Multiphase Pumping

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    Multiphase Pumping as an Alternative to ConventionalSeparation, Pumping and Compression

    Mack Shippen, Schlumberger - Baker JardineDr. Stuart Scott, Texas A&M University

    Prepared for Presentation at the 34th

    Annual PSIG meeting

    Portland, Oregon

    October 25, 2002

    Abstract

    This study explores the application of multiphase pumps as an alternative to conventionalseparation using rigorous steady-state simulation models incorporating a newly developedmultiphase pumping model. The simulation results show that multiphase pumps areadvantageous in not only reducing facilities, but can also increase production rates by loweringthe backpressure on wells. Additionally, the complexities associated with multiphase flow througha single pipeline are compared to running dual single-phase pipelines and importantconsiderations observed with the steady-state simulation are highlighted.

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    1.0 Introduction

    Following its emergence from research labs a decade ago, multiphase pumping has become a viable

    solution to a wide number of field development plans. While the technology is seen to be particularlybeneficial in remote locations such as the deepwater Gulf of Mexico, pumps have also been deployed to a

    number of onshore locations ranging from Alaskan North Slope to Columbia and from West Africa to the

    Middle East.

    Multiphase production systems require the transportation of a mixture of oil, water and gas, often for many

    miles from the producing well to a distant processing facility. This represents a significant departure fromconventional production operations in which fluids are separated before being pumped and compressed

    through separate pipelines. By eliminating this equipment, the cost of a multiphase pumping facility is

    about 70% that of a conventional facility (Dal Porto, 1996) and significantly more savings can be realized

    if the need for an offshore structure is eliminated altogether. However, multiphase pumps do operate lessefficiently (30-50%, depending on Gas volume fraction and other factors) than conventional pumps (60-

    70%) and compressors (70-90%). Still, a number of advantages in using multiphase pumps can be realized,

    including: 1) Increased production through lowering backpressure on wells; 2) elimination of vapor

    recovery systems; 3) reduced permitting needs; 4) reduction in capital equipment costs; and, 5) reduction infootprint of operations.

    Interest in the subsea deployment of multiphase pumps has grown as operators search for methods toimprove recoveries and economics for subsea completed wells. While subsea completed wells enable

    development of deepwater resources as well as marginal fields in normal water depths, without some form

    of subsea processing, these wells are expected to experience poor ultimate recoveries due to the high

    backpressures. For example, conventional production operations routinely drawdown wellhead pressures to100-200 psig. A subsea completed well, however, may have abandonment wellhead pressures of 1,000-

    2,000 psig due to the backpressure added by the long multiphase flowline. In addition, operating as such a

    continual high backpressure has been shown to have a direct impact on production decline behavior, acting

    to reduce ultimate recovery (Martin & Scott, 2002). Maintaining a high backpressure can be viewed as aproduction practice that wastes reservoir energy. Energy that could be used to move reservoir fluids to the

    wellbore and out of the well is instead lost to flow through a choke or a long flowline. It is anticipated that

    some form of subsea boosting and/or processing of produced fluids will be necessary to improveefficiencies, allowing longer production from these wells and better recovery factors. Subsea processing

    covers a wide spectrum of subsea separation and boosting scenarios. Subsea multiphase pumpingtechnology is perhaps a decade ahead of subsea separation and provides many advantages in terms ofintervention when compared with wellbore artificial lift methods.

    Multiphase pumping is a relatively new technology and acceptance has been hampered by a lack of

    engineering design tools. Recently, pipeline simulation codes have incorporated the ability to modelmultiphase pump performance as part of the overall multiphase production system. This paper illustrates

    the use of such a model to evaluate the benefits of subsea multiphase pumping.

    2.0 Multiphase Pumping Technologies

    Over the past decade, several multiphase pump technologies have emerged for gas-liquid multiphaseflow in the petroleum industry. As shown in Figure 1, these methods fall into the broad categories of thepositive displacement and rotodynamic pumps. Figure 2 shows that the number of multiphase pump

    installations has increased rapidly over the past 5-7 years (Scott, 2002). This figure also shows the

    breakdown between the different multiphase pump technologies. It should be noted that while the helico-axial technology only represents a small number of the total multiphase pump installations, they are used in

    the majority of offshore and subsea applications and have the capacity to pump much large volumes of

    fluids than the positive displacement technologies.

