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Upstream Research
Slugging in a Subsea Compact Separation System
Ed GraveFractionation & Separation Advisor Houston, TX USA
MCE Deepwater DevelopmentApril 8 & 9, 2014Madrid, Spain
Upstream Research
ExxonMobil Subsea Compact Separation SystemExxonMobil Upstream Research Company (URC) designed and is testing a compact separation system for application in 3000m water depth and internal pressures up to 690 barEM qualification philosophy is to qualify for a wide range instead of specific field conditions to reduce timeline of applicationRobust, flexible to inlet fluids, and scalable
API Gravity: 19˚‐38˚Oil Rate: 60 kBPD/trainGas Rate: 1250 – 4000 Sm3/dayWater Cut: 0‐90%Slug Size: 5m3
Currently being qualified at ProlabNL(3) Crudes with API 19˚, 28˚ & 38˚Scaled to 10‐15 kBPDMethane Gas at 45 barsGas Rate: 33‐497 Am3/hrWater cuts 10‐70%Slug Tests: 0.2 to 0.6m3 Upstream Research
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Simplified Schematic of ExxonMobil Subsea Compact Separation System
being tested at ProLabNL.
ExxonMobil’s Subsea Compact Separation System
OilURC Inlet Gas/Liquid Slug‐Catcher
URC Liquid/Liquid Pipe Separator and Level Controls
Inlet
Gas
Water
ASCOM Inline De‐sander
Cyclonic Inline Gas Polisher
Reject
Fast‐Acting MokveldSubsea Control Valve
Liquid Slug Generator
FMC‐CDS IEC tested at FMC separately
Aker CEC™
OiWMonitors
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ASCOM Hiper™ MixedFlow 2‐stage de‐oiling Hydrocyclones and Canty Oil/Water Monitors
Slugging in a Compact Separation SystemCompact Inline Separation devices do not perform well during slugging conditions
Very small residence time and buffer volumeNormally optimized for one phaseSensitive to change in fluid density (GVF) and flow rates…inlet momentum changes and potential collapse of the swirlHomogenous flow is desired
This results in lower separation performance with undesirable liquid entrainment and gas carryunderSlugging effects can propagate through other downstream equipmentSlugging effects can be minimized with sophisticated slug dampening control systems in combination with a flow conditioning device
Deliquidizer - Courtesy of FMC Technologies, Inc.
Ref: Hannisdal, et. al. 2012 OTC 23223
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Slugging in a Compact Separation SystemSubsea Compact Three Phase Separation System Studied the effects of hydrodynamic slugsStudied different size slugs and frequency to determine:
Effectiveness of ExxonMobil’s Subsea Slug Catcher in buffering slugsThrough CFDs air/water tests model fluid high pressure tests studied a number of proprietary designs. Final design more effective for liquid dominated servicesMinimize liquid carryover to the ASCOM Monoline on the gas outletReduce dramatic liquid rate fluctuations downstreamMeasure the liquid outlet GVF to downstream equipmentLiquid level control & hold-up
ASCOM MonolineLiquid CarryoverMeasure gas carryunder from bootLiquid level control
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Slugging in a Compact Separation SystemStudied different size slugs and frequency to determine:
ExxonMobil’s Pipe Separator The effect on oil-water separationChange on interface height and control. Effect on emulsion stability due to increased GVF and rate changesMeasure oil outlet GVFMeasure OIW & WIOLiquid level control & hold-up
Dynamic simulation based on a potential field case
Optimized control systemsIP around novel control system
Never the intention to validate dynamic model based on flow loop data
Due to pressure balance around a close loop systemNo oil/water pumps on dischargePreferred control system could not be implemented 6
Slugging in a Compact Separation System
Slug Generator at ProlabNL
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Slug GeneratorAllowed for controlled slug size feeding the system of various sizes: 0.1 to 0.6m3
Number and frequency could be controlledSplit flow possible with steady state flow and liquid slug volume
ExxonMobil’s Subsea Slug CatcherMain function to separate the gas and liquid phasesTemporary storage of liquids to buffer downstream equipment and maintain steady state conditionsIt did not consider the increase in flow rate tolerance of the downstream equipment as this was a test loopLimitations of a closed flow loop
