L2 - FLOW ASSURANCE ISSUES •
BASIS PRINCIPLES OF SUBSEA PRODUCTION SYSTEMS
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FLOW ASSURANCE & SYSTEMS DESIGN ISSUES - FLOW HYDRAULICS - MULTIPHASE FLOW - HYDRATES - WAX DEPOSITION - PIGGING - THERMAL ISSUES & COLD POINTS - CORROSION / EROSION - EMULSIONS - SAND - NEW TECHNOLOGIES
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IFP FACILITIES
BASIC PRINCIPLES OF SUBSEA PRODUCTION - FLOW ASSURANCE ISSUES 2 - 100 km
SEPARATOR PLATFORM OR FLOATER
50 - 2000 m
RISER
TREE
DISTRIBUTE CHEMICALS
PROCESS FACILITIES
FLOWLINES RISER BASE SUPPLY LINES SEA BED
1000 - 10000 m
FLOW ASSURANCE 1) HYDRAULICS - Is there enough energy in the flow to reach the processing host? 2) CORROSIVE COMPONENTS in the oil i.e.. H2S and CO2 - It can be corrected by chemical injection. GAS OIL
WATER
3) Is there any WAX in the oil that may block the lines on cooling. 4) Combinations of Gas and Water may form HYDRATES which block the line.
Flow Assurance Design Issues
Gas Hydrates
Paraffin/
Sand/Erosion
Asphaltenes
FLOW ASSURANCE DESIGN Liquid Slugging
Corrosion
Scale
Emulsion/ Foam
FLOW ASSURANCE -
H y d r a t e s - F o r m a t io n o f ic e c r y s t a ls in c o r p a r a t in g m e th a n e a n d o t h e r h y d r o c a r b o n s in lo w t e m p e r a tu r e s , h ig h p r e s s u r e , w e t s y s t e m s p r o d u c in g g a s , c o n d e n s a t e o r o il.
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W a x / A s p h a l t e n e s - T h e d e p o s it io n o f s o lid s in s id e t h e f lo w lin e s a n d r is e r s r e d u c in g f lo w c a p a c it y a n d u lt im a t e ly b lo c k in g t h e lin e .
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S l u g g i n g - T h e p h e n o m e n a c a u s e d b y t h e in s t a b ilit ie s o f th e g a s a n d liq u id in t e r f a c e s a n d liq u id s w e e p - o u t b y g a s in e r t ia l e f f e c t s .
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C o r r o s i o n - W e a r in g o f t h e p ip e w o r k a n d f lo w lin e w a ll t h ic k n e s s d u e to c h e m is t r y o f th e p r o d u c e d f lu id s .
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E m u l s i o n s - O il a n d w a t e r m ix t u r e s a t a p p r o x im a te ly 4 0 t o 6 0 % w a t e r c u t t h a t c a u s e e x c e s s iv e p r e s s u r e lo s s e s in th e w e lls o r t h e S P S s y s t e m .
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S c a l i n g - S o lid s b u ild u p , e s p e c ia lly o n t o t h e w e ll b o r e t u b in g d u e t o t h e c h e m is t r y o f th e p r o d u c e d w a t e r .
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S a n d P r o d u c t i o n - S a n d p r o d u c t io n f r o m t h e r e s e r v o ir c a u s in g b lo c k a g e o f s y s t e m c o m p o n e n t s s u c h a s f lo w lin e s .
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E r o s i o n - W e a r in g o f t h e m a n if o ld p ip e w o r k a n d t h e f lo w lin e w a lls d u e to s o lid p a r t ic le s s u c h a s s a n d o r liq u id s im p in g e m e n t p a s s in g a t h ig h v e lo c it ie s .
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C o l d P o i n t s - M u lt ip le n o n in s u la t e d d e v ic e s in t h e s y s t e m in c o n ta c t w it h t h e s u r r o u n d in g c o ld w a t e r a c t in g a s f a s t h e a t e x c h a n g e r s in p a r t ic u la r d u r in g w e ll s h u t d o w n a n d o th e r o p e r a t in g m o d e s .
The successful design and operation of a multiphase production system must consider design parameters and issues for the entire system, from the reservoir to the processing and export facilities. To assure that the entire system can be designed to operate successfully and economically, system designers must consider flow assurance fundamentals such as reservoir characteristics, production profiles, produced fluid chemistry, and environmental conditions as well as mechanical, operational, risk, and economic issues for all parts of the system. Important system parameters established as part of the design effort include tubing and flowline diameters, insulation (on wellbore tubing, trees, jumpers, manifolds, flowlines and risers), chemical injection requirements, flow blockage intervention provisions, host facility requirements, capital and operating costs, operating boundaries (e.g. maximum and minimum production rates), and risk mitigation. All production modes including startup, normal steady state operation, rate change, and shutdown must be considered throughout the system life-cycle.
