The effect of formate brines on the emulsification of enzymatic surfactants

GreenZyme is a protein molecule produced by oil-seeking microbes in batch fermentation and can be considered as a zwitterionic surfactant. It has been used mostly in enzyme enhanced oil recovery processes to change the wettability of the rock to increase recovery.

This is a brief extract from the Published article. Please follow the link for the original work. https://doi.org/10.1016/j.ces.2022.118016

Surfactants have vast applications in the petroleum industry in all production stages of an oil field. They are commonly utilised during flooding to aid additional oil recovery by reducing surface tension. Surfactants are also a usual component of stimulation and completion fluids to prevent formation damage or corrosion in the pipelines.

Surfactants aid in the emulsion creation also known as emulsification. These occupy two important roles in the process; lowering the interfacial tension and to some extent preventing recoalescence.

Surfactants produce two-phase dispersions in which two immiscible fluids are mixed. To create these dispersions requires the presence of oil and water phases in addition of a surface agent. In the petroleum industry these components are: Oil, which is contained in drilling mud or crude oil; brines, which can be either formation or operational brines, and the surfactant, that is an element in numerous well operations as mentioned previously.

There are several types of brines that can be found in an oil well, which can be classified as organic or inorganic. Formate brines are divided in sodium, potassium and caesium formate and were initially developed to overcome off-shore drilling and completion challenges. These types of salts present a very high water solubility. It is possible to combine formate salts to target a wide range of densities.

1. Surface tension or interfacial tension at the water–air interface/water–oil interface can be decreased by the addition of a surface agent which is adsorbed at the interface.

2. Formation damage is also improved when formate brines are used improving the performance of the production of the well.

Greenzyme presented the highest surface tension values in comparison with the other two surfactants.

Enzymes mostly modify solid to liquid interactions, therefore having more impact on the rock surface than in the oil–water interface. The de-adhesion of the crude oil from the rock is totally related to the catalytic effect of the enzymes that is dependent on the oil composition.

Therefore, the molecules would first adsorb at the surface before commencing the micellization process. The most negative energy values correspond to Greenzyme, for both, adsorption and micellization. This indicates that Greenzyme tends to adsorb to the interface better and the larger size of its molecules require less monomers to incite aggregation. It can be inferred then, that the performance of Greenzyme can improve as the complexity of the oil is increased.

Figure 16 extract: Water segregation for Greenzyme/crude oil emulsions

As mentioned, there was a considerable increase of 108 % in the IFT for Greenzyme when the solutions tested contained dissolved salts.

Best emulsification was found with low salinity water. Going above 10 g/dL of any

type of salt tested will result in a complete phase separation between minutes of mixing. Greenzyme presented very unstable emulsions even at low salinities. With time the oil phase starts to separate from the emulsion and in some cases complete phase separation is achieved.

A polymer (xanthan gum) was added to emulsions and the samples were tested to determine if the emulsions could demonstrate better stability:

1. Greenzyme attained full emulsification only for Deionized water (DIW); any salt concentration, even with the polymer added, had full separation when the phases were mixed.

2. Greenzyme could only be emulsified with DIW.

3. Greenzyme emulsions with this type of oil and xanthan gum could only hold with DIW and 5 g/dL Sodium Formate; other types of salt or concentrations resulted in full separation.

4. Emulsification of Greenzyme is not possible if the salinity is even slightly high with the salts tested (Sodium and Potassium Formate and Sodium Chloride).

Continuing Aberdeen's Enzyme Surfactant Research

This study is not a standalone data point. It directly continues earlier University of Aberdeen research on GreenZyme by Udoh and Vinogradov (2019). Lezama's own measurements for GreenZyme's critical micelle concentration (0.176 mMol/L) and surface tension (47.2 mN/m) landed within a fraction of a percent of Udoh's previously published figures (0.174 mMol/L, 47.1 mN/m) — an independent confirmation of the earlier results, from the same lab, three years apart. Read more about that earlier stage of the research in our post on Controlled Salinity and GreenZyme.

---

Sources & Credits

Linda Tatiana Lezama, Roozbeh Rafati, Amin Sharifi Haddad — School of Engineering, Kings College, University of Aberdeen.

Chemical Engineering Science 263 (2022) 118016. Read the source →