Flow Control in Oil/Gas
Wells and Pipelines
Flow Control in Oil/Gas Wells and Pipelines
Trial Lecture
Ph.D Dissertation
Even Solbraa
14.February 2003
Flow Control in Oil/Gas
Wells and Pipelines
Outline
1. Introduction to flow control
2. Multi-phase flow with emphasis on slug flow
3. Stabilization of flow in Oil/Gas wells and pipelines
4. Examples of flow control for selected oil and gas fields
5. Conclusions
Flow Control in Oil/Gas
Wells and Pipelines
Norwegian Oil and Gas Production
•
Platforms
•
Floating production units
•
Pipelines directly to shore
•
Oil to refineries
•
Gas exported to Europe
(illustrations: Statoil picture library)
Flow Control in Oil/Gas
Wells and Pipelines
Trends and Facts in Oil and Gas Production
• Few new ‘giant’ oil and gas fields are likely to be discovered
• More than a quarter of the world’s oil and more than 15%
of its natural gas lies offshore
• Most of the new discoveries are expected to occur offshore
• New large fields are probable in deep waters
• Develop new and cost effective solutions for small fields
• Multiphase transport directly to shore
• Tie-in of well stream from sub sea installation to platform
(Oliemans, 1994, Sarica and Tengesdal, 2000)
Flow Control in Oil/Gas
Wells and Pipelines
Multiphase Transport Solutions
The Åsgard field:
Floating production system
The Snøhvit solution:
Transport directly to shore
(www.statoil.com)
Flow Control in Oil/Gas
Wells and Pipelines
Multi-Phase Fluid Flow (Oil/Water/Gas)
Flow Control in Oil/Gas
Wells and Pipelines
What is the sea depth of future fields ?
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•
•
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Norwegian Sea
Gulf of Mexico
West Africa
Brazil
Caspian Sea
Venezuela
1500 meter
2500 meter
1500 meter
300 meter
600 meter
300 meter
Common: Deep water nature of the provinces
Flow Control in Oil/Gas
Wells and Pipelines
Callenges for Deep Water Developments
(Hassanein and Fairhurst, BP 1997)
Flow Control in Oil/Gas
Wells and Pipelines
Flow Control
The ability to actively or passively manipulate a
flow field in order to effect a beneficial change.
(Gad-el-Hak, 1989)
Flow Control in Oil/Gas
Wells and Pipelines
Flow assurance
The ability to produce hydrocarbon fluids economically
from the reservoir to export over the life of a field in any
environment.
(Forsdyke 1997)
Challenges:
Hydrates
Wax/paraffin deposition
Scale
Emulsions
Slugging
Sand
Fluid control
Flow control
Flow Control in Oil/Gas
Wells and Pipelines
Flow control: emulsion viscosity
Oil-water mixtures:
Increase in viscosity close
to inversion point
Emulsion viscosity as a function of water cut
Use of emulsion breaker
to lower viscosity
350
Viscosity (mPa*s)
300
2 m/s without emulsion breaker
2 m/s with emulsion breaker
250
200
150
100
50
0
0
20
40
60
Water cut (%)
80
100
Flow Control in Oil/Gas
Wells and Pipelines
Sand Control
• Sand will follow the oil and gas from the reservoir
• Sand can deposit in the pipeline and process equipment
• Oscillating pressure and well production will increase sand
production
Flow Control in Oil/Gas
Wells and Pipelines
Outline
1. Introduction to flow control
2. Multi-phase flow with emphasis on slug flow
3. Stabilization of flow in Oil/Gas wells and pipelines
4. Examples of flow control for selected oil and gas fields
5. Conclusions
Flow Control in Oil/Gas
Wells and Pipelines
Multiphase Transport
• Flow with one or several components in more than one
phase
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Gas-liquid flows
Gas-solid flows
Liquid-solid flows
Three-phase flows (e.g. gas-oil-water)
• Simulation tools
– Industry standard: OLGA (two fluid model)
– PETRA objectoriented implementation in C++
Flow Control in Oil/Gas
Wells and Pipelines
Horizontal Two-Phase Flow
• Segregated flow
– Stratified
– Annular
– Wavy
• Intermittent
– Slug flow
– Plug flow
• Distributive flow
– Bubble/mist flow
– Froth flow
Flow Control in Oil/Gas
Wells and Pipelines
Example – horizontal slug flow
From Multiphase Flow Laboratory, Trondheim
Movie provided by John-Morten Godhavn, Statoil
Flow Control in Oil/Gas
Wells and Pipelines
Inclined flow
• Waves!
