spe-122829-pa

192 December 2010 SPE Projects, Facilities & Construction

A Conceptual Study of Finger-Type Slug Catcher for Heavy-Oil Fields

J. Mrquez, C. Manzanilla, and J. Trujillo, PDVSA Intevep

Copyright 2010 Society of Petroleum Engineers

This paper (SPE 122829) was accepted for presentation at the SPE Latin American and Caribbean Petroleum Engineering Conference, Cartagena, Bolivar, Colombia, 31 May to 03 June 2009, and revised for publication. Original manuscript received 19 February 2009. Revised manuscript received 23 December 09. Paper peer approved 20 January 2010.

SummaryThe gas/liquid-separation processes in heavy- and extra-heavy-oil fields are performed mainly with gravity conventional separators. However, the separation efficiency of this equipment depends on the operating conditions, an appropriate design, and the proper-ties of the fluids. Therefore, the separation efficiency is affected mainly by the high liquid viscosity, low pressures, and the low gas-flow rate that are present in heavy- and extra-heavy-oil fields. Additionally, these conditions increase the probability of slug-flow formation through pipelines, which causes operational problems, mainly in the separation process.

This situation raises the need to design a gas/liquid separator able to handle viscous liquid, reduce the effects of slug flow, and perform an efficient separation. There are different technologies that can help improve gas/liquid separation, among them the finger-type slug catcher. This technology is usually used in gas fields or light- and medium-oil fields as a flow conditioner and slug-flow mitigator. However, this paper has changed that focus toward considering a heavy-oil design.

This paper presents an improvement in the methodology of Sarica et al. (1990), predicting the dimensions of a finger-type slug catcher for heavy-oil fields. It is derived from the effect from the transition of stratified flow to nonstratified flow when the liq-uid phase is viscous and only considers slug-flow characteristics under normal flow; on the basis of the improvement, the required diameter and length of the finger are determined.

This improvement is used to design a finger-type slug catcher for heavy-oil fields in the Orinoco belt. An economic comparison against conventional separators is presented, demonstrating the finger-type slug catcher to be more economical than the conventional separator.

IntroductionMultiphase flow through pipelines in heavy-oil fields is a daily occurrence, and the slug-flow pattern is promoted because of the high oil viscosity, the low pressure, and the low gas flow. In fact, the envelope of slug flow in a gas/liquid flow-pattern-transition map is increased with an increase in liquid viscosity or liquid-flow rate. Pipelines transport the production streams to the processing facilities where the separator is the initial receiving process device. Separators could be affected by severe operational conditions caused by slug flow. Therefore, it is necessary to use an adequate gas/liquid separator to mitigate the slug-flow effects and perform an efficient separation.

Although several gas/liquid-separation technologies have been available for many years, a study was conducted to identify the more-suitable technologies for heavy-oil applications. This study concluded that conventional separators are widely used in heavy-oil-field developments and that there are preseparators that can be used as flow conditioners to improve the separation. However, the preseparators also could be used as a primary separator. Among the found technologies, there are conventional separators, slug catch-ers, T-junctions, ultrasonic equipment, and others, but through a selection process the finger-type slug catcher was chosen to make a conceptual design that considers the viscous-liquid effects.

The traditional design of conventional separators is based on typical residence time, depending on the oil density, and does not consider the liquid-viscocity effects on the rise velocity of gas bubbles entrained in the liquid. Even when considering the bubble velocity, traditional design derived simplifications do not reproduce accurately the hydrodynamic behavior of the gas/liquid separation in the equipment when the liquid is viscous.

The desired hydrodynamic behavior in a gas/liquid separator is achieved when the gas and liquid phases are stratified, but if slug flow arrives to the separator, the ideal situation is achieved when the effective area of flow is sufficiently increased to reduce the velocity and mitigate the slug affect. Thus, the inviscid Kel-vin-Helmholtz (IKH) instability criterion enables identifying if stratified flow can exist under the given conditions, including the pipeline geometry. On the basis of the IKH criterion that was used by Taitel and Dukler (1976), which is widely used in the oil industry to predict the stratified/nonstratified transition, Sarica et al. (1990) proposed a design methodology for sizing a slug catcher. However, according to Lin and Hanratty (1986) and Barnea (1990), the IKH criterion does not properly predict the transition when the liquid phase is viscous. On the other hand, Barnea and Taitel (1993) proposed a criterion called viscous Kelvin-Helmholtz (VKH) instability that considers the effects of the shear stress but not the interfacial-tension effects (i.e., the viscous effect is considered).