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    Piston

    Helico-Axial

    Single-Screw (PCP)

    Twin-Screw

    Positive Displacement

    Twin Screw

    Progressing Cavity (PCP)(Single Screw)

    Piston

    Diaphram

    Rotodynamic

    Helico-axial(Poseidon type)

    Multi-Stage Centrifugal(ESP type)

    Multiphase Pumps

    Figure 1: Types of Multiphase Pumps

    Figure 2: Worldwide Usage of Multiphase Pumps (MPUR Survey, Scott, 2002)

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    A good summary of the development of multiphase pumping technology is given by Cooper et al (1996)

    and Scott & Martin (2001). Recently, a transient model has been proposed to describe the behavior of a

    rotodynamic pump (Ramberg and Bakken, 1997). Ideas on modeling the twin-screw pump have been

    presented by Vetter & Wincek (1993) and Egashira et al. (1996) and these pumps have been successfullyincorporated into field use (Oxley & Shoup, 1994; Jaggernauth et al., 1996; Caetano et al., 1997; Guevara,

    1999; and Giuggioli et al., 1999)). The following sections discuss the most commonly used types of

    multiphase pumps.

    2.2 Positive Displacement Pumps

    Positive displacement pumps operate on the principal that a definite amount of fluid is transferred through

    the pump based on the volume created by the pumping chamber and the speed at which this volume is

    moved. The amount of differential pressure that develops in the pump is a function of the resistance toflow downstream of the pump - that is, the pressure losses that must be overcome to deliver the fluid to a

    set pressure downstream of the pump. For any positive (or near positive) displacement pump, the

    interaction between the pump and the adjacent pipeline segments determines pump performance.

    2.2.1 Twin-Screw Pumps

    The twin-screw is by far the most popular multiphase pump in use and is manufactured by Bornemann,Flowserve and Nuovo Pignone. Twin-screws are particularly adept at handling high Gas Volume Fractions

    (GVF) and fluctuating inlet conditions. These pumps remain functional even at GVFs of 95% and with re-

    circulation systems can function at 100% GVF for short periods of time.

    Figure 3 gives a schematic of a twin-screw pump. The multiphase mixture enters one end of the pump and

    split into two flow streams that feed into inlets situated on opposite sides of the pump a design that

    equalizes stresses associated with slugging. Flow then passes through a chamber (created by theinterlocking screws) that moves along the length of the screws to the outlet. The volumetric flow rate is

    dependent on the pitch and diameter of the screws and the rotational speed. As the gas is compressed, a

    small amount of liquid will slip back through the small gaps between the screws and the containment

    chamber wall resulting in a reduced volumetric efficiency.

    Figure 3: Twin-Screw Pump (after Bornemann)

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    2.2.2 Progressing Cavity Pumps (Single-Screw)

    Widely used in shallow wells as an artificial lift method, the Progressing Cavity Pump (or Moyno pump)

    has been adapted for surface multiphase pumping. Note that the number of PCP pumps listed in Figure 2

    represents only the surface installations of this technology. The PCP pump is comprised of a rubber statorand a rotating metal rotor (Fig. 4). This pump is effective for low flow rates (less than 30,000 bbl/day total

    volume of gas, oil and water) and for lower discharge pressures (maximum of 400 psig). This pump hasthe unique ability to tolerate considerable amounts of solids (sand). However, high sand production ratesresult in the need to replace the stator on a regular basis.

    2.2.3 Piston Pumps

    One of the simplest forms of multiphase pumping is the use of a large double-acting piston to compress themultiphase oil, water and gas mixture. This approach is effective in the low and moderate flow rate ranges

    with a maximum capacity of approximately 110,000 bbl/day (total volume of gas, oil and water) andmaximum discharge pressure of approximately 1,400 psig. The first type of piston pump, the Mass

    Transfer Pump, was installed June 1998 by National Oil Well in Canada. As shown in Figure 5, this

    pump makes use of the same gear box and prime mover that is utilized in conventional sucker rod pumpingunits. Also, the pumping chamber functions much like a downhole sucker rod pump. It is comprised of

    two check valve assemblies which operate is the same fashion as the standing valve and traveling valve in a

    downhole pump. There are currently 8 installations of this pump in Canada.

