode on each side on the inside of 
the spool and allowing the mixture to flow through the pipe, the electrical field generated 
between the electrodes will be affected by the permittivity of the oil/gas/water mixture. The 
electrodes will act as a capacitance detector and the resulting capacitance can be measured 
between the electrodes. Therefore, this capacitance will vary when the permittivity changes, 
i.e. according to the amount of oil, gas and water in the mixture. 
 
Figure 3 X- section of the capacitance sensor 
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This capacitance measurement works as long as the flow is oil continuous, i.e. as long as 
water is dispersed in the oil and does not form a continuous path of water between the 
electrodes. This would short-circuit the electrodes, and the unit would be unable to perform 
correct measurements. Normally, the flow is oil continuous as long as the water cut is below 
approximately 60 – 70%. For higher water cuts the flow will normally become water 
continuous. In this case, the inductive sensor is applied. 
3.4 Inductive sensor 
The capacitance principle is not suitable in water-continuous flow. For this reason, the 
mixture conductivity of the oil/water/gas flow is measured by an inductive sensor during 
water continuous liquid. Magnetic coils are used to induce a current through the liquid inside 
the sensor (hence the name inductive sensor). 
 
Conductivity is a measure of how well a substance allows the transport of 
electric charge. 
Conductor is an electrical phenomenon where a substance contains 
electrically charged particles and can carry electricity. 
 
The inductive sensor is integrated into the same sensor unit as the capacitance sensor and 
comprises a set of coils (B1 & B2) and also a set of electrodes (marked as [] on Figure 4 
below). The set-up is illuminated in Figure 4 showing the two coils situated on each end of 
the PEEK spool. These are used to set up an electrical field which induces a current that 
flows through the oil, water and gas mixture. As long as the flow is water continuous, the 
water will act as a conductor and the current will flow from one side of the meter to the other 
side. The potential detector electrodes, also shown in the figure, will pick up the differential 
voltage created by the induced current. Then, this information is entered into the Flow 
Computer for calculation of oil, water and gas fractions. 
 
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Figure 4 Inductive measurement principle. As the flow approaches oil continuous, the 
amount of power required to set up the current - I - through the flow increases. When 
the flow becomes oil continuous the current practically faces an insulator and the power 
required to make it flow approaches infinite. This means that the power circuitry feeding 
the loop reaches saturation; The Automatic Gain control (AGC) saturates and no current 
can be fed through the flow. 
 
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3.5 Gamma densitometer 
The purpose of the gamma densitometer of the MPFM 1900VI® is to measure the totaldensity of the mixture flowing in the pipe. Because of the significant difference in the 
densities of the liquid and gas of an oil/gas/water mixture, the rate of the absorption gives an 
accurate measurement of the liquid and gas fractions of the mixture. The absorption of 
gamma radiation in a medium is a function of the mean density along the path of the gamma 
particle beam. This is a well-known principle used for many other applications. 
 
The gamma detector used in the MPFM 1900VI® is a standard Tracerco PRI116 detector 
clamped on to the outside of the capacitance sensor. The radioactive source used is Cesium 
137 (Cs 137), having an IP 65 protection with a dose rate of less than 7.5µ Sieverts per hour 
on any accessible surface. Provided instructions and regulations are followed, the gamma 
densitometer is completely safe and does not pose any form of danger. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5 The gamma densitometer measurement principle 
 
W ater fraction
G as fraction 
M ixture density 
 
 
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3.6 Venturi 
Venturi Tube: A section of tube forms a relatively long passage with smooth entry and exit. 
A Venturi tube is connected to the existing pipe, first narrowing down in diameter then 
opening up back to the original pipe diameter. The changes in cross section area cause 
changes in velocity and pressure of the flow. 
 
The MPFM 1900 VI® utilizes this variation in pressure. The point being that the differential 
pressure across a Venturi is proportional to the kinetic energy of a mixture passing through. 
Thus, the response curve of a Venturi meter is related to the mass of the mixture and its 
velocity. 
 