This paper proposes an improvement to the original methodol-ogy of Sarica et al. (1990) to design a finger-type slug catcher. The improvement considers the use of the VKH instability criterion proposed by Barnea and Taitel (1993). In this way, the diameter of the finger-type slug catcher is determined to guarantee stratified flow through the device. This methodology was applied to design a slug catcher for heavy oils, and an economic comparison against conventional separators is presented.

Selection of TechnologyOn the basis of a technological survey carried out by Manzanilla (2007), seven gas/liquid-separation technologies are identified that could work properly in a heavy-oil field. In the study, the following technologies were identified: conventional separator as the most used in heavy-oil fields, double-helix separator, auger separator, ultrasonic gas/liquid separator, T-junction, and slug catcher (con-ventional and finger-type). The general characteristics related to pros and cons of these technologies are given in the Table 1.

Derived from this survey, a preselection of two technologies is made on the basis of the available technical information (Table 1). Therefore, four of the technologies founddouble-helix, auger, T-junction, and ultrasonicwere rejected for the following reasons:

The design does not consider handling slug-flow conditions. There is no experience in Venezuelan oil fields with the

technology. The technology is in the experimental development stage. The technology operation is unstable.Thus, conventional separators and slug catchers were consid-

ered as the preselected technologies. The final selection inherent to these technologies was made using the criteria and solutions weighting method proposed by Vilchez (2008). Therefore, seven criteria and two solutions are considered. The criteria are priori-tized below according to the level of importance.

1. Capacity to handle viscous liquids (C1)2. Capacity to handle slug flow (C2)3. Separation efficiency (C3)4. Residence time (C4)

December 2010 SPE Projects, Facilities & Construction 193

5. Operational stability (C5)6. Complexity of construction (C6)7. Process control levels (C7)The criteria were evaluated hierarchically. The qualification

range was given between 1 and 7. The most important criterion (C1) obtained the greater weighting (seven points), and the less important criterion (C7) received the minimum value. The cor-responding weighting is shown in Table 2.

The solutions are conventional separator (S1) and slug catcher (S2), and because only two solutions are considered, the numerical qualifying scale will range from 1 to 2. Thus, each criterion (C1 through C7) assesses for each solution, and the highest value (2) is given to the solution that meets this criterion better (Table 3).

Derived from the assessment in Tables 2 and 3, the final value of each probable solutionconventional separator (PS1) and slug catcher (PS2)was calculated through the following equations:

PS C S C S C SC C C1 2 1 2 1 7 11 2 7= + + +... . . . . . . . . . . . . . . . . . . . . . (1)

PS C S C S C SC C C2 2 2 2 2 7 21 2 7= + + +... . . . . . . . . . . . . . . . . . . . . . (2)

Now, the values in Tables 1 and 2 are substituted into Eqs. 1 and 2 to obtain the algebraic value of each solution:

PS1 7 2 6 1 5 2 4 1 3 1 2 2 1 1 42= + + + + + + =* * , . . . . . . (3)

PS2 7 1 6 2 5 2 4 2 3 2 2 1 1 2 47= + + + + + + =* . . . . . . . (4)

According to the values of the probable solutions (PS1 and PS2), the applicable solution is PS2 (i.e., the slug catcher is the best solution to perform the gas/liquid separation in heavy-oil fields). Relative to this solution, a conventional or a finger-type slug catcher could be selected. According to detailed research, a conventional slug catcher is more expensive than a finger-type slug catcher (Vergara and Foucart 2007) designed for the same operational conditions; therefore, the conventional slug catcher is discarded and the finger-type slug catcher is selected.

