Deoilers (reverse demulsifiers / water clarifiers)

Produced water discharge throughout the world is regulated to ensure that minimal oil enters our oceans and waterways.

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, flotation units

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).

Deoiler Selection and Application
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.