 
Figure 6 Typical Venturi tube 
 
The standard Venturi equation is modified for use in three-phase flow. The modified 
equation takes into account the gas volume fraction (GVF) of the flow. Since the mixture 
density is measured with the composition meter, the mean liquid velocity and gas velocity 
can be determined from the measured differential pressure. 
P1 
P2 
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3.7 Pressure and temperature transmitters 
The meter unit comprises one differential pressure transmitter, one pressure 
transmitter and a temperature element/transmitter. The following provides a short 
introduction to these measurements principles and devises1. 
 
General on pressure 
Pressure is the action of one force against another force. Pressure is force applied to, or 
distributed over, a surface. The pressure P of a force F distributed over an area A is defined 
as 
A
FP = 
 
All pressure measurement systems consist of two basic parts: a primary element, which is in 
contact, directly or indirectly, with the pressure medium and interacts with pressure changes; 
and a secondary element, which translates this interaction into appropriate values for use in 
indicating, recording and/or controlling. 
 
Differential Pressure Measurement 
The differential pressure is the magnitude between some pressure value and some 
reference pressure. 
In a sense, absolute pressure may be considered as a differential pressure with total 
vacuum or zero absolute as the reference. 
 
Pressure Measurement 
A pressure measurement represents the positive difference between measured 
pressure and existing atmospheric pressure. It may be converted to absolute pressure 
by adding actual atmospheric pressure value. 
 
Temperature transmitter 
The MPFM 1900VI® utilizes the traditional “resistance temperature detector – RTD” 
principle. A PT-100 element is applied. Its resistance (i.e. the resistance of the 
 
1 The introduction to pressure measurement fundamentals is provided by the courtesy of Rosemount. 
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platinum element) will vary in accordance with alternating temperatures and this 
variation is measured very precisely. In this way, an accurate measurement of the flow 
temperature is achieved as the PT-100 element is connected with the multiphase flow 
running through the meter. 
3.8 Meter configuration 
The configuration of the system is simple and can be carried out both by the service 
Console PC and the operator’s production monitoring and control system. 
The input parameters to the meter are PVT data such as oil, water and gas densities 
at the measurement conditions as well as oil permittivity and water salinity. 
 
The Flow Computer can work with up to 5 internal pre-defined PVT data sets for a 
corresponding number of wells. Changing between data sets can easily be controlled 
from the operator’s control system by remotely sending the desired well number to the 
MPFM Flow Computer. This can also be controlled from the service console PC. In 
addition to the 5 internal PVT data sets, a theoretical infinite number of PVT data sets 
can be selected and downloaded from set-up files stored in the service console PC. 
 
The meter is commissioned and serviced using a menu based configuration and 
monitoring software tool installed in the Service Console PC. The software is run in 
order to carry out the following tasks: 
 
• Download new PVT data sets to the meter 
• Select PVT data set to be used for current logging 
• Configure the meter data, like engineering units and data averaging properties 
• Trend and display real time measurements 
• Log instantaneous and accumulated data, either as text files or as an Excel DDE 
exchange format. Text files can be imported in to standard spread sheets like Excel or 
Lotus (not included) 
• Generate log files containing time stamped process alarms and technical alarms 
• Define passwords for users 
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4. PRINCIPLE OF OPERATION 
The overall principle of operation is shown in Figure 7. The multiphase meter sensor collects 
raw measurement data from the flow, the data being pressure, temperature, Venturi 
differential pressure, density and time series data from the capacitance and inductive 
sensor. The raw data is analysed using physical and empirical models, resulting in 
calculated values for flow fractions and velocity. 
 