TABLE 1CHARACTERISTICS OF SEPARATION TECHNOLOGIES

Separator Type Separation Principle scitsiretcarahC rotarapeS

Conventional horizontal Gravitational force It is commonly used for low gas/liquid ratios and heavy-oil fields Great sizes and weight

Retention time increased to high viscosity tcapmoC secrof lagufirtnec dna raehS xileh elbuoD

Technology in R&D stage Separation efficiency is moderate

tcapmoC ecrof lagufirtneC reguASusceptible to erosion and plugging

Separation efficiency is low Does not work in slug flow

sevaw cinosartlU cinosartlU Promotes bubbles agglomeration Generates mechanical vibration between 800 KHz and 20 KHz

Could be promoted cavitation phenomenon Reqiures high control levels Does not work in slug flow

Does not have experience in Venezuela Juntion T It is used as a preseparator device

Dynamic separation process Compact

Requires low control levels Separation efficiency is low

Finger-type slug catcher Gravitational lellarap ni sebut fo swoR ecrof It is commonly used as preseparator

Handles large amounts of liquid Few operational problems Requires low control levels

It is designed to handle slug flow Conventional slug catcher Gravitational fo rotarapeserp sa desu ylnommoc si tI ecr

It can handle large amounts of liquid Few operational problems Requires low control levels

It is commonly used in places with limited space It can be used as a gas-liquid-liquid separator

It is designed to handle slug flow

TABLE 2WEIGHTING OF CRITERIA

Criterion gnithgieW

C1 7 C2 6 C3 5 C4 4 C5 3 C6 2 C7 1


Finger-Type Slug Catcher. This slug catcher is defi ned as a gas/liquid separator that performs primary separation of gas and liquid and is commonly installed at the end the production lines (i.e., as the fi rst process equipment at fl ow stations). There are two main types of slug catchersconventional and fi nger.

Finger-type slug catchers function both as a gas/liquid separator and as a slug-flow mitigator. They are designed to stratify the gas and liquid phases and consist of four parts that are made mainly of pipeline materials (Fig. 1). The different areas are inlet header, separation, the gas- and liquid-outlet header, and they are shown in Fig. 1 and will be explained in the following.

The inlet header takes the incoming gas/liquid main stream, reduces its mixture velocity, and splits the main stream into a number of smaller streams according to the size of the separation pipe or finger. The inlet header should allow uniform distribution of flow rate to the separation area.

The separation consists of several pipes where gas/liquid sepa-ration is accomplished. Separation occurs because the diameter of pipes is made to ensure stratified flow into them. Required design of this part is a function of gas and liquid flow, fluid properties, and other operational conditions to be specified.

The gas-outlet header gathers the separated gas to send it to downstream processes. The liquid-outlet header gathers the sepa-rated liquid to send it to downstream processes.

Design MethodologyThe proposed conceptual design for a finger-type slug catcher for heavy oil is based on the methodology proposed by Sarica et al. (1990). The design requires information related to the characteristics of slug flow determined at the slug-catcher inlet-pipeline conditions.

This also requires calculations of liquid accumulation to obtain the main dimensions of the equipment: diameter and length.

The methodology assumes along with Sarica et al. (1990) the following:

When the liquid slug is produced, some of this liquid is spilled to the liquid film of the Taylor bubble because of the velocity dif-ference between the slug and the Taylor bubble. For this reason, the volume of liquid accumulation is less than that calculated.

It is supposed that before producing the liquid slug, the opera-tional holdup is the minimum. In other words, the liquid level into slug catcher is reduced when the Taylor bubble is produced.

These two assumptions provide a safety factor to the design of the equipment that slightly increases the slug-catcher dimensions. Another consideration is that the fingers must be in a horizontal position because negative or positive inclinations generate waves of high amplitude, producing early liquid carryover, and under this condition, additionally, the criteria to predict the stratified/no stratified transition do not work properly (Barnea 1990; Barnea and Taitel 1994).

The methodology is given for one finger, but can be adapted to more than one finger if the liquid distribution among the fingers is considered.

