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This article was downloaded by:[Ecopetrol]On: 6 March 2008Access Details: [subscription number 777765763]Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Petroleum Science and TechnologyPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713597288
Drag Reducing Agents in Multiphase Flow Pipelines:Recent Trends and Future NeedsB. A. Jubran a; Y. H. Zurigat b; M. F. A. Goosen ca Department of Aerospace Engineering, Ryerson University, Toronto, Ontario,Canadab University of Jordan, Amman, Jordanc School of Science and Technology, University of Turabo, Puerto Rico
Online Publication Date: 01 November 2005To cite this Article: Jubran, B. A., Zurigat, Y. H. and Goosen, M. F. A. (2005) 'DragReducing Agents in Multiphase Flow Pipelines: Recent Trends and Future Needs',Petroleum Science and Technology, 23:11, 1403 - 1424To link to this article: DOI: 10.1081/LFT-200038223
URL: http://dx.doi.org/10.1081/LFT-200038223
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Petroleum Science and Technology, 23:1403–1424, 2005Copyright © Taylor & Francis Inc.ISSN: 1091-6466 print/1532-2459 onlineDOI: 10.1081/LFT-200038223
Drag Reducing Agents in Multiphase FlowPipelines: Recent Trends and Future Needs
B. A. JubranDepartment of Aerospace Engineering, Ryerson University,
Toronto, Ontario, Canada
Y. H. ZurigatUniversity of Jordan, Amman, Jordan
M. F. A. GoosenSchool of Science and Technology, University of Turabo, Puerto Rico
Abstract: In this paper, recent work on drag reducing agents in single and multiphaseflow pipelines is reviewed. Focus is placed on theories of drag reduction, the influenceof drag reduction agent types, and hydrodynamic and heat transfer characteristics offlows in the presence of drag reducing additives. Questions are raised, shortcomingsare assessed, and future research needs are outlined.
Keywords: drag reducing agents, heat transfer, multiphase flow, flow conditioner
INTRODUCTION
Drag reduction in pipe flow using polymeric drag reduction agents (DRAs)is a problem of great practical engineering interest because DRAs reducepumping power and increase piping system capacity. DRAs have been usedin several engineering systems, such as district heating and cooling, oil pro-duction and transportation pipelines, and others. Its first commercial use wasin the 1.2 m diameter Trans-Alaskan Pipeline in 1979, where a 50% dragreduction was achieved, thereby increasing the capacity of the pipeline from1.45 to 2.1 MBPD (Burger et al., 1982). This resulted in eliminating theneed for installing two pumping stations, which were planned to achieve the
Received 4 March 2004; accepted 23 April 2004.Address correspondence to B. A. Jubran, Department of Aerospace Engineering,
Ryerson University, 350 Victoria Street, Toronto, Ontario, Canada, M5B 2K3. E-mail:[email protected]
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1404 B. A. Jubran et al.
mentioned increase in capacity. Since that time, the DRAs have been usedin many petroleum product pipeline installations, such as the Iraq-Turkey oilpipeline and Oseberg Field in the North Sea (Berge and Solvik, 1996). Thus,the use of DRAs has the following advantages:
1. Increased pipeline capacity (throughput).2. Savings in pumping power.3. Pressure reduction with the associated reductions in pipe thickness and
pressure surge.4. Reduction in pipe diameter in the design phase as well as the number or
size of pumping facilities.
The result of DRA application is a reduction in systems’ overall costs.One further advantage of using drag reducing agents is that the DRAs canbe implemented immediately or temporarily, giving high operational flexibil-ity. Typical dosage rates for 10–30% flow improvement in oil pipelines are1–2 ppm of polymer per injection site. Berge and Solvik (1996) found thatthe required DRA-injection rates for multiphase flows were four times higherthan those needed for stabilized crude oil. This was attributed to the highershear degradation that resulted from the higher degree of flow turbulencein the multiphase system. The performance of DRAs is measured using theeffectiveness defined by:
effectiveness (ε) = �Pwithout DRA − �Pwith DRA
�Pwithout DRA(1)
The performance of DRAs is affected by several factors, such as pipediameter, temperature, fluid viscosity, and the presence of paraffin and/orwater. Comparisons of effectiveness and costs for new and conventional DRAsare shown in Figures 1, 2, and 3 (Berge and Solvik, 1996). Over a 14-yearperiod (between 1980 and 1994) the effectiveness of drag reducing agentshad increased 14 times.
The aim of this paper is to review recent work on drag reduction insingle and multiphase flow in pipelines. Focus is placed on theories of dragreduction, the influence of drag reduction types, and hydrodynamic and heattransfer characteristics of the flows in the presence of DRAs. Questions areraised, shortcomings are assessed, and future research needs are outlined.
THEORIES OF DRAG REDUCTION
Drag reducing agents (DRAs) are applied in pipelines with turbulent flow,hence, they are not effective in laminar flows. The reduction is achieved by theinteraction between the polymer molecules and the turbulence componentsof the flow. Polymers tend to stretch in the flow and absorb the energy in thestreak, which in turn stops the burst that produces the turbulence in the coreand results in a reduction in turbulence (Lester, 1985; Mizunuma et al., 1996).
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Drag Reducing Agents in Multiphase Flow Pipelines 1405
Figure 1. Comparison of conventional gel-type DRA and new generation type.
Figure 2. Performance comparison of new generation type and conventional gel-typeDRA.
Figure 3. Cost comparison of conventional gel-type DRA with new generation typeDRA.
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Thus, the principal effect of DRAs is to reduce the velocity fluctuations inthe normal direction and Reynolds stresses thereafter. Cationic surfactants areanother class of DRA which form rod-like micelles. Under shear stress, mi-celles line up in the direction of flow and build the so-called shear-inducedstate, which leads to a damping of radial turbulence and a subsequent re-duction in pressure loss. The various theories used to explain drag reductionphenomena are summarized by Kostic (1994) (see Table 1).