The different steps in the principle are further explained in the following sections. 
Fl
ow
 ra
te
 o
f g
as
Fl
ow
 ra
te
 o
f g
as
 
 
 
 Q GAS
Fl
ow
 ra
te
 o
f 
Fl
ow
 ra
te
 o
f 
oi
l a
nd
 w
at
er
oi
l a
nd
 w
at
er
Q OIL
Q WATER
Flowrate of Flowrate of 
liquidliquid
Water fraction
Liquid fraction
Q LIQ
Density
Cap.
Cond.
Ti
m
e 
se
rie
s 
an
al
ys
is
 a
nd
 m
od
el
lin
g
Ti
m
e 
se
rie
s 
an
al
ys
is
 a
nd
 m
od
el
lin
g
Fraction of gas in
dispersed flow 
Velocity of 
dispersed flow
Q GD
Flowrate of Flowrate of 
dispersed gasdispersed gas
Velocity of large
bubbles
Total fraction of
large gas bubbles
Q GB
Flowrate ofFlowrate of
gas in largegas in large
bubblesbubbles
 
Figure 7 Overall view of the operating principle of the Roxar MPFM 1900VI® 
 
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4.1 Fraction measurement 
The equations (1) and (2) are describing the relationship between the mixture composition 
and the corresponding mixture permittivity / conductivity and density. Equation (3) states the 
obvious fact that all fractions sum up to 1 (or 100%). In oil continuous flow the multiphase 
meter uses equations (1a), (2) and (3). In water continuous flow equations (1b), (2) and (3) 
are used.Permittivity: εflow = f (αεgas, βεwater, γεoil) (1a) 
 
Conductivity: σflow = f (ασgas, βσwater, γσoil) (1b) 
 
Density: ρflow = f (αρgas, βρwater, γρoil) (2) 
 
 α + β + γ = 1 (3) 
 
 
where: 
 
 ρoil = Single phase oil density 
 ρwater = Single phase water density Input fluid parameters 
 ρgas = Single phase gas density to the multiphase meter 
 εoil = Single phase oil permittivity (PVT) 
 σwater = Single phase water conductivity 
 
 εwater = Single phase water permittivity ≈ 70 
 εgas = Single phase gas permittivity ≈ 1 Constants 
 σoil = Single phase oil conductivity = ∞ 
 σgas = Single phase gas conductivity = ∞ 
 
 εflow = Permittivity of the flow 
 σflow = Conductivity of the flow Measured by the 
 ρflow = Density of the flow multiphase meter 
 
 α = Gas fraction 
 β = Water fraction Unknown phase fractions 
 γ = Oil fraction 
 
 
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Inside the sensor these equations are simultaneously valid as the flow properties 
permittivity/conductivity and density as well as temperature and pressure are measured at 
the same physical location and at the same moment in time. Therefore, the equations form 
an equation system with three equations and three unknowns, the phase fractions. As the 
properties of single phases are known, the equation system can be solved using a numerical 
equation solver in the Flow Computer finding the unknown phase fractions. 
 
Relationship between fractions and the flow properties 
Permittivity 
The permittivity, or dielectric constant, of a fluid, is a measure of the ability the fluid has to 
interact with an electric field, for example in a capacitor. The influence on the electric field is 
increasing with the permittivity value. Water has a high relative permittivity, around 80 
depending on the salinity, oil is typically in the range of 2.0 -2.4. Hydrocarbon gas has a 
relative permittivity of 1 to 1.1. 
 
Thus, in a multiphase mixture of gas, oil and water, the permittivity of the mixture will vary 
between 1 and 80 depending of the individual fractions. Note that because the permittivity of 
water is so high compared to the permittivity of oil and gas, the sensitivity for changes in 
water fraction is high. 
 
Figure 8 indicates how the permittivity will change for a water-in-oil mixture. With no water, 
the permittivity in the mixture is equal to the oil permittivity. As the water fraction increases, 
the permittivity will increase. 
 
Figure 9 shows the influence on the mix permittivity if gas is introduced in the water-in-oil 
mixture. As the gas fraction increases, the permittivity will decrease if the water cut is 
constant, visualized by the stippled lines in the direction of the arrow. 
 
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The permittivity of an oil/water mixture (Figure 8) and the permittivity of a multiphase flow 
(Figure 9). 
 