Flow Control in Oil/Gas
Wells and Pipelines
Horizontal Flow Map
Bubble
• Flow pattern map for
horizontal flow
• Often specified in terms of
superficial velocity of the
phases
Slug
Annular
-1°
+1°
Stratified
Stratified Wavy
Flow Control in Oil/Gas
Wells and Pipelines
Vertical flow
• Bubble flow
– Continuous liquid phase with
dispersed bubbles of gas
• Slug flow
– Large gas bubbles
– Slugs of liquid (with small
bubbles) inbetween
• Churn flow
– Bubbles start to coalesce
– Up and down motion of liquid
• Annular flow
– Gas becomes the continuous
phase
– Droplets in the gas phase
Flow Control in Oil/Gas
Wells and Pipelines
Example - vertical flow
Slug flow
Bubble flow
From Multiphase Flow Laboratory, Trondheim
Movies provided by John-Morten Godhavn, Statoil
Flow Control in Oil/Gas
Wells and Pipelines
Vertical Flow Map
• Partly dependent on
upstream geometry
Flow Control in Oil/Gas
Wells and Pipelines
Slug Flow
-
A fascinating but unwanted and damaging flow pattern
Flow Control in Oil/Gas
Wells and Pipelines
Consequences of Slugging
• Variations in flowrate to 1.stage separator
– Shutdowns, bad separation, level variations
– Pressure pulses, vibrations and tearing on
equipment
– Flow rate measurement problems
• Variations in gasflow
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–
–
–
Pressure variations
Liquid entrainment in gas outlet
Flaring
Flow rate measurement problems
Flow Control in Oil/Gas
Wells and Pipelines
Slug Flow Classification
•
”Normal” steady slugs – Hydrodynamic slugging
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Slugs generated by compressibility effects
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Severe slugging in a riser system (riser induced)
Hilly terrain slugs (terrain induced)
Other transient compressible effects
Long period
Transient slugs
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•
Unaffected by compressibility
Incompressible gas (high pressure) or high liquid rate
Normally not an operational problem
Short period
Generated while changing inlet rate
Reservoir induced slug flow
Flow Control in Oil/Gas
Wells and Pipelines
Slug flow generation
Hydrodynamic slug growth
Two criteria:
• Wave growth due to Kelvin Helmholtz
instabilities
• Slug growth criteria (the slug has to
grow to be stable)
(Oliemans 1994)
Flow Control in Oil/Gas
Wells and Pipelines
Hydrodynamic slugging
• Formed when waves reach the upper pipe wall; the
liquid blocks the pipe, and waves grows to slugs
• Short slugs with high frequency
• Gas rate, liquid rate and topography influences degree of
slugging
• Triggers riser slugging
Eksempel fra flerfaseanlegget på Tiller.
Flow Control in Oil/Gas
Wells and Pipelines
Slugs from Gas Lift
•
Gas lift is a technology to produce
oil and gas from wells with low
reservoir pressure
•
Gas lifts can result in highly
oscillating well flow
•
Casing-heading instabilities
Annulus
Flow Control in Oil/Gas
Wells and Pipelines
Slug formation in pipeline/riser
1.
Initiation and Slug formation
•
•
•
•
2.
Gas velocity too low to sustain liquid film
in riser
Liquid blocking
Gas pressure increases in pipe
No/low production
Slug production
•
•
•
3.
Gas pressure equals liquid head
Liquid accelerates when gas enters riser
Large peak in liquid flow rate
Gas blow down
•
•
•
4.
Pressure drops as gas enters riser
Gas bubbles become continuous, liquid film
at wall
Gas velocity too low...
