Feb. 6 - 10, 2012 2012 Gas-Lift Workshop 1

To Dry or Not to Dry A Dehydration Discussion

John Martinez Production Associates pa.amart@juno.com

35th Gas-Lift Workshop Houston, Texas, USA February 6 – 10, 2012

"To dry or not to dry" A Dehydration Discussion

by phone Jim Hall

Qatar Shell Services Jim.Hall@shell.com

"To dry or not to dry" A Dehydration Discussion

• Safe and profitable oil production via gas lift – Experienced people – Quality hardware – Processes that keep the system operating 24/7

• Gas lift gas dehydration prevents these hidden dangers – Hydrates – Corrosion – Shut down production and/or unsafe conditions

• Hardware specifications - API or ISO industry standards – Valves/mandrels – API 19G and ISO 17078 (multiple sections) – Compressors – API Std 617 and Std 618 – Dehydration equipment – API Spec 12GDU

• Process specifications require acceptably dry gas (water vapor removed) depending on geographical location

• Review the perils of not adhering to these guidelines

Gas Dehydration Don’t Install or Shut It Down

• You will appear to reduce CAPEX and OPEX by justifying no dehydration facilities or by shutting them down.

• Your manager will be very happy because of the short term savings that can be reported.

• The manager will not consider life cycle cost increases.

• You will move to your next posting before – Life cycle cost impacts become apparent – Then it's SEP (Somebody Else's Problem)

Without Dehydration You Can Expect • Gas pipelines fill with water (occurs faster with

pipelines in the sea) – Increased pressure drop

• Kickoff more difficult • Valve pressures not correct for reduced available pressure

– Liquid slugs • Over load liquid knockout vessels • Fill orifice meter tubes – bad gas measurement

– Valve erosion • More frequent wireline work • More difficult well surveillance challenges

• Safety is compromised – Additional well interventions – Maintenance depressuring of vessels and gas meters – Relief valves pop when liquid slugs arrive – Lose a work boat at sea

Without Dehydration You Can Expect

• Corrosion – Accelerated with CO2 and partial pressure of 7 psia – Corrosion inhibitor required

• Chemical cost and handling • Pump and tank maintenance • Liquid soluble and mist phase inhibitor

choices – Holes in pipelines

• Pipeline repair • Leak bubbles a hazard to personnel and

boats

Without Dehydration You Can Expect

• Hydrates – Problem

• Hydrates at chokes due to cooling • Reduces or stops production from one well

– Crisis • Pipeline plugs and shuts down an entire platform or more • All well chokes plug (at least the plug is at the wellhead)

– Methanol injection • HSE issue • Methanol poisons refinery catalysts (your oil value is reduced) • Maintenance increases with pumps, tanks • Methanol interferes with corrosion inhibitor

What Are Hydrates?

Ice-like crystals formed when liquid water and natural gas cool under pressure

Hydrate formation occurs when pressurized water and natural gas components cool below 15-25 °C (60-75 oF)

Water Cage

Gas

Vapor Phase Hydrates

Hydrates will burn….

Hydrate plugs are a safety issue

• Pressure reduction – Depressure both sides of plug

– Not always possible

• Thermal – Potentially dangerous if gas trapped between plugs

– External heating may be limited by insulation

• Chemical – Must be able to get the chemical to the plug

• Mechanical – Coiled tubing

HYDRATE PLUG REMOVAL

Hydrate Plug

Add Heat

Hydrate Plug

Gas Pressure Buildup

METHANOL INJECTION

Wet gas above its hydrate point

Gas cools below hydrate point

Methanol

Water phase is protected from hydrates/freezing with MeOH

HC Liquid phase contains MeOH

HC Vapor phase contains MeOH

Methanol is Methyl Alcohol (CH3OH), abbreviated MeOH

How About Corrosion?

• WATER AND ELECTRON FLOW REQUIRED FOR CORROSION – DEHYDRATE – COATINGS - CHEMICAL OR MATERIAL – IMPOSE CATHODIC FIELD (OUTER SURFACE ONLY)

• DETECT METAL LOSS – ACOUSTIC, RADIOGRAPHIC, ELECTROMAGNETIC – MECHANICAL OR VISUAL – COUPONS OR PROBES

Dehydration

• Triethylene Glycol (TEG) Absorbs Water Vapor • Must have good scrubber to remove liquid water • Gas temperature must be cool, not hot • Dehydrate at 800 - 1200 psi (55 - 85 bar) best • Glycol scrubber downstream to capture carryover • Very high pressure (>2500 psi – 175 bar) can cause

excessive TEG loss

McKetta-Wehe Water Content Chart

McKetta-Wehe Water Content Chart Effect of gas gravity

Effect of CO2

TEG Absorption Process

Molecular Sieve Adsorption

Four-Tower Mol Sieve Dehydrator

Wet gas

Water Water

Dry gas to NRU

Dry gas to NRU

Regen and cool-down gas Regen and cool-down gas

Dust Filter Dust Filter

• 2 towers on 12-hour dry cycle • 6-hour regeneration cycle •

• 2 towers on 12-hour dry cycle • 6-hour regeneration cycle • 6-hour cool-down cycle

Blower Blower

Regen gas for processing

• Do Not Dry the Gas Lift Gas – Operating cost reduction – Capital cost reduction on new facilities – Hydrates will require methanol treatment – Corrosion inhibition required – Long term cost is higher – Safety compromised

• Dry the Gas Lift Gas – Must process gas at correct pressure and temperature – Hydrates eliminated – Corrosion eliminated – Gaseous hydrocarbon (rich gas) can still condense to

liquid in pipelines

"To dry or not to dry" A Dehydration Discussion

Feb. 6 – 10. 2012 2012 Gas-Lift Workshop 21

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Feb. 6 – 10, 2012 2012 Gas-Lift Workshop 22

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