    Figure 5: Mass Transfer Pump (after National Oil Well)

    Figure 4: Progressing Cavity Pump (after R&M)

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    In 1999, Weatherford Artificial Lift Systems introduced their RamPumpTM (Fig. 6) which is comprised of

    a hydraulically actuated vertical piston. This pump was first utilized in an on-shore installation, but has

    recently been applied offshore in the U.S.A. Gulf of Mexico (Sommer, 2002). Large clearances allow for

    moderate amounts of sand production. The vertical configuration of the piston provides an advantage foroffshore installations where deck space is at a premium.

    2.2.4 Diaphragm Pumps

    The diaphragm pump is a reciprocating pump consisting of two pumping chambers. The piston and motorare immersed in hydraulic oil supplied by a conventional axial-piston hydraulic pump. An elastomeric

    diaphragm separates the hydraulic oil from the pumped fluids. While these pumps have been primarilyassociated with the liquid-solids flow associated with deepwater drilling operations, they can be modified

    to accommodate 100% GVF fluids with high efficiency. Rates of up to 30,000 BPD and differential

    pressures of 550 psi have been achieved with prototype pumps (Beran, 1995).

    2.3 Rotodynamic Pumps

    Dynamic pumps operate on the principal that kinetic energy is transferred to fluid which is then converted

    into pressure. In rotodynamic pumps, this occurs when angular momentum is created as the fluid is

    subjected to centrifugal forces arising from radial flow though an impeller. This momentum is thenconverted into pressure when the fluid is slowed down and redirected through a stationary diffuser.

    2.3.1 Helico-axial pumps

    The Helico-axial pump is a type of rotodynamic pump developed by the Poseidon Group (IFP, Total and

    Statoil) and manufactured by Framo and Sulzer.

    The fluid flows horizontally through a series of pump stages, each consisting of a rotating helical shaped

    impeller and a stationary diffuser (Fig 7). This configuration is akin to a hybrid between a centrifugal

    RAM (during upstroke)

    Figure 6: RAMPump

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    pump and an axial compressor. Each impeller delivers a pressure boost with the interstage diffuser acting

    to homogenize and redirect flow into the next set of impellers. This interstage mixing prevents the

    separation of the gas-oil mixture, enabling stable pressure-flow characteristics and increased overall

    efficiency. As the gas is compressed though successive stages, the geometry of the impeller/diffuserchanges to accommodate the decreased volumetric rate.

    The impeller clearances are sufficient to allow production of small amounts of sand particles. While

    helico-axial pumps are more prone to stresses associated with slugging, installation of a buffer tankupstream of the pump is generally sufficient to dampen slugging effects such that they are not a problem.

    2.3.2 Multistage Centrifugal Pumps

    Downhole Electric Submersible Pumps (ESPs), manufactured by companies such as Schlumberger-Reda

    and Baker-Centrilift, are widely used as an artificial lift method in oil wells. So far, this technology has

    tended to focus on liquid pumping with incidental amounts of entrained gas. Recently, these pumps havebeen adapted for surface pumping applications and their ability to handle gas has been extended.

    Figure 7: Helico-axial Pump (after Sulzer)

    Figure 8: Multistage Centrifugal Pump

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    3.0 Multiphase Pump Performance Analysis

    Unlike single-phase pumps and compressors, no generalized model exists that is able to accurately

    characterize the performance of multiphase pumps. This is due in part to complex and highly proprietaryinternal pump geometries. Additionally, the variety of fluid properties and in-situphase distributions make

    it extremely difficult to rigorously describe the thermo-hydraulics occurring within the pump. For these

    reasons it is common practice to characterize multiphase pumps with performance curves of the typedepicted in Figure 9. Such curves are constructed on the basis of specified gas volume fractions, suction

    pressures and liquid density and viscosity. As inlet conditions change, the curve becomes invalid and

    other curves must be applied.

    Commercial simulators often base designs on boundary conditions established upstream of the pump inlet.