Figure 8 The permittivity of an oil/water mixture 
 
Figure 9 The permittivity of a multiphase flow 
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The density of a multiphase flow as a function of gas volume fraction and water cut (Figure 
10). 
0
0 % 100 %
Gas Volume Fraction
Fl
ow
 d
en
si
ty
Increasing water cut
WC = 100%
WC = 0%
Water density
Oil density
Gas density
 
 
Figure 10 The density of a multiphase flow as a function of gas volume fraction and 
water cut 
 
Density 
The variation in density for a multiphase flow is shown in the principle sketch in Figure 10. 
The solid lines show how the density will vary with the gas fraction going from 0 to 100% 
when the water cut in the liquid is kept constant from left to right. The lower solid line shows 
the course for water cut = 0%. The arrow shows the influence of increasing water cut up to 
100% for the upper solid line; i.e. the higher the WC, the higher the flow density. 
4.2 Velocity measurement 
In order to determine the volume flow of oil, water and gas, the velocity of the flow must be 
measured. Then, the volumetric flow can be calculated as 
 
 vAQ ⋅= (4) 
where 
 Q = Volumetric flow rate 
 A = Area of pipe cross section 
 v = Flow velocity 
 
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Slip flow 
In multiphase flow, almost all combination of liquid and gas fractions result in a flow pattern 
where the liquid and gas phases travel at different velocities, with the gas traveling with the 
higher velocity. This phenomenon is called slip flow (the gas phase slips by the liquid 
phase). Even if no-slip conditions could be generated, for example by using a mixing device, 
slip would re-occur at a very short distance downstream the mixing point. The strategy in 
development of the Roxar MPFM 1900VI® has therefore been to utilize methods that give 
reliable measurements even under slip conditions. Hence the Roxar MPFM 1900VI® uses 
two different methods for flow velocity measurement: 
 
• Differential pressure measurement over a Venturi meter 
• Cross correlation of time series signals from the capacitance and inductance sensor 
 
The cross-correlation technique and the Venturi measurement combined constitute a very 
robust method of finding both the gas velocity and the liquid velocity. 
 
Cross correlation velocity measurement 
The multiphase meter sensor consists of pairs of capacitance/conductance measurement 
electrodes (see also section 2.3 and 2.4) each pair of electrodes set at specified intervals 
along the direction of flow. The electrodes perform continuous measurements of the flow, 
utilizing the variations both in velocity and composition inherent in a multiphase flow. The 
sensor electronics collect data at a rate of approximately 3000 times pr. second. The 
collected data forms a time serial signal and contains information about the flow pattern 
inside the sensor. 
The flow pattern will continuously change as the flow passes through the meter, but the rate 
of change can be regarded as slow compared to the time the flow takes to move from one 
electrode to the next. Thus, the time series signal from the two electrodes in a pair will look 
similar in form making it possible to recognize the flow pattern at the next electrode by 
studying the two time series. The technique is illustrated in Figure 11. 
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Figure 11 Cross-correlation velocity measurement in the MPFM 1900VI®. The sensor has 
two electrodes a known distance d apart. In the upper plot, the time series signals from 
the two electrodes are plotted in real time. The signal from the upstream electrode is the 
green curve; the signal from the downstream electrode is the red curve. Note that the 
curves have almost the same shape but are shifted in time. 
 
The time series data from the two electrodes are collected simultaneously, and if plotted in 
the same graph in real time, the signals will look like the upper plot in Figure 11. The shape 
of the two curves is approximately the same, but they are shifted in time. 
 
The statistical method cross-correlation, which compares the similarities between the 
signals picked up by the electrode pair, are now used to find the time shift. The cross 
correlation function plotted versus time returns its first and highest maximum at a time T 
representing the time shift between the signals. A cross correlation function is shown in the 
lower graph in Figure 11. 
 
The velocity can now be found as 
 
 Vflow = d/T (5) 
where 
 Vflow = Flowvelocity 
 d = Distance between the electrodes in an electrode pair 
 T = Time shift found by cross correlation of time series 
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The cross correlation calculations must satisfy certain quality requirements to be regarded 
as valid. They are: 
 
• The maximum of the cross-correlation function must be well defined and satisfy a 
minimum threshold value 
• The number of successively approved velocities must be over a specified percentage 
• The calculated velocity must not be less than the Venturi velocity 
• The calculated velocity must be reasonable compared to Venturi velocity (i.e. not 
extremely high) 
 
Venturi velocity 
In many applications, the combination of a mass based Venturi meter and a volume based 
cross-correlation is beneficial. At very high GVFs (typical around 95-99%) the cross 
correlation technique may not work accurately due to lack of dynamics in the measurement 
signals from the capacitance/inductive sensor. A typical example would be annular flow 
where the gas mainly travels in the center of the MPFM sensor with the liquid concentrated 
along the walls of the sensor. 
 
