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Lecture15:SubseaSubsea Flow line Design, Transient Flow
& Terrain Slug Prediction
Arun S Chandel
Assistant Professor. . .
09997200339
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This lecture focuses on Flow lines andSlugging
w
Slu in
Riser
slug
Downwardpipe
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Flow lines tie fields back to a productionplatform in shallower waters
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Any vertical undulation in flow line w ill allow one
w w w r r
The erratic regime that results from gas liquidflow slippage between phases is known as slugflow
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Slug accumulation: the liquid can not flowout of the riser due to low velocity
Riser
slug
Downwardpipe
Slug accumulation
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Slug production: liquid eventually flow sinto separator w ith a high velocity w ithlittle or no gas production.
Downwardpipe
Slug production
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d) Gas blowout large volume of gas surge intoe separa or a g ve oc y w e or no
liquid flow into separator
Downwardpipe
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The possibility of occurrence of slug canbe predicted using Pots number
g ZRTW
)1(
lgl
ss
HgLMW
ss = Pots number
gW lW, = gas and liquid mass flowrate
Z = gas compressibility factorR = universal gas constant
T = pipeline temperature
gM = gas molecular weightg = acceleration due to gravity
l = average qu o up ns e t e p pe ne
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Slug length prediction is done byempirical correlation
5.0=Brill et al
ms
sl = length of slug, ft
D = diameter of pipe, inch
m = m x ure ve oc y, s
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Slug frequency is determined by usingempirical correlations
2.12.1
6.2120226.0
+
= msl
s VU
f
Greskovich and Shrier2.1
25276.79
0226.0
+=V
f ms mg
gsls
ls
UU
U
+
=
D = diameter of pipe, inch
slU = super icia iqui ve ocity, t s
mV = mixture velocity, ft/ s
sg = super c a gas ve oc ty, t s
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Slug frequency is determined by using
He wood and RichardsonZabaras
2.125276.790434.0
+=gD
V
Df ms
(sin75.2836.06.212
0226.025.0
2.12.1
+
+
= sl VU
gsls
ls
UU
U
+
=
mVgD
D = diameter of pipe, inch
sl = super c a qu ve oc y, s
mV = mixture velocity, ft/ s
sg = super c a gas ve oc y, s
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Several options are available to eliminateterrain-induced slugging
Favourable pipeline bathymetry: Upward flowline is better in reducing slugging
Gas-lift riser: Severe slugging can be mitigated by injecting
gas at the riser base
characteristics from slug flow to churn andannular flow .
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Several options are available to eliminateterrain-induced slugging
Topside chocking: Size and frequency of slugging can be reduced
Subsea se aration: Severe slugging can be eliminated by
separating gas and oil at the bottom of the seaand then allowin oil and as to flow throu h
different
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In summary, flow line should be designedw ith consideration for flow assurance
Slugging is a severe problem forcontinuous production for later life of a
available to predict slugging
Various mechanisms are available toreduce slugging problem