www.agarcorp.comProcess Measurement & Control Solutions

MPFM-050A Novel Multiphase, Non-Nuclear, Solid Flow Meter

Motion & OW-201 in Duri

Installation in Indonesia Agar OW-201 for Watercut, and Coriolis for mass flow

Since complete and ideal separation of liquid and gas is impossible, entrapped gas is carried under with the liquid. Agitation due to turns and bends in the pipe causes the gas to break out of the liquid forming foam. This foamy liquid is measured in the Agar water-monitor as less water, and more volume passing through the flow meter, resulting in a cumulative positive error. Foam is essentially gas surrounded by thin sheet of liquid. The Agar meter reports lower amounts of water since 1% gas looks like 1% of liquid hydrocarbon, so the ratio of oil present is reported higher than what actually exist. The Coriolis meter in this picture reports the additional amount of gas as additional volume of liquid, again giving a higher number in the positive direction.

Foam is not only limited to high viscosity oil, but is a problem with all types of crude oils. For example water which has a viscosity of 1 can turn foamy just by addition of small amounts of detergent. Foaming is dependent on pH, polymer content and surface tension, among other factors.

1. IntroductionThe AGAR MPFM-50 is a low cost, compact, portable multiphase flow meter (MPFM) that is the newest addition to the stable of excellent multiphase meters provided by Agar for over 20 years. The Agar MPFM-50 is based on a coriolis flow meter which is modified to work across the entire Gas Volume Fraction (GVF) from 0 100%, i.e. multiphase flow and wet-gas regimes, and ancillary sensors such as the Agar water-cut meter which is based on microwave technology and has the ability to measure 0-100% water-cut, across all multiphase flow regimes. The coriolis meter described above is not off-the-shelf and certain modifications have been made mechanically and to the electronics which enabled it to continue performing in multi-phase flow and measure the density and flow rate of the multi-phase fluid mixture accurately using Agar proprietary advanced fluid dynamical models.

Agar MPFM-50 Design Approach

No nuclear radioactive source

No moving parts

Handles full range of flow regimes

No phase separation

2. General SpecificationsThe table below gives the general specifications of the MPFM. The oil and water flow rates can be measured to within 1% FSL3% R and the gas flow rate to within 2% FSG5% R with 2 sigma confidence. FSL is the liquid full scale which for a 2 inch unit is 5000 BBL/day (800 m3/day). The accuracies are not affected by changes in salinity, viscosity, density, temperature, pressure, or pH. The general specifications of the MPFM-50 are given below.

Table 1. General Specifications of MPFM-50

Gas Void Fraction0 to 100%Water Cut0 to 100%Flow RegimesAll: (e.g. bubbly, wavy, slug, annular, etc.)PressureUp to 2500#Ambient Temperature-4F to 160F (-20C to 70C)Optional Low Temp -40F to 160F (-40C to 70C)Process TemperatureStandard Model 32F to 212F (0C to 100C)High Temp Model 32F to 450F (0C to 232C)Liquid ViscosityLow Viscosity Model: 0.1-30 cPHigh Viscosity Model: 0.1-2000 cPSalinity0 to 20% NaCl by weight (up to saturation)Sand/ParticulateUp to 5% by volume and less than 1mm particle sizeMax Pressure DropLess than 15 PSI (1 bar)Wetted PartsStandard: 316 Stainless Steel; Hastelloy, and other materials available on special order. According to ASME B31.1 and B31.3. PEEK; Ceramic Isolators

3. Schematic and Operating PrincipleThe operating principle of the MPFM-50 is that we measure the bulk density and flow of a multi-phase flow stream in real-time, and use simultaneous equations to correct for the slip which is common in both. Adding another independent flow measurement sub-system increases the number of equations and allows a wider band of flow conditions to be used. We make additional measurements e.g. power, viscosity to increase the accuracy. Also, the advantage of measuring bulk density as opposed to spot density, such as the measurement of density over a cross-section of the pipe, is that bulk density is less sensitive to changes in slip (velocity difference) between gas and liquid. The MPFM is described by means of the arrangement sketched in Figure 1. A coriolis meter is used to measure the density of the fluid flowing through it by measuring the natural frequency of oscillation of the tubes inside it. We measure the power and frequency of the coriolis driving circuit to obtain two equations. We also measure the coriolis twist of the tubes which, in general, is proportional to the mass flow rate.