    For example, if a pressure is set at the reservoir or at a manifold located some distance upstream of the

    pump, the pressure at pump suction becomes flowrate dependant. Thus, it is not possible to move about theperformance curve to explore different flowrates without affecting a change in the suction pressure, thereby

    invalidating the curve. In such cases, it becomes impractical to use series of individual curves to size

    pumps and explore the operational envelope for changing conditions. The need arises for a model thatresponds to these changes - not only during iterative calculations performed for one set of conditions, but

    for sensitivities performed on system parameters and analysis of overall system properties that change over

    time.

    The steady-state multiphase flow simulator used in this study (PIPESIM) addresses this issue with three

    types of pump performance models a generic model, a twin-screw model, and a helico-axial model. Thesimplest approach is to use the generic model that treats the multiphase pump as a single-phase liquid pump

    and gas compressor operating in parallel. Conventional pump and compressor theory is used to calculatethe shaft horsepower required. Efficiencies of the pump and compressor can be adjusted based on typical

    values taken from field conditions. Due to the limiting assumptions in this approach, use of the generic

    multiphase pump model is recommended only as a preliminary analysis.

    The twin-screw pump performance model is derived from empirical data covering wide range of gas

    volume fractions, suction pressures and pump speeds. Pump performance at specific inlet conditions is

    Increasing powerrequirement

    increasing speed

    P

    Total volumetric suction flowrate

    Valid for given:

    Gas volume fraction

    Suction pressure

    Liquid viscosity

    Liquid Density

    Figure 9: Typical multiphase pump performance curve

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    calculated by a rigorous interpolation routine that determines differential pressure, flow rate, pump speed

    and power requirement. The test data is based on a liquid viscosity of 6 cSt. with corrections applied for

    different actual viscosities. Seven pump sizes are available and are characterized in terms of nominal

    capacity that is, the theoretical rate at 100% speed, 0% GVF, zero differential pressure and with nointernal leakage. Available nominal rates range from of 37,500 to 300,000 BPD (250-2000 m3/hr) of total

    suction flowrate. Additional pumps can be modeled with data supplied by the vendor or acquired in

    precomissioning tests.

    The helico-axial pump model characterizes pump performance using three correlating parameters. The

    flow parameter and the head parameter characterize the size of the impellers and the number of stages

    respectively, thus defining a specific pump. A speed parameter representing the percentage of maximumspeed is then adjusted based on the desired differential pressure for a given rate (or vice-versa). The power

    requirement is calculated based on a combination of pump performance and drive mechanism. Drive type

    options include a hydraulic turbine drive, electric air-cooled drive and an electric oil-cooled drive.

    4.0 Example

    The following example illustrates the benefits of a subsea twin-screw multiphase pump installation incomparison to a satellite platform with conventional separation facilities. Steady-state multiphase flow

    simulation models are used to evaluate the two alternatives.

    4.1 System Models

    An oil well is planned to be drilled in a water depth of 3600 and 8 miles from a host platform. In a

    traditional development, a satellite platform would be fixed directly above the wellhead with fluids

    producing up a riser to a separator operating at 200 psia (Fig. 10). Gas is compressed and liquid is pumpedthrough separate lines to the host platform. Alternatively, a twin-screw multiphase pump can be installed

    subsea to facilitate full wellstream production through a single subsea tieback to the host platform at an

    arrival pressure of 200 psia. (Fig. 11).

    8 mile gas line

    Host platform

    36008 riser

    8 mile liquid line

    compressor

    pump

    Satellite platform

    Psep = 200psia

    wellhead

    Figure 10: Schematic of Production System using satellite platform

    38F 2 ft/s

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    Pressure specified boundary conditions are set at the reservoir (which changes over time) and the separator(assumed constant at 200 psia for both cases). A simple productivity index is applied to determine pressure

    losses across occurring in the reservoir and the Hagedorn-Brown and Beggs-Brill flow correlations are used

    to calculate the two-phase pressure loss for vertical and horizontal flow respectively. The ambienttemperature along the flowline is 38 F and the water current is 2ft per second, typical values for deepwater

    environments.