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11:57:20 AM 11:59:20 AM 12:01:20 PM 12:03:20 PM 12:05:20 PM 12:07:20 PM
Level (mm)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Flow Slug Catcher outFlow Oil outLevel Slug GeneratorLevel Slug CatcherFlow water out
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Level (mm)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Flow Slug Catcher out
Flow Oil out
Level Slug Generator
Level Slug Catcher
Flow water out
Slugging in a Compact Separation SystemResults – Slug Catcher Medium Crude
API 28˚ 50˚C 20%WC – 0.4m3 Slug Auto Control
Slug ReleasedSlug Released
Fluid out of SC feed to PSFluid out of SC feed to PS
Oil out of PSOil out of PS• Slug catcher caught the slug effectively. • However, control valve released the slug
too quickly• Manual control of water outlet valve did
not help
API 28˚ 50˚C 20%WC – 0.4m3 Slug Manual Control
Manually opened water valveManually opened water valveRef: run 221M50SLmRef: run 221M50SLm
Ref: run 221M50SLaRef: run 221M50SLa Fluid out of slug generatorFluid out of slug generator
8 All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemResults – Monoline Medium Crude
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Level (mm) a
nd Gas flow
(m
3/h)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Purgeflow MonoLine
Level Slug Catcher
Gas flow System in
Gasflow MonoLine out
Slug ReleasedSlug ReleasedGas rate leaving boot through purge lineGas rate into monoline decreased during sluggingGas rate leaving boot through purge lineGas rate into monoline decreased during slugging
0.01
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12:37:50 PM 12:39:50 PM 12:41:50 PM 12:43:50 PM 12:45:50 PM 12:47:50 PM GVF
(%), Ve
locity (m
/s) a
nd Residen
ce time
(min)
Flow
(m3/h) and
Level (%
)
Time (hh:mm)
Level and flow vs Time
Flow Slug Catcher out
Filling Slug Catcher
GVF Slug Catcher out
Velocity Gas
Velocity Liquid
Residence time
GVF increases due under carry from additional turbulenceGVF increases due under carry from additional turbulence
Results – Slug Catcher Medium Crude• Liquid carryover rate to the Monoline during slug
trials were <2-3%LVF
• Decreased gas flow rate into Monoline due to liquid slug
• GVF in liquid leaving slug catcher remained fairly constant ~1%
Ref: run 221M50SLaRef: run 221M50SLa
Courtesy of Ascom Advanced Separation Company
ASCOM Monoline
9 All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemResults – Pipe Separator Medium Crude
12:37:50 PM 12:39:50 PM 12:41:50 PM 12:43:50 PM 12:45:50 PM 12:47:50 PM
Den
sity (k
g/m3)
Time (hh:mm)
Density Tracerco vs TimeSlug ReleasedSlug Released
API 28˚ 50˚C 20%WC – 0.4m3 Slug Manual Control
Interface level increased as the slug was releasedInterface level increased as the slug was released
Slug ReleasedSlug Released
• Interface level remains fairly constant with some effect on oil-water separation quality. WIO suddenly increased
• Note there’s a process delay and a smoothing function with the TRACERCO ProfilerTM
Interface level at steady state conditions prior to sluggingInterface level at steady state conditions prior to slugging
Ref: run 221M50SLaRef: run 221M50SLa
10 All data generated by or on behalf of ExxonMobil
8:43:10 PM 8:47:09 PM 8:51:10 PM 8:55:09 PM 8:59:09 PM 9:03:10 PM
Flow
(m3/hr)
Time (hh:mm)
Flow vs Time
Water inOil inSlug Generator & Catcher inPipeSep inOil outWater out
Slugging in a Compact Separation SystemResults – Slug Catcher Heavy Crude
API 19 70˚C 20%WC – 0.4m3 Slug Manual Control
Changed parameters on control valve to limit %openChanged parameters on control valve to limit %openSlug ReleasedSlug Released
• With this crude slate modified parameters on oil outlet control valve
• Slug Catcher now holding and buffering flow better
• Interface level in pipe separator remains constant
• Temporary change in oil-water separation
Results – Pipe Separator Heavy Crude
Slug ReleasedSlug Released
Ref: run 221H70 DMSLRef: run 221H70 DMSL
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All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemResults – Slug Catcher Light Crude; Multiple slugs
