Application of Three Oilfield Scale Inhibitors

In underground crude oil production, many anions and cations that may cause fouling are dissolved in the formation water.

During the oil recovery process, changes in pH, temperature, and formation pressure caused the original chemical balance of the groundwater to be destroyed. As a result, crystal precipitation precipitates, resulting in the formation of scale.

These scaling have severely affected crude oil production and production efficiency of the oil recovery plant. In this paper, the causes, influencing factors, scale types and fouling mechanism of oilfield fouling are briefly reviewed.

There are suspended solids and various scale-forming ions in the injected water. The formation solution changes as the injection time changes. The scaled ions combine with each other to form a water-insoluble carbonate.

In general, a small amount of carbonate forms the core and adheres to the surface of the pipe. When the concentration of the scaled ions in the system reaches a certain level, no scale deposits are formed. The system gradually entered equilibrium.

But the system will eventually reach the limit equilibrium of the scaled ions. This limit equilibrium is related to the temperature, ion composition, thermodynamics and other conditions of the system. And follow the basic chemistry.

These scale ions will accumulate in the alkali storage tank, the alkali transfer pump, the static mixer, the binary flow meter, the injection line, the injection pump valve body and the like in the injection system.

Injecting suspended solids and various scale-forming ions present in the water. The types of scale mainly include calcium carbonate, calcium sulfate, barium sulfate, barium sulfate, iron compounds and the like.

The scale inhibition mechanism of scale inhibitors includes four kinds of reaction complexation mechanism, lattice distortion mechanism, electrostatic repulsion mechanism, and dispersion.

At present, research on phosphorus-free and non-nitrogen scale inhibitors have become a trend of research at home and abroad. PASP and PESA are representative of environmentally friendly non-phosphorus and non-nitrogen scale inhibitors.

The scale inhibitor mainly acts by chelation of the metal, adsorption, and dispersion of crystallites and lattice distortion. Prevents the deposition of scaled salts in the water on the surface of the equipment.

The water treatment scale inhibitors developed and applied in China are mainly divided into three categories, inorganic phosphate scale inhibitors, organic phosphonic acid scale inhibitors, and polymer scale inhibitors.

Inorganic phosphate is the first chemical scale inhibitor to be used.

Inorganic phosphorus scale inhibitors mainly include sodium hexametaphosphate and sodium tripolyphosphate. A trace amount of tripolyphosphate is added to the water, which destroys the growth process of the calcium carbonate crystals. Prevent the formation of calcium carbonate crystals.

Inorganic phosphate scale inhibitors have the advantages of low dosage, low price, and simultaneous release properties.

Since P-O is easily hydrolyzed in a high-temperature environment to form PO₄^3-. Moreover, PO₄^3- can also combine with Ca²⁺ to form a Ca₂(PO₄)₂ precipitate, resulting in a decrease in scale inhibition efficiency.

But the phosphorus in it can cause eutrophication of water bodies. A large number of colonies and algae are rapidly multiplied in water. Thereby seriously polluting the environment and destroying the ecology.

At present, the scale of scale inhibition using inorganic phosphate as a scale inhibitor has been gradually eliminated.

The organic phosphonic acid scale inhibitor contains a phosphonic acid group in the molecular structural formula. Part of the organic phosphonic acid molecule also contains a hydroxyl group, a carboxyl group, and a sulfonic acid group.

The organic phosphonic acid scale inhibitors mainly include the following: a methylidene phosphonate type, a homocarbodiphosphonic acid type, and a carboxyphosphonic acid type.

When the scale inhibitor is added to the water, the pyridinium type scale inhibitor can form a stable double five-membered ring chelate with the scale ions such as calcium and magnesium. The chelate has a large solubility to achieve scale inhibition.

Unlike the bisphosphonate type scale inhibitors, the same carbon diphosphonic acid type scale inhibitor molecules generally contain only C-P bonds. This bond has strong antioxidant properties. A multi-ring chelating compound is formed in the aqueous solution with a scale ion such as calcium or magnesium.

This type of scale inhibitor not only has a good scale inhibition effect on Ca²⁺. At the same time, it also has excellent inhibition and dispersion for Fe³⁺.

The main characteristic of the carboxyphosphonic acid type scale inhibitor is that it contains a carboxyl group in its molecular structure. The carboxyl group and the phosphonic acid group in the aqueous solution are capable of sequestering the scale ions such as calcium and magnesium in the solution. Thereby avoiding the formation of precipitates to achieve scale inhibition.

Polycarboxylic acid scale inhibitors can be classified into acrylic acid, maleic acid, maleic acid/acrylic acid, sulfonic acid, and phosphorus-containing polymer scale inhibitor.

Some experts have used water as a solvent, H₂O₂as an initiator, maleic anhydride as a monomer, and hydrolyzed polymaleic anhydride (HPMA) in one step.

In HPMA, hydroxyl functional groups have a strong chelation against Ca²⁺. When the amount is up to 2 mg•L^-1, the scale inhibition rate of Ca²⁺ is 100%. Shows a good low dose effect.

Other experts used maleic anhydride (MA), sodium allyl sulfonate (SAS) and acrylic acid (AA) as raw materials to synthesize MA-SAS-AA copolymer scale inhibitor. The effects of the dosage, temperature and pH value on the scale inhibition performance were analyzed.

The results show that the scale inhibitor has the advantages of low dosage, suitable temperature, and wide application range.

The above is an overview of the application of three oilfield scale inhibitors. For questions regarding water treatment chemicals, please contact us.