    4.2 Initial Producing Conditions

    Initial producing conditions are represented with a nodal analysis plot (Fig. 12). The intersection of the

    well curve with the flowline curve shows that the well is capable of naturally flowing at 23,500 STBD with

    a wellhead pressure of 1100 psia. To achieve higher rates, a pressure boost is provided to reduce thewellhead pressure. The amount of differential pressure required for a specific rate is equivalent to the

    difference of these two curves and is represented as a single curve in Fig 13. The key difference between

    this figure and typical curves (Fig. 9) is that the different rates correspond with different suction conditionsspecific to the system being modeled. This allows one to determine the pump speed required for various

    rates and corresponding differential pressure required to meet the delivery pressure. As shown, at

    maximum speed, the pump is able to produce 33,100 STBD with a differential pressure of 937 psia. Amarginally higher rate can be achieved using a larger pump, though at the expense of higher upfront capital

    costs and lower operating efficiencies later in life.

    The pressure profile for this case (shown in Figure 14) indicates that pressure losses in the 8 mile flowlineare roughly equivalent to that in the 3600 vertical riser. The pressure losses occurring in the flowline are

    100% frictional, while the pressure losses occurring in the riser are 90% elevational. As rates decline over

    time, the elevational losses in the riser will become the dominant factor in the total pressure loss.

    8 mile 8 subsea tieback

    Host platform

    3600 8 riser

    wellhead

    Multiphasepump

    Psep = 200 psia

    Figure 11: Schematic of Production System using subsea multiphase pump

    38F 2 ft/s

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    Pr = 6000 psi, GOR = 400, wcut = 10%

    Stock-tank Liquid (STB/d)35,00030,00025,00020,00015,00010,0005,0000

    Pressure(psia)

    3,200

    3,000

    2,800

    2,600

    2,400

    2,200

    2,000

    1,800

    1,600

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    PumpP

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    Well curve

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    Pump Performance

    PumpDP(psi)

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    Stock-tank Liquid (STB/d)35,00030,00025,000

    60%

    70%

    80%90%

    100%speed

    Pump P = 937 psi

    33,100

    Figure 13: Twin screw pump performance at initial Producing Conditions

    System curve

    Figure 12: Nodal Analysis at Initial Producing Conditions

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    4.3 Future Performance Forecast

    To account for system performance over time, a reservoir performance table is used which correlates

    pressure decline to cumulative production (Fig 13). The reservoir is initially undersaturated with a bubble

    point pressure of 3700 psia. As the reservoir depletes, the watercut and gas-oil ratio increase. Productioncontinues until an economic watercut is 85% is reached.

    0

    1

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    9

    0 5 10 15 20 25

    % WC X 10

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    (scf/STB)

    Pressure Profile

    Total Distance (ft)40,00030,00020,00010,0000

    Pressure(psia)

    1,300

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    P Pump

    Wellhead pressure

    P flowline

    P riser

    Arrival pressure

    Figure 14: Pressure Profile at Initial Producing Conditions

    Bubble point

    Figure 13: Reservoir Performance Table

    Cumulative Liquid (MMSTB)

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    The performance of several twin screw pump models was considered on the basis of operational flexibility

    throughout the life of the well. The pump is designed to initially operate at maximum capacity while not

    exceeding a maximum pressure differential of 1000 psi. As rates decline and watercut and gas-oil ratio

    increase, the pump speed is reduced to maintain the wellhead pressure at 200 psia while still operating at anacceptable efficiency. In this example, a Nuovo Pignone PSP 210 having a nominal rate of 151,000 BPD

    (1000 m3/hr) was selected to best meet changing conditions.

    Table 1 shows pump performance over time. For the first year of production the pump operates at a speedof 100%, after which the pump speed is adjusted to maintain a wellhead (suction) pressure of 200 psia. The

    gas volume fraction increases as suction pressure drops then remains fairly constant with countering effects

    of increasing watercut and GOR. At initial conditions, the pump operates efficiently at 54% dropping offto 41% prior to abandonment. At a watercut of 50% a water-oil emulsion is present which significantly

    increases the overall liquid viscosity resulting in lower pump efficiency and a higher pump differential

    pressure to accommodate higher frictional pressure losses in the line.