The existence of multiphase flow (oil/gas and oil/water/gas mixture) inpipelines is common in the oil and gas industry. This is due to the fact that oiland gas wells are drilled far away from the separation site, which necessitatestransport by multiphase pipeline flow. Drag reducing agents have been usedfor a long time to lower the friction component of the pressure in a single-phase flow during the transport of oil or gas in pipelines. However, recentlyit has been shown that DRAs are also effective in multiphase flow and workvery well on all components of pressure drop: frictional, accelerational, andgravitational (Dass et al., 2000). This is because of the DRA’s ability tomodify the flow pattern, which will be discussed later in this paper.
Drag reduction phenomena in multiphase flow are still far from beingwell understood in spite of the numerous investigations. This is due to thedependence of such phenomena on a large number of parameters, such as oilviscosity; pipe diameter; liquid and gas velocities; composition of oil, suchas the wax content, pipe surface roughness, water cut, pipeline inclination,DRA concentration, types of DRA; shear degradation of DRAs, temperature,and pH (Kang and Jepson, 2000).
DRAG REDUCING AGENTS
Drag reducing agents (DRAs) are high molecular weight, long chain poly-mers, such as polymethacrylate (PMMA), polyethyleneoxide (PEO), andpolyisobutylene (PIB). DRA polymers commonly used are x-olefin polymersand copolymers of very high molecular weight. A new generation of dragreduction agents is now available commercially. In general, the new DRAis characterized by high polymer content. The active component is still apolyalphaolefin polymer with a fast dissolution rate and a slow degradationrate. Moreover, they are characterized by low viscosity and are much easierto handle. Berge and Solvik (1996) reported field results in crude oil and mul-tiphase flows using the new generation DRA, which is an emulsified powderproduct with a polymer content of 20–25%, as compared to conventionalgel-type product with polymer content of 5–8%. They reported that the newDRA tends to be four times more effective than the conventional gel-typeDRA, with cost savings of 25%. Table 2 summarizes drag reducing additivesand their properties, while Table 3 lists the drag reduction and heat transferbehavior as reported by Kostic (1994).
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Tabl
e1.
The
orie
sof
drag
redu
ctio
nph
enom
ena
The
ory
Des
crip
tion
Shea
rth
inni
ngO
rigi
nally
itw
assp
ecul
ated
that
near
-wal
l-la
yer,
byvi
rtue
ofsh
ear-
thin
ning
,m
ayha
veex
trem
ely
low
erfr
ictio
nco
effic
ient
than
pure
solv
ent.
Lat
erth
isth
eory
was
disc
ount
edsi
nce
itw
aspr
oved
that
shea
r-th
inni
ngfr
ictio
nis
som
ewha
tlo
wer
,bu
tno
tne
arly
that
ofdr
ag-r
educ
tion
fric
tion.
Vis
co-e
last
icity
and
norm
al-s
tres
ses
Thi
sm
ayw
ell
beth
em
ost
unfo
rtun
ate
theo
ry.
Dra
g-re
duci
ngpo
lym
erso
lutio
nsar
evi
scoe
last
ican
dsh
owth
eno
rmal
-str
ess
diff
eren
ces,
but
for
conc
entr
atio
nsex
trem
ely
high
bydr
ag-r
educ
tion
stan
dard
s.V
ery
dilu
teso
lutio
nsdo
not
exhi
bit
any
mea
sura
ble
elas
ticity
,no
rch
ange
ofvi
scos
ityfr
ompu
reso
lven
t,st
illth
eyar
eve
ryst
rong
drag
redu
cers
.A
lso,
visc
oela
stic
,cr
oss-
linke
dpo
lyac
rylic
acid
(Car
bopo
l)so
lutio
nsdo
not
show
any
drag
-red
uctio
n,ex
cept
for
shea
r-th
inni
ngef
fect
.It
may
wel
lbe
that
visc
oela
stic
itydo
esno
tpl
ayan
ym
ajor
role
indr
agre
duct
ion,
but
ism
erel
yan
acco
mpa
nyin
gpr
oper
tyof
som
edr
ag-r
educ
tion
fluid
s.It
iskn
own
that
both
visc
oela
stic
and
non-
elas
ticflu
ids
may
prod
uce
drag
-red
uctio
n.M
olec
ular
“str
etch
ing”
Gre
atly
exte
nded
linea
rm
acro
mol
ecul
esin
shea
rdi
rect
ion
inte
rfer
ew
ithtu
rbul
ence
,pr
ovid
ing
ast
iffe
ning
effe
ct,
thus
redu
cing
fric
tion
drag
.O
ther
spo
stul
ate
that
mol
ecul
aren
tang
lem
ents
are
resp
onsi
ble
for
inte
rfer
ing
with
and
enla
rgin
gth
esu
blay
ered
dies
.So
me
have
argu
edth
atm
acro
mol
ecul
es’
elas
ticpr
oper
ties
and
cont
inuo
usde
form
atio
n,lik
ea
“yo-
yo”
effe
ct,
are
resp
onsi
ble
for
dam
ping
smal
ltu
rbul
ent
eddi
es,
stor
ing
and
reco
veri
ngot
herw
ise
diss
ipat
edtu
rbul
ent
ener
gy.
How
ever
,fo
rex
trem
ely
dilu
teso
lutio
nsit
seem
sun
likel
yth
atsu
cha
hypo
thes
isco
uld
beva
lid.
Dec
reas
edtu
rbul
ence
prod
uctio
nSo
me
rese
arch
ers
sugg
est
that
poly
mer
addi
tives
inte
rfer
ew
ithth
epr
oduc
tion
oftu
rbul
ence
,an
dth
atth
ere
duct
ion
phen
omen
aar
eno
tdu
eto
turb
ulen
cedi
ssip
atio
n,bu
tar
edr
iven
byre
duce
dge
nera
tion
oftu
rbul
ence
.Si
nce
the
two
have
tobe
inba
lanc
e,th
eir
role
sm
aybe
easi
lym
ista
ken.
(con
tinu
ed)
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Tabl
e1.
(Con
tinu
ed)
The
ory
Des
crip
tion
Dec
reas
edtu
rbul
ence
diss
ipat
ion
Tur
bule
nce
ener
gydi
ssip
atio
nvi
afin
est
eddi
esis
grea
tlyre
duce
d(s
uppr
esse
d)by
addi
tives
inte
rfer
ence
,to
anex
tent
equa
lto
the
drag
-red
uctio
n,w
hile
larg
ered
dies
and
larg
e-sc
ale
flow
inst
abili
tyar
epr
esen
t(s
till
turb
ulen
tflo
w),
but
with
diff
eren
tan
dm
ore
favo
rabl
est
ruct
ure.