Slug-Flow Characterization. A proper design of a slug catcher requires predicting the characteristics of slug fl ow at the catcher inlet with the least possible uncertainty. In this sense, a review and selection of the best mathematical models and correlations to predict these characteristics for heavy oil was made. The character-istics include slug holdup, slug length, slug velocity, translational velocity or Taylor-bubble velocity, and slug frequency and basic

TABLE 3ASSESSMENT OF SOLUTIONS BY EACH CRITERION

noiretirC

Solution (C1) (C2) (C3) (C4) (C5) (C6) (C7)

S1Cn 2 1 2 1 1 2 1 S2Cn 1 2 2 1 1 2 1

Separation area

Inlet header

Gas-liquid flow

Gas-outlet headerSeparated gas flow

Separated liquid flow

Liquid header

Fig. 1Finger-type slug catcher.


parameters in multiphase fl ow. Some of these characteristics can be represented through a schema of a slug unit, such as that shown in Fig. 2. Selected mathematical models and correlations are described later.

The slug holdup is the fraction of a volume element in the two-phase flow field occupied by the liquid phase in the slug zone (Fig. 2) and is determined according to the liquid viscosity. If the viscosity is less than 500 cp, the holdup is calculated using the Gregory et al. (1978) correlation as

Hv

LLSM

=

+

1

18 66

1 39

.

.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (5)

The slug holdup for viscosity greater than 500 cp is determined using a correlation obtained in experiments carried out a 2-in.-test-loop facility at PDVSA Intevep. Lubrication oil and air were the testing fluids, and lubrication-oil viscosities from 500 to 1,300 cp were used. Data of slug-flow characteristics are collected through a combination of high-speed video camera in the viewing section and fast signal for pressure drops and wall pressure fluctuations. The holdup is measured with a set of quick-closing valves. The correla-tion is based on the Shoham (2000) model, and it is given by

H eLLSReL

= ( )1 0046 0 0022. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (6)

The holdup in the Taylor bubble (the film zone; see Fig. 2) is determined using the equation obtained by Shoham (2000) as

Hv v H

vLTB

TB L LLS

TB

=

( ) . . . . . . . . . . . . . . . . . . . . . . . . . . (7)

The gas-void fraction is the fraction of a volume element in the two-phase-flow field occupied by the gas phase in the slug zone. It is expressed using the following equation proposed by Beggs (1991):

S LLSH= 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (8)

The film length of the slug unit (Fig. 2) is predicted by use of a correlation developed from experiments conducted with a 2-in.-test-loop facility at PDVSA Intevep using lubrication oil (480 cp) and air as testing fluids. Slug-flow-characteristics data are acquired in the same manner as for Eq. 6. This correlation is based on the Taitel and Barnea (1990) model and is given by

LF SLSL SG

=

+

0 03650 8606

.

ReRe Re

.

. . . . . . . . . . . . . . . . . . . (9)

The slug-length (Fig. 2) correlation is obtained by inserting LF into the correlation developed by Shoham (2000) to predict the film length. This correlation considers only hydrodynamic slug flow.

Lv HS

SL

SL SG

L LLS=

+

0 03650 8606

.

ReRe Re

.

vvSL1

. . . . . . . . . . . . . . . . . . . (10)

The next correlations require the estimations of velocities, such as mixture velocity and liquid, and gas superficial velocities. Also, prediction of the translational velocity (Taylor-bubble velocity) and the drift velocity is required. Translational velocity is composed of a superposition of the bubble velocity in stagnant liquid (i.e., the drift velocity and the maximum velocity in the slug body), and it is given by the Nicklin (1962) correlation as

v cv vTB M D= + , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (11)

where c is derived according to the flow type. If the flow is laminar, c = 2. If it is turbulent c = 1 2. . If flow lies between laminar and turbulent, the Xiao et al. (1990) correlation is used:

c

L

CL

CL

L

=

+

+

+

2 0

1

1 20

12 2

.

ReRe

.

ReRe

. . . . . . . . . . . . . . . . . . . . . . (12)

The drift velocity is the velocity of a phase relative to a surface moving at the mixture velocity and is calculated depending on the pipe inclination, as follows.