Liquid fallback
•
Liquid film flows down the riser
Flow Control in Oil/Gas
Wells and Pipelines
Conditions for severe slugging
• Flow maps for pipe/riser
• Conditions from literature
– Bøe ’81, Taitel et al ’90, Schmidt
et al ’85, Fuchs ‘87
– Pressure limits
– Depend on pipe geometry
• Based on steady state analysis
– Inaccessible variables
• Dynamic simulation
• When does slugging occur?
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–
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Pipelines with dips and humps
Low gas-oil ratio
Decreasing pressure
Long pipelines
Deep water production
Flow Control in Oil/Gas
Wells and Pipelines
Important Severe Slugging Parameters
• Gas and oil flowrate
• Pipeline pressure
• Upstream geometry
Graph from Fuchs (1997)
Flow Control in Oil/Gas
Wells and Pipelines
Important Severe Slugging Parameters
• Gas and oil flowrate
Pressure:
30 bar
• Pipeline pressure
• Upstream geometry
Pressure:
50 bar
Figures from Fuchs (1997)
Flow Control in Oil/Gas
Wells and Pipelines
• Gas and oil flowrate
• Pipeline pressure
Pipe buckling upstream
• Upstream geometry
Stright pipe upstream
Important Severe Slugging Parameters
Flow Control in Oil/Gas
Wells and Pipelines
Outline
1. Introduction to multi-phase flow
2. Slug flow
3. Stabilization of flow in Oil/Gas wells and pipelines
4. Examples of flow control on some oil and gas fields
5. Conclusions
Flow Control in Oil/Gas
Wells and Pipelines
Slug reduction/elimination techniques
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Design changes
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Operational changes
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Slug catchers and separators
Rate/GOR change or pressure change
Pipe diameter regulation (use of many smal pipes) (Yocum, 1975)
Gas injection at riser base (Hill, 1990)
Pipe insertion (self induced gaslift) (Sarica & Tengesdal, 2000)
Venturi tubes
Dynamic simulation (Xu et al, 1997)
Choking (Schmidt et al., 1979, Taitel, 1986, Jansen et al., 1996)
Feed-forward control of separator level
Dynamic simulation (Xu et al., 1997)
Pigging operations
Use of flow-improver
Foaming (Hassanein et.al., 1998)
Artificial gas lifts
Optimise well production
Increase gas injection in well
Feedback control
– Miniseparators
– Active choking
– Model based regulation
Flow Control in Oil/Gas
Wells and Pipelines
Robust design -
Gas injection at riser base
(Hill, 1990)
Qgas
+
•Reduced static head (weight of liquid)
• Prevent severe slugging
• Smoothen start-up transients
• Large amounts of injection gas needed
• Extra injection pipe needed
Flow Control in Oil/Gas
Wells and Pipelines
Robust design -
Self gas lifting
(Sarcia & Tengesdal, 2000)
+
• Reduced static head (weight of liquid)
• Prevent severe slugging
• Smoothen start-up transients
• No extra injection gas needed
• Extra injection pipe needed – will be expensive
Flow Control in Oil/Gas
Wells and Pipelines
Robust operation –
Choking
(Schmidt et al., 1979, Taitel, 1986, Jansen et al., 1996 )
+
• Higher pressure and smaller severe slug flow regime
• Easy and cheap technique
• Manual work
• Lower capacity of pipe
Flow Control in Oil/Gas
Wells and Pipelines
Feedback control –
Active Choking
(Statoil, 2003)
+
• Reduces the slug length by opening the hock valve when
the slugs starts to develop – sucks the slug up.
• Easy and cheap technique
SP
MV
-
PIC
Used as
regulation valve
• Lower capacity of pipe
• Can be a problem for deep waters
1.stage
separator
PT
PT
D
Flow Control in Oil/Gas
Wells and Pipelines
Robust operation –
Optimize Well Production
(ABB)
OptimizeIT Active Well Control
- stabilizes the oil production
from the well by active
control of the production
and/or injection choke
Flow Control in Oil/Gas
Wells and Pipelines
Robust operation –
Increased/controled gas injection rate in gas lifts
+
• Increased gas flow rate and GOR (less chance for severe slugging)
• Less static head
• Increased frictional losses
• Joule-Thomson Cooling
• Need injection gas
Annulus
Flow Control in Oil/Gas
Wells and Pipelines
Feedback control -
Miniseparators
(Hollenberg, 1995, S3TM)
• Principle is to keep the mixture flow rate constant
through the operation with a control vale.