Vor
tex
stre
tchi
ngIt
ispo
stul
ated
that
resi
stan
ceto
vort
exst
retc
hing
redu
ces
the
mix
ing
and
ener
gylo
sses
.It
isfu
rthe
rsh
own
that
dilu
tepo
lym
erso
lutio
nsm
ayha
veth
ousa
nds
oftim
eshi
gher
exte
nsio
nal
visc
osity
than
the
stea
dy-s
tate
visc
osity
,w
hich
may
have
ast
rong
influ
ence
ondr
ag-r
educ
tion
mec
hani
sm,
belie
ved
topl
aya
maj
orro
lein
are
gion
just
outs
ide
the
lam
inar
subl
ayer
(5<
y+
<50
).N
on-i
sotr
opic
prop
ertie
san
dtu
rbul
ence
Sinc
evi
scos
ityis
shea
r-ra
tede
pend
ent
and
the
shea
r-ra
teis
dire
ctio
nal,
the
solu
tion
stru
ctur
ebe
com
esan
isot
ropi
c;he
nce
visc
osity
(inc
ludi
ngdy
nam
ican
dhi
gher
-ord
erst
ress
coef
ficie
nts)
has
tobe
anis
otro
pic:
for
shea
rth
inni
ngflu
ids,
itis
low
erin
the
flow
dire
ctio
nan
dhi
gher
incr
oss-
flow
dire
ctio
ns,
thus
supp
ress
ing
cons
ider
ably
the
cros
s-flo
wflu
ctua
ting
velo
city
com
pone
nts
(esp
ecia
llysm
all-
scal
eed
dyflu
ctua
tions
).L
amin
ariz
atio
nof
turb
ulen
tflo
wT
urbu
lenc
eis
the
“was
tefu
l”di
ssip
atio
nof
fluid
ener
gyvi
ath
efin
est
turb
ulen
ted
dies
,th
usit
dire
ctly
incr
ease
sfr
ictio
ndr
ag.
The
refo
re,
drag
redu
ctio
nis
adi
rect
mea
sure
ofpa
rtia
lflo
wla
min
ariz
atio
n.B
yde
finiti
on,
turb
ulen
ceim
plie
sra
ndom
fluct
uatio
nsan
den
ergy
diss
ipat
ion,
othe
rwis
eflo
win
stab
ility
will
have
som
eor
derl
yse
cond
ary
(and
unst
eady
)flo
wpa
ttern
s.U
nans
wer
edqu
estio
ns:
•D
oes
visc
oela
stic
ityha
vean
ydi
rect
rela
tion
with
turb
ulen
tdr
agre
duct
ion?
•Is
influ
ence
ofw
all
cruc
ial
sinc
epo
lym
ers
may
prof
ound
lym
odif
yje
tsan
dfr
eetu
rbul
ence
?•
Wha
tis
the
influ
ence
ondr
agre
duct
ion
ofin
tern
alan
dex
tern
albo
unda
ryla
yers
and
how
can
conc
epts
beun
ified
?•
Why
is“O
nset
”of
drag
redu
ctio
npr
esen
tw
ithso
me
but
not
all
drag
-red
ucin
gflu
ids?
•W
hydo
addi
tives
prod
uce
the
max
imum
fric
tion
and
heat
-tra
nsfe
rre
duct
ion
asym
ptot
es,
but
cann
otfu
llyla
min
ariz
eflo
w(U
ltim
ate
Dra
gR
educ
tion)
?•
Why
isth
eas
ympt
otic
heat
-tra
nsfe
rre
duct
ion
stro
nger
and
occu
rsfo
rhi
gher
poly
mer
conc
entr
atio
nth
anfr
ictio
ndr
ag?
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Tabl
e2.
Dra
gre
duci
ngad
ditiv
esan
dth
eir
prop
ertie
s
Type
ofad
ditiv
eC
hara
cter
istic
prop
ertie
s
Hig
h-po
lym
ers
—Po
lyet
hyle
neox
ide
(the
best
)—
Poly
isob
utyl
ene
(oil-
solu
ble)
—Po
lyac
ryla
mid
e—
Car
boxy
met
hylc
ellu
lose
Mac
rom
olec
ules
—hi
gh-m
olec
ular
wei
ght
(106
orhi
gher
),lin
ear
stru
ctur
e,w
ithm
axim
umex
tens
ivity
,ex
celle
ntso
lubi
lity.
Soap
and
surf
acta
ntag
greg
ates
Low
-mol
ecul
ar-w
eigh
tal
kali-
met
alan
dam
mon
ium
soap
mol
ecul
esfo
rmag
greg
ates
or“m
icel
les”
inlo
ng-c
hain
s.Fi
bers
—A
sbes
ton
—N
ylon
—W
ood
pulp
Asb
esto
sfib
ers
are
extr
emel
ylo
ng(h
air-
like)
.N
ylon
fiber
sar
esh
orte
r(l
engt
h-to
-dia
met
erra
tioab
out
50).
Woo
dpu
lpsu
spen
sion
sin
wat
erre
duce
turb
ulen
tfr
ictio
n.D
rag
redu
ctio
nis
less
infib
er-g
assu
spen
sion
s.
Solid
-liq
uid
part
icle
s—
Tho
ria
—Sa
ndan
ddu
stpa
rtic
les
—D
ropl
ets
inga
ses
Pneu
mat
icsy
stem
sha
vehi
gher
flow
rate
sw
hen
dust
-lad
enth
anw
ithcl
ean
air
only
.Su
spen
sion
ofth
oria
inw
ater
show
drag
redu
ctio
n.E
ven
drop
lets
inga
ses
redu
cefr
ictio
n.
Oth
erna
tura
lso
urce
sN
atur
algu
ms
(lik
egu
ar),
alga
e,an
dba
cter
iaus
ually
prod
uce
copi
ous,
high
-mol
ecul
ar-w
eigh
tpo
lysa
ccha
ride
.Pr
inci
pal
prop
ertie
sof
drag
-red
ucin
gad
ditiv
es•
Ext
ende
dle
ngth
and/
orsu
ffici
ent
mas
s(i
nert
ia)
toin
terf
ere
and
supp
ress
turb
ulen
tflu
ctua
tions
,pa
rtic
ular
lytr
ansv
erse
ones
.•
Rig
idity
and/
orel
astic
ityto
supp
ress
and
abso
rbtu
rbul
ent
fluct
uatio
ns.