In these situations, a Venturi-based flow meter will still work. Also, including a Venturi meter 
to the MPFM produces redundancy in velocity measurement. If one unit fails, the Flow 
Computer will automatically start to use the other unit. 
 
The differential pressure across a Venturi is proportional to the kinetic energy of a mixture 
passing through. Thus, the response curve of a Venturi meter is related to the mass of the 
mixture and its velocity. See section 0 for more information about the Venturi measurement 
principle. 
 
The starting point for the application of the Venturi is the general Venturi equation. 
 
 dPACEM ⋅= ρε 2& 
where 
 M& = Mass flow 
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 dP = pressure difference between upstream pressure tapping P1 and down 
stream pressure tapping P2. See Figure 6 on page 11. 
 C = Discharge coefficient = f(ReD, β) 
 E = velocity of approach factor = )1(/1 4β− 
 ReD = Reynolds number 
 β = Diameter ratio, ID of Venturi throat divided by ID of Venturi inlet 
 ε = expansibility factor = f(dP/P, β, γ) 
 γ = Ratio of specific heat of the fluid at constant pressure and volume = Cp/Cv 
 A = cross sectional area of the Venturi throat 
 
In the Roxar MPFM 1900VI® the general Venturi equation is modified for use in three-phase 
flow. The modified equation takes into account the gas volume fraction (GVF) of the flow. 
Since the mixture density is measured with the gamma densitometer means that the 
average liquid velocity and gas velocity can be determined from the measured differential 
pressure. 
 
Venturi measurement sizing 
In designing a Venturi for a specific application, the throat diameter of the Venturi meter is 
sized to ensure best results. Since the response of the Venturi meter is related to the square 
of the velocity, a turndown ratio larger than 10 : 1 is difficult to achieve while maintaining 
good accuracy; the problem being friction losses at high velocity and uncertainty in 
differential pressure at low velocity. 
4.3 Signal analysis 
The time series signals from the capacitance and inductance sensor are subject to an 
extensive signal analysis in order to extract information about the flow regime. The output 
from this analysis will be liquid and gas velocity and the distribution of gas and liquid. 
 
Signal variations 
The signals picked up from the electrodes will vary over time since the composition of the 
mixture changes when flowing through the sensor. Liquid containing a lot of gas, and hence 
large gas bubbles, will create large variations in the measured signals. Likewise, liquid 
containing only small gas bubbles (dispersed gas) will result in small signal variations. 
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Therefore, periods with large gas bubbles can be easily distinguished from periods with 
dispersed flow. 
 
Moreover, the large bubbles will represent the gas velocity while the dispersed gas bubbles 
will tend to follow the liquid and will therefore represent the liquid velocity. 
 
Two electrode sets 
The sensor contains two different shaped sets of electrodes, large and small. The large pair 
of electrodes will be most sensitive to variations generated by large gas bubbles, whereas 
the small pair of electrodes will be most sensitive to variations generated by the small gas 
bubbles. 
 
Hence, the velocity of the gas can be determined by cross correlating signals from the large 
electrodes and the liquid velocity can be determined by cross correlating signals from the 
small electrodes. 
 
Improved Venturi velocity measurements 
The basic Venturi measurement is a mean velocity measurement and does not give 
information about the slip between gas and liquid. However, as long as the cross-correlation 
method works well, the gas velocity will be determined using the cross-correlation. This 
information together with the GVF is then used as input to the modified Venturi equation 
before the liquid velocity is calculated. Since the velocity of the gas and the gas fraction is 
measured independently of the Venturi total mass flow measurement, the slip between liquid 
and gas phase can be determined. This method of combining Venturi and cross-correlation 
results in a very robust velocity measurement and will work for all flow regimes and for all 
gas fractions. This is one of the main aspects of the Roxar MPFM 1900VI® as the meter 
does not rely on the use of installation specific calibration constants (slip models) or the use 
of a mixing device. 
 
