hydrocarbon processing

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Hydrocarbon Processing

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Page 1: Hydrocarbon Processing

Hydrocarbon Processing

Page 2: Hydrocarbon Processing

Hydrocarbon Chemistry• Alkanes

– CnH2n+2

– Methane and Ethane (natural gas)– Propane and Butane (fuels in cars/lighters etc)– Pentane and Octane (fuels in combustion engines)– Hexadecane (diesel and aviation fuels)

• Alkenes– CnH2n

– Predominately used in plastics

Page 3: Hydrocarbon Processing

• Cycloalkanes– CnH2n

– Used in fuels and other heavy oils

• Alkynes– CnH2n-2

• Aromatics– C6H6

Page 4: Hydrocarbon Processing

Properties of Hydrocarbons• Dew Point

– The point at which, when heat is removed from a vapour mixture, the first drop of liquid is formed.

• Bubble Point– Temperature at which, when heat is applied to a liquid, the

first vapour escapes as a bubble.

• Vapour Pressure– The Pressure Exerted by the vapour formed above the liquid.

• Reid Vapour Pressure– Absolute vapour pressure exerted by a liquid at 38.5oC (100oF)– Take into account air and water vapour (different from true VP)

Page 5: Hydrocarbon Processing

• Flash Point– Temperature at which, when a source of ignition is introduced

to a vapour above a liquid it will ignite.

• Auto-ignition Temperature– The point at which a fluid will ignite spontaneously in the air

without the requirement for a source of ignition.

Page 6: Hydrocarbon Processing

Reservoir Fluid• In addition to hydrocarbons:

• H2S/CO2

» Forms acids which can cause corrosion» Removed by amine treating

• N2

» Reduces the calorific value of the gas» Cryogenic Processing (Methane B.P of -161.6oC vs Nitrogen of -196.69oC)

• Water» Can produce hydrates and promotes corrosion» Removed by Gas Dehydration Process and Bulk Water

Separation

Page 7: Hydrocarbon Processing

• Sand» Brought up from the well with fluids.» Erodes the pipework and can accumulate at the bottom

of elbows, tees etc.» Removed through gravity separation.

• Mineral Salts» Chlorides, sulphates and carbonates of sodium,

potassium, calcium and magnesium.» Can cause fouling (particularly in heat exchangers).

Page 8: Hydrocarbon Processing

Disposal

Page 9: Hydrocarbon Processing

Gas Disposal

• Produced gas can be disposed of through:– Flaring– Re-injection– Piped to market– Liquefied

• Gas must be treated to remove impurities.

Page 10: Hydrocarbon Processing

Water Disposal

• Produced gas can be disposed of through:– Discharging into sea– Re-injection

• If produced water is to be discharged into the sea it must 1st be treated to remove oil and solids.

Page 11: Hydrocarbon Processing

Solids Disposal

Page 12: Hydrocarbon Processing

Reservoir Characteristics & Well Fluids

• Reservoir formed in porous, sedimentary rock.• Surrounded by impervious rock (cap rock).

Page 13: Hydrocarbon Processing

• Pc - Critical Pressure» Pressure required to liquefy a gas at its

• Tc - Critical Temperature» Temperature at which the vapour of the substance cannot be

liquefied

Tc

Pc

Phase Diagram

Page 14: Hydrocarbon Processing

API Gravity

• A measure of how heavy or light a petroleum liquid is compared to water.

• Expressed as:» 141.5/SG – 131.5

• If its API gravity is greater than 10, it is lighter than water; if less than 10, it is heavier and sinks.

• “Units” in degrees.

Page 15: Hydrocarbon Processing

Reservoir Drives & Artificial Lift

Page 16: Hydrocarbon Processing

Natural Lift

• 4 Types of natural drive» Depletion or solution drive» Gas drive» Water drive» Gravity Drainage

Page 17: Hydrocarbon Processing

Depletion or Solution Drive• Pressure in reservoir is greater than bubble point

» All gas is dissolved in the oil

• As pressure falls, bubbles form in the oil. – Causing the reservoir pressure to increase due to expansion of

the gas bubbles» Supporting production

• Eventually the bubbles in the oil reach critical saturation levels.

– This causes the gas to join together and flow as a single gas phase.» Due to the lower viscosity of gas over oil, the gas flows to

the well bore more rapidly than the oil

Page 18: Hydrocarbon Processing

• Inefficient recovery » 5 – 25% recovery

• Little water is produced

Solution Drive

Page 19: Hydrocarbon Processing

Gas Drive

• Pressure in reservoir is less than bubble point» Gas forms as a cap above the oil.

