During the complex process of oil and gas production, depressurization of the mixture of hydrocarbons can easily lead to the formation of stable foam.

Foams can be found throughout the process, ranging from production separators, through gas dehydration or sweetening processing water for injection. Foam can have dire consequences when carryover of liquid occurs in the associated gas stream and when liquid hydrocarbon carryover contaminates dehydration or amine units.

The presence of gas dissolved in the crude oil, especially when viscosity is high, can initially produce a gas dispersion or spherical foam upon depressurization. This can occur in the tubing or separation system. As the bubbles rise through the liquid and come to the surface, they can produce conventional polyhedral foam. Under these conditions, a chemical defoamer is required to perform a dual function: to accelerate the ascent of the gas bubbles and to counteract the formation of the stable polyhedral foam.

The severity of the foam in the production system is dependent on several factors:

• Oil production rate and associated gas;

• Pressure and temperature;

• Chemical composition of the produced fluids;

• System design;

• Other chemicals used in the process such as corrosion inhibitors or contaminants such as fines, scales or corrosion by-products.

Defoamer operation

Production systems can be optimized with respect to oil production rate and pressure to reduce the risk of foaming, but this might not be enough-or may impose unacceptable constraints on production-in which case defoamers might be necessary for constraints on production –in which case defoamers might be necessary for constant, smooth operation. Defoamers can be highly cost-effective and can work at injection rates of just a few ppm. They act in one of two ways: either by displacing stabilizers from the bubble wall, or by locally rupturing them. Displacement of foam stabilizers occurs after a thin defoamer layer is spread over the bubble surface. Bursting occurs when a defoamer, with a lower surface tension than the oil, causes localized surface-tension depression.

Tailored defoamer solutions

runze offers a range of generic defoamer types for various oilfield applications. Sillicones are the most commonly applied in crude oil, glycol units for dehydration, and water injection systems where silicone defoamer may be less popular.