When the two flow velocities are determined, these are combined with information from the 
fraction measurements in order to determine the individual flow rates of oil, gas and water. 
Refer to equation (4) on page 19 where the area A, in this case, will be the area of which 
each fraction occupies in the cross section of the pipe. 
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4.4 Oil continuous and water continuous flow 
Figure 12 shows the relation between the permittivity and the conductivity of an oil/water 
mixture. As the figure indicates, there is a hysteresis in the transition point between oil 
continuous and water continuous phases. This means that the capacitance sensor might 
work up to approximately 80% water cut when the mixture changes from oil continuous to 
water continuous, while the inductive sensor might work down to approximately 75% water 
cut when the transition point is gained from the top portion of the water cut range. However, 
no matter where on the water cut range, one of the two meters will always work. 
 
Which phase (oil or water) is the continuous phase, is determined by monitoring the 
Automatic Gain Control (AGC) of the inductive sensor. When the flow is changing to oil 
continuous, the conductivity of the bulk will approach zero and the AGC will be saturated (no 
current can be sent through the flow), thus indicating an oil continuous flow. 
 
Oil-in-water
Inductive sensor
Capacitive / Inductive sensor
Capacitive sensor
Water-in-oil
Pe
rm
itt
iv
ity
 o
f m
ix
tu
re
0 50 100
2
80
40
Percentage water in oil 
Figure 12 Measurement range for capacitance and inductive sensors 
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5. OPERATING RANGE AND ACCURACY 
Preceding any discussion of operating range and accuracy,it is pertinent to address 
recommended meter installation in order to achieve optimal performance characteristics. 
5.1 Recommended installation method 
In order to ensure the optimal working conditions for the meter, it is essential to address the 
flow regime on site. The point is that applications vary from site to site all over the world. 
Roxar have installed meters on all continents in an array of applications. The experience 
gained from these installations provides first hand knowledge on how to ensure the most 
favourable installation. 
 
The drawing below provides a pointer to how an optimal installation may be designed. 
However, some general guidelines elaborating on the stringency of this installation method 
may be useful. 
 
• Applications having demanding flow regimes such as very high GVF, low velocity 
flow rate, surging conditions and/or partial separation, should take special heed 
of the recommendations below. 
• If the installation has optimal flow conditions, often characterised by deployment 
close to choke, high velocity flow rate and/or high GVF, the below 
recommendations may not be applied. 
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Section Flow element Size Length (*) Comment 
 
A Pipe section No requirements No requirements 
B Crossover No requirements If the inlet is more than one size 
larger than the Meter, a crossover 
is required. 
C Pipe section Same as Meter or one size larger Min 1 m E.g. 2” MPFM ⇒ 2” or 3” pipe 
 3” MPFM ⇒ 3” or 4” pipe 
 etc 
D Tee / Reducing 
Tee 
Inlet same as Meter or one size 
larger, outlet ID same as meter -
5 % to +20% 
I Bulb or blind flange. 
E Inlet pipe section Same as Meter -5 % to +20% Minimum 3 x ID 
Recommended 5 x 
ID 
If the inner diameter of standard 
piping is different, a spool piece 
with coned inner diameter can be 
applied. 
F Outlet pipe 
section 
Same as Meter -5 % to +20% No requirements 
 
Not required 
G Crossover If a crossover is required to match 
project piping, the crossover should 
be installed after the bend. 
Table 2 Pipe section Dimensions. (*) ID refers to Meter’s inner diameter. 
 