• As pressure falls, the gas cap above the oil expands. – The expansion of the gas cap increases the pressure of the

reservoir.» Pushing the GOC down, and forcing oil into the well bore.

• Eventually the gas cap reaches the well bore.– This causes the GOR to increase rapidly until only gas is

produced.

Page 20: Hydrocarbon Processing

• Relatively efficient recovery » 20 – 40% recovery

• Small GOR• Little water is produced

Gas Drive

Page 21: Hydrocarbon Processing

Water Drive

• As oil is extracted from the reservoir, the aquifer expands into the reservoir, displacing the oil.

» Solution drive will most likely be taking place too.

• The displacement of oil pushes the OWC up. » maintaining the reservoir pressure.

• Eventually the aquifer reaches the well bore.– This causes the OWR to decrease rapidly until only water is

produced.

• Constant GOR– Unless there is a high pressure decrease

» In which case, GOR increases due to the oil forming gas bubbles (solution drive)

Page 22: Hydrocarbon Processing

• Relatively efficient recovery » 40 – 80% recovery

Water Drive

Page 23: Hydrocarbon Processing

Gravity Drainage

Page 24: Hydrocarbon Processing

Artificial Lift• Oil flow only occurs when

• Reservoir pressure > static head– Static head = h * p * g

• If static head is too great then oil wont flow.• Inject fluid into reservoir to maintain pressure• Equipment in production tubing to assist flow.

Page 25: Hydrocarbon Processing

Water Injection• Water injected into reservoir

– Simulates water drive

• Sources of water• Sea Water

» Most convenient source for offshore production» Water intake is placed at sufficient depths to reduce the

concentration of algae» Filtering, deoxygenating and biociding required.

• Produced Water» Reduces Risk of causing damage to formation» Risk of scaling or corrosion still exists.» Make-up water must be provided

• Aquifer Water• River Water

Page 26: Hydrocarbon Processing

• Filters– Clean water to remove impurities (e.g. shells & algae).– Poor water quality, clogging of the reservoir and loss of

oil production.• De-oxygenation– Promotes corrosion and growth of bacteria.

– Bacteria can produce hydrogen sulphide.

– De-oxygenation tower brings the water into contact with a dry gas stream.

– May also use a oxygen scavenging agent– Sodium bisulphate and ammonium bisulphate.

• Water Injection Pumps– High pressure and high flowrates

– 3000 to 5000 psi and 2 barrels of water for every barrel of oil produced.

Page 27: Hydrocarbon Processing

Gas Injection• Gas injected into reservoir

– Simulates gas drive

• Can be used where there is no economic gas export route or to fast track oil production.

» Where gas export infrastructure has not been completed.

• Gas maybe be recoverable later• Higher pressure injection pumps required

» 6500 psi

• Gas must 1st be treated to ensure it does not:• Cause corrosion in well equipment• Form hydrates• Contaminate the reservoir.

Page 28: Hydrocarbon Processing

Gas Lift

• Gas injected into annulus of the well.– Simulates depletion drive.

• Reduces hydrostatic head at bottom of production tubing.

» By lowering the density of the fluid.

• May only be used in wells where natural drive still exists.

Page 29: Hydrocarbon Processing

• Gas enters production tubing through non-return valve

• Creates a foam when mixed with well fluids– Foam has lower density than well fluids.

• Flow of gas into the tubing is determined by pressure difference.

• Due to variable hydrostatic head in tubing, the gas can be injected at several points.

• Packers around inner tubing seal lower ends of the annulus.

• Annulus safety valve prevents reservoir pressure entering gas lift supply should tubing rupture

Page 30: Hydrocarbon Processing

Pumps

• Lift Pump– Displacement device– Driven from surface by piston or sucker rod

• Submersible Pump– Centrifugal pump– Located at bottom of well– Flow rate is proportional to speed

Page 31: Hydrocarbon Processing

Submersible Pump

• Electric motor driven centrifugal pump• Attached to bottom of production tubing

• Main Problems are:• Solid ingress• Lubrication• Required a well work-over to remove them

Page 32: Hydrocarbon Processing
Page 33: Hydrocarbon Processing

Oil & Gas Separation

Page 34: Hydrocarbon Processing

Purpose

• Separate gas from oil to meet vapour pressure specifications

• Separate water from oil to meet water specification

• To Prevent corrosion and formation of hydrates

• Separate sand and sediment from oil to meet BS&W specification

Page 35: Hydrocarbon Processing

Types• Test Separator

• Used to separate and meter the well fluids

• Production Separator• Used to separate the produced well fluid

• Low-Temperature Separator• High pressure well fluid enters the vessel through a choke (or

pressure reducing device).» This lowers the temperature to below well-fluid temperatures by

the Joule-Thomson Effect• This causes condensation of vapours that would have

otherwise exited the separator in the vapour state

Page 36: Hydrocarbon Processing

3-Phase Separator

• Impingement Baffle• Mist entering the separator is impinged against a surface• The mist gathers on the surface and coalesces into larger droplets, which will gravitate in

to the liquid section of the vessel

• Density Difference• At standard condition, droplets of liquid hydrocarbon have a density of