Fundamental EquationsMVenturi = MCoriolis ; 2) MC = f2(TWIST; S);Mv= f3(P; m; S); 4) m = f4();5)m = G*GVF + L(1 GVF);6) L = wWC + O(1 WC);G = Sg*P/Tz; 8) WC = f5(w; O; G; GVF);

Where: M =Fluid Mass Flow; m =mixture of oil+water+gasS =Slip between flow liquid (L) and gas (G); = frequency of oscillation of the tubes;P =differential pressure across the venturi; GVF = Gas Void Fraction; Sg = specific gravity of gas; WC = Water/Liquid volume ratio; Z = Supercompressability of the gas. = density

Figure 1. Schematic of MPFM-50

Eqn.1

Eqn.2

Eqn.3

In the above equations, is the density of the mixture, QG is the volumetric flow rate of the gas, QO is the volumetric flow rate of the oil, QW is the volumetric flow rate of the water, S is the slip ratio, and is the flow averaged viscosity of the liquid.Obviously, one cannot solve for 8 unknowns with only 3 equations. To arrive at additional equations, we use another meter, such as a venturi meter or an orifice plate shown in Figure 1. The pressure drop from the inlet of the venturi to the throat also depends on the slip, as given in the Fourth equation Eqn. 4

The fifth equation is obtained from the water-cut meter, which is connected in tandem with the coriolis and the venturi meters to measure the water cut and thus compute the oil, water, and gas flow rates. The Agar water-cut meter measures the complex dielectric of the fluid and we use the Bruggemans equation to determine the concentrations of oil and water in the liquid. Eqn.5As noted in the introduction, variation in viscosity () influences slip (S), among other variables, and contributes significantly to the errors in flow measurement. We therefore need a Sixth equation if the viscosity is changing drastically. We measure viscosity by measuring the pressure-drop across a short straight section of the piping, and use this to compensate for the errors introduced due to varying viscosity Eqn.6We measure the line pressure, P, and temperature, T, to convert the flow rates measured at line conditions to those at standard conditions. The above system of nonlinear simultaneous equations is solved in order to arrive at the flow rates, density, and water-cut.

4. Results from Lab Tests:In this section, we present some results obtained from laboratory tests conducted in the Agar Flow Loop. Figure 2 shows the density of the mixture as a function of Gas Volume Fraction (GVF). We start the test, by flowing Salt Water with a density of 1020 kg/m^3 at a steady flow rate. At the start of the test only salt water is flowing through the meter and there is no air, thus the GVF is 0% and we slowly increase the amount of air, i.e. increase the GVF. As GVF increases the mixture density decreases. We plot the density measured by the coriolis, using the new electronics and the algorithm as described in previous sections, and for comparison we have also plotted the theoretical no-slip density curve. The close agreement between the measured density and the theoretical no-slip density across the entire GVF range and at different liquid flow rates indicates the robustness of the slip measurement procedure and is note worthy.

Figure 2. Density of Mixture vs. Gas Volume Fraction, measured by the Agar MPFM_Vertical Installation

For measuring in the wet-gas regime, we rely on an electronic signal from the coriolis meter which is very sensitive to the presence of gas, as is shown Figure 3. This signal enables us to measure the GVF accurately in the wet-gas regime.Figure 3. Measurement in wet-gas regime

5. Field Performance of MPFM-50:Summary results and conditions with actual site pictures.

Oxy Petroleum - New MxicoEnCana - CanadaSttatsolie - SurinamePetrom - RomaniaMPFM in the Field

MPFM-50 AdvantagesWorks in any flow pattern and does not rely on Magic Algorithms.Not affected by pipe configurationMost suitable for Oil wells and Wet Gas optimization. Non nuclear (no radioactive source) thus independent on minerals content.Minimum human intervention, such as entering fluid properties before each test.Based on proven and familiar instruments.

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