L02 - FLOW ASSURANCE

L2 - FLOW ASSURANCE ISSUES

• BASIS PRINCIPLES OF SUBSEA PRODUCTION SYSTEMS

• FLOW ASSURANCE & SYSTEMS DESIGN ISSUES

- FLOW HYDRAULICS - MULTIPHASE FLOW - HYDRATES

- WAX DEPOSITION - PIGGING

- THERMAL ISSUES & COLD POINTS - CORROSION / EROSION

- EMULSIONS - SAND

- NEW TECHNOLOGIES

BASIC PRINCIPLES OF SUBSEA PRODUCTION - FLOW ASSURANCE ISSUES SEPARATOR PLATFORM OR FLOATER GAS RISER BASE FLOWLINES SUPPLY LINES DISTRIBUTE CHEMICALS TREE 2 - 100 km SEA BED 100 0 -10000 m OIL WATER 50 -2 000 m RISER PROCESS FACILITIES 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. 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

FLOW ASSURANCE DESIGN Paraffin/ Asphaltenes Gas Hydrates Liquid Slugging Scale Corrosion Sand/Erosion 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 t u 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. - 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 . - 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 . - 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 . - 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 . - 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 . - 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 . - 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 . - 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 t a 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 t h 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.

Gas

Lift

Topsides

boundary

condition

Well

Choke

Jumper

Field

Joints

Cover

Flowline

Riser

Pipework

TYPICAL FLOW HYDRAULICS MODEL Headers

& Levels Diagram

ANNULAR-DISPERSED FLOW _{SLUG FLOW DISPERSED-BUBBLE FLOW} 100 103 102 104 101 10-3 ₁₀-2 ₁₀-1 ₁₀0 ₁₀1 ₁₀2 ₁₀3 ₁₀4 ANNULAR-DISPERSED LIQUID DISPERSED-BUBBLE SLUG INTERMITTENT PLUG STRATIFIED-WAVE STRATIFIED-SMOOTH

STRATIFIED-WAVY FLOW STRATIFIED FLOW PLUG FLOW

LIQUID PHASE MOMENTUM FLUX

GAS PHASE MOMENTUM FLUX

NORMAL SLUGGING

•

Produced by Slug Flow or Intermittent Flow

•

Tends to Increase in Size with Flow Rate

•

Predicted by Flow Map or by Computer based

Information Schemes (OLGA / PLAC etc)

SEVERE SLUGGING

•

Produced by Combinations of Segregated

Flow and Terrain

•

Particularly a problem in Risers

•

Can be reduced by Discouraging Segregated

Flow

•

Predicted by Transient Flow Computer

Models

A. SLUG FORMATION C. GAS PENETRATION

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

GAS HYDRATES

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

• REMOVAL OF WATER (Dehydration)

- Liquid or Solid Desiccants - Subsea Separation

DIPSIS - SUBSEA WATER SEPARATION AND RE-INJECTION

Diagrammatic Representation

SEPARATOR

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

PIGGING

CLEANING PIG

POSSIBLE COLD POINTS IN SUBSEA PRODUCTION SYSTEM

Poor Insulated Riser

Non-Insulated connection between Tree or Manifold & flow Jumper or Flowline

Non-Insulated

connection between or Flowline & Riser Base Pressure Drop in Chokes or Flow

Path leading to Joule-Thompson Cooling

Poor Insulation of Trees and Manifolds

INCREASED USE OF

INSULATION ON

FLOWLINE INSULATION

SIMPLE PIPE

_{PIPE IN PIPE}

STEEL PIPE INSIDE ANOTHER WITH PU FOAM BETWEEN CONDUCTIVITY = 0.2 – 0.4 W/m/K STEEL PIPE DESIGNED FOR PRESSURE CONTAINMENT CONDUCTIVITY = 1.4 W/m/K

INSULATED FLOW BUNDLE

FLOWLINE BUNDLE

INDIVIDUAL PIPES INSIDE A CARRIER PIPE.

CAN HAVE HOT WATER CIRCULATED BUNDLE BUT WITH INSULATION FOAM SURROUNDING CARRIER PIPES

6” ID pipe 20 m long 24 heat tracing armours 16 electrical cables

7 SS tubes

+ Optical Fibres for monitoring (Distributed Temperature Sensing)

FLEXIBLE PIPE

Deepwater Solution - Integrated

Production Bundle – Heat Traced