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Tabl
e3.
Kno
wn
fric
tion
and
heat
-tra
nsfe
rbe
havi
orof
drag
redu
cing
fluid
s Cha
ract
eris
ticph
enom
ena
Fric
tion
fact
orH
igh
fric
tion
drag
redu
ctio
nfo
rve
rysm
all
conc
entr
atio
nsgi
ves
afr
ictio
nre
duct
ion
of40
%,
whi
ch,
with
incr
ease
ofpo
lym
erco
ncen
trat
ion,
reac
hes
the
limiti
ngas
ympt
otic
valu
eup
to80
%.
Hea
ttr
ansf
erSt
rong
erhe
at-t
rans
fer
redu
ctio
nth
anfr
ictio
ndr
agre
duct
ion;
over
90%
ofco
rres
pond
ing
New
toni
anva
lues
for
the
limiti
ngas
ympt
otic
case
.G
ener
ally
,th
isph
enom
enon
isno
tus
eful
,as
incr
ude-
oil
pipe
lines
.In
cont
rast
,he
attr
ansf
eris
incr
ease
din
boili
ngan
din
lam
inar
flow
thro
ugh
non-
circ
ular
duct
s.E
ntra
nce
leng
ths
Muc
hlo
nger
than
the
corr
espo
ndin
gN
ewto
nian
valu
es,
onth
eor
der
of10
0an
d50
0hy
drau
licdi
amet
ers
for
hydr
odyn
amic
and
ther
mal
entr
ance
leng
ths,
resp
ectiv
ely.
Tra
nsiti
onto
turb
ulen
ceSm
ooth
ertr
ansi
tion
from
lam
inar
totu
rbul
ent
flow
,as
oppo
sed
toab
rupt
tran
sitio
nof
New
toni
anflu
ids.
Als
o,hi
gher
tran
sitio
nal
Rey
nold
snu
mbe
rva
lues
(muc
hhi
gher
than
2000
,of
ten
5000
orhi
gher
).In
som
eca
ses
the
“ons
et”
ofdr
ag-r
educ
tion
isen
coun
tere
d.M
ean
velo
city
profi
les
Flat
ter
velo
city
profi
les
(in
cent
ral
regi
on)
than
the
solv
ent
alon
e.T
hat
isqu
iteth
eop
posi
tefr
omth
ein
fluen
ceof
pipe
roug
hnes
son
the
profi
le.
Tur
bule
nce
stru
ctur
eFl
uctu
atin
gv′ v
eloc
ityco
mpo
nent
isre
duce
d,w
hile
axia
lco
mpo
nent
u′ i
sle
ssaf
fect
ed;
thou
ghso
me
resu
ltsar
eco
nflic
ting.
Spac
ing
betw
een
larg
e-sc
ale
slow
-str
eaks
ism
ore
than
doub
led,
and
time
betw
een
the
“bur
sts”
(flui
dlu
mps
)ej
ecte
dfr
omth
ew
all
regi
onis
incr
ease
dte
n-fo
ld.
Oth
erC
avita
tion
isof
adi
ffer
ent
char
acte
ran
dis
ofte
ngr
eatly
redu
ced.
Ext
ensi
onal
flow
sth
roug
hpo
rous
med
ia(a
nap
plic
atio
nin
enha
nced
-oil-
reco
very
)an
dje
tflo
ws
have
diff
eren
tch
arac
teri
stic
sth
anin
pure
solv
ent.
Seve
ral
othe
rbe
havi
ors
ofm
ore-
conc
entr
ated
poly
mer
solu
tions
,su
chas
die-
swel
l,W
eiss
enbe
rgro
d-cl
imbi
ngef
fect
,tu
bele
sssi
phon
,in
vers
ese
cond
ary
flow
,et
c.ar
em
arke
dly
diff
eren
tfr
omN
ewto
nian
flow
s.
1410
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Drag Reducing Agents in Multiphase Flow Pipelines 1411
Generally, higher molecular weight polymers perform much better thanidentical but lower molecular weight polymers. A major drawback of polymersolutions is the degradation in high shear flows. This degradation is causedby the pump and piping system. Injecting the polymers downstream of thepipeline booster pumps can minimize this effect. Choi and Kasza (1989) re-ported the dependency of degradation on the flow temperature. They foundthat dilute polymer solutions tend to degrade rapidly at 87.8◦C while nodegradation was experienced at 7.2◦C. Moreover, they reported a drag reduc-tion of 50% for one month of circulation.
Kwack and Hartnett (1982) investigated the effect of degradation on thefriction factor and heat transfer in a recirculating flow system. They observedno effect of DRA degradation on the friction factor, but there was an effect onthe heat transfer. The degree of degradation was presented using the criticalWeissenberg number. High concentrations were used to make up for thedegradation. The effectiveness obtained was very much dependent on thetype of drag reducing agent used.
Sitaramaiah and Smith (1969) reported experimental results on drag re-duction in turbulent flow using several acrylamide based polymers. Theycompared their effectiveness with that of polyethylene oxides and found thatdrag reduction increased with higher molecular weight, concentration andflow rate for all polymers approaching values of 70–80%. The main conclu-sion was that low-salt content solvents should be used for better efficiencieswhen polymers with ionic groups are used as fluid-friction reducers. The se-lection of the drag reduction agent was very much related to the applicationunder consideration and the cost.
Virk (1975a, 1975b) and Hoyt (1984) identified two asymptotic, additive-intensive flow regimes of zero and maximum drag reduction that envelopea third polymeric regime wherein additives’ properties exert certain influ-ences. The polymeric regime, based on Prandtl-Karman (P-K) coordinates,consisted of two extremes of flow behavior called types A and B. Type Awas a family of additive solutions that produced a “fan” of friction factorsegments which radiated outward from a common “onset” point on the P-Klaw (Figure 4) (Virk et al., 1997). Type B included a variety of additives, suchas polyelectrolytes and fibers, with a ladder of segments on the P-K law.