    Cum Liquid tot. suct. suction suction pump pump power pump

    Liquid t ime rat e vol. rat e Wcut GVF liq. visc. p ressure P speed req. eff.

    MMSTB (years) (STBD) (BPD) (%) (%) (cp) (psia) (psi) (%max) (HP) (%)

    0.0 0.0 33,100 121,800 10 70 1.2 403 937 100 2573 544.7 0.4 26,650 123,300 10 76 1.3 306 856 100 2365 50

    9.5 0.9 21,320 123,300 15 81 1.6 225 848 100 2345 44

    17.0 1.8 14,770 100,400 50 84 8.3 200 906 86 2154 39

    21.7 2.7 13,500 102,000 70 86 0.3 200 600 85 1428 44

    24.6 3.3 11,000 77,600 80 85 0.3 200 591 68 1125 42

    27.4 4.0 10,000 73,500 85 86 0.3 200 566 66 1039 41

    A forecast of both development scenarios (Fig. 16) was made based on the reservoir performance table.

    The higher rates achieved with the multiphase pump allow for a shorter production cycle (4 years vs. 6years for conventional separation). Additionally, in the satellite platform scenario, the well is not able to

    naturally produce at reservoir pressures less than 3000 psia (wellhead pressure of about 520 psia) and must

    be abandoned. By lowering the backpressure on the wellhead, the multiphase pump is able to produce to

    the economic watercut (85%) which corresponds to a reservoir pressure of 2600 psia. The result is an

    overall recovery of 15.1 MMSTB vs. 13 MMSTB, or an increased recovery of 16%.

    0

    5000

    10000

    15000

    20000

    25000

    30000

    0 1 2 3 4 5 6

    Time (yrs)

    Oil

    Rate(STB/D)

    Boosted

    Cum Oil = 15.1 MMSTB

    Unboosted

    Cum Oil = 13 MMSTB

    Table 1: Pump Performance Over Time

    Figure 16: Oil Rate Vs. Time

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    4.4 Pump Operational Considerations

    To operate in a subsea environment, the pump must be marinized and designed to withstand external

    pressures of approximately 1600 psia. The most frequent operational issue is seal failure which requiresintervention using service vessels equipped with Remotely Operated Vehicles (ROVs) to conduct repairs.

    An umbilical must be installed to deliver power to the pump and significant voltage losses will occur in the

    line. The actual operating efficiency of the pump will be significantly less than calculated in the simulation

    because of the voltage losses in the umbilical and in the pump motor.

    4.5 Additional Multiphase Flow Considerations

    While the multiphase pump improves recovery and eliminates the need for a satellite platform, a number of

    operational issues involving multiphase flow are introduced. The Taitel-Dukler (1976) flow regime mapindicates that slug flow is the predominant flow regime throughout the producing life. A slug catcher

    located on the host platform must be sized to receive large slugs associated with long flowlines. Statistical

    analysis applied to the Scott (1986) slug length correlation indicates that the 1/1000 slug length, that is the

    longest slug of 1000 occurrences, is 3557 feet (221 bbl) and occurs at the highest (initial) flow rate.

    Should severe slugging occur, a larger slug catcher will be required. The Pots (1985) method suggests

    severe slugging at the riser base is likely for all cases in this example. This occurs when the length of theliquid slug exceeds the length of the riser causing liquid to accumulate at the riser base trapping gasupstream until the flowline pressure is high enough to drive the slug out of the riser. This results in

    unstable production rates and pressure control problems at the separator. Severe slugging can be mitigated

    by means of riser base gas lift injection with gas supplied from the topsides or through a mechanism thattransfers in-situ pipeline gas to a point above the riser base (Sarica and Tengesdal, 2000).

    The formation of emulsions at watercuts in the range up to about 60% is also an issue. The viscosity of

    emulsions are significantly greater than oil or water alone and is calculated using the (Woelflin, 1942)correlation. The higher viscosity increases the frictional pressure losses in the flowline and reduces pump

    efficiency as shown in the pump performance table for the 50% watercut case.