 
 
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 Rated conditions of use: 
 
Pressure: < 800 bar Temperature: -20 - 130oC 
Oil density: 600 - 1050 kg/m3 Oil viscosity: No influence 
Water density: 950 - 1200 kg/m3 Gas viscosity: No influence 
Flow regimes: All regimes (single phase, bubbly flow, churn flow, slug flow, 
annular flow) 
Table 3 Rated conditions of use 
5.2 Operating range 
The volumetric flow through a multiphase meter is to a large degree directly linked to the 
flow line pressure at the measurement point due to the compressibility of the gas. The point 
is that the volumetric flow will vary significantly even to small changes in pressure. 
Consequently, the selection of meter size for a given application is based on input from the 
customer describing the variation in influencing parameters over the field life. 
 
Roxar Multiphase Flow Meters of different sizes have a large operating envelope; covering 
water cuts from 0 to 100% and gas void fractions from 0 up to 95-99%. 
 
The lower limit for mixture velocity is defined to avoid percolation effects, where the liquid 
surges upwards and then falls back through the meter. The gas must have enough 
momentum to carry the liquid without dropping it. Higher velocities are required as the GVF 
increases. For low GVF’s a minimum superficial velocity of 1.5 m/s is required. For high 
GVF’s a minimum superficial velocity of 3.5 m/s is required. 
 
The maximum velocity through the meter also depends on the GVF. Two factors limit the 
upper velocity range. The first limitation is the maximum differential pressure which is 
measured by the DP transmitter. As the Venturi measures mass flow, the generated 
differential pressure will depend upon the amount of gas in the flow. A high GVF will result in 
a lower differential pressure than a low GVF. The second limitation will be the resolution of 
the cross correlation meter. As the velocity of the flow increases, the accuracy of the cross 
correlation will gradually decrease. At 30 m/s the resolution in flow velocity will be 
approximately ± 0.2 m/s. For low GVF’s a maximum superficial velocity of 15 m/s is 
specified. For high GVF’s a maximum superficial velocity of 35 m/s is specified (higher 
velocities must be evaluated in each case). 
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An extension of the operational window for a meter can be evaluated on a case-by-case 
basis. Operating pressure, liquid viscosity, accuracy limits, and water cut can all affect 
operational limits such as the maximum GVF. 
 
The meters are generally more accurate at high flow rates. When there is a choice between 
a meter operating at the bottom of its envelope and a smaller meter operating in the middle 
of its envelope, then the smaller meter should be used. 
 
Note that neither the upper or lower velocity ranges are absolute limits. The MPFM 1900VI® 
will continue to operate below and above these limits. However, the accuracy of the 
measurements will decrease and cannot be expected to be within the specifications. 
 
A general example of an operating envelope for the Roxar MPFM 1900VI® is shown in 
Figure 13 below. 
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
Superficial gas velocity (m/s)
Su
pe
rf
ic
ia
l l
iq
ui
d 
ve
lo
ci
ty
 (m
/s
)
GVF=96%
GVF=90%
GVF=80%
F
E
D
C
B
A
GVF=60%
GVF=30%
 
Figure 13 Operating envelope for a 3” meter. Note that for each delivery of a MPFM 
1900VI®, a meter size has carefully been selected based on production data received 
from the customer. The same information can also be used to generate a specific 
operating envelope for the same supply. See the User Manual and in the Design 
Calculations for further information. 
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5.3 Measurement uncertainty 
In general, the measurement uncertainty is more precise when all three components (oil, 
water and gas) are present at similar void fractions. If one of the constituents is present in 
very small quantities, this will be difficult to measure with high accuracy. The uncertainty 
specification of the MPFM 1900VI® is indicated in Table 4 below. 
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Table 4 Measurement uncertainties MPFM 1900VI 
Confidence level: 95% (k=2) Combined expanded uncertainties 
Sub range GVF range Gas Liquid WLR 
A 0 – 25 % 10(1) 3,5 2,5 
B 25 – 85% 4,0 3,0 
C 85 – 96 % 5,5 4,0 
D 96 – 98 % TBA TBA 
E 98– 100% 
8 
 
- - 
Repeatability: ¼ of % ¼ of % ¼ of % 
Response time: 5 s Update frequency: 3000 Hz 
Abbreviations: 
 
GVF = Gas Volume Fraction 
WLR = Water in Liquid Ratio 
WTr = Transition point oil/water continuous liquid phase 
rel % = Relative uncertainties in gas and liquid flow rates(2) 
abs % = Absolute uncertainty for Water in Liquid Ratio (WLR) (2) 
TBA = For GVF in the range 96-98%, the uncertainty specifications will depend on 
 a number of factors and will be advised in each case. 
 