Wahl et al. (1982) reported field experimental results on two drag re-ducing agents to increase the capacity of crude oil pipelines. The pipelinestested varied in diameter and length, and were in the range of 8–48 in and 12–167 km, respectively. Two DRAs were used: CDR drag reducer and a modi-fied drag reducer that is a more viscous polymer solution. The performance ofthe modified drag reducer increased by approximately 10-fold, that is, 2 ppmof the modified polymer gave the same level of performance as 20 ppm ofthe standard drag reducer for a pipe of 8-in diameter and 4–5 fold for a 48-indiameter pipe. The most important conclusion of their work was that high per-formance, low concentration modified polymers were very attractive for off-shore production operations where space and deck loading are critical factors.
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1412 B. A. Jubran et al.
Figure 4. (a) Type A “fan” for collapsed conformation of B1120, in 0.3 N NaCL(b) type B “ladder for extended conformation of B1120, in 0.0003 N NaCl.
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Drag Reducing Agents in Multiphase Flow Pipelines 1413
The effect of surface roughness of the pipe on drag reduction usingdifferent types of DRAs was reported by Derrule and Sabersky (1974) andBewersdoff and Berman (1987). Derrule and Sabersky observed that whenpolyethelyne oxide was used as the surface roughness of the pipe was in-creased, drag reduction also increased. Bewersdoff and Berman (1987) ob-served no change in the drag reduction effectiveness for rough pipe whenpolyacrylamide was employed for both smooth and rough pipes. A summaryof effectiveness for different types of DRAs is shown in Table 4.
HYDRODYNAMICS OF PIPE FLOW IN THE PRESENCE OFDRAG REDUCING AGENTS
Drag reducing agent performance is very sensitive to any shear generatedin the flow, as it results in the degradation of the agent. The hydrodynamiccharacteristics of the flow, such as turbulence, single pass or recirculatoryflow, and single phase or multiphase flow have a significant impact on dragreduction effectiveness. Reddy (1986) observed a reduction in effectivenessin recirculatory flow compared to turbulent rheometer and single pass flows.This was attributed to the adverse effect of pipe fittings on the flow of poly-mer solution and the rapid degradation in recirculatory flow. This degradationwas generated by the resulting shearing effects, which increased as the pipingnetwork became more complex. They further developed empirical correla-tions that could be used for the prediction of drag reducing effectiveness ofpolymers in recirculatory flow systems.
Gyr and Tsinober (1997) concluded that drag reducing fluids are essen-tially non-Newtonian in the turbulent flow state and generally Newtonian inmany laminar flows. They presented a critical discussion of the momentumdeficit of drag reducing flows and a simple unequivocal demonstration forthe claim that the drag reduction phenomena in a number of fluid systemsare of rheological nature. Berge and Solvik (1996) reported that, in general,a higher degree of fluid turbulence resulted in a higher drag reduction. If thisis to be related to the Reynolds number (Re), then this implies increasing ve-locity and decreasing viscosity. They reported that when the DRA dissolvedrapidly in the fluid, it resulted in a modified structure of the turbulence and,hence, better performance.
Su and Gudmundsson (1994) presented the basic equations used for thecalculation of the total pressure drop in perforated pipe flow as applied tohorizontal wells. They divided the pressure drop into two components: re-versible and irreversible. The reversible pressure drop was due to accelerationas more fluid entered the wellbore through perforations, while the irreversiblepressure drop was due to friction and mixing effects. They computed the ac-celeration terms using both momentum and energy equations. Their compu-tations showed that the acceleration terms were about one-third higher whenthe momentum equation was used compared to that obtained when the energy
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Tabl
e4.
Perf
orm
ance
and
appl
icat
ions
ofva
riou
sty
pes
ofdr
agre
duci
ngag
ents
Con
cent
ratio
nD
rag
redu
cing
agen
tsPr
oper
ties
App
licat
ions
Flui
ds(p
pm)
Eff
ectiv
enes
sR
efer
ence
s
CD
Rpo
lym
er(w
ater
solu
ble
poly
mer
s)In
ject
ion
conc
entr
atio
n,w
t%10
%;
solv
ent
flash
poin
t,PM
,60
◦ C;
dens
ity,
g/cm
3
0.81
4,K
=23
0Pa
.s
Hor
izon
tal-
oil
pipe
line,
(fiel
dte
sts)
,di
amet
er48
-in
Oil,
sing
leph
ase
5,10
,20
6–23
%B
urge
ret
al.
(198
0)
CD
Rpo
lym
ers
Inje
ctio
nco
ncen
trat
ion,
wt%
10%
;so
lven
tfla
shpo
int,
PM,
60◦ C
;de
nsity
,g/
cm3
0.81
4,K
=23
0Pa
.s
Hor
izon
tal-
oil
pipe
line,
(fiel
dte
sts)
,di
amet
er8,
12,
and
48-i
n
Oil,
sing
leph
ase
10,
20%
14–2
3%W
ahl
etal
.(1
982)
Mod
ified
CD
RIn
ject
ion
conc
entr
atio
n,w
t%10
%;
solv
ent
flash
poin
t,PM
,60
◦ C;
dens
ity,
0.81
4,K
=28
0Pa
.s
Hor
izon
tal-
oil
pipe
line,
(fiel
dte
sts)
,di
amet
er8,
12,
and
48-i
n
Oil,
sing
leph
ase
5,2%
23–4
6%W
ahl
etal
.(1
982)
Gua
rgum
(GM
),X
anth
angu
m(X
M),
Poly
acry
lam
ide
(PA
M),
Car
boxy
met
hylc
ellu
lose
(CM
C),
and
asbe
stos
fiber
(AF)
Hor
izon
tal
wat
erpi
pelin
e,di
amet
er1-
in,
Re
=20
,000
to60
,000
Wat
er,
sing
leph
ase
250–
1500
ppm
17%
for
CM
C,
37%
for
GM
,40
%fo
rX
M,
33%
for
PAM
,and
28%
for
AF
Red
dy(1
986)
Oil
solu
ble
DR
AH
oriz
onta
l10
-cm
diam
eter
pipe
line
Mul
tipha
se,
oil/g
as20
and
50pp
m82
%fo
rsl
ugflo
wan
d47
%fo
ran
nula
rflo
w;
slug
freq
uenc
yde
crea
sed
sign
ifica
ntly
with
addi
tion
ofD
RA
Kan
gan
dJe
pson
(200
0)
GE
M(D
eter
gent
)H
oriz
onta
l2.