    Finally, a detailed flow assurance study must be performed to ensure that that the temperature in the

    flowline does not fall below the cloud point for wax deposition or below the hydrate formation temperature.The low ambient temperature along the flowline (38 F) and a swift water current (2ft/s) leads to significant

    forced convection and heat loss especially at low rates when the fluid velocity is the lowest. It is thereforenecessary to insulate the line and in this case 1 thick insulation having a conductivity of 0.1 BTU/hr/ft/F

    is sufficient to avoid hydrate formation. Still, it may be necessary to run a separate line to the pump outlet

    to perform pigging operations in order to remove hydrate or paraffin buildup that may occur during shut-inand start-up operations.

    5.0 Conclusions

    Multiphase pumps have emerged as a viable alternative to conventional separation, pumping and

    compression. Significant cost savings can be realized through the reduction of conventional equipment.

    Additionally, the use of multiphase pumps can increase recoverable reserves, especially in remote operatingenvironments. A variety of multiphase pumps technologies have been developed and the two most

    promising types, twin-screw and helico-axial, have been incorporated into multiphase flow simulation.

    Special considerations surrounding multiphase pumping operations include the need to handle producedslugs, flow assurance issues and pump operability.

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    6.0 References

    Beran, W.T.: On the Threshold Subsea Multiphase Pumping, Journal Of Petroleum Technology, pg

    326 (April, 1995).Caetano, E.F, R.M. Silva , R.G. da Silva, R.M.T Camargo and G. Rohlfing: Cooperation on Multiphase

    Flow Pumping, paper presented at the Offshore Technology Conference (May 1997).

    Cooper, P., et al.: Tutorial on Multiphase Gas-Liquid Pumping, presented at the 13th

    International PumpUsers Symposium, Houston (March 5-7, 1996).

    Dal Porto, D.F, Larson, L.A.: Multiphase Pump Field Trials Demonstrate Practical Applications for the

    Technology, SPE paper 36590 presented at the Society of Petroleum Engineers (SPE) AnnualTechnical Meeting, Houston (Oct. 6-9, 1996).

    Egashira, K., S. Shoda, T. Tochikawa and A. Furukawa: Backflow in Twin-Screw-Type Multiphase

    Pump, SPE paper 36595 presented at the Society of Petroleum Engineers (SPE) Annual

    Technical Meeting, Denver (Oct. 6-9, 1996).Giuggioli, A., M. Villa, G. De Ghetto, P. Colombi: Multiphase Pumping for Heavy Oil: Results of a Field

    Test Campaign, SPE paper 56464 presented at the Society of Petroleum Engineers (SPE) Annual

    Technical Meeting, Houston (Oct. 3-6, 1999).

    Guevara, E.: Evolution of Multiphase Pumping in Venezuela, presentation given at the Texas A&MMultiphase Pump User Roundtable, Houston (May 6, 1999).

    Jaggernauth, J.U. Brandt and D. Muller-Link: Offshore Multiphase Pumping Technology - Identifying theProblems; Implementing the Solutions - Part 1, paper presented at the SPE/NFP EuropeanProduction Operations Conference, Stavanger, Norway (April 16-17, 1996).

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    About the Authors

    Mack Shippen is a Petroleum Engineer at Schlumberger-Baker Jardine in Houston, TX where he provides

    user support, training and consulting for multiphase flow simulation software. He is currently serving aschair of the SPE Reprint on Offshore Multiphase Production Operations. Shippen holds B.S. (1999) and

    M.S. (2001) degrees in Petroleum Engineering from Texas A&M University, where his research focused on

    the development of a neural network model for predicting liquid holdup in two-phase horizontal flow.

    Dr. Stuart L. Scott is an Associate Professor of Petroleum Engineering at Texas A&M University where

    he conducts research on a variety of aspects of multiphase flow including compact separation, multiphaseleak detection and multiphase pumping. Scott holds a B.S.(1982) degree in Petroleum Engineering, an

    M.S.(1985) degree in Computer Science and a Ph.D.(1987) degree in Petroleum Engineering all from The

    University of Tulsa. He is currently the chair of the Production Committee for the ASME Petroleum

    Division. Before joining Texas A&M, he was an Assistant Professor at Louisiana State University and alsoworked nine years for Phillips Petroleum.