Comments: 
 
• For WLR > WTr WLR is 1.4 x listed value (WTr = Transition point oil/water continuous liquidphase) 
• Uncertainties are given for pressure > 10 barG 
• (1)For GVF > 5% 
 
Calculation of oil and water flow rate uncertainty: 
 
( )( )
WLR
UUWLR
U WLRliqOil −
+⋅−
=
1
1 22
 
 
( )
WLR
UUWLR
U WLRliqWat
22 +⋅
= 
 
Where 
 
Uoil : Relative uncertainty of oil flow rate 
Uwat : Relative uncertainty of water flow rate 
Uliq : Relative uncertainty of Liquid flow rate 
WLR : Water in Liquid Ratio (‘water cut’) 
UWLR : Absolute uncertainty of water cut 
 
Repeatability: ¼ of measurement uncertainty 
 
Uncertainties: Based on 95% confidence interval as described in the 
 NFOGM handbook of Multiphase Metering 
 
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5.4 Effects from changes in fluid properties 
The MPFM 1900VI® has a configuration which contains information about the fluid properties 
like oil/water/gas densities and oil permittivity. These properties may change over time. 
Unless the fluid properties fed to the meter, are updated as they vary over time, this will 
result in inaccurate measurements. However, the MPFM 1900VI® can tolerate relatively 
large changes in fluid properties before the error becomes significant. For example, a 
change in oil density of +1% relative will result in an error of only +0.9% in measured liquid 
flow rate. 
 
Impact of varying densities, conductivities and permittivity are as follows: 
Quantity 
Change 
% rel 
Liq. rate 
% rel 
WLR 
% abs 
Gas rate. 
% rel 
Note 
Oil density: +1 % +0.9 % -0.2 % -0.2 % 1 
Gas density: +10 % +1.1 % -0.3 % -0.3 % 1 
Water density: +1 % +0.3 % -0.1 % -0.1 % 1 
Oil permit. + 5 % -0.3 % +1.3 % +0.1 % 1 
Water conduct: + 1 % -0.02 % + 0.9 % - 0.0 % 2 
Table 5 Uncertainty specification MPFM 1900VI®: 
Note 1: Given at 80% GVF, 20 % WLR 
Note 2: Given at 80% GVF, 80 % WLR 
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6. EFFECT OF SAND, SCALE, WAX AND EROSION 
6.1 Deposition of wax 
Wax present in the flow or deposited inside the sensor will be measured as oil. This is due to 
the fact that the density and dielectric properties of wax and oil are very similar. Large 
amounts of wax deposited inside the sensor, may limit the flow area and result in too high 
flow rate readings. However, wax inhibitors used to prevent wax deposition do not effect the 
measurements performed by the meter. Finally, since the MPFM 1900VI® are full-bore and 
non-intrusive, thick layers of wax are unlikely to build up inside the meter. 
6.2 Presence of solids/sand 
Sand has dielectric properties very similar to the ones for oil. Hence, any sand will be 
measured as part of the oil. However, as the dielectric measurements are based on volume, 
sand will have hardly any effect on the performance of the meter. In fact, Roxar has never 
detected any effects caused by sand on any installation. 
6.3 Scale 
The MPFM 1900VI® can accept small amounts of scale without the measurements being 
affected. Nevertheless, thick layers (typical > 1-2mm) of scale should be removed from the 
internals of the meter. 
6.4 Erosion 
Except for the Venturi, the meter is non-intrusive without any moving or static parts limiting 
the flow area. The sensor electrodes are in-flush with the inside of the sensor wall and will 
not be subject to erosion. Roxar have not experienced any installations where erosion has 
affected the performance of the Venturi, nor the meter itself.