5–10
cmdi
amet
erpi
pelin
esSi
ngle
crud
eoi
l10
–500
ppm
10%
(2.5
and
5cm
dia.
),35
%(7
.5cm
dia.
)an
d50
%(1
0cm
dia.
)
Man
sour
and
Asw
ad(1
989)
New
gene
ratio
nD
RA
Em
ulsi
fied
pow
der
with
apo
lym
erco
nten
tof
20–2
5%
Hor
izon
tal
14-i
ndi
a,9.
5m
iles,
28in
dia,
75m
iles
Sing
lecr
ude
oil,
mul
tipha
seflo
w10
–100
ppm
70%
,ne
wge
nera
tion
DR
A;
50%
,co
nven
tiona
lD
RA
Ber
gean
dSo
lvik
(199
6)
1414
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Drag Reducing Agents in Multiphase Flow Pipelines 1415
equation was used. Moreover, they conducted experimental investigations ona perforated pipe with 144 perforations, geometrically similar to the wellborecasing. They found that the total pressure drop consisted of 80% wall friction,15% mixing effects, and 5% pressure drop due to acceleration.
It is interesting to note here that most of the work carried out so far onperformance of horizontal wells only considered the friction component ofthe total pressure (Dikken, 1990; Landman, 1994). Little work has been doneon drag reduction other than that used by friction (Dass et al., 2000). Themain outcome of this work was that the semi-empirical relationship developedfor pipe junction in hydraulics cannot be used for flow in horizontal wellsbecause the flow ratio and perforation diameters are different.
The effect of pipe diameter on the performance of the drag reducing agentis an important parameter which cannot be accounted for through Reynoldsnumber (Re) as was done for Newtonian fluids. A good account of the effectof diameter on drag reduction fluids was shown in the work reported by Sellinand Ollis (1983) and Matthys (1991). Matthys pointed out that the effect ofthe diameter must be included in an additional parameter that is necessary forthe prediction and characterization of friction in the non-asymptotic regime.However, Re may be used provided the viscosity of the solvent rather thanthe viscosity of the actual solution is used in the calculation of Re. Therationale behind this is that very dilute solutions tend to have a viscosity thatis independent of the shear rate in the high shear rate regime. However, if theviscosity is much larger than that of the solvent, then the approximation usingsolvent-based Re will be justifiable, particularly when the drag reductionobtained is small (Matthys, 1991). It was also reported that using smallerdiameter pipes to predict the performance of drag reduction in larger diameterpipes would not result in an accurate prediction (Jepson and Taylor, 1993).
Mansour and Aswad (1989) conducted an experimental investigation onthe effect of pipe diameter on DRA using a detergent called GEM in a re-circulating system. They reported that increasing the pipe diameter increaseddrag reduction, which was contrary to the findings of Lester (1985), whofound that increasing the pipe diameter decreased drag reduction. Jubranet al. (1992) conducted an experimental investigation on the effect of pipediameter on drag reduction of GEM in a recirculating system. They foundthat as the diameter of the thermoplastic pipe was increased, the drag re-duction decreased. Gasljevic and Matthys (1993) investigated the effect ofdrag-reducing surfactant additives on heat transfer exchangers. Their resultsindicated that increasing the diameter of the pipe from 2 to 52 mm resultedin a decrease in the drag reduction effectiveness. This effect was diminishedas Re increased beyond 105. The general consensus was that increasing thediameter of the pipe tends to decrease drag reduction effectiveness.
Another focus research area for drag reducing agents is their influenceas flow conditioners for two-phase flow in pipelines (i.e., effects on flowstructure). Again, the effect depends on the type of DRA used. Rosehartet al. (1972) investigated the presence of DRAs on the structure of single and
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1416 B. A. Jubran et al.
two-phase flow in horizontal pipes using visual observation. The addition ofDRAs to the flow did not change the slug transitional velocity and the slugfrequency at low polymer concentration. It was found to be the same forthe air/water system, but decreased at higher polymer concentration. Kanget al. (1998) investigated DRA in three-phase flow and oil/water/gas flow.They concluded that DRA was effective in reducing drag for different flowpatterns, such as stratified, slug, and annular flow. DRA was found to changethe flow patterns in horizontal pipes. Their results agreed well with those ofRosehart (1972) which showed that for three-phase flow DRA concentrationdid not affect the slug transitional velocity. The amount of drag reductionobtained is very much dependent on the type of flow regimes, as can be seenin Table 5.
Kang et al. (1999) conducted an experimental investigation on usingdrag reducer agents in multiphase flow in vertical pipes. In addition to theperformance of drag reduction, they reported flow conditioning due to DRAs.Adding DRAs shifted the transition to slug flow to higher superficial liquidvelocities. No effect was reported on the superficial gas velocity for theflow to remain in transition. The effectiveness of DRAs tended to decreasewith increasing superficial liquid velocity at the same superficial gas velocity(Table 5). Kang and Jepson (2000, 1999) reported experimental investigationson using drag reduction as a flow conditioning agent in multiphase pipe flows.They reported that DRAs did not change the slug transitional velocity, butdecreased the slug frequency and the height of the liquid film.
The effect of DRAs in two-phase flow in annular flow was investigatedexperimentally by Al-Sarkhi and Hanratty (2001, 2001a) and Soleimani et al.(2002). In air-water flow in a horizontal 9.53 cm diameter pipe the DRAinjection resulted in drag reduction of 48% with only 10–15 ppm DRA con-centrations (Al-Sarkhi and Hanratty, 2001). It was noted that the DRA’s ef-fectiveness is sensitive to the method of injection as well as the concentrationof polymer in the injected solution (maser solution). At maximum drag re-duction the annular flow became stratified with smooth interface. Also, forthe same DRA concentration in the flow there is an optimum concentration ofthe master solution that maximizes the effectiveness. A master solution con-centration of 1000 ppm of Percol 727 was suggested (Al-Sarkhi and Hanratty,2001). In the work of Al-Sarkhi and Hanratty (2001), two injection locationsalong the pipe were used: one 0.6 m upstream of the air-water mixing teein the liquid line and one 5.5 m downstream of the tee where two-phaseflow exists. It was observed that when the DRA is injected in the upstreaminjection location its effectiveness decreased with increasing the gas velocity,while it was insensitive when injection took place in the downstream injec-tion location. Thus, in annular flow the injection of DRAs should be in theliquid film.