400 to 1600 times that of natural gas• This difference decreases with increasing temperature

• Therefore oil gas separators operate at as low pressures as is possible

• Change of Flow Direction• When the direction of a gas stream containing liquid mist is changed

abruptly, inertia causes the liquid to continue in the original direction of flow.

• Change of Flow Velocity• When the velocity of a gas stream containing liquid mist is changed

abruptly, the higher inertia of the liquid carries it forward away from the gas.

Page 37: Hydrocarbon Processing

Coalescing Pad

Page 38: Hydrocarbon Processing

Oil/Gas Separation Schematic

HP Separator

LP Separator

IP Separator

Gas Dehydration

Flash Gas Compression

http://www.offshorecenter.dk/artikel.asp?id=175&name=Offshore_oil_and_gas_production_and_processing

Scrubber

Page 39: Hydrocarbon Processing
Page 40: Hydrocarbon Processing

Produced Water

Page 41: Hydrocarbon Processing

What is Produced Water?

• Produced water is a term used to describe water that is produced when oil & gas are extracted from the ground.

• Historically disposed of in evaporation ponds.• Can be re-injected into reservoir or disposed

of into the sea– However it must first be treated to remove impurities

Page 42: Hydrocarbon Processing

Water separation Methods

• Water flash drum– Used on gas platforms with light hydrocarbons– De-gases water in a flash drum– The pressure is reduced • Enables volatile hydrocarbons to vaporise.

– Then flared or vented, and the water dumped.

• Coalescer– Small dispersed oil droplets coalesce which

separate under gravity

Page 43: Hydrocarbon Processing

Water separation methods

• Skimmer tanks– Form of gravity separator. – Low liquid velocity required.

– Resulting in requiring large vessels.

– Demulsifies sometimes added to aid separation by breaking up oil emulsions

– Oil layer pumped back to the process, and water dumped.

Page 44: Hydrocarbon Processing

Water separation methods

• Flotation treatment– Involve production of small bubbles in produced

water which attach to oil and solids particles present, thus increasing buoyancy and gravitational separating efficiency.

Page 45: Hydrocarbon Processing

Water separation methods

• Plate separators• Tilted Plate Separators• Hydrocyclones

Page 46: Hydrocarbon Processing

Gas Treatment

Page 47: Hydrocarbon Processing

Associated Gas• Found with crude oil deposits.– Separated from crude oil at point of production.– Drying is also carried out at point of production to

prevent hydrate formation and reduce possibilities of corrosion.

– Further treatment required to remove Contaminants.– Either offshore or at on-shore terminals

• Can be flared, re-injected or exported as sales gas.• $30 billion flared annually

Page 48: Hydrocarbon Processing

Natural Gas

• Found with light volatile hydrocarbons (condensate)• Found with crude oil deposits.– Separated from crude oil at point of production.– Drying is also carried out at point of production to

prevent hydrate formation and reduce possibilities of corrosion.

• Pressure must be increased before entering pipelines

Page 49: Hydrocarbon Processing

Gas processing

• Normally gas processing will involve some or all of the following– Compression– Drying mol sieve or glycol contracting– Acid gas removal– Hydrocarbon dew point adjustment

Page 50: Hydrocarbon Processing

Common contaminants in gas streams

• Water– Can cause hydrate formation– Can freeze at low temperature processes– Can dew out in pipelines– May exceed specification2 for sales gas

• Nitrogen – Lowers gas calorific value

• Hydrogen Sulphide H2S– Toxicity– Forms acid solutions with water leading to corrosion– May exceed specification for domestic gas

• Carbon dioxide (CO2)– Forms acid solutions with water leading to corrosion– Lowers gas calorific value

Page 52: Hydrocarbon Processing

Gas compression

• Gas must be compressed to 40 – 100 bar (4000-10000 kPa) for;– Export– Processing for NGL recovery– LNG

• If used as gas turbine fuel– Needs compression to 10 – 50 bar

Page 53: Hydrocarbon Processing

Compressor selection

• Two basic types of compressors– Dynamic– Positive displacement

• Positive displacement are sub-divided:– Reciprocating– rotary

Page 54: Hydrocarbon Processing