Flow assurance encompasses the thermal-hydraulic design and assessment of multiphase production/transport systems as well as the prediction, prevention, and remediation of flow stoppages due to solids deposition (particularly due to hydrates and waxes). In all cases, flow assurance designs must consider the capabilities and requirements for all parts of the system throughout the entire production life of the system to reach a successful solution. Operating philosophies, strategies, and procedures for successful system designs must be robust. They must be developed with system unknowns and uncertainties in mind and should be readily adapted to work with the system that is found to exist after production starts, even when that system is different from what was assumed during design (which often happens). System Design is the synthesis of Flow Assurance and Operability features and attributes with those of all other aspects of the system. These include Reservoir, Completions, Subsea Hardware, Controls, Pipelines, Facilities, Production Operations, Transportation, Economics, and others. The successful flow assurance design will represent a system solution that best meets the needs of all groups.
Well Gas Lift
Topsides boundary condition
Choke Jumper
Pipework Cover Riser Field Joints
Flowline
TYPICAL FLOW HYDRAULICS MODEL Headers & Levels Diagram
ANNULAR-DISPERSED FLOW
SLUG FLOW
DISPERSED-BUBBLE FLOW
GAS PHASE MOMENTUM FLUX
104 ANNULAR-DISPERSED LIQUID
DISPERSED-BUBBLE
103 SLUG STRATIFIED-WAVE
102
INTERMITTENT
PLUG
101
STRATIFIED-SMOOTH 100 10-3
10-2
10-1
100
101
102
103
104
LIQUID PHASE MOMENTUM FLUX
STRATIFIED-WAVY FLOW
STRATIFIED FLOW
MULTI-PHASE FLOW REGIMES
PLUG FLOW
MULTIPHASE FLOW REGIMES
NORMAL SLUGGING •
Produced by Slug Flow or Intermittent Flow
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Tends to Increase in Size with Flow Rate
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Predicted by Flow Map or by Computer based Information Schemes (OLGA / PLAC etc) A. SLUG FORMATION
C. GAS PENETRATION
SEVERE SLUGGING •
Produced by Combinations of Segregated Flow and Terrain B.
SLUG PRODUCTION
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Particularly a problem in Risers
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Can be reduced by Discouraging Segregated Flow
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Predicted by Transient Flow Computer Models
D. GAS BLOW-DOWN
GAS HYDRATES
Hydrates are snow-like crystals which form at low temperatures and high pressures. They are a combination of water and methane (gas) molecules. Once formed they are quite stable. If formed in pipelines they can cause a total blockage. Their formation can be predicted from temperature – pressure data
Methane hydrate phase diagram. The horizontal axis shows temperature from -15 to 33 Celsius, the vertical axis shows pressure from 0 to 120,000 kilopascals (0 to 1,184 atmospheres). For example, at 4 Celsius hydrate forms above a pressure of about 50 atmospheres
HYDRATES PREVENTION • OPERATING PIPELINES AT LOW PRESSURE • OPERATING OR MAINTAINING PIPELINES AT HIGH TEMPERATURES •
Insulation of Lines Active heating of lines (hot Water or Electrical Heating)
INHIBITION BY CHEMICAL ADDITION - Use of Methanol or Glycol Chemicals - Other Chemicals which block Hydrates Initiation
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REMOVAL OF WATER (Dehydration) - Liquid or Solid Desiccants - Subsea Separation
Hydrate Plug
SEPARATOR
PUMPS
UMBILICAL
ELECTRIC POWER CONNECTOR
SUBSEA CONTROL SYSTEM
DIPSIS - SUBSEA WATER SEPARATION AND RE-INJECTION Diagrammatic Representation
WAX DEPOSITION • 10% to 20% of Crudes are considered Waxy • The Formation of Wax can completely Block Flow • Waxy Crude is characterised by one or more of the following :- Cloud Temperature - Pour Point Temperature - Inversion Temperature (melting) • Wax Deposition Prediction - By Models and Predictions based on Fluid Properties
WAX PREVENTION • Insulation to Maintain Temperature • Scraper Pigging • Heating using Steam or Electricity • Hot Oil Flushing • Chemical Injection of Wax Inhibitors
Wax Plug
PIGGING
CLEANING PIG
SUBSEA PIG LAUNCHER
POSSIBLE COLD POINTS IN SUBSEA PRODUCTION SYSTEM Poor Insulated Riser
Poor Insulation of Trees and Manifolds
Non-Insulated connection between Tree or Manifold & flow Jumper or Flowline
Pressure Drop in Chokes or Flow Path leading to Joule-Thompson Cooling
Non-Insulated connection between or Flowline & Riser Base
INCREASED USE OF INSULATION ON SUBSEA EQUIPMENT
FLOWLINE INSULATION SIMPLE PIPE
PIPE IN PIPE STEEL PIPE DESIGNED FOR PRESSURE CONTAINMENT CONDUCTIVITY = 1.4 W/m/K
FLOWLINE BUNDLE INDIVIDUAL PIPES INSIDE A CARRIER PIPE. CAN HAVE HOT WATER CIRCULATED
STEEL PIPE INSIDE ANOTHER WITH PU FOAM BETWEEN CONDUCTIVITY = 0.2 – 0.4 W/m/K
INSULATED FLOW BUNDLE BUNDLE BUT WITH INSULATION FOAM SURROUNDING CARRIER PIPES
6” ID pipe 20 m long 24 heat tracing armours 16 electrical cables
FLEXIBLE PIPE Deepwater Solution - Integrated Production Bundle – Heat Traced
7 SS tubes + Optical Fibres for monitoring (Distributed Temperature Sensing)
TORE Sand Removal
