3 puk eng 2012 leistritz

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8 Pumps, Compressors and Process Components 2012

Pumps

Screw pumps

Abstract

During the past two decades multi-

phase pumps experienced growing

acceptance. Especially twin screw

multiphase pumps which cover a wide

range of ow rates and pressures have

found many applications on ageing

and matured oilelds but also on re-

cent discoveries with high gas con-tent. Low installation costs go along

with small dimensions which makes

twin screw multiphase pumps parti-

cularly suitable for the installation on

offshore platforms.

Introduction

Since the rst discoveries and pro-

duction of abundant oil wells in the

middle of the 19th century, crude oil

and petroleum gas have been funda-mental sources of modern industrial

developments. As feed stock for the

chemical industry or source for the ge-

neration of electrical energy and fuel

for the dramatically increasing moto-

rization, oil and gas have considerab-

ly contributed to improved wealth in

many countries of the world. The stea-

dy rise of world population and the in-

dustrial growth in emerging econo-

mies results in increasing demand for

energy.

Powerful multiphase pumps for increased oil & gasproduction in the Gulf of Mexico

Jrg Narewski, Sven Olson, Hans Jrgen Schner, Dr. Michael Radke

However, manhood is since long

aware about the fact that the times

that hydrocarbons which are easily

available at low costs are over. Most

of the oil producing countries in the

world have reached their peak produc-

tion years ago and now face decrea-sing hydrocarbon reserves which do

not cover their demands. The biggest

consumers of energy are not always

large producers. However, successful

exploration opens access to new oil

and gas elds.

Production by region: Million

barrels daily world oil production

increased by 1.8 million b/d in 2010;

growth was broadly-based, with in-

creases in all regions except Europe &

Eurasia. Moreover, growth was broad-

ly split between OPEC and non-OPEC

countries. World oil consumption in-

creased by 2.7 million b/d; growth was

above average in all regions, although

Asia Pacic countries accounted for

the majority (54 %) of global consump-

tion growth. (Graphic: source BP)These new reservoirs, however, are

not easy to produce and the oil com-

panies are faced with many challen-

ges. Most of the remaining oil and

gas reserves of the world are located

close to the arctic circle, in the oceans

in shallow, deep or ultra-deep water,

in deserts and other not easily acces-

sible areas. Many of these areas are

not developed and a suitable infra-

structure must be created to allow

successful exploration and produc-

tion of these oil and gas elds. A large

growth in new oil and gas eld disco-

veries has been in South and Central

America. Particularly Mexico and Bra-

zil developed assets which will gua-

rantee sufcient national reserves for

many years.

A large number of todays oilelds

are maturing elds. The reservoir pres-

sure has decreased over the years and

articial lift by means of gas or water

injection or ESPs (Electrical Submer-

sible Pumps) must be used to bringthe well-ow to the surface and create

sufcient pressure to operate conven-

tional separation equipment. The use

of multiphase pumps with their abilityFig. 1: Production by region (Million barrels daily) and consumption by region (Million barrels

daily)

Fig. 2: Distribution of proved reserves in 1990, 2000 and 2010 percentage

(Graphic: source BP)


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Pumps, Compressors and Process Components 2012 9

Pumps

Screw pumps

to operate at very low well head pres-

sures can economically increase the

production life of matured wells.

Many oil producing countries have

not yet developed sufcient infra-

structures to use the associated gas

produced as feed stock, automotive

fuel, power generation or heating pur-

poses. This gas is still widely ared

or vented after separation and con-

tributes signicantly to the global

warming by releasing CO2

or even

worse CH4

emissions to the atmos-

phere. Most countries are taking sta-

tutory measures to ban all aring and

venting during the next few years.

Multiphase pumps contribute to the

successful achievement of this tar-get by transferring the untreated well

ow to centralized treatment facilities

were the petroleum gas can be econo-

mically processed.

The twin screw pump as multi-phase system

Twin screw multiphase pumps are ro-

tary positive displacement pumps of

double volute design. They are hydrau-lically balanced with no thrust loads

on the pump bearings. After entering

through the suction port of the pump

the ow splits to either side and is

pressurized within the screw packages

with opposed thread. The screws are

machined from single piece bar stock

for maximum stiffness in order to

maintain minimum shaft deection

under all operating conditions. They

are installed in the replaceable cast

steel casing insert. The surface of the

screws is nitrided for wear protec-tion. The torque from the drive screw

is transmitted to the idler screw via oil

lubricated timing gears. An external

lube oil system provides well tempe-

rated lube oil to the timing gears and

the heavy duty and lifetime optimized

tapered roller bearings which carry

the drive screws and the idler screws.

The bearing span is kept as short as

possible in order to minimize the shaft

deection.

There is no contact between pumpscrews and casing insert. To maintain

a clearance between the pump screws

and the casing insert under all opera-

ting conditions is a basic and essential

Fig. 4: Cut-a-Way of a twin screw multiphase pump

Fig. 3: Comparison between conventional handling and multiphase pumping


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design criteria for twin screw multi-

phase pumps.

