Liquid and gas separation

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Oil and gas processing (Onshore)

Oil & gas separationSEPARATOR:

Pressure vessel separating well fluids into gaseous/ vapour and liquid components

Main facilities and operations in oil installation1)Well head & choke 1)Well 2)Flow lines 2)Flow 3)Manifold facilities 3)Manifold 4)Testing of wells 4)Testing 5)Liquid and gas separation facilities 5)Liquid 6)Oil and gas dehydration system 6)Oil 7)Desalting 7)Desalting 8)Storage 8)Storage 9)Shipment of products 9)Shipment

Main facilities and operations in GGS-Oil and gas metering -Instrumentation and control system Instrumentation -Maintenance of equipments Maintenance -Information & communication system Information -Utilities e.g. power, water and air Utilities -Office building Office -Fire fighting facilities Fire -Transportation Transportation -

Oil & gas separationSEPARATORS OF PRODUCING FIELD: Oil & gas separator Stage separator Trap Knock out vessel/drum/trap or

liquid knock out Flash chamber /vessel/ trap Expansion separator /vessel Gas scrubber (dry/wet ) Gas filter ( dry/wet) Filter /Separator

Well head and well fluids Multiphase HC mixture with varying compositions and densities Gas phase Liquid phase: 2 immiscible liquids Oil Water

FTHP FTHT

ABP ABT Choke

3.5/4 4/5 km. API 5L

SBHP FBHP SBHT

Well manifoldTo HP separator WELL#1 WELL#2 PG NRV

PG

NRV To MP separator

WELL#3

PG

NRV HP MP Test Headers

To test separator

Block diagram well fluids processingWell Fluid from header Gas to GDU/ Consumers

Separator Crude oil to dehydrator Produced water to ETP

Utilization of gas and oil

Gas is used for value added products -LPG -C2/C3 -Gas to consumers

Oil is supplied to refineries for distillation

Classification of Installationsa)For one or two wells: well head installation (WHI) a)For b)For many oil wells: group gathering station (GGS) b)For c)For gas wells: gas collecting station (GCS) c)For d)For oil storage and shipment : central tank farm (CTF) d)For e)For gas shipment : gas compressor plant (GCP) e)For f)For gas conditioning: Gas dehydration unit (GDU) f)For & gas sweetening unit (GSU) g) For water handling: Effluent treatment plant (ETP) h)Other plants: LPG recovery, C2-C3 unit, CSU etc. h)Other

Well connection configuration Multiphase HC mixture and water flowing through individual lines (preferred)WELL WELL

WELL WELL

WELL

GGS

WELL WELL WELL WELL

Well connection configuration Multiphase HC mixture and water flowing through interconnected lines (not preferred)WELL WELL WELL WELL WELL

GGSWELL

WELL WELL WELL

Well connection configurationMultiphase mixture flowing through well pads and group & test lines to GGS

WELL

WELL

WELL WELLPad

WELL

Pad

WELL

WELL

GGSWELL WELL

Well connection configuration Central Tank Form (CTF)Well Well Well Well Well Well Well Well

GGS

Well Well Well

Well Well Well

GGSWell

Well Well

WellGGS

CTFPump

Typical PFD of GGSFlare headerBath heater

BH HP MP

KOD

Flare

To consumers BH BH HP MP Test Scrubber To flare Oil Stb. To ETPHeater treater

Test HT Tank

Pump

Typical PFD of GCSFlare headerMeOH or BH KOD

Flare

HP

MP Scrubber

Consumers

To flare Test HP MP Test Cond. Stb. To ETP Cond. Stb. Tank Pump

Oil & gas separationWELL FLUIDS: Mixture of oil, gas and water / Free gas

Impurities / Extraneous material Nitrogen, CO2, H2S etc., Water, Paraffin Sand, silt etc.,

Oil & gas separationQuality of separated fluids

Separated crude oil

Depending on retention time, Free gas content in separated oil = 1.5% to 20% Water content of separated Oil = 0.05% to 8%

Quality improvement possible by chemical,

equipment, techniques and procedures

Oil & gas separationQuality of separated fluids

Separated water: Depending on retention time, Oil content in eff. Water = 0.004% to 2.0%

Special methods and separating techniques can improve water quality. Difference in sp.gr. of oil and water less than 0.2 results in limited and incomplete separation.

Oil & gas separationQuality of separated fluids

Separated Gas: For a separator with suitable mist extractor, Oil content in separated gas = 0.101 to 1.0 gal/mmscf In case of gas scrubbers oil content in effluent gas should be less than 0.1 gal/mmscf.

Oil & gas separation

Measurement

Instruments for measuring quality of separated fluids:

Instrument

Oil in separated gas Gas in separated oil Water in separated oil Oil in effluent water

Laser liq. Particle spectrometer Nucleonic densitometer BS&W monitor Ultraviolet absorption unit/ Solvent extraction/

Oil & gas separationFunctions of separatorsPrimary functions1.