• Difficulty in measuring flowrates is solved by
using minisparators
• Lower capacity of pipe
Flow Control in Oil/Gas
Wells and Pipelines
Slug reduction/elimination techniques
•
Design changes
–
–
–
–
–
–
–
•
Operational changes
–
–
–
–
–
–
–
–
–
•
Slug catchers and separators
Rate/GOR change or pressure change
Pipe diameter regulation (use of many smal pipes) (Yocum, 1975)
Gas injection at riser base (Hill, 1990)
Pipe insertion (self induced gaslift) (Sarica & Tengesdal, 2000)
Venturi tubes
Dynamic simulation (Xu et al, 1997)
Choking (Schmidt et al., 1979, Taitel, 1986, Jansen et al., 1996)
Feed-forward control of separator level
Dynamic simulation (Xu et al., 1997)
Pigging operations
Use of flow-improver
Foaming (Hassanein et.al., 1998)
Artificial gas lifts
Optimise well production
Increase gas injection in well
Feedback control
– Miniseparators
– Active choking
– Model based regulation
Flow Control in Oil/Gas
Wells and Pipelines
Outline
1. Introduction to flow control and multi-phase flow
2. Slug flow
3. Stabilization of flow in Oil/Gas wells and pipelines
4. Examples of flow control on some oil and gas fields
5. Conclusions
Flow Control in Oil/Gas
Wells and Pipelines
Slugg Control at Heidrun Nordflanken
Use of active slug control




Simulation before startup indicated slugging
Field measurements after startup proved slugging
Continuous slug regulation since startup
Also in use under startup of new wells
D
Elevation -355m
4700m
Flow Control in Oil/Gas
Wells and Pipelines
Slugging in riser Heidrun D-line
Trykk toppside oppstrøms choke
•Large pressure variations
•Periods ca. 17 minutes.
•Disapears when chocking upstream
Tetthet toppside
Flow Control in Oil/Gas
Wells and Pipelines
Active Well Control at Brage A-21
Flow Control in Oil/Gas
Wells and Pipelines
OptimizeIT Active Well Control on Brage A-21
Brage WellCon data (Day 0 = 24-Aug-2001 07:59:00)
88
PT -13-217
Starting Active Control
86
84
Pres. [bar]
82
Downhole pressure
80
78
76
2
2.5
3
Days
3.5
4
Flow Control in Oil/Gas
Wells and Pipelines
Conclusions
•
•
•
•
•
•
Introduction to flow control
Unstable multiphase flow – what, why
Severe slugging in gas/oil pipelines
Methods for control of severe slugging
Still an unresolved problem for deep waters
Successful practical examples
Flow Control in Oil/Gas
Wells and Pipelines
Thanks
• Institute for Energy and Process Technology, NTNU
• Statoil
• Norwegian Research Council
• People who have helped my with this trial lecture
Lars Imsland, Elling Sletfjerding, John Morten Godhavn
Flow Control in Oil/Gas
Wells and Pipelines
Flow control in petroleum production
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Noise suppression
Drag reduction
Water-oil flow
Flow assurance
Slug control
Multiphase flow simulation
Flow Control in Oil/Gas
Wells and Pipelines
Drag reduction
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Internal flows (pipes, ducts)
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Wall modifications
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~100% skin friction
Increased throughput
Reduced pumping power
Reduced pipe/duct size
Smoothing (paintings, coatings, pigging)
Riblets (shark-skin)
Compliant walls, flexible skin
MEMS (Micro-electromechanical systems)
Additives
– Particles, dust, fibres
– Polymers, surfactants (Drag reducing agents)
– Micro-bubbles, fluid films