Produced water discharge throughout the world
is regulated to ensure that minimal oil enters our oceans
Effluent water from production separators
typically contains 100 – 800ppm oil, depending on the effectiveness
of the separator, demulsifier and residence time of the system.
Current UK legislation sets offshore disposal at 40ppm maximum
oil in water, with some operators setting there own standard
to 30ppm. It is therefore necessary to ensure that the oil
in water emulsion, which remains after crude oil and water
separation, is resolved prior to overboard discharge. In addition,
if produced water is to be re-injected into the reservoir
it is important that any solids present are removed in this
water treatment stage.
In general, operators achieve destabilisation
of oil in water emulsions through a combination of mechanical
and chemical means:
- Industrial hydrocyclones, centrifuges,
- Deoiler chemicals
Both mechanical and chemical methods aim
to coalesce the oil suspended in the water by either flocculation
of the oil droplets (grouping the oil droplets in to a loose
association) or coagulation of the oil droplets (making the
size of the droplets bigger).
Selection of Deoilers is performed using an in field bottle
test similar to that used for demulsifier selection. Fresh
emulsion is used to test numerous base chemicals under exact
operating conditions. The exact test employed will vary dependant
on the process equipment present. Where possible Roemex will
screen more environmentally benign deoiler chemistries as
and when they become available.
Deoiler chemicals are applied dependant on
whether water is discharged directly overboard or whether
the produced water is collected in slop tanks prior to discharge.
If water is discharged directly, then chemical addition would
normally be downstream of separation and upstream of any water
treatment vessels. If water is retained in slops tanks prior
to discharge then chemical addition would generally be downstream
of water treatment vessels and prior to slops.
Roemex’s Deoiler Range
Roemex’s range of deoilers consist of a wide range of various
polymer chemistries formulated to produce a definitive finished
product to aid the removal of the oil droplets from the produced
water at the best optimum dose.