The screw shafts are sealed by

double acting mechanical seals with

SiC vs. SiC seal faces on both product

and atmospheric side. An external

seal system in accordance with the

requirements of API Plan 54 provides

clean and cool seal oil to each seal. All

mechanical seals are installed on the

suction side of the pumps and hence,

exposed to suction pressure only.

A large multiphase productionsystem in the Gulf of Mexico

The Gulf of Mexico is historically the

most important area in North Ame-rica for providing oil and gas and raw

material in the petrochemical industry

to the USA and Mexico. From the start

with oil and gas production offshore

in the 1960s its importance is con-

tinuing to grow with new larger hy-

drocarbon deposits discovered every

year. Initially, shallow water reser-

voirs at water depth up to 100 m were

produced along the US and Mexican

coastlines. Development of new ex-

ploration and prospecting techno-logies made it possible to go deeper

and deeper. Today reservoirs at a wa-

ter depth of 3000 m can be economi-

cally produced. Despite the belief that

the Gulf would run out of hydro car-

bon deposits one day, actually more oil

and gas are discovered and made eco-

nomically possible to produce, thanks

to 3-D seismic imaging, directional

drilling and deep water trees and pro-duction manifolds.

In the Mexican territorial wa-

ters signicant ndings of oil and gas

have been done in the last 30 years.

The largest reservoir ever found in the

western hemisphere was Cantarel,

which only recently lost its rst place

to the pre-salt Tupi eld in Brazil. Be-

sides Cantarel there are other signi-

cant elds in the shallow water (up to

100 m) depth in Mexico. The giant Ku-

Maloob-Zaap eld started to develop

in the 1980s and 1990s. It is a large

complex of xed platforms in 6080 m

water depths. Some platforms are

wellhead platforms whereas others

have processing and power genera-

tion equipment. Also, an FPSO is an-

chored nearby and serves as an exten-

ded production and storage facility.The oil is typically heavy with an

API grade of 18 to 22 with signicant

amounts of gas produced as associa-

ted gas with the oil. The oil and some

Pumps

Screw pumps

Fig. 5: Platform locations and power distribution

Fig. 7: Completed multiphase pump skid be-

fore dispatch

Fig. 6: Completed multiphase pump skid in 3D


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gas is exported to shore from

pipelines. A lot of the gas is used

in power generation with gas tur-

bine driven pumps and compres-

sors and in the processing of the

crude oil. When the wells started

to ow initially, water injection

was used to maintain reservoir

pressure. As the wells were age-

ing gas lift was introduced. With

gas lift compressed natural gas

is sent down the annulus of the

well and through a gas lift valve,

the gas lightens the column of oil

in the production tubing to lift it

to the surface. For some time this

method of production is sufcient

to bring up the oil and providesenough pressure in the pipelines

to overcome line losses and the

arriving pressure of the rst stage

separator.

Gradually the gas lift is not

enough to recover the oil in the re-

servoir and bottom hole pressure

of well reaches a point where the

oil cannot any longer move from

the formation to the well bore.

At that moment there are

some few remedies left to savethe reservoir from abandonment

and one of these is the fast deve-

loping technique of multiphase

pumping.

In the case of the Ku-Maloob-

Zaap eld the production from

the wells were estimated to drop

very quickly and in the next few

years reach a point where they

would have to be abandoned. Af-

ter lengthy studies it was decided

by the Mexican State Oil Compa-

ny that three of the wellhead plat-

forms were going to be equipped

with multiphase pumps.

The objective was to be able

to continue production for many

years to come and delay the aban-

donment of the reservoir and dra-

matically increase the total re-

covery of hydrocarbons from the

formation.

The multiphase pumps pro-

positioned was analysed in detail.

Production curves were showing a

pressure draw down at the well-

head of 12 bar would have a signi-

cant positive impact on the bot-

tom hole pressure and the abilityof the wells to continuous produ-

cing. At this low well head pres-

sure the associated gas will ex-

pand signicantly which means at

pump inlet the gas fraction (GVF)

can be up to 97 % with the wells

sometimes intermittent liquid

production (oil and water) it was

necessary to provide the pumps

with a liquid recirculation system

to keep the pump primed at all

times even with long gas slugs co-ming from the wells. Each of the

three platforms have 24 produ-

cing wells tied to a common suc-

tion manifold which in turn is con-

nected to either ve or six of the

multiphase pumps, depending on

the platform. The pumps operate

in parallel driven by 1900 kW vari-

able frequency controlled electri-

cal motors. The speed of the mo-

tors which control the pumping

Fig. 8: Arrangement of the multiphase pumps on the platform deck in 3D


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capacity and thereby the pressure in

the suction manifold are automati-

cally set to follow the desired optimal

manifold pressure.

All pumps are packaged in modules,

including controls and instrumenta-

tion per the customer specication.

The packaging was done on the U.S.

Gulf coast and each pump module

was transported by barge to the plat-

form for direct installation. In addi-

tion to the pumps (16 in total), three

so-called E-buildings were supplied

which contains all the frequency con-

verters, automation, switchgear and

controls. The E-buildings are air condi-

tioned although each platform is spe-cied for unmanned operation.