To investigate the effect of diameter size on drag reduction in annularflow Al-Sarkhi and Hanratty (2001a) used a smaller diameter (2.54 cm) andachieved drag reductions of 63% compared with 48% for the 9.53 cm pipe
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Tabl
e5.
Eff
ect
ofdr
agre
duct
ion
agen
tfo
rdi
ffer
ent
flow
regi
me
Dra
gPi
peFl
owre
gim
eef
fect
iven
ess
incl
inat
ion
Flow
cond
ition
sR
efer
ence
Full
pipe
flow
(100
%oi
l)42
%H
oriz
onta
lpi
peD
RA
:10
ppm
,sup
erfic
ial
liqui
d:ve
loci
ty0.
25m
/sK
ang
etal
.(1
998)
Stra
tified
flow
Mor
eth
an40
%H
oriz
onta
lpi
peD
RA
:10
ppm
,su
perfi
cial
liqui
d:ve
loci
ty0.
03m
/s,
gas
velo
citie
s4–
7m
/sK
ang
etal
.(1
998)
67–8
1%H
oriz
onta
lpi
peD
RA
:75
ppm
,su
perfi
cial
liqui
d:ve
loci
ty0.
03an
d0.
11m
/s7
m/s
Kan
get
al.
(199
8)
90%
Ver
tical
pipe
Supe
rfici
alliq
uid
velo
city
:0.
5m
/s,
supe
rfici
alga
sve
loci
tyle
ssth
an4
m/s
Kan
get
al.
(199
9)
Slug
flow
50%
Ver
tical
pipe
Supe
rfici
alliq
uid
velo
city
:al
lve
loci
ties;
supe
rfici
alga
sve
loci
tym
ore
than
4m
/sK
ang
etal
.(1
999)
1417
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1418 B. A. Jubran et al.
used previously (2001). However, they found that compared with the largediameter pipe, a larger concentration of polymer is required in the smallerdiameter pipe to achieve the maximum drag reduction (10 ppm in 9.53 cmpipe and 30 ppm in 2.54 cm pipe). Differences in the resulting flow patternwere also observed. At the large diameter pipe the resulting flow pattern wasstratified with smooth interface while at the smaller diameter pipe the patternwas characterized by stratified-annular.
The study of Soleimani et al. (2002) investigated the effect of DRAs onthe transition form stratified to slug flow in a horizontal 2.54 cm pipe. It wasfound that at gas superficial velocities greater than 4 m/s the DRAs delaythe transition to slug flow; i.e., transition occurs at larger liquid holdup. AsDRAs are added into a stratified flow, a higher thickness of the liquid layeris required to initiate the slugging. In view of these findings, the additionof DRAs to multiphase flow has potential in flow conditioning. In general,limited work has been done on the role of DRAs as a flow conditioner andmore comprehensive work is needed.
Dass et al. (2000) reported a model to predict the components of pressuredrop in slug flow in a horizontal pipe. The aim of their work was to shedlight on the contributions of the frictional and acceleration components tototal pressure drop in horizontal slug flow in the presence of drag reducingagents. The predicted and experimental results showed good agreement. TheDRA was active in reducing both components of the pressure drop. It wasfound that the acceleration component was dominant and contributed morethan 80% of the total pressure. This increased significantly as the superficialgas velocity was increased. Both components of the pressure were reducedby 67% and 78% at DRA of 20 and 50 ppm, respectively. However, dragreduction was decreased as the superficial gas velocity was increased. It isinteresting to note in their study that the drag reduction obtained was mainlyin the acceleration component, indicating that the DRA was effective in themixing zone of the slug flow. Fan and Hanratty (1993) developed a model topredict the pressure drop across a stable slug flow. They treated the slug as ahydraulic jump and assumed that the pressure change takes place at the rearof the slug, where the change could be positive or negative.
Dukler and Hubbard (1975) developed a model to predict the frictionaland acceleration components of total slug pressure drop in an air-water sys-tem. The model assumed that the two phases within the slug body werehomogeneously mixed with negligible slip. The frictional component of thepressure was predicted using an equation similar to that used in a single phaseflow after modifying the density of the mixture and the friction factor. Theacceleration contribution was found by assuming a stabilized slug flow bodythat is receiving and losing mass at equal rates. The acceleration pressure dropwas then calculated from the force required to accelerate the liquid to slugvelocity. Vlachos and Karabelas (1999) investigated shear stress circumfer-ence in stratified flow. They used the momentum equations for both phasesto predict the liquid holdup, axial pressure gradient, and average liquid to
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Drag Reducing Agents in Multiphase Flow Pipelines 1419
wall shear stress, for the wavy stratified and stratified/atomization gas/liquidflow in a horizontal pipe.
HEAT TRANSFER IN PRESENCE OF DRAG REDUCING AGENTS
Drag reduction and heat transfer phenomena associated with drag reducingfluids are far from being well understood. Certain applications for the uti-lization of drag reduction agents necessitate a closer look at the heat transferprocess as well as the hydrodynamics process involved. However, it is inter-esting to note that in the case of using drag reduction in crude oil pipelines,the effect of these agents on the heat transfer process can be useful in keep-ing the loss of heat to the atmosphere to a minimum, while keeping the oilflowing at a lower pumping power. Moreover, in certain cases it brings downthe cost of thermal insulation of the pipelines.
