W7- Oil Treatment & Specifications Flashcards
2 and 3 phase Separators
Separate oil, gas and water in 2/3 phase separator; Separation train is interface between wells and processing- design to prevent bottlenecking of capacity
2 phase: typical in slug catchers (compressor suction scrubber- vertical slug catcher) & primary separation
3 phase: horizontal use weirs; vertical need downcomer and chimney
Tubes/plates aid liquid coalescence, increasing drop size- reduces settling time and aids phase split
Separator design criteria and considerations
Design criteria: gas/liquid flow rate; physical properties; operating T&P; degree of separation
Design considerations: surging/slugging tendancies; impurities/solids; foaming/corrosive behaviour; platform space limitations
Key separator subsystems
Inlet diverter: absorbing momentum of liquid
Liquid collection section: allow bubble to leave- liquid held for enough time
Gravity settling section: liquid droplets fall and coalesce into bulk- gas held
Mist extractor section: remaining fine droplets coalesce
Horizontal & vertical separators
Horizontal: higher velocities can be used as perpendicular flow; smaller and cheaper for same flow; easier access/service; structural robustness easier to achieve
Vertical: better with solids but harder to install; less floor area but multiple horizontal stacked could overcome this; better with dealing with waves/liquid surges
Coalescer
Liqui-liquid separator; fine separation/last stage to remove water from oil (emulsion layer)
High temp & fine pads/mesh- coalesce small droplets to facilitate separation
Electric coalescer- electric field to break oil-water emulsion
Separator internals
Inlet diverter: absorbs fluid momentum and allows to separate
Wave breakers: perforated baffles/plates perpendicular to flow (preventing bulk movement)
Defoaming plates: foam can be a problem when surfactants present
Vortex breaker: plate over liquid outlet to prevent gas being entrained in a vortex
Sand jets/drains: solids removal is required in horizontal separators
Mist extractors: used to remove remaining fine drops of liquid in gas stream (wire mesh/vane packs)
Separator operation
Pressure control: feedback loop vs gas exit stream sensor
Level control: feedback control loop vs level sensor
Temp indicator: inlet/outlet to control flow through exit
Flow indicator: slug catcher to avoid surges
Separator operation problems
Liquid slugs: allow for volume available to cope with slug at low/high liquid levels
Gas blowby: gas via bottom (liquid) exit risk as causes vortex formation, low liquid, level control failure
Liquid carryover: liquid leaving with gas from high liquid level
Sand accumulation: poor well finishing -> erosion
Scaling: forms if salts precipitate from solution causing blockages. Use neutrilising salt/scale inhibitor
Foaming: certains crude foam-> filling vessel space cause liquid carryover and poor separation. Use anti-foaming agents
Chemical treatment separation issues
Wax formation: paraffins solidify at processing temps; Increases pressure drop of fluid; blockages; reduces separation efficiency and stabilises emulsions.
Use wax inhibitors
Biological fouling: from algae/bacterial growth that can block pipelines and cause problems with sensors.
Inject biocide to prevent growth
Corrosion: acids interact with iron pipelines- pitting, cracking, fractures caused.
Use oxygen scavenger/corrosion inhbitors
Emulstions: mixtures of finely dispersed oil+water- layer formed that reduces effective residence time and separation efficiency.
Use de-mulsifiers as reduce surface tension and aid separation
Alternative to dumping water into sea
Water injection (EOR):
Minimal environmental impact, but particles in reinjected water can black pipes (pre-treatment cost)
Separator types
Polishing: final treatment to reduce oil contamination; filters or coalescers used
Hydrocyclones: very efficient oil-water separation via density differences; compact (saves space)
Flash drums: reduces water to P=1atm and removes contaminants dissolved at higher pressure and not soluble at atm
Flotation drum (oil skimmer tank): additional gas injected at base to aid liquid-liquid separation from gas evolution (small oil droplet attach to rising gas bubbles)
Compact flotation unit (CFU): efficient separator relying on cyclonic movement and flotation to separate oil from water; solids fall and removed at base
Solids removal
Cyclone/filters to remove solids which can cause erosion, bloackage, accumulation -> reduce contamination
Cyclone: separate solids based on density differences; solids forced outside and drop at base
Filters: force fluid through narrow channel; no reliance on density differences
