1. Forming conditions of foam

The precondition for the formation of foam is that there must be gas and liquid contacting each other. The contact between gas and liquid can be achieved through three ways: first, directly introducing enternal gas into the liquid; The second is to utilize the agitation of the airflow in the gas well; The third is that the additives in the drilling fluid react under certain conditions to produce insoluble gases.

Stirring or blowing soapy water can produce foam. Careful observation shows that foam is a system separated by many bubbles and liquid. On the surface, both foam and emulsion are separated by liquid membrane, but there is a big difference in essence. Emulsion is a liquid separated by another immiscible liquid, while foam is a dispersion system in which gas is dispersed in the liquid. Gas is a dispersion phase (discontinuous phase), and liquid is a dispersion medium (continuous phase). Because the density of gas and liquid is very different, the bubbles in the liquid always rise to the liquid level quickly, forming bubble aggregates separated by liquid film composed of a small amount of liquid, which is commonly called foam.

Generally speaking, when the gas content in foam is low, it is uniformly dispersed as a small ball; when the gas content is high, it is polyhedral.The foam in drilling (well) operation is the foam with high gas content, which is called concentrated foam or dry foam. It is difficult to form stable foam with pure liquid.

2. Methods of Defoaming

In the process of oil drilling, when encountering gas bearing formations, hydrocarbons, CO2, H, S, and other gases in the formations diffuse or invade the drilling fluid. The circulating drilling fluid plays a stirring role in the generation of bubbles, and in addition, the treatment agents of the drilling fluid are generally surface active. Therefore, the drilling fluid is often prone to foaming. The foaming of drilling fluid can have many adverse effects on drilling engineering. The following three methods are commonly used for defoaming at present.

①.Physical Defoaming Method

The commonly used physical defoaming method is to raise or lower the temperature to burst the foam. When the temperature rises, the liquid viscosity decreases, the solvent evaporates, and the foam bursts. At low temperature, the surface elasticity of foam decreases, and foam is unstable due to icing, so as to achieve the purpose of defoaming. In addition, methods such as X-ray and ultraviolet radiation are also used for defoaming.

②.Mechanical Defoaming Method

This method is generally used when adding defoamer will cause pollution, heating will cause product deterioration or foam separation is required. For example, rapid pressure changes, centrifugal separation of solution and foam; The methods of spraying foam system with compressed air, ultrasonic wave and filtration are all of these methods.

③.Chemical Defoaming Method

Adding defoamer in foam system is a common defoaming method. In addition, the purpose of eliminating foam can be achieved by changing pH value, salting out, adding chemical reagents that react with foams, etc.

Among the three methods mentioned above, the better one is to use defoamers or a combination of defoamers and mechanical defoamers. Although other methods can achieve certain results in some situations, they can not deal with a large number of foam and are only suitable for some emergency measures. Due to the emergence of many defoamers with excellent performance, defoamers are increasingly being valued and widely used.

3. Cementing Defoamer

Cementing defoamer, as its name implies, is a reagent to eliminate a large number of foam produced in the process of oilfield industrial production. Adding defoamer is the simplest and commonly used method to control and eliminate foam at present. However, due to different foaming systems and usage conditions, the defoamers used are also different. To meet various needs, a variety of defoamers with different properties should be produced.Defoamers should meet the following conditions in terms of their physical and chemical properties:

①.Defoamers have an efficient defoaming effect on the foaming system, with lower surface tension than the foaming medium, are insoluble in the foaming medium, and are not affected by the compatibilization and degradation of the foaming system;

②.Defoamers are inert to the foaming system, do not react chemically, have no side effects on the final product, and do not affect product performance and appearance;

③.Defoamers also need to meet special conditions during the drilling process, such as pH and temperature requirements;

④.Defoamers are easy to operate, easy to handle, have good storage stability, do not deteriorate during long-term storage, and are safe for humans, livestock, and the natural environment.

3.1 The Principle of Defoamers

①.The local surface tension of foam decreases, resulting in the bursting of foam. The origin of this mechanism is that higher alcohols or vegetable oils are sprinkled on the foam, and when they are dissolved into the foam liquid, the surface tension there will be significantly reduced. Because these substances generally have low solubility in water, the reduction of surface tension is limited to the local part of foam, while the surface tension around foam has almost no change. The part with reduced surface tension is strongly pulled and extended around, and finally bursts.

②.Breaking the elasticity of the membrane and causing bubbles to burst. When defoamer is added to the foam system, it will diffuse to the gas-liquid interface, making it difficult for the surfactant with foam stabilizing effect to recover the membrane elasticity.

③. Promoting liquid film drainage. Defoamer can promote liquid discharge of liquid film, thus leading to bubble burst. The rate of foam discharge can reflect the stability of foam. Adding a substance to accelerate foam discharge can also play a role in defoaming.