Matthys et al. (1987) reported local and heat transfer measurements incircular tubes for suspensions of betonite and for a combination of betoniteand polyacrylamide in water for both laminar and turbulent flow. It was foundthat a viscosity model based on rheological measurements could represent theresults with a Newtonian relationship. It was also found that combining clayand polymer in a fluid produced viscoelastic solutions that were very sen-sitive to mechanical degradation. The local heat transfer results were wellcorrelated using the Colburn and Reynolds analogies, regardless of the con-centration of bentonite. Yoo et al. (1993) investigated experimentally the heattransfer characteristics of drag reducing polymer solutions in the thermal en-trance region of circular tube flows. The tests were conducted in two stainlesssteel tubes with length to diameter ratios of 710 and 1100. The fluids usedwere aqueous poly-acrylamide solutions of Separan AP-273 with a concen-tration range of 300 to 1000 wppm. The main finding of this investigationwas that the order of magnitude of the thermal entrance length of the maxi-mum drag reducing polymer solutions was much higher than that of turbulentNewtonian fluids in tube flows.
Gasljevic and Matthys (1994) reported local heat transfer results andfriction in the entry region of a circular pipe in the presence of a drag re-duction surfactant. Two entrance arrangements were used: a cone contractionand a wire mesh plug fitted to flatten the velocity profile. The main findingsof this work were the restructuring of the fluid itself due to high local en-ergy dissipation in the inlet region, and the stronger coupling between thehydrodynamic and thermal field development in the case of surfactant so-lutions than in the case of polymer solutions. The Reynolds analogy andthe direct relation between the friction and heat transfer coefficients werenot valid for drag reducing fluids; i.e., the Reynolds and Colburn analogieswere not valid for this type of flow. The reasoning behind this is still notclear and further research is needed (Matthys, 1991; Matthys and Sabersky,1987).
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Toh and Ghajar (1988) and Matthys (1991) observed that the thermalentrance and hydrodynamic lengths for drag reducing solutions were morethan that observed for Newtonian fluid flow with values of more than 20 and100 diameters, respectively.
Matthys (1991) carried out a comprehensive survey on the most impor-tant results and the current research needs of heat transfer, drag reduction,and fluid characterization for turbulent flow of polymer solutions in pipes.He investigated the problem of the reduction in convective heat transfer inthe presence of a drag reducing agent. It was pointed out that the reductionproduced by the addition of the agent was upset by the greater reduction pro-duced in the convection heat transfer. He attributed the lack of investigationson heat transfer of polymer solutions to the complexity of viscoelastic flows.This required a more demanding experimental set up to accurately record thedata. Matthys (1991) indicated the availability of macroscopic and correla-tion work for purely viscous non-Newtonian fluids, but not for viscoelasticnon-Newtonian fluids that cover flows with drag reduction agents.
Gasljevic and Matthys (1991) investigated the thermal and hydrodynamiccharacteristics of drag-reducing surfactant solutions in the entry region of thepipe, as well as after fittings. In addition, they provided an excellent literaturereview on the subject. It was reported that for surfactant solutions the frictioncoefficient and the Nusselt number were varying at the same rate beyond 300diameters. Heat transfer downstream of an elbow tended to increase over thatobtained for fully developed flow, but it did not degrade the fluid.
Gasljevic et al. (1993) conducted a comprehensive experimental investi-gation on the performance of various types of heat exchangers in the presenceof drag reducing surfactants in the working fluid. The working fluid used wasa solution of 2300 ppm of Ethoquad T/13 and 2000 ppm of NaSal in deionizedwater. Pressure and heat transfer measurements were taken at an operatingtemperature in the range of 312–319 K and fluid velocities of 0.2–3 m/s.They compared their results with those obtained when tap water was used asthe working fluid and concluded that the thermal and hydrodynamic charac-teristics are very much dependent on the geometry and flow conditions in theheat exchanger. It was also noted that a significant drag reduction could beachieved in heat exchangers with little penalty in the heat transfer process.
Gasljevic and Matthys (1993, 1991) reported an investigation to explorethe use of surfactant drag reducing additives to reduce the pumping powerin hydronic heating and cooling systems. Various issues were investigated,namely the matching of the additives with system characteristics, drag reduc-tion in fittings and valves, and the heat transfer process in the presence ofreduction agents. It was concluded that the use of drag reducing agents inheating and cooling systems can be implemented at a small cost and wouldlead to significant energy savings.
Kostic (1994) carried out a critical review on turbulent drag, heat transferreduction phenomena, and laminar heat transfer enhancement in non-circularduct flow of non-Newtonian fluids. The review outlined peculiar behaviors
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and applications of DRAs. Kostic reported that the underlying mechanismthat produces drag and heat reduction is far from being understood. He notedthat this should keep researchers busy for many years to come. Despite thelimited research to date on the heat transfer aspects of viscoelastic fluids,there was enough evidence to conclude that such fluids tend to enhance heattransfer in laminar non-circular duct flow. Moreover, he reported that flowlaminarization, due to flow-induced anisotropic fluid structure and properties,was the predominant factor for the reduction phenomena rather than fluidelasticity. On the other hand, fluid elasticity was responsible for laminar heattransfer augmentation. Hartnett and Kwack (1986) reported that for a polymersolution the reduction in friction was not accompanied by a reduction in heattransfer. For a comprehensive review of research work related to heat transferin the presence of drag reducing agents, see studies by Dimant and Poreh(1976) and Cho and Hartnett (1982).
CONCLUDING REMARKS
This paper has highlighted research conducted on drag reduction in single andmultiphase flows with particular reference to the oil industry. It has examinedwork related to theories of drag reduction, the influence of drag reductiontypes, and hydrodynamic and heat transfer characteristics of the flows in thepresence of a drag reducing agent. Moreover, it has raised questions andshortcomings that need answers, as well as pin-pointing potential areas thatneed further research.
Drag reduction phenomena and theories related to multiphase flow arestill far from being well understood. More work is needed in the areas ofshear degradation, and the effect of wax content, water cut, and pipe incli-nation on the performance of drag reduction in smooth and perforated pipeswith emphases on oil wells. Most of the work carried out on the performanceof horizontal wells consider only the friction component of the total pressurewithout taking into consideration the acceleration component. Limited workhas been done on the role of drag reducing agents as a flow conditioner, espe-cially for large pipe inclinations with a high water cut. Further fundamental,experimental, and analytical investigations are needed to better understandthe heat and hydrodynamic processes associated with drag reduction in sin-gle and multiphase flows, since the Reynolds and Colburn analogies are notvalid for drag reducing fluids.
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