Secondary functions1. Maintain optimum pressure 2. Maintain liquid seal

Removal of oil from gas

2. Removal of gas from oil 3. Removal of oil from water

Oil & gas separationProcess of separation:Separation of bulk liquid from gas Scrubbing of the gas Retaining liquids long enough for free gas separation Controlling and maintaining gas oil interface. Removal of all products from their respective out lets.

Reduction in gas velocity to allow liquids to drop out

Oil & gas separationClassification of separatorsPrinciple of primary sep. Operating pressure

Configuration Application

Function 2-phase 3-phase

Vertical Horizontal Spherical

Test sep. Prodn. Sep. L.T.S. Elevated sep. Stage sep. Metering sep. Foam sep.

Low pr. Sep. (10 - 225psi) Med. Pr. Sep. (225 - 750 psi) High pr. Sep. (750 - 1500 psi Gravity sep. Impingement/ coalescence sep. centrifugal sep.

Oil & gas separation

Stage separation of oil and gas:Series of separators operating at sequentially reduced pressures. Liquid is discharged from high pressure separator into the next lower pressure separator Aims at maximum recovery of liquid hydrocarbon and maximum stabilization of separated fluids. Economics limits the no. of stages of separation to 3 to 4

Oil & gas separation

Stabilization of crude oil :Operation of separator under vacuum / at high temp.

Liquid discharged completely stabilized Liquid recovery comparable to that of 4-6 stage separation Results in increased profit for highly volatile liquids Initial cost of stabilizer less than initial cost of multiple stage oil and gas separators.

SeparatorsBenefits of separation Separated gas, crude oil and produced water can be processed easily at low cost Removal of water helps in reducing damage due to corrosion Less costly MOC can be used if water is removed Less energy is required to move single phases

SEPARATION Depends on following factors: Pressure Temperature Gas Oil Ratio (GOR) Flow rate Fluid properties like density, viscosity etc.

Oil & gas separationPrinciples of separation of Oil from gas Density difference Impingement Change of flow direction Change of flow velocity Centrifugal force Coalescence Filtering

Oil & gas separation

Principles of separation of Gas from oil Settling Agitation Baffling Heat Chemicals

PRINCIPLES OF SEPARATION: Based on one or more of the following: Removal of Oil from Gas Gravity Separation Impingement Change of flow direction Change of flow velocity Filtering Coalescence Centrifugal Removal of Gas from Oil Settling Agitation Baffling Heat Chemicals

PRINCIPLES OF SEPARATION (OIL FROM GAS) : Gravity Separation Diff. Liquid phases Diff. Densities Diff. momentum

PRINCIPLES OF SEPARATION (OIL FROM GAS) : Gravity Separation: Terminal / Free settling velocity of droplet

Max. allowable gas velocityVt = [4 g Dp ( l - g) / 3 g C]

PRINCIPLES OF SEPARATION (OIL FROM GAS) : Impingement : If a flowing stream of of gas containing liquid mist is impinged against a surface, the liquid mist may adhere to and coalesce on the surface.

PRINCIPLES OF SEPARATION OIL FROM GAS : (OIL FROM GAS) Change of flow direction: Change in flow direction: Change in inertia Gas assumes change in direction readily Liquid gets retarded and flow back

PRINCIPLES OF SEPARATION OIL FROM GAS : : (OIL FROM GAS) Change of flow velocity: Change in flow velocity: Change in inertia Increase / decrease in velocity: High inertia liquid moves away from gas

PRINCIPLES OF SEPARATION OIL FROM GAS : : (OIL FROM GAS) Filtering : Porous filters are effective to remove liquid mist. Uses the principles of impingement, change in direction, change in velocity and coalescence.

PRINCIPLES OF SEPARATION OIL FROM GAS : : PRINCIPLES OF SEPARATION : FROM GAS) (OIL Coalescing Coalescing of small droplets (mist/fog)

Formation of large droplets

Settling by gravity

PRINCIPLES OF SEPARATION OIL FROM GAS : (OIL FROM GAS): Centrifugal force: Fluids allowed to flow in circular motion at high velocity. Centrifugal force throws liquid mist outward against the walls of the vessel.

PRINCIPLES OF SEPARATION (GAS FROM OIL ): Settling : Non solution gas separate on adequate retention time Optimum removal of gas if body of oil is thin

PRINCIPLES OF SEPARATION (GAS FROM OIL ): Agitation/Baffling: Controlled agitation helps removing non solution gas Disperses oil in such a manner that gas readily escapes Allows gas bubbles coalesce and separate

PRINCIPLES OF SEPARATION (GAS FROM OIL ): Heat : Hydraulically retained gas releases reduction of surface t