API 38 50˚C 70%WC – 0.6m3 Triple Slugs
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Level (mm)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Flow Slug Catcher outFlow Oil outLevel Slug GeneratorLevel Slug CatcherFlow water out
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0.1
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GVF
(%), Ve
locity (m
/s) a
nd
Reside
nce tim
e (m
in)
Flow
(m3/h) and
Level (%
)
Time (hh:mm)
Level and flow vs Time
Flow Slug Catcher outFilling Slug CatcherGVF Slug Catcher outVelocity GasVelocity LiquidResidence time
Slugs ReleasedSlugs Released Flow and level of slug catcher the same…different scalesFlow and level of slug catcher the same…different scales
• Very large slugs of 0.6m3
• Lighter crudes lower overall separation efficiency due to higher GOR
• Separation efficiency about 98%• Liquid carried over to monoline
GVF out of slug catcher peaked at ~0.3%GVF out of slug catcher peaked at ~0.3%Ref: run 710aL50SLRef: run 710aL50SL
12 All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemResults – Monoline; Multiple Slugs
Liquid entered the slug catcher into monolineNote liquid density…lower due to gas carryunderLiquid entered the slug catcher into monolineNote liquid density…lower due to gas carryunder
Gas leaving from boot stops as it’s mostly liquid with gas carryunder. Insufficient time to degas inside the boot
Gas leaving from boot stops as it’s mostly liquid with gas carryunder. Insufficient time to degas inside the boot
• Monoline effectively captures the liquid carryover with an efficiency of 99.97% for this run
• Due to sudden increase in liquid, boot did not have sufficient time to degas. This gas carryunder had insignificant effect on the pipe separator due to overall small liquid volume.
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nd Gas flow
(m3/h)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Flow monoline boot out.
Level MonoLine boot
Density Boot out
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5
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nd Gas flow
(m3/h)
Flow
(m3/h)
Time (hh:mm)
Level and flow vs Time
Purgeflow MonoLine
Level Slug Catcher
Gas flow System in
Gasflow MonoLine out
API 38˚ 50˚C 70%WC – 0.6m3 Triple Slugs
Ref: run 710aL50SLRef: run 710aL50SL
13 All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemResults – Pipe Separator Light Crude; Multiple slugs
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Den
sity (k
g/m3)
Time (hh:mm)Density Tracerco vs Time
Slug ReleasedSlug Released
API 38˚ 50˚C 70%WC – 0.6m3 Triple Slugs
Note: Interface level higher at 70% WC than at 20%
Note: Interface level higher at 70% WC than at 20%
• Very little effect downstream into the pipe separator on interface control
• WIO temporary increased
Ref: run 710aL50SLRef: run 710aL50SL
14 All data generated by or on behalf of ExxonMobil
Slugging in a Compact Separation SystemConcluding Remarks
Slugging effects in a compact separation system can be dampened and controlled with a properly designed flow conditioning systemAttention to control system is a MUST!!Pressure drop around each piece of equipment needs to be considered to balance flows during upset conditionsRecycling streams to diminish slugging effects or increase turndown capabilities not necessaryClean 3-phase separation that meets target performance was achievedCompact separation system much more complex than traditional gravity separation vesselValidation of dynamic simulation not possible in a closed test flow loopHigh pressure testing provided valuable dynamic and separation performance data to be incorporated into the dynamic simulation.Fast acting control valves are not requiredCompact separation systems are less forgiving to reservoir model prediction errors
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Thank You!! Questions?
Upstream Research
Thank You! Questions?
Ed GraveFractionation & Separation Advisor [email protected]‐713‐289‐4770Houston, TX USA
BACK‐UP SLIDES
ProlabNL Simplified Flow Loop Schematic
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ExxonMobil URC Subsea Compact Separation System
Test Unit