For pipes slightly inclined, the drift velocity is estimated by the Bendiksen (1984) correlation as

v v vD D D= ( ) ( ) + ( ) ( )horizontal verticalcos sin . . . . . . . . . . . . . . (13)The following correlation is used for horizontal pipes:

v gDD( ) =horizontal 0 54. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (14)And for vertical pipes,

v gDD( ) =vertical 0 35. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (15)The slug frequency is the rate of recurrence of the slug through

the pipelines and is estimated using the correlation proposed by Colmenares et al. (2001) as

f vLS

TB

U

= , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (16)

where slug unit length is given by

L L LU S F= + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (17)

Other parameters of interest for slug-flow characterization are the liquid and gas instantaneous flow at the inlet of the catcher. They are calculated using the Miyoshi et al. (1988) model.

For the liquid,

Q v A Hp LLSinsL Mins= . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (18)

And for the gas,

Q v A Hp LLSinsG Mins= ( )1 . . . . . . . . . . . . . . . . . . . . . . . . . . . (19)Prediction of Liquid Accumulation. The liquid accumulation in the slug catcher is estimated by applying a liquid mass bal-ance between the inlet and outlet of the equipment (Sarica et al. 1990), as

Liquid-inputmass rate

Liquid-discharge

mmass rate

Liquid-accumulationmass rate

=

.

. . . . . . . . . . . . . . . . . . . . . . . (20)

Slug zone Film zone

VLLS

VGLS

VGTB

VLTBHLTB

LULFLS

VTB

Fig. 2Schematic for a slug unit (Colmenares et al. 2001).


The liquid-input mass rate is determined through the Miyoshi et al. (1988) model, to calculate the liquid instantaneous flow, whereas the liquid-discharge mass rate is related to the outlet liquid flow that depends on the flow-control-valve size.

On the basis of the liquid mass balance presented by Sarica et al. (1990), the accumulated liquid volume is given as,

V t Q Lv

v H A Qsp STB

M LLS paccum acum dis= = max . . . . . . . . . . . . (21)

Finger-Type-Slug-Catcher Sizing. The most important param-eter in the slug-catcher design is the diameter of the slug-catcher fi ngers, which is calculated to obtain stratifi ed fl ow. In this sense, models to predict the transition from slug fl ow to stratifi ed fl ow are necessary, such as the IKH instability criterion, the VKH instability criterion, and the Taitel and Dukler (1976) model.

To predict the transition, Sarica et al. (1990) used the IKH criterion presented by Taitel and Dukler (1976). However, in this work it is proposed to use the VKH criterion presented by Barnea and Taitel (1993) to determine the transition from slug flow to stratified flow because it better predicts transition for a larger range of viscosities (100 to 5,000 cp). The criterion is expressed as

v K R R g AAh

Gtran V L G G LL G

L G

P

L +( )

LL

1 2/

. . . . . . . . . (22)

In this expression, KV is a correction factor given as

KC C

g AAh

VV IV

L G P

L

L

=

( )

12

cos d

d

. . . . . . . . . . . . . . . . . . . . (23)

The VKH criterion provides minimum diameter from which stratification is obtained. When the actual gas velocity is less than the transition gas velocity, stratified flow is expected. Thus, the catcher diameter should be bigger than the minimum diameter to receive the incoming liquid. The catcher diameter is determined by increasing minimum diameter until stratified flow into the equip-ment is ensured. Also, one must consider the incoming-liquid flow, available space for installation, and the costs.

For a given gas superficial velocity, there is a transition liquid holdup and an operation liquid holdup. The first is given by the maximum liquid superficial velocity for stratified flow and is cal-culate using the VKH criterion. The second is given by the average operation flow rates of liquid and gas at the slug catcher. The differ-ence between these two holdups will provide the available volume to handle the accumulation of liquid in the slug catcher; thus, the catcher length for the designed diameter is given as

L VA H HL L

fingeraccum

finger trans oper

=

. . . . . . . . . . . . . . . . . . . . . . (24)

Results and DiscussionThe proposed methodology is used to design a finger-type slug catcher for a heavy-oil field in the Orinoco belt. The designed catcher was compared economically with the design of a con-ventional horizontal separator that is commonly used in the field. The field data for the design are given in Table 4. The calculated procedure to design the catcher using the methodology presented in the preceding is explained in following.