Pump operating data and designdetails

The twin screw multiphase pumps in-

stalled on each of the three platforms

are designed for the following para-

meters:

phase ow with a minimum efciency

of 97 percent. The separated liquid is

collected in the reservoir of the liquid

management system. A recirculation

cessary. The volume of the reservoir of

the liquid management system is ad-

apted to the maximum expected gas

slug length specied by the customer.

Before dispatch all pumps were

subject to a witnessed hydrostatic

test and a witnessed factory accep-tance test.

The future

After completion and successful in-

spection of the skids and all accesso-

ries, they have been loaded on barges

for transport to their nal destinations

on the particular platforms. The instal-

lation at the three platforms and the

commissioning is scheduled for 2012.

Fig. 9

The pump casing is manufactured

from fabricated carbon steel with the

suction port on side and the discharge

port on top. All welds were subject to

extensive quality control by means of

non-destructive testing.Both pump screws are made from

carbon steel nitrided in order to mini-

mize wear. The replaceable casing in-

sert is manufactured from cast carbon

steel.

The construction materials for all

wetted and pressurized pump parts

meet the requirements of the NACE

Standard MR 0175 latest edition.

All pumps are equipped with a li-

quid management system (recircula-

tion system). These systems are loca-ted on the skid downstream the pump

discharge but within the skid limits.

During the pump operation liquid is

constantly separated from the multi-Fig. 11: Bare shaft multiphase pump during

testing

Fig. 12: Multiphase pump skids and electric

building loaded on a barge

Engine driven multiphase produc-

tion systems in the Gulf of Mexico

During the past years several twin

screw multiphase pumps have been

installed on offshore platforms in the

Fig. 10: P & ID of the liquid management system

volume equal to approx. 3.0 percent

of the actual ow rate is constant-

ly injected from the liquid reservoir

into both suction areas of the pumps.

During possible gas slugs this amount

of liquid is sufcient to ensure con-tinuous gas compression. The large

surface of the liquid reservoir contri-

butes to the quick heat dissipation

and renders additional cooling unne-

Pumps

Screw pumps


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Pumps, Compressors and Process Components 2012 13

Authors: Jrg Narewski

(Managing Director LeistritzPumpen GmbH),

Sven Olson President Leistritz

Corporation),

Hans Jrgen Schner (Mana-

ger Sales Multiphase Pumps

& Systems Leistritz Pumpen

GmbH), Dr. Michael Radke

(Member of Executive Board

Leistritz Aktiengesellschaft

US territorial of the Gulf of Me-

xico. Lack of electrical power on

these platforms required gas en-

gine driven equipment.

fer a mixture of oil, water and

gas with a GVF of 95 % at a ow

rate of 991 m/h and differential

pressure of max. 44 bar to a cen-

Fig. 13: twin screw multiphase pump with 630 kW gas engine

Fig. 14: Oil production platform in the Gulf of Mexico

Smaller footprints

Less equipment

Less weight

Lower capital costs

Quick amortization

Twin screw crude oil exportpumps on a platform in theGulf of Mexico

In 2012 four twin screw pumps as

heavy crude oil export pumps willbe installed on a production plat-

form in the Mexican sector of the

Gulf of Mexico. The units are gas

turbine driven and pumping hea-

vy crude oil with an API gravity

of 15 at a ow rate of 1,070 m/h

and 56 bar differential pressure.

The oil contains a small amount

of water, traces of H2S as well as

chlorides. Double acting mecha-

nical seals in the suction area of

the pumps and a seal oil supp-

ly system in accordance with APIPlan 54 safeguard an operation

without pollution of the atmos-

phere.

Conclusion

Twin screw multiphase pumps

and conventional twin screw

pumps are successfully used off-

Fig. 15: Gas turbine driven twin screw pump

shore in the Gulf of Mexico. The

increasing number of ageing and

maturing elds, the life exten-

sion of brown elds or the spe-

cial characteristics of green elds

will generate a consistent de-

mand for multiphase technology.

The versatile twin screw pumps

have a large operating window

and handle combinations of li-

quid and gas in any concentra-

tion and cover a large range of vis-cosities at ow rates up to 5,000

m/h and differential pressures up

to 150 bar. Capital and operatio-

nal expenditures are low for twin

screw multiphase pump installa-

tions and they contribute to the

protection of our environment by

eliminating the need for aring

and venting.An independent operator in-

stalled an twin screw multiphase

pump for a ow rate of 880 m/h,

a differential pressure of 19 bar

and a GVF of 97 %. The gas engineis rated at 630 kW. A liquid ma-

nagement system to safeguard

the operation during gas slugs is

an integrated part of the skid.

A large twin screw multiphase

pump was installed by a major in-

ternational operator on another

platform in the Gulf of Mexi-

co. The unit is designed to trans-

tralized separation facility. With

the liquid management system

and the 1,500 kW gas engine this

is one of the largest multiphase

pump skids ever built.The objectives to use twin

screw multiphase pumps versus

conventional equipment on both

applications were:

The reduction of the well pres-

sure to increase the oil recovery

The reduction of the gas lift re-

quirements

Pumps

Screw pumps

3 puk eng 2012 leistritz

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