④.Adding hydrophobic solid particles can cause bubbles to burst. Hydrophobic solid particles on the surface of bubbles attract the hydrophobic end of surfactants, causing hydrophobic particles to develop hydrophilicity and enter the aqueous phase, thereby playing a defoaming role.

⑤.Solubilizing and foaming surfactants can cause bubbles to burst. Some low molecular substances that can be fully mixed with the solution can increase the solubility of bubble surfactants and reduce their effective concentration. Low molecular substances with this effect, such as octanol, ethanol, propanol and other alcohols, can not only reduce the surfactant concentration in the surface layer, but also dissolve into the surfactant adsorption layer, reducing the compactness of surfactant molecules, thus weakening the stability of foam.

⑥.Electrolyte disintegration of surfactant double layer. For the surfactant double electric layer interaction with foam to produce a stable foaming solution, the double electric layer of the surfactant can be disintegrated by adding ordinary electrolyte to defoamer.

3.2 Composition of Defoamer

The main components of defoamers include active ingredients, emulsifiers, carriers, etc.

• The active ingredients are the most important part, playing a role in reducing surface tension and defoaming.
• Emulsifiers are used to disperse active ingredients into small particles for better dispersion in oil or water, resulting in better defoaming effects.
• Carriers account for a large proportion of defoamers, and their surface tension is not high. They mainly play a role in supporting media and reducing costs, and are beneficial to inhibiting foam, such as aliphatic hydrocarbons, hydroxyl containing solvents, etc.

3.3 Types and Characteristics of Defoamers

Commonly used defoamers can be divided into four categories based on their composition: fatty defoamers, polyether defoamers, silicone defoamers, and polyether silicone defoamers. 

①.Fatty defoamers - Fatty defoamers are the first generation of defoamers, mainly composed of organic compounds such as mineral oils, fatty acids or fatty esters, fatty alcohols, and lower alcohols. This type of defoamer is cheap, easy to obtain raw materials, and simple in process. It is suitable for use when the liquid shear force is small and the foaming ability of the foaming agent is moderate, but it has poor ability to eliminate dense foam. This type of defoamer is mainly used in the papermaking industry.

②.Polyether based defoamers - Polyether based defoamers are a type of non ionic defoamers prepared by ring opening polymerization of ethylene oxide and propylene oxide. Their defoaming and foam suppression capabilities can be adjusted by adjusting factors such as the ratio and molecular weight of ethylene oxide to propylene oxide. This type of defoamer has the characteristics of non-toxic, easy to use, easy to disperse, high temperature resistance, and strong alkali resistance, so it is commonly used in fields such as fermentation engineering and biopharmaceutical.

③.Organic silicone defoamers - The main component of organic silicone defoamers is silicone oil. Due to its lower surface tension than aqueous and general oil solutions, silicone oil is suitable for both water-based and oil-based foaming systems. Organic silicon defoamers have the characteristics of high activity and low toxicity, so they are commonly used in industries such as petrochemical, papermaking, and wastewater treatment.

④.Polyether organosilicon defoamer - Polyether modified organosilicon is a compound obtained by grafting hydrophilic polyether groups onto hydrophilic polysiloxane segments. This type of defoamer effectively combines the high temperature resistance, strong alkali resistance, strong foam suppression ability of polyether defoamers, as well as the non-toxic, pollution-free, and strong defoaming ability of organic silicon defoamers, greatly improving the application field of defoamers, widely used in fields such as petrochemical, printing and dyeing, coatings, and agriculture.

4. Development Trend of Defoamers

Due to their different structures, various types of defoamers exhibit varying defoaming and foam inhibiting properties and application ranges. Among them, polyether modified organosilicon defoamers have the advantages of both polyether and organosilicon defoamers, and have good and long-lasting defoaming and foam inhibition properties in both water and oil phases. Undoubtedly, polyether modified organosilicon defoamers have enormous development potential. The future research on polyether modified organosilicon defoamers can start from the following aspects:

①.From the perspective of molecular design, the structure of polyether modified silicone oil is optimized. By adjusting the ratio of ethylene oxide and propylene oxide, molecular weight, and the ratio of polyether to organic silicon in the used polyether, a defoamer with better defoaming and foam inhibition performance is prepared.

②.By introducing special functional monomers, such as fatty chains, polyether modified organosilicon defoamers are endowed with more special functions to be suitable for special systems.

③.Continue to explore the defoaming mechanism of the defoamer, and optimize the composition of the defoamer based on the mechanism or mix with other more suitable additives to achieve better performance.

Our company, Zoranoc, has developed and produced list of cementing defoamer products.The detailed information of each product can be found on our official website www.zoranoc.com.