Procedure To Design a Finger-Type Slug Catcher. To obtain the main dimensions of the fi nger-type slug catcher, a computational procedure is elaborated that is derived from the equations presented previously.

1. As input data are required operational conditions, properties of the fluid and the geometry of the inlet pipeline are required, such as temperature, pressure, API gravity, gas- and liquid-flow rate, and pipeline diameter and roughness (Table 4).

2. The gas-liquid-flow pattern into the inlet pipeline of the slug catcher is determined using the model proposed by Barnea and Taitel (1993). In this sense, a gas/liquid flow-pattern map is generated for the operational conditions given in Table 4. In the map, the only areas represented are intermittent flow, annular flow, and stratified flow. According to Fig. 3, the flow pattern in the inlet line (pipe diameter is 10 in.) of the slug catcher is located in the intermittent-flow area as a yellow point called operation point (pipeline).

3. As detailed in the mapping (Fig. 3), the flow pattern is slug flow. Therefore, a slug-catcher design is necessary. Without slug flow, of course, the slug catcher is not necessary. The procedure to determine the main dimensions of the slug catcher (diameter and length of fingers) is the following.

a. Slug-flow characteristics are calculated according to correla-tions and models discussed in this paper (Eqs. 5 through 17).

b. The diameter and quantity of fingers are assumed such that diameter must be large enough that the quantity of fingers must be greater than one. In this scenario, four fingers are considered and an initial diameter of 10 in.

c. Gas- and liquid-flow rates through each finger are determined considering an even flow distribution among the fingers.

d. The finger diameter is determined using the VKH crite-rion through an iterative process in which the finger diameter is increased until obtaining a stratified flow. Thus, minimum diameter is obtained when the transition curve between stratified flow and intermittent flow is reached. The point that represents this condi-tion is shown superimposed on the transition curve in the Fig. 4 (green point), and it is called transition point. The minimum diameter is increased to the next pipeline commercial diameter to guarantee stratified flow. In this scenario, the operation point (blue point) of the finger-type slug catcher is shown in Fig. 4, which corresponds to a finger-design diameter calculated at 20 in.

e. The catcher length is determined by use of the accumulated liquid volume and calculated diameter. In this scenario, the length is 26.2 ft.

f. Finally, the catcher weight is determined considering all pipe sections, such as inlet header, separation area, gas-outlet header, and liquid-outlet header. The finger-type slug catcher weight is 7,887 lbm.

Economic Comparison. This subsection presents an economic comparison between the designed catcher and a conventional horizontal separator that is commonly used in fi eld applications and is sized under the same conditions as those of the catcher. It is necessary to clarify the cost estimation. It should be used only as a reference point because it is made for a conceptual design.

Cost estimation is based on fabrication cost because opera-tion costs are considered comparable because they operate under the same working principle (gravitational sedimentation), use the

TABLE 4FIELD DATA

61 IPATemperature (F) 7295 Pressure (psig) 105.80

QL 55.343,41 )DPB( QG 655,8 )DFSMM(

56.24 )%( W&SB

G 55.0 01 ).ni( pD


same process-control systems, and will require regular cleaning because of solids accumulation. Therefore, the fabrication cost of the catcher and conventional separator is estimated relating to the vessel weight and steel price, as Powers (1990) proposed:

Cost Weight kg Steel price USDestimated kg= ( ) ( ). . . . . . . . . (25)The horizontal conventional separators diameter is 72 in., and its

length is 20 ft. The separator weight is approximately 10,214 lbm.Steel price is considered approximately 30 USD. Using this

referenced price and Eq. 25, the cost of each separator is estimated (Table 5).

According to Table 5, the fabrication cost of the finger-type slug catcher is 23% less than that of the horizontal conventional separator.

ConclusionsOn the basis of the methodology of criteria and solutions weight-ing proposed by Vilchez (2008), the finger-type slug catcher was selected and designed as the separation technology for heavy-oil fields.

The slug-flow characteristics must be known to carry out a proper design for a finger-type slug catcher. Thus, various cor-relations and models are selected in a rigorous manner to predict slug-flow characteristics for heavy oil.

VKH HL/D=0.5 Operation point

Intermittent

10

10VsG [ft/s]

VsL

[ft/s

]

100

1

1

0.1

0.10.01

Stratified

Annular

Fig. 3Flow-pattern map for the inlet conditions of the catcher.

Fig. 4Flow-pattern map for the designed slug catcher.

Intermittent

10

10VsG [ft/s]

VsL

[ft/s

]

100

1

1

0.1

0.10.01

Stratified

Annular

VKH

Operation point Transition point

HL/D=0.5


This work proposed an improvement on the Sarica et al. (1990) methodology on the basis of the use of the VKH criterion to predict the stratified/no-stratified transition in a more rigorous way to determine the dimensions of a finger-type slug catcher to handle viscous liquids. This improvement allows performing a better design of the slug catcher to guarantee the segregation and separation of the phases while slug mitigation is achieved for a heavy-oil field.

Economic comparison demonstrates that the slug catcher costs approximately 23% less than the conventional separator. Therefore, it could be used as a separator in heavy-oil fields. However, further studies conducted in laboratory-scale tests and in fluid-dynamics sim-ulations have to be conducted before field applications are feasible.

Nomenclature API = API gravity A = cross-sectional area, m2 C = wave velocity fs = slug frequency, slugs/s g = gravity acceleration, m/s2 HLLS = liquid holdup in the slug zone HLTB = liquid holdup in the fi lm zone (Taylor Bubble zone) Kv = coeffi cient of stability L = Length, m Q = fl ow rate, m3/s Re = Reynolds number t = time, s = velocity, m/s V = volume, m3

Subscripts accum = accumulation D = drift dis = discharge f = liquid fi lm (Taylor bubble zone) G = gas ins = instantaneous IV = inviscid M = mixture gas-liquid max = maximum oper = operational p = pipe S = slug zone sG = superfi cial gas sL = superfi cial liquid TB = translational or Taylor-bubble zone trans = transition U = slug unit V = viscous

Greek Letters = specifi c gravity = inclination angle = density [kg/m3]

AcknowledgmentThe authors want to express our gratitude to Joe Bradford and Maite Bradford (Gazprom Latin America) and Alexis Gammiero

(PDVSA Intevep) for their help and collaboration in the structur-ing of this work.

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TABLE 5FABRICATION-COST ESTIMATION Separator Type Weight (lbm) Cost (USD)

00.818,532 00.788,7 rehctac guls epyt-regniFConventional separator 00.283,503 00.412,01


Xiao, J.J., Shonham, O., and Brill, J.P. 1990. A Comprehensive Mechanistic Model for Two-Phase Flow in Pipelines. Paper SPE 20631 presented at the SPE Annual Technical Conference and Exhibition, New Orleans, 2326 September. doi: 10.2118/20631-MS.

Jos Mrquez is currently a research and development support engineer at PDVSA Intevep, Los Teques, Venezuela. He joined PDVSA Intevep in 2002 and has been working on the develop-ment of phase-separation technologies and multiphase-flow modeling. He works for the flow assurance and phase sepa-ration research and development project of PDVSA Intevep, focusing on multiphase technologies for heavy-oil applica-tions. Also, he works in the engineering of surfaces facilities of a pilot project of in-situ combustion. He holds an ME degree from

Universidad de Los Andes (ULA), Venezuela, and an MSc degree from Universidad Central de Venezuela. Carlos Manzanilla is a mechanical maintenance supervisor for Nestle of Venezuela. He worked for PDVSA Intevep in the flow assurance and phase sep-aration research and development project from 2007 to 2008. Jorge Trujillo is currently a research and development associate engineer at PDVSA Intevep, Los Teques, Venezuela. He joined PDVSA Intevep in 2002 and since then has been working on the development of high capacity/high efficiency phase-separa-tion technologies and multiphase-flow modeling. He leads the flow assurance and phase separation research and develop-ment project of PDVSA Intevep, focusing on multiphase tech-nologies for heavy-oil applications. He holds an ME degree from Universidad Nacional Experimental Politecnica, Venezuela, and an MSc degree from La Universidad